//////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 18478 SUBJECT: GRB 151027A: Swift detection of a burst with a bright optical afterglow DATE: 15/10/27 04:16:31 GMT FROM: David Palmer at LANL A. Maselli (INAF-IASFPA), A. D'Ai (INAF-IASFPA), A. Y. Lien (GSFC/UMBC), D. M. Palmer (LANL), B. Sbarufatti (INAF-OAB/PSU), M. H. Siegel (PSU), M. Stamatikos (OSU/NASA/GSFC) and T. N. Ukwatta (LANL) report on behalf of the Swift Team: At 03:58:24 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 151027A (trigger=661775). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 272.491, +61.381 which is RA(J2000) = 18h 09m 58s Dec(J2000) = +61d 22' 51" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a complex peaked structure lasting at least 150 seconds. The peak count rate was ~6000 counts/sec (15-350 keV), at ~110 sec after the trigger. The XRT began observing the field at 03:59:51.1 UT, 87.0 seconds after the BAT trigger. XRT found a bright, uncatalogued X-ray source located at RA, Dec 272.4886, 61.3515 which is equivalent to: RA(J2000) = +18h 09m 57.26s Dec(J2000) = +61d 21' 05.4" with an uncertainty of 4.8 arcseconds (radius, 90% containment). This location is 106 arcseconds from the BAT onboard position, within the BAT error circle. No event data are yet available to determine the column density using X-ray spectroscopy. UVOT took a finding chart exposure of 150 seconds with the White filter starting 95 seconds after the BAT trigger. There is a candidate afterglow in the rapidly available 2.7'x2.7' sub-image at RA(J2000) = 18:09:56.68 = 272.48615 DEC(J2000) = +61:21:13.4 = 61.35373 with a 90%-confidence error radius of about 0.61 arc sec. This position is 9.06 arc sec. from the center of the XRT error circle. The estimated magnitude is 14.46 with a 1-sigma error of about 0.14. No correction has been made for the expected extinction corresponding to E(B-V) of 0.05. Burst Advocate for this burst is A. Maselli (maselli AT ifc.inaf.it). Please contact the BA by email if you require additional information regarding Swift followup of this burst. In extremely urgent cases, after trying the Burst Advocate, you can contact the Swift PI by phone (see Swift TOO web site for information: http://www.swift.psu.edu/too.html.) //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 18479 SUBJECT: GRB 151027A: KAIT optical afterglow confirmation DATE: 15/10/27 04:22:02 GMT FROM: Weikang Zheng at UC Berkeley WeiKang Zheng and Alexei V. Filippenko (UC Berkeley) report on behalf of the KAIT GRB team: The 0.76-m Katzman Automatic Imaging Telescope (KAIT), located at Lick Observatory, responded to Swift GRB 151027A (Maselli et al., GCN 18478) immediately after receiving the trigger. Observations were performed with an automatic sequence in the clear (roughly R), V, and I filters, and the exposure time was 20 s per image. Inside the XRT error circle we detected an un-cataloged varying source with coordinates of : RA = 18:09:56.70 (J2000) DEC= +61:21:13.01 (J2000) The object location is consistent with the position reported from UVOT (Maselli et al., GCN 18478). The object has clear band mag of ~13.0 at the moment. Follow-up observations are encouraged. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 18480 SUBJECT: GRB 151027A : ISON-NM early optical detection DATE: 15/10/27 05:47:05 GMT FROM: Alexei Pozanenko at IKI, Moscow L. Elenin (KIAM), E. Mazaeva (IKI), A. Volnova (IKI), I. Molotov (KIAM), A. Pozanenko (IKI) report on behalf of larger GRB follow-up collaboration: We observed the field of the Swift GRB 151027A (Maselli et al., GCN 18478) with 0.4-m telescope of ISON-NM observatory in robotic mode starting on Oct., 27 (UT) 03:59:43 i.e. 79 seconds after burst trigger. We obtained 50 unfiltered images of 30 s exposure. We clearly detect the optical counterpart of GRB 151027A (Maselli et al., GCN 18478; Zheng and Filippenko, GCN 18479) in coordinates (J2000) 18 09 56.69 +61 21 13.2. In the first image we estimated brightness of the optical counterpart as ~14m. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 18481 SUBJECT: GRB 151027A: P60 afterglow confirmation and rebrightening DATE: 15/10/27 05:57:03 GMT FROM: Daniel Perley at Caltech D. A. Perley (DARK/NBI) and S. B. Cenko (NASA/GSFC) report: The Palomar 60-inch robotic telescope responded automatically to the alert for GRB 151027A (Maselli et al., GCN151027A) and began a sequence of i, r, and z-band imaging at 04:00:49 UT, 145 seconds after the BAT trigger. We identify a very bright afterglow consistent with the UVOT and KAIT (Zheng et al., GCN18479) positions in all filters. The preliminary afterglow light curve shows a slow rise to a peak at about ~5 minutes after the GRB trigger, then slowly fades by about 1 magnitude between then and approximately 30 minutes after the trigger. Over the next 20 minutes it then rapidly rebrightens by about 0.7 magnitude. Little or no fading is seen after that point (through to at least 90 minutes after the trigger.) Continued monitoring is encouraged, and should remain possible even from small telescopes for quite some time. High-resolution spectroscopy is also strongly encouraged. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 18482 SUBJECT: GRB 151027A: Enhanced Swift-XRT position DATE: 15/10/27 09:37:18 GMT FROM: Phil Evans at U of Leicester M.R. Goad, J.P. Osborne, A.P. Beardmore and P.A. Evans (U. Leicester) report on behalf of the Swift-XRT team. Using 1445 s of XRT Photon Counting mode data and 3 UVOT images for GRB 151027A, we find an astrometrically corrected X-ray position (using the XRT-UVOT alignment and matching UVOT field sources to the USNO-B1 catalogue): RA, Dec = 272.48695, +61.35344 which is equivalent to: RA (J2000): 18h 09m 56.87s Dec (J2000): +61d 21' 12.4" with an uncertainty of 1.7 arcsec (radius, 90% confidence). This position may be improved as more data are received. The latest position can be viewed at http://www.swift.ac.uk/xrt_positions. Position enhancement is described by Goad et al. (2007, A&A, 476, 1401) and Evans et al. (2009, MNRAS, 397, 1177). This circular was automatically generated, and is an official product of the Swift-XRT team. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 18483 SUBJECT: Tentative redshift for GRB 151027A from Swift-XRT data DATE: 15/10/27 10:03:40 GMT FROM: Sergio Campana at INAF-OAB S. Campana (INAF-OAB) report on behalf of the Swift Team: Swift BAT triggered on the early activity of GRB 151027A (Maselli et al. 2015, GCN 18478). Swift XRT started observing 87 s after the trigger observing the main event. By using the Swift/XRT spectrum repository at http://www.swift.ac.uk/xrt_spectra/ (see Evans et al. 2009, MNRAS, 397, 1177) we selected a time interval with an almost constant hardness ratio, starting at 150 s after the burst onset and lasting 281 s. We then fit the Window Timing (WT) spectrum with XSPEC using the model tbabs*ztbabs*pow. We assume a Galactic column density of 3.75x10^20 cm^-2 (Willingale et al. 2013, MNRAS, 431, 394) and we allow for a 30% uncertainty in the fit. We fit the spectrum using C-statistics (C-stat=593.74 with 637 d.o.f.). In the intrinsic column density vs. redshift plane there is just one deep minimum hinting for a redshift z=0.38+/-0.17 (90% confidence level) and an intrinsic column density N_H(z)=(3.6+/-0.7)x10^21 cm^-2. The X-ray spectrum is soft with Gamma=2.6, (assuming a cut-off power law spectrum the allowed redshift range expands to 0.27-1.38). The contour plot is available at http://www.brera.inaf.it/utenti/campana/151027.gif //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 18485 SUBJECT: GRB 151027A: Weihai optical observations DATE: 15/10/27 12:17:48 GMT FROM: Dong Xu at NAOC/CAS D. Xu (NAOC/CAS), C.-M. Zhang, C. Cao, S.-M. Hu (SDU) report: We observed the field of GRB 151027A (Maselli et al., GCN 18478) using the 1m telescope located at Weihai, Shandong, China. Observations started at 09:44 UT on 2015-07-27, i.e., 5.77 hr after the burst. We obtained 5x300s R-band and 5x150s I-band frames. The afterglow (e.g., Maselli et al., GCN 18478; Zheng & Filippenko, GCN 18479; Elenin et al., GCN 18480; Perley & Cenko, GCN 18481) is clearly detected in each image, and it has decayed to m(R) = 16.0 +/- 0.1 mag for the first R-band exposure, calibrated with the nearby USNO B1 stars (with R2 magnitudes). //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 18487 SUBJECT: GRB 151027A: Keck/HIRES redshift DATE: 15/10/27 13:57:31 GMT FROM: Daniel Perley at Caltech D. A. Perley (DARK/NBI), L. Hillenbrand (Caltech), and J. X. Prochaska (UCO/Lick) report: We obtained a 900s spectrum of the optical afterglow of GRB 151027A (Maselli et al., GCN 18478) with Keck/HIRES starting at UT 06:54 on 2015-10-27. In the preliminary reduction, we identify a series of strong absorption lines including the MgII doublet at z=0.81. Associated MgI, FeII, and (likely) FeII* are also present, indicating that this is the redshift of the GRB. Analysis is ongoing. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 18490 SUBJECT: GRB 151027A: Swift-XRT refined Analysis DATE: 15/10/27 16:16:03 GMT FROM: Phil Evans at U of Leicester K.L. Page (U. Leicester), P. D'Avanzo (INAF-OAB), V. D'Elia (ASDC), A. D'ai (INAF-IASFPA), T.G.R. Roegiers (PSU), L.M. McCauley (PSU), J.A. Kennea (PSU), C. Pagani (U. Leicester), A.P. Beardmore (U. Leicester) and A. Maselli report on behalf of the Swift-XRT team: We have analysed 6.0 ks of XRT data for GRB 151027A (Maselli et al. GCN Circ. 18478), from 80 s to 18.9 ks after the BAT trigger. The data comprise 1.6 ks in Windowed Timing (WT) mode (the first 5 s were taken while Swift was slewing) with the remainder in Photon Counting (PC) mode. The enhanced XRT position for this burst was given by Goad et al. (GCN Circ. 18482). The light curve can be modelled with a series of power-law decays. The initial decay index is alpha=4.1 (+1.1, -1.0). At T+208 s the decay flattens to an alpha of 1.46 (+0.10, -0.14). The light curve breaks again at T+537 s to a decay with alpha=0.04 (+0.06, -0.09), and again at T+2494 s s to alpha=1.11 (+0.15, -0.26), before a final break at T+11.6 ks s after which the decay index is 2.01 (+0.26, -0.25). A spectrum formed from the WT mode data can be fitted with an absorbed power-law with a photon spectral index of 1.851 (+0.024, -0.023). The best-fitting absorption column is 1.96 (+0.18, -0.17) x 10^21 cm^-2, at a redshift of 0.81, in addition to the Galactic value of 3.8 x 10^20 cm^-2 (Willingale et al. 2013). The PC mode spectrum has a photon index of 1.99 (+/-0.08) and a best-fitting absorption column of 3.3 (+/-0.6) x 10^21 cm^-2. The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 3.5 x 10^-11 (4.7 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Galactic foreground: 3.8 x 10^20 cm^-2 Intrinsic column: 3.3 (+/-0.6) x 10^21 cm^-2 at z=0.81 Photon index: 1.99 (+/-0.08) If the light curve continues to decay with a power-law decay index of 2.01, the count rate at T+24 hours will be 0.035 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.3 x 10^-12 (1.7 x 10^-12) erg cm^-2 s^-1. The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00661775. This circular is an official product of the Swift-XRT team. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 18491 SUBJECT: GRB 151027A: MITSuME Akeno Optical observation DATE: 15/10/27 16:23:13 GMT FROM: Taketoshi Yoshii at Tokyo Tech Y. Yano, T. Yoshii, Y. Saito, Y. Tachibana, H. Ohuchi, S. Kurita, Y. Ono, T. Fujiwara, S. Harita, Y. Muraki, Y. Yatsu, and N. Kawai (Tokyo Tech) report on behalf of the MITSuME collaboration: We observed the field of GRB 151027A (A. Maselli et al., GCN Circular #18478) with the optical three color (g', Rc, and Ic) CCD cameras attached to the MITSuME 50 cm telescope of Akeno Observatory, Yamanashi, Japan. The observation started on 2015-10-27 09:13:52 UT ( 5.25 h after the burst). We detected the previously reported optical afterglow of GRB 151027A (WeiKang Zheng et al., GCN Circular #18479) in the g',Rc and Ic band. The measured magnitudes are listed below. T0+[sec] MID-UT T-EXP[sec] g' Rc Ic ------------------------------------------------------------------------------------------------------------------ 18928 09:34:24 2220 16.72+/-0.06 15.62+/-0.05 16.00+/-0.04 ------------------------------------------------------------------------------------------------------------------ T0+ : Elapsed time after the burst T-EXP: Total Exposure time We used GSC2.3 catalog for flux calibration. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 18492 SUBJECT: GRB 151027A: Fermi GBM observation DATE: 15/10/27 16:31:56 GMT FROM: Hoi-Fung Yu at MPE Kilian Toelge, Hoi-Fung Yu (both MPE), and Charles A. Meegan (USRA) report on behalf of the Fermi GBM Team: "At 03:58:24.03 UT on 27 Oct 2015, the Fermi Gamma-Ray Burst Monitor triggered and located GRB 151027A (trigger 467611108 / 151027166), which was also detected by the Swift (Maselli et al. 2015, GCN 18478) The GBM on-ground location is consistent with the Swift position. The angle from the Fermi LAT boresight at the GBM trigger time is 10 degrees. This burst was also independently detected by INTEGRAL SPI-ACS. The GBM light curve consists of three pulses with a duration (T90) of about 124 s (50-300 keV). The time-averaged spectrum from T0-2.048 s to T0+133.120 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -1.41 +/- 0.04 and the cutoff energy, parameterized as Epeak, is 340 +/- 63 keV. The event fluence (10-1000 keV) in this time interval is (1.94 +/- 0.09)E-05 erg/cm^2. The 1.024-sec peak photon flux measured starting from T0+0.3840 s in the 10-1000 keV band is 11.37 +/- 0.34 ph/s/cm^2. The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog." //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 18493 SUBJECT: GRB 151027A: GMG observation DATE: 15/10/27 16:43:32 GMT FROM: Jirong Mao at Yunnan Obs J. Zhang, J. Mao and J. Bai (YNAO) report: We observed the field of GRB 151027A (Maselli et al., GCN 18478) with the 2.4-meter optical telescope at Gao-Mei-Gu of Yunnan Observatories. Observations began at 11:34:08 UT, Oct 27, 2015, about 7.5 hr after the trigger. We obtained a low S/N spectrum. The feature of absorption line identified as MgII by Perley et al. (GCN 18487) is clearly shown, and redshift is 0.81. However, we noticed that some possible absorption lines might be identified as OVI and NaID, indicating a redshift of 0.33. We cannot have confirmation due to the low S/N of the spectrum. We also performed multi-band photometry and we obtained R~16.9 mag. Further analysis is ongoing. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 18495 SUBJECT: GRB 151027A: Early RAPTOR Observations DATE: 15/10/27 18:16:09 GMT FROM: James Wren at LANL J. Wren, W.T. Vestrand, P. Wozniak, and H. Davis, of Los Alamos National Laboratory report: The RAPTOR network of robotic optical telescopes made follow-up observations of Swift trigger 661775 (Maselli et al., GCN 18478). Our narrow-field instruments in Los Alamos, NM USA, began imaging at 03:58:48.01 UT (23.86 s after the BAT trigger time). From the first frame we detected a bright optical counterpart at the location reported by UVOT. Starting with a magnitude of R~13.7 the RAPTOR telescopes measured a complex, fading lightcurve with seveal re-brightening intervals. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 18496 SUBJECT: GRB 151027A: Swift-BAT refined analysis DATE: 15/10/27 18:51:53 GMT FROM: Amy Lien at GSFC D. M. Palmer (LANL), S. D. Barthelmy (GSFC), J. R. Cummings (GSFC/UMBC), N. Gehrels (GSFC), H. A. Krimm (GSFC/USRA), A. Y. Lien (GSFC/UMBC), C. B. Markwardt (GSFC), A. Maselli (INAF-IASFPA), T. Sakamoto (AGU), M. Stamatikos (OSU), T. N. Ukwatta (LANL) (i.e. the Swift-BAT team): Using the data set from T-239 to T+963 sec from the recent telemetry downlink, we report further analysis of BAT GRB 151027A (trigger #661775) (Maselli et al., GCN Circ. 18478). The BAT ground-calculated position is RA, Dec = 272.498, 61.361 deg which is RA(J2000) = 18h 09m 59.6s Dec(J2000) = +61d 21' 39.6" with an uncertainty of 1.1 arcmin, (radius, sys+stat, 90% containment). The partial coding was 18%. The mask-weighted light curve shows a complex structure with roughly two main pulses. The first pulse starts at ~T0, peaks at ~T+1 s, and ends at ~T+5 s. The second pulse starts at ~T+90 s, peaks at ~T+110 s, and ends at ~T+170 s. T90 (15-350 keV) is 129.69 +- 5.55 sec (estimated error including systematics). The time-averaged spectrum from T-0.74 to T+164.70 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.72 +- 0.05. The fluence in the 15-150 keV band is 7.8 +- 0.2 x 10^-6 erg/cm2. The 1-sec peak photon flux measured from T+0.20 sec in the 15-150 keV band is 6.8 +- 0.6 ph/cm2/sec. All the quoted errors are at the 90% confidence level. The results of the batgrbproduct analysis are available at http://gcn.gsfc.nasa.gov/notices_s/661775/BA/ //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 18499 SUBJECT: GRB 151027B: Swift detection of its 1000-th burst DATE: 15/10/27 22:56:57 GMT FROM: Scott Barthelmy at NASA/GSFC T. N. Ukwatta (LANL), S. D. Barthelmy (GSFC), W. H. Baumgartner (GSFC/UMBC), A. D'Ai (INAF-IASFPA), N. Gehrels (NASA/GSFC), J. A. Kennea (PSU), N. P. M. Kuin (UCL-MSSL), A. Y. Lien (GSFC/UMBC), F. E. Marshall (NASA/GSFC), A. Maselli (INAF-IASFPA), K. L. Page (U Leicester), D. M. Palmer (LANL), B. Sbarufatti (INAF-OAB/PSU) and R. L. C. Starling (U Leicester) report on behalf of the Swift Team: At 22:40:40 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 151027B (trigger=661869). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 76.238, -6.427, which is RA(J2000) = 05h 04m 57s Dec(J2000) = -06d 25' 35" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve shows a peak with a duration of about 50 sec. The peak count rate was ~1000 counts/sec (15-350 keV), at ~40 sec after the trigger. The XRT began observing the field at 22:44:04.0 UT, 203.4 seconds after the BAT trigger. Using promptly downlinked data we find a bright, uncatalogued X-ray source located at RA, Dec 76.21944, -6.45010 which is equivalent to: RA(J2000) = 05h 04m 52.67s Dec(J2000) = -06d 27' 00.4" with an uncertainty of 3.9 arcseconds (radius, 90% containment). This location is 106 arcseconds from the BAT onboard position, within the BAT error circle. This position may be improved as more data are received; the latest position is available at http://www.swift.ac.uk/sper. We cannot determine whether the source is fading at the present time. A power-law fit to a spectrum formed from promptly downlinked event data gives a column density consistent with the Galactic value of 9.43 x 10^20 cm^-2 (Willingale et al. 2013). The initial flux in the 2.5 s image was 5.37e-10 erg cm^-2 s^-1 (0.2-10 keV). UVOT took a finding chart exposure of 150 seconds with the White filter starting 209 seconds after the BAT trigger. No credible afterglow candidate has been found in the initial data products. The 2.7'x2.7' sub-image covers 100% of the XRT error circle. The typical 3-sigma upper limit has been about 19.6 mag. The 8'x8' region for the list of sources generated on-board covers 100% of the XRT error circle. The list of sources is typically complete to about 18 mag. No correction has been made for the expected extinction corresponding to E(B-V) of 0.25. Burst Advocate for this burst is T. N. Ukwatta (tilan.ukwatta AT gmail.com). Please contact the BA by email if you require additional information regarding Swift followup of this burst. In extremely urgent cases, after trying the Burst Advocate, you can contact the Swift PI by phone (see Swift TOO web site for information: http://www.swift.psu.edu/too.html.) //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 18501 SUBJECT: GRB 151027B: NOT optical afterglow candidate DATE: 15/10/28 00:19:30 GMT FROM: Daniele Malesani at Dark Cosmology Centre, Niels Bohr Inst Daniele Malesani (DARK/NBI), Nial R. Tanvir (Univ. Leicester), Dong Xu (NAOC/CAS), Jussi Harmanen (NOT and Univ. Turku), Thomas Reynolds (NOT and Turku Univ.), and Pere Blay Serrano (IAC/NOT), report on behalf of a larger collaboration: We observed the field of the #1000 Swift GRB 151027B (Ukwatta et al., GCN 18499) with the Nordic Optical Telescope equipped with the StanCam imager. Observations started on 2015 Oct 27.988 UT (1.04 hr after the GRB trigger), as soon as the field was observable from La Palma. In our first 5-minute image taken in the R band, we detect a single source consistent with the XRT position (Ukwatta et al., GCN 18499), at coordinates (J2000): RA = 05:04:52.69 Dec = -06:27:00.8 with an uncertainty of 0.5". Calibrating the image against nearby USNO stars, we measure for this object R = 18.44 +- 0.05 (Vega). While we have not yet any variability information, the positional consistency with the XRT error circle and the lack of any object in the DSS at this location suggest that this is the optical afterglow of GRB 151027B. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 18502 SUBJECT: GRB 151027A: UVOT Observations DATE: 15/10/28 01:04:14 GMT FROM: Mike Siegel at PSU/Swift MOC B. G. Balzer (PSU), M. H. Siegel (PSU) and A. Maselli (INAF-IASFPA) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 151027A 96 s after the BAT trigger (Maselli et al., GCN Circ. 18478). We confirm the source initially reported by Maselli et al. (GCN Circ. 18478) and since observed by numerous ground-based observatories (Zheng and Filippenko, GCN Circ. 18479; Elenin et al., GCN Circ. 18480; Perley and Cenko, GCN Circ. 18481; Xu et al., GCN Circ. 18485; Yano et al., GCN Circ. 18491; Wren et al., GCN Circ. 18495). We report a position of: RA(J2000) = +18h 09m 57.26s Dec(J2000) = +61d 21' 05.4" The light curve shows complex behavior, with marginal evidence of brightening after the initial finding chart, then fading with a decay slope of 0.6-0.8 over the first orbit. The second orbit magnitudes are consistent with no fading from those measured at the end of the first orbit while the third orbit shows significant fading. Preliminary detections using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the early exposures are: Filter T_start(s) T_stop(s) Exp(s) Mag white (fc) 95 245 147 14.52+-0.02 white 589 609 19 14.44+-0.04 white 762 782 19 14.71+-0.04 white 858 1008 147 14.81+-0.02 white 1161 1354 38 15.07+-0.04 white 1510 1529 19 15.23+-0.04 white 6449 6649 197 15.28+-0.01 white 23966 24662 677 17.14+-0.01 v 639 1579 116 15.12+-0.04 b 564 1505 97 15.37+-0.03 u 308 1479 323 14.00+-0.03 w1 688 1455 77 14.71+-0.05 m2 663 1598 88 14.98+-0.06 w2 615 1555 116 15.12+-0.05 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.05 in the direction of the burst (Schlegel et al. 1998). //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 18503 SUBJECT: GRB 151027A: THO optical observations DATE: 15/10/28 02:54:58 GMT FROM: Veli-Pekka Hentunen at Taurus Hill Obs,A95 Veli-Pekka Hentunen, Markku Nissinen and Tuomo Salmi (Taurus Hill Observatory, Varkaus, Finland) report: We have detected GRB 151027A optical afterglow at Taurus Hill Observatory (A95) using Meade 16" ACF 0.40-m/8.0 telescope and SBIG ST-8XME CCD. The observations were started at 2015-10-27 17:11:39 (UT). Eight photometric R filter and eight photometric V filter images with 300 sec exposure time were taken. The afterglow was detected at the following position RA 18:09:56.72 and DEC +61:21:13.2. The following magnitudes were obtained from the observations using NOMAD1 1512-0243178 (R=13.200 and V=13.670) as a comparison star: Tmid(h)+T0 Filter Exp. time Mag Mag. Err. 13.393 R 4x300s 17.06 0.12 13.747 V 4x300s 17.56 0.25 14.103 R 4x300s 17.06 0.09 14.457 V 4x300s 17.49 0.10 --- This email has been checked for viruses by Avast antivirus software. https://www.avast.com/antivirus //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 18504 SUBJECT: GRB 151027B: Enhanced Swift-XRT position DATE: 15/10/28 03:56:46 GMT FROM: Phil Evans at U of Leicester J.P. Osborne, A.P. Beardmore, P.A. Evans and M.R. Goad (U. Leicester) report on behalf of the Swift-XRT team. Using 1168 s of XRT Photon Counting mode data and 3 UVOT images for GRB 151027B, we find an astrometrically corrected X-ray position (using the XRT-UVOT alignment and matching UVOT field sources to the USNO-B1 catalogue): RA, Dec = 76.21941, -6.45016 which is equivalent to: RA (J2000): 05h 04m 52.66s Dec (J2000): -06d 27' 00.6" with an uncertainty of 1.8 arcsec (radius, 90% confidence). This position may be improved as more data are received. The latest position can be viewed at http://www.swift.ac.uk/xrt_positions. Position enhancement is described by Goad et al. (2007, A&A, 476, 1401) and Evans et al. (2009, MNRAS, 397, 1177). This circular was automatically generated, and is an official product of the Swift-XRT team. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 18505 SUBJECT: GRB 151027B: VLT/X-shooter redshift DATE: 15/10/28 06:34:50 GMT FROM: Nial Tanvir at U.Leicester D. Xu (NAOC/CAS), N. R. Tanvir (U. Leicester), D. Malesani, J. Fynbo (DARK) report: We observed the optical afterglow of GRB 151027B (Ukwatta et al. GCN 18499, Malesani et al. GCN 18501) with the VLT X-shooter spectrograph covering a spectral range 3400A to 18000A. Observations began at 2015 Oct 28 03:50 UT, approximately 5h09m post-burst. The spectrum shows a clear continuum in the red, with a strong break corresponding to Ly-alpha at a redshift of z=4.063. This is supported by detection of absorption lines of Si II 1259/1260, Si II* 1265, CII 1335, CII* 1336, OI 1302, SiII 1304, S IV 1394/1403, CIV 1548/1551, FeII 1608 and Al II 1671 at that redshift. We therefore propose this as the redshift of the 1000th Swift GRB. We thank the staff at Paranal, particularly T. Rivinius, for their support in obtaining these observations. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 18507 SUBJECT: GRB 151027B: GROND Optical/NIR Afterglow Detection DATE: 15/10/28 07:40:47 GMT FROM: Philip Wiseman at MPE/Swift P. Wiseman, J. Greiner (both MPE Garching) report on behalf of the GROND team: We observed the field of GRB 151027B (Swift trigger 661869; (Ukwatta et al., GCN 18499) simultaneously in g'r'i'z'JHK with GROND (Greiner et al. 2008, PASP 120, 405) mounted at the 2.2 m MPG telescope at ESO La Silla Observatory (Chile). Observations started at 06:24 UT on 28/10/2015, 7 hrs 45 mins after the GRB trigger, and are continuing. They were performed at an average seeing of 0.9" and at an average airmass of 1.1. We found a single point source within the enhanced 1.8" Swift-XRT error circle reported by Evans et al. (GCN 18504), common with that reported by Malesani et al. (GCN 18501) and Xu et al. (GCN 18505). Based on 6.6 min of total exposures in g'r'i'z'JHK at a mid time of 06:33:39 UT, we estimate preliminary magnitudes (all in AB system) of g' > 22.4 mag, r' = 20.8 +/- 0.08 mag, i' = 20.1 +/- 0.07 mag, z' = 20.1 +/- 0.07 mag, J = 20.1 +/- 0.4 mag, H = 19.1 +/- 0.3 mag, and K > 18.3 mag. A clear g'-band drop out in the SED leads to a photo-z of 4.3 + 0.3,-0.2, consistent with the redshift derived from the X-shooter spectrum (Xu et al., GCN 18505). The source appears to be fading relative to the NOT report (Malesani et al., GCN 18501), and has continued to do so during our observations. Given magnitudes are calibrated against GROND zeropoints (g'r'i'z') as well as 2MASS field stars (JHK) and are not corrected for the expected Galactic foreground extinction corresponding to a reddening of E_(B-V)=0.2 mag in the direction of the burst (Schlegel et al. 1998). //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 18508 SUBJECT: GRB 151027A: VLA detection DATE: 15/10/28 08:47:38 GMT FROM: Tanmoy Laskar at UC Berkeley T. Laskar (NRAO / UC Berkeley), K. Alexander, and E. Berger (Harvard) report on behalf of a larger collaboration: "We observed GRB 151027A (Maselli et al.; GCN 18478) at multiple frequencies with the VLA beginning on 2015 October 27.95 UT (0.78 days after the burst). At a mean frequency of 21.8 GHz, we detect a bright radio source with a preliminary flux density of ~ 1.7 mJy at RA = 18:09:56.691 +/- 0.001 Dec = 61:21:13.03 +/- 0.02 consistent with the enhanced Swift/XRT position (Goad et al.; GCN 18482) and the optical position (Maselli et al.; GCN 18478, Zheng et al.; GCN 18479, Hentunen et al.; GCN 18503). Follow-up observations are planned. We thank the VLA staff for rapidly scheduling these observations." //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 18509 SUBJECT: GRB 151027B: Swift-XRT refined Analysis DATE: 15/10/28 10:57:09 GMT FROM: Phil Evans at U of Leicester V. D'Elia (ASDC), A. D'ai (INAF-IASFPA), A. Maselli (INAF-IASFPA), L.M. McCauley (PSU), J.A. Kennea (PSU), B. Sbarufatti (INAF-OAB/PSU), C. Pagani (U. Leicester), A.P. Beardmore (U. Leicester), P.A. Evans (U. Leicester) and T.N. Ukwatta report on behalf of the Swift-XRT team: We have analysed 12 ks of XRT data for GRB 151027B (Ukwatta et al. GCN Circ. 18499), from 191 s to 32.5 ks after the BAT trigger. The data comprise 61 s in Windowed Timing (WT) mode (the first 8 s were taken while Swift was slewing) with the remainder in Photon Counting (PC) mode. The enhanced XRT position for this burst was given by Osborne et al. (GCN Circ. 18504). The light curve can be modelled with an initial power-law decay with an index of alpha=5.7 (+/-0.6), followed by a break at T+332 s to an alpha of 0.66 (+0.05, -0.06). A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 1.81 (+0.14, -0.13). The best-fitting absorption column is 4.1 (+2.5, -2.2) x 10^22 cm^-2, at a redshift of 4.063, in addition to the Galactic value of 9.4 x 10^20 cm^-2 (Willingale et al. 2013). The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 3.8 x 10^-11 (4.8 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Galactic foreground: 9.4 x 10^20 cm^-2 Intrinsic column: 4.1 (+2.5, -2.2) x 10^22 cm^-2 at z=4.063 Photon index: 1.81 (+0.14, -0.13) If the light curve continues to decay with a power-law decay index of 0.66, the count rate at T+24 hours will be 0.026 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 9.9 x 10^-13 (1.2 x 10^-12) erg cm^-2 s^-1. The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00661869. This circular is an official product of the Swift-XRT team. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 18510 SUBJECT: GRB 151027A: LCOGT-McDonald afterglow observations DATE: 15/10/28 12:16:09 GMT FROM: Cristiano Guidorzi at Ferrara U,Italy S. Dichiara (U. Ferrara, ICRANet), D. Kopac (U. Ljubljana), C. Guidorzi (U. Ferrara), S. Kobayashi (LJMU), A. Gomboc (U. Ljubljana) on behalf of a larger collaboration report: The 1-m LCOGT McDonald observatory began observing Swift GRB 151027A (Maselli et al. GCN 18478) on October 28, 01:29:27 UT (0.90 days after the burst trigger) with SDSS R and I filters. We clearly detect the optical afterglow (Maselli et al.; Zheng & Filippenko GCN 18479; Elenin et al. GCN 18480; Perley & Cenko GCN 18481; Xu et al. GCN 18485) with the following magnitudes: Mid Time Exposure Filter Magnitude (days) (s) ------------------------------------------------------- 0.90 5x120 R 16.87 +- 0.04 0.91 6x120 I 17.26 +- 0.05 ------------------------------------------------------- Calibration is done against nearby USNOB-1 star RA(J2000)=18:09:53.742, DEC(J2000)=+61:20:57.27, assuming R2=17.21 mag and I=17.17 mag. We note the presence of another USNOB-1 object at RA(J2000)=18:09:56.489, DEC(J2000)=+61:21:10.64, lying at 3.1 arcsec from the GRB afterglow. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 18511 SUBJECT: GRB 151027B: MASTER-NET early OT detection DATE: 15/10/28 13:24:39 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs D.Buckley, S. Potter, A.Kniazev, M.Kotze South African Astronomical Observatory R. Rebolo, M. Serra, N. Lodieu, G. Israelian, L. Suarez-Andres The Instituto de Astrofisica de Canarias E. Gorbovskoy, V. Lipunov, N.Tyurina, V.Kornilov, P.Balanutsa, A.Kuznetsov, D.Kuvshinov, D. Vlasenko, E.Popova Lomonosov Moscow State University, Sternberg Astronomical Institute K.Ivanov, S.Yazev, N.M.Budnev, O.Gres, O.Chuvalaev, V.A.Poleshchuk Irkutsk State University A. Tlatov, A.V. Parhomenko, D. Dormidontov, V.Sennik Kislovodsk Solar Station of the Pulkovo Observatory V.Yurkov, Yu.Sergienko, D.Varda, E.Sinyakov Blagoveschensk Educational State University, Blagoveschensk V.Krushinski, I.Zalozhnih Ural Federal University, Kourovka Hugo Levato and Carlos Saffe Instituto de Ciencias Astronomicas, de la Tierra y del Espacio (ICATE) Claudio Mallamaci, Carlos Lopez and Federico Podest Observatorio Astronomico Felix Aguilar (OAFA) Two MASTER II robotic telescope (MASTER-Net: http://observ.pereplet.ru) located in SAAO and IAC was pointed to the GRB151027B (Ukwatta et. al GCN 18499) 25 sec after notice time and 156 sec after trigger time at 2015-10-27 22:43:19 UT. On our first (30s exposure) set we haven`t found optical transient (Malesani et. al. GCN 18501, Xu et. al. GCN 18505, Wiseman et. al GCN 18507) within SWIFT error-box. The 2-sigma upper limit has been about 17.7 mag. The observations were significantly complicate the closest distance to the Moon (~ 35 d). The Moon background light is picked up the sky background on our cameras more than 10 times. Therefore, we could not get deep enough image. Nevertheless, we detect OT on a several coadd images in consequent time in SAAO. The first time we see OT 475 seconds after the trigger with magnitude ~ 18.9. OT had a slight brightening 1736 seconds after the trigger to 18.5 mag. The preliminary photometry available at table below. Table 1. GRB151027B MASTER-SAAO Early photometry. T-Ts T-Tm Exptime Mag.(P/+P\) Coadd 159 174 2 x 30 >17.7 1 201 221 2 x 40 >18.0 1 252 277 2 x 50 >18.3 1 313 343 2 x 60 >18.3 1 384 424 2 x 80 >18.4 1 159 311 2 x 260 >19.0 5 475 842 2 x 690 18.9 5 1235 1736 2 x 900 18.5 5 2264 3280 2 x 1800 18.9 10 3499 4515 2 x 1800 19.1 10 T - is trigger time, Ts - exposure start time, Tm - exposure middle time. We see OT in separate polarizations on s/n~5 confidence lewel. Table 1 shows the averaged data from two mutually perpendicular polarization. The message may be cited. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 18512 SUBJECT: GRB 151027B: RATIR Observations DATE: 15/10/28 14:10:19 GMT FROM: Nat Butler at UC berkeley Alan M. Watson (UNAM), Nat Butler (ASU), Alexander Kutyrev (GSFC), William H. Lee (UNAM), Michael G. Richer (UNAM), Ori Fox (UCB), J. Xavier Prochaska (UCSC), Josh Bloom (UCB), Antonino Cucchiara (GSFC/STScI), Eleonora Troja (GSFC), Owen Littlejohns (ASU), Enrico Ramirez-Ruiz (UCSC), José A. de Diego (UNAM), Leonid Georgiev (UNAM), Jesús González (UNAM), Carlos Román-Zúñiga (UNAM), Neil Gehrels (GSFC), Harvey Moseley (GSFC), John Capone (UMD), V. Zach Golkhou (ASU), and Vicki Toy (UMD) report: We observed the field of GRB 151027B (Ukwatta et al., GCN 18499) with the Reionization and Transients Infrared Camera (RATIR; www.ratir.org) on the 1.5m Harold Johnson Telescope at the Observatorio Astronómico Nacional on Sierra San Pedro Mártir from 2015/10 28.26 to 2015/10 28.51 UTC (7.46 to 13.55 hours after the BAT trigger), obtaining a total of 3.51 hours exposure in the r, i, and z bands. We detect a source at 05:04:52.69 -06:27:00.8 (J2000, +/-0.05), within the Swift-XRT error circle. In comparison with the USNO-B1 and 2MASS catalogs, we obtain the following detections: r = 20.83 +/- 0.05 i = 20.18 +/- 0.04 z = 19.49 +/- 0.21 These magnitudes are in the AB system and are not corrected for Galactic extinction in the direction of the GRB. This source coincides with the source reported by Malesani et al. (GCN 18501), Xu et al. (GCN 18505), Wiseman et al. (GCN 18507), and Buckley et al. (GCN 18511). The source appears to have faded since these earlier observations and furthermore fades by about 0.5 mag in i over the course of our observations. We thank the staff of the Observatorio Astronómico Nacional in San Pedro Mártir. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 18513 SUBJECT: GRB 151027A: continued GMG observation DATE: 15/10/28 14:16:34 GMT FROM: Jirong Mao at Yunnan Obs J. Zhang, J. Mao and J. Bai (YNAO) report: We observed the field of GRB 151027A (Maselli et al., GCN 18478) with the 2.4-meter optical telescope at Gao-Mei-Gu of Yunnan Observatories. Observations began at 11:32:30 UT, Oct. 28, 2015, about 31.5 hr after the trigger. We clearly detected the afterglow of GRB 151027A. The magnitude was estimated as R=18.9 +/- 0.1 mag. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 18514 SUBJECT: GRB 151027B: Swift-BAT refined analysis DATE: 15/10/28 14:29:31 GMT FROM: Amy Lien at GSFC T. Sakamoto (AGU), S. D. Barthelmy (GSFC), J. R. Cummings (GSFC/UMBC), N. Gehrels (GSFC), H. A. Krimm (GSFC/USRA), A. Y. Lien (GSFC/UMBC), C. B. Markwardt (GSFC), D. M. Palmer (LANL), M. Stamatikos (OSU), T. N. Ukwatta (LANL) (i.e. the Swift-BAT team): Using the data set from T-239 to T+963 sec from the recent telemetry downlink, we report further analysis of BAT GRB 151027B (trigger #661869) (Ukwatta, et al., GCN Circ. 18499). The BAT ground-calculated position is RA, Dec = 76.188, -6.428 deg which is RA(J2000) = 05h 04m 45.0s Dec(J2000) = -06d 25' 40.2" with an uncertainty of 2.4 arcmin, (radius, sys+stat, 90% containment). The partial coding was 17%. The mask-weighted light curve shows a complex structure with several overlapping peaks that starts at ~T0 and ends at ~T+100 s. T90 (15-350 keV) is 80.00 +- 35.78 sec (estimated error including systematics). The time-averaged spectrum from T+1.00 to T+97.00 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.83 +- 0.27. The fluence in the 15-150 keV band is 1.5 +- 0.3 x 10^-6 erg/cm2. The 1-s peak photon flux is unconstrained due to the weakness of the burst. All the quoted errors are at the 90% confidence level. The results of the batgrbproduct analysis are available at http://gcn.gsfc.nasa.gov/notices_s/661869/BA/ //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 18515 SUBJECT: GRB 151027A : Xinglong TNT optical observation DATE: 15/10/28 14:37:57 GMT FROM: L.P. Xin at NAOC L. P. Xin, X. F. Wang, J. Y. Wei, Y. L. Qiu, J. S. Deng, J. Wang, X. H. Han and C. Wu on behalf of EAFON report: We observed GRB 151027A (Maselli et al., GCN 18478) with Xinglong 0.8-m TNT telescope at 2015-10-27 and 2015-10-28. The optical afterglow (Maselli et al., GCN 18478; Zheng & Filippenko GCN 18479; Elenin et al., GCN 18480; Perley & Cenko GCN 18481; Xu et al, 18485; Zhang et al., GCN 18513) was clearly detected in our multi-band images. The brightness of the optical afterglow is decayed for about 2.5 mag in R-band during our observations as shown in follows: ============================== Date Time(UT) filter mag merr 2015-10-27 11:21:59 R 16.2 0.1 2015-10-28 11:04:00 R 18.7 0.1 ============================== Calibrated by the USNO B1.0 R2 mag More observations are encouraged. The message may be cited. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 18516 SUBJECT: Konus-Wind observation of GRB 151027A DATE: 15/10/28 14:43:29 GMT FROM: Dmitry Svinkin at Ioffe Institute S. Golenetskii, R. Aptekar, D. Frederiks, V. Pal'shin, P. Oleynik, M. Ulanov, D. Svinkin, A. Tsvetkova, A. Lysenko, A. Kozlova, and T. Cline on behalf of the Konus-Wind team, report: The long-duration GRB 151027A (Swift-BAT trigger #661775: Maselli et al., GCN Circ. 18478, Palmer et al., GCN Circ. 18496; Fermi GBM detection: Toelge et al., GCN Circ. 18492) triggered Konus-Wind at T0=14304.154 s UT (03:58:24.154). The burst light curve consists of at least three pulses with a total duration of ~120 s. The emission is seen up to ~5 MeV. The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB151027_T14304/ As observed by Konus-Wind, the burst had a fluence of 1.42(-0.21,+0.37)x10^-5 erg/cm2, and a 64-ms peak flux, measured from T0+0.432 s, of 2.22(-0.61,+0.62)x10^-6 erg/cm2/s (both in the 20 keV - 10 MeV energy range). The time-averaged spectrum of the burst (measured from T0 to T0+131.328 s) is best fit in the 20 keV - 5 MeV range by a power law with exponential cutoff model: dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep) with alpha = -1.44(-0.21,+0.24) and Ep = 173(-46,+135) keV (chi2 = 78/77 dof). Fitting by a GRB (Band) model yields the same alpha and Ep, and an upper limit on the high energy photon index: beta < -2.0 (chi2 = 77/76 dof) The spectrum near the maximum count rate (measured from T0 to T0+8.448 s) is best fit in the 20 keV - 2 MeV range by a power law with exponential cutoff model: dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep) with alpha = -0.96(-0.28,+0.32) and Ep = 91(-11,+14) keV (chi2 = 56/61 dof). Fitting by a GRB (Band) model yields the same alpha and Ep, and an upper limit on the high energy photon index: beta < -2.7 (chi2 = 56/60 dof) Assuming the redshift z=0.81 (Perley et al., GCN Circ. 18487) and a standard cosmology model with H_0 = 70 km/s/Mpc, Omega_M = 0.27, and Omega_Lambda = 0.73, we estimate the following rest-frame parameters: the isotropic energy release E_iso is ~2.4x10^52 erg, the peak luminosity L_iso is ~7x10^51 erg/s, and the rest-frame peak energy of the time-integrated spectrum, Ep,i, is ~310 keV. All the quoted errors are at the 90% confidence level. All the quoted values are preliminary. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 18517 SUBJECT: GRB 151027B: Swift/UVOT Upper Limits DATE: 15/10/28 15:45:21 GMT FROM: Alice Breeveld at MSSL-UCL A. A. Breeveld (UCL-MSSL) and T. N. Ukwatta (LANL) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 151027B 210 s after the BAT trigger (Ukwatta et al., GCN Circ. 18499). No optical afterglow consistent with the XRT position (Osborne et al. GCN Circ. 18504) is detected in the initial UVOT exposures. Preliminary 3-sigma upper limits using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the first finding chart (FC) exposure and subsequent exposures are: Filter T_start(s) T_stop(s) Exp(s) Mag white_FC 210 359 147 >20.0 white 210 4545 344 >20.5 v 366 4956 216 >18.8 b 4141 5737 354 >20.6 u 3935 5571 393 >20.4 w1 415 5366 397 >20.4 m2 4961 5161 197 >19.1 w2 4551 4751 197 >19.9 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.25 in the direction of the burst (Schlegel et al. 1998). //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 18518 SUBJECT: GRB 151027A: T100 observations DATE: 15/10/28 17:37:17 GMT FROM: Eda Sonbas at NASA/GSFC E. Sonbas (Adiyaman Univ.), T. Guver (Istanbul Univ.), E. Gogus (Sabanci Univ.), O. Erece, M. Kocak, S. Eryilmaz, H. Kirbiyik (TUG) report on behalf of a larger collaboration We observed the field of Swift GRB 151027A (Maselli et al., GCN#18478) with the 1.0 meter T100 telescope (Bakirlitepe, TUBITAK National Observatory, Turkey), starting October, 27, 18:32:21 UT (~ 14.5 hours after the trigger). Observations were carried out in the R filter. The afterglow is detected in the R band images with an exposure time of 150 s. Using USNO-B1 star USNO-B1 1513-0237223 (R.A.=272.49, Dec=+61.37) in the field, the magnitudes of the OT were estimated as follows; t-t0 (hr) exp.(s) filt mag err (+/-) 14.56 150 R 16.8 0.06 14.61 150 R 17.2 0.08 Analysis of further observations with the same filter is ongoing. We thank to TUBITAK National Observatory for a partial support in using T100 telescope with project number 10CT100-95 and technical support. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 18519 SUBJECT: GRB 151027A: NOT optical and NIR observations DATE: 15/10/28 18:13:41 GMT FROM: Zach Cano at U of Iceland Z. Cano (U. Iceland), D. Malesani (DARK/NBI), Jussi Harmanen (NOT & U. Turku), Thomas Reynolds (NOT & U. Turku.), Pere Blay Serrano (IAC/NOT) and P. Jakobsson (U. Iceland) report on behalf of a larger collaboration: We observed the field of Swift GRB 151027A (Maselli et al., GCN Circ. 18478) with the Nordic Optical Telescope equipped with the StanCam (optical) and NOTCam (NIR) imagers, in filters BVRI and JHK, respectively. Observations started at 20:53 UT on 27 October 2015. The OT (Maselli et al.) is detected all filters. A summary of our observations follows: Filter t-t0 (hr) Mag +- Merr ----------------------------------------- B 17.94 21.4 +- 0.2 R 18.17 20.6 +- 0.1 I 18.28 19.2 +- 0.1 J 16.92 18.2 +- 0.1 H 17.38 18.3 +- 0.1 K 17.60 17.2 +- 0.2 The optical filters are calibrated to USNO-B1 and the NIR filters to 2MASS, where a single star that appeared in both catalogs was used for the zeropoint calculation. These magnitudes are not corrected for foreground extinction. When these extinguished magnitudes are converted to monochromatic fluxes (using the zeropoints from Fukugita et al. 1995; Hewett et al. 2006), a single power-law with an exponent of -1.25 provides an acceptable fit to the optical-to-NIR spectral energy distribution. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 18520 SUBJECT: GRB 151027B: LCOGT FTN afterglow observations DATE: 15/10/28 20:13:07 GMT FROM: Simone Dichiara at Ferrara U/Italy S. Dichiara (U. Ferrara, ICRANet), D. Kopac (U. Ljubljana), C. Guidorzi (U. Ferrara), S. Kobayashi (LJMU), A. Gomboc (U. Ljubljana) on behalf of a larger collaboration report: The 2-m Faulkes Telescope North in Hawaii began observing Swift GRB 151027B (Ukwatta et al., GCN 18499) on October 28, 12:18:25 UT, i.e., ~ 13.6 hours after the burst trigger, with the r' and i' filters. Although we did not detect the optical counterpart (Malesani et al., GCN 18501; Xu et al., GCN 18505; Wiseman et al., GCN 18507; Buckley et al., GCN 18511; Watson et al., GCN 18512) in the r' filter (R > 20.3), the source is detected in the i' filter with I = 19.6 +/- 0.3 mag at a mid time of 13.9 hours post burst (total exposure in i' of 600 s). The magnitude is calibrated against nearby USNO-B1 stars. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 18521 SUBJECT: GRB 151027A: SAO RAS optical observations DATE: 15/10/28 23:18:01 GMT FROM: Moskvitin Alexander at SAO RAS A. Moskvitin (SAO RAS, Russia), report on behalf of the larger GRB follow-up team: The field of the GRB 151027A (Maselli et al., GCNC #18478) was observed with the Zeiss-1000, 1 meter telescope of SAO RAS on the October, 28. The observations started 36.3 hours after the trigger. Two series of 300 sec. images in Rc band: 6 frames (16:13:57--16:56:20 UT) and 3 frames (17:32:15--17:50:33 UT) were obtained under the tolerable weather conditions. The OT is clearly detected in the stacked frames: # T_mid-T0,h exp,s R_mag 1 36.612 6 x 300 18.7 +/- 0.1 2 37.717 3 x 300 18.9 +/- 0.1 The photometry is based on nearby USNO-B1 stars proposed by A. Pozanenko (IKI RAS). The observations were provided with the help of the SAO RAS staff: V. Komarov, O. Spiridonova and R. Uklein. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 18525 SUBJECT: GRB 151027A: MAXI/GSC detection DATE: 15/10/29 11:01:12 GMT FROM: H. Negoro at Nihon U. T. Masumitsu, H. Negoro, (Nihon U.), N. Kawai (Tokyo Tech), T. Sakamoto (AGU), S. Ueno, H. Tomida, S. Nakahira, M. Kimura, M. Ishikawa, Y. E. Nakagawa (JAXA), T. Mihara, M. Sugizaki, M. Serino, M. Shidatsu, J. Sugimoto, T. Takagi, M. Matsuoka (RIKEN), T. Yoshii, Y. Tachibana (Tokyo Tech), A. Yoshida, Y. Kawakubo, H. Ohtsuki (AGU), H. Tsunemi, R. Imatani (Osaka U.), M. Nakajima, K. Tanaka (Nihon U.), Y. Ueda, T. Kawamuro, T. Hori (Kyoto U.), Y. Tsuboi, S. Kanetou (Chuo U.), M. Yamauchi, D. Itoh (Miyazaki U.), K. Yamaoka (Nagoya U.), M. Morii (ISM) report on behalf of the MAXI team: MAXI/GSC performed scanning observations at the region of GRB 151027A (Maselli et al. GCN 18478) for 48 sec each at the centroid time 03:38:56, 1168 s before the Swift trigger, and 05:11:32, 4388 s after the Swift trigger. No positive 4-10 keV flux was obtained at the former scan transit with the 3 sigma upper limit of 0.037 photons/cm2/s (~ 31 mCrab). At the latter scan transit, the 4-10 keV flux was 0.0166 +/- 0.0175 photons/cm2/s (~ 14 +/- 15 mCrab). The detection is not significant, but the flux is consistent with the interpolation from the Swift/XRT light curve (V. D'Elica et al. #18509). //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 18529 SUBJECT: GRB 151027B: Swift UVOT detection DATE: 15/10/29 15:34:43 GMT FROM: Alice Breeveld at MSSL-UCL A. A. Breeveld (UCL-MSSL) and T. N. Ukwatta (LANL) report on behalf of the Swift/UVOT team: In Swift/UVOT followup observations of GRB 151027B (Ukwatta et al., GCN Circ. 18499) a source is found in the summed up V filter exposures at a position consistent with the XRT (Osborne et al., GCN Circ. 18504) and the optical/NIR counterparts reported by Malesani et al. GCN Circ. 18501, Xu et al. GCN Circ. 18505, Wiseman and Greiner GCN Circ. 18507, Buckley et al. GCN Circ. 18511, Watson et al. GCN Circ. 18512, and Dichiara et al. GCN Circ. 18520. A preliminary detection using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for V data taken in the first and second segment is: Filter T_start(s) T_stop(s) Exp(s) Mag v 191 28529 1986 20.8 ± 0.3 The magnitudes in the table are not corrected for the strong Galactic extinction due to the reddening of E(B-V) = 0.25 in the direction of the burst (Schlegel et al. 1998). //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 18533 SUBJECT: GRB 151027A: Optical counterpart detection DATE: 15/10/29 21:34:24 GMT FROM: Valentyna Golovnya at Main Astro Obs,Kyiv Yu. Protsyuk (RI NAO), O. Kovalchuk (RI NAO) report:   We observed the field of the Swift GRB 151027A (Maselli et al. GCN 18478) with 0.5-m telescope Mobitel KT-50 of Nikolaev observatory with Alta-U9000 CCD-camera with R filter in robotic mode from Oct., 28 (UTC) 20:34:16 till 20:59:59. We obtained 19 unfiltered images of 60 s exposure and calculated coordinates and magnitudes of all detected objects in UCAC4 system. We don't detect any optical counterpart of GRB 151027A (Maselli et al. GCN 18478; Zheng and Filippenko, GCN 18479) in coordinates near (J2000) 18 09 56 +61 21 12 up to ~17.2- 17.5 m . After that we filtered all images and detected optical counterpart in 6 images in coordinates (J2000) 18 09 56.680 (SD=0.s081) +61 21 12.08 (SD=0."63) with brightness near 18.3m (SD=0.3m) //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 18537 SUBJECT: GRB 151027A: Continued P60 Monitoring DATE: 15/10/30 14:37:08 GMT FROM: S. Bradley Cenko at NASA/GSFC S. B. Cenko (NASA-GSFC) and D. A. Perley (DARK/NBI) report on behalf of a larger collaboration: We have continued to image the optical afterglow of GRB151027A (Maselli et al., GCN 18478) with the robotic Palomar 60-inch telescope (see Perley et al., GCN 18481). We report the following r’-band photometry, calibrated with respect to nearby point sources from the APASS survey: t_mid time since burst (d) Magnitude ————————————————————————————————— 2015-10-29T02:14:14 1.93 19.63 +/- 0.04 2015-10-30T02:02:28 2.92 20.48 +/- 0.08 This implies a relatively steep power-law decay index of ~ 1.9 at these times. Continued observations are planned. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 18539 SUBJECT: GRB 151027A: optical follow-up observations DATE: 15/10/31 06:39:13 GMT FROM: Patrick Wiggins at Wiggins Obs P. Wiggins reports: Observed GRB 151027A with a .35-meter optical telescope at my home observatory, IAU 718, on 2015 October 27 from 0433 to 0732 UTC using a clear filter and obtained the following: GRB Countpart: 18h 09m 56.71s +61d 21m 12.78s Reference One: 18h 10m 05.68s +61d 23m 14.97s Reference Two: 18h 09m 51.53s +61d 22m 48.87s Julian Date Date Ref. C Ref. K Var. V C-K Differential Mid Exposure yyyy-mm-dd.ddddd Raw Mag. Raw Mag. Raw Mag. Differ. Mag. -------------- ---------------- --------- --------- --------- --------- ------------ 2457322.689715 2015 10 27.18972 -2.937 -3.111 -1.085 0.174 15.051 2457322.692866 2015 10 27.19287 -2.433 -2.622 -1.355 0.190 14.278 2457322.700101 2015 10 27.20010 -2.732 -2.925 -1.433 0.192 14.499 2457322.703174 2015 10 27.20317 -2.921 -3.112 -1.605 0.191 14.516 2457322.724392 2015 10 27.22439 -2.909 -3.088 -1.391 0.180 14.718 2457322.758285 2015 10 27.25829 -2.949 -3.142 -1.151 0.193 14.998 2457322.786495 2015 10 27.28649 -2.906 -3.085 -0.916 0.180 15.189 2457322.801286 2015 10 27.30129 -2.901 -3.108 -0.722 0.207 15.379 2457322.814370 2015 10 27.31437 -2.879 -3.079 -0.406 0.201 15.673 END //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 18543 SUBJECT: GRB 151027B: RATIR Late-Time Upper Limits DATE: 15/10/31 15:12:21 GMT FROM: Nat Butler at UC berkeley Nat Butler (ASU), Alan M. Watson (UNAM), Alexander Kutyrev (GSFC), William H. Lee (UNAM), Michael G. Richer (UNAM), Ori Fox (UCB), J. Xavier Prochaska (UCSC), Josh Bloom (UCB), Antonino Cucchiara (GSFC/STScI), Eleonora Troja (GSFC), Owen Littlejohns (ASU), Enrico Ramirez-Ruiz (UCSC), José A. de Diego (UNAM), Leonid Georgiev (UNAM), Jesús González (UNAM), Carlos Román-Zúñiga (UNAM), Neil Gehrels (GSFC), Harvey Moseley (GSFC), John Capone (UMD), V. Zach Golkhou (ASU), and Vicki Toy (UMD) report: We observed the field of GRB 151027B (Ukwatta, et al., GCN 18499) with the Reionization and Transients Infrared Camera (RATIR; www.ratir.org) on the 1.5m Harold Johnson Telescope at the Observatorio Astronómico Nacional on Sierra San Pedro Mártir from 2015/10 31.23 to 2015/10 31.52 UTC (78.85 to 85.85 hours after the BAT trigger), obtaining a total of 5.20 hours exposure in the r, i, and z bands. We no longer detect the optical afterglow (Malesani et al., GCN 18501). In comparison with the USNO-B1 and 2MASS catalogs, we obtain the following upper limits (3-sigma): r > 23.45 i > 23.39 z > 18.57 These magnitudes are in the AB system and are not corrected for Galactic extinction in the direction of the GRB. We thank the staff of the Observatorio Astronómico Nacional in San Pedro Mártir.//////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 18548 SUBJECT: GRB 151027B: ATCA radio detection DATE: 15/11/01 07:01:04 GMT FROM: Jochen Greiner at MPI J. Greiner (MPE), M. Wieringa (CSIRO), P. Wiseman (MPE) report for a larger consortium: We observed the field of GRB 151027B (Swift trigger 661869; Ukwatta et al., GCN 18499) simultaneously at 5.5 and 9 GHz with the Australia Telescope Compact Array (ATCA), beginning at October 30.54 UT for 3.3 hrs. At a mean frequency of 9 GHz (with 2 GHz bandwidth) we detect a source at ~67+/-10 microJy at the position of the optical afterglow (Malesani et al., GCN 18501; Wiseman et al., GCN 18507). At the redshift of z=4.063 (Xu et al., GCN 18506) this is among the most luminous GRB radio afterglows. We are grateful to P. Edwards for scheduling this observation. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 18552 SUBJECT: GRB 151027A: Correction to GCN 18519 DATE: 15/11/02 19:12:53 GMT FROM: Zach Cano at U of Iceland ​Z. Cano (U. Iceland) reports on behalf of a larger collaboration: Upon further investigation, it was discovered that the magnitudes given in GCN Circ. 18519 are incorrect. The presented photometry was not for the optical and NIR afterglow of GRB 151027A, but rather the fainter object that is 3.1 arcsec SW of the afterglow (Dichiara et al. GCN Circ. 18510). A revised summary of the NOT observations follows: Filter t-t0 (hr) Mag +- Merr ----------------------------------------- B 17.94 18.2 +- 0.1 R 18.17 17.9 +- 0.1 I 18.28 17.4 +- 0.1 J 16.92 16.4 +- 0.1 H 17.38 15.5 +- 0.1 K 17.60 15.1 +- 0.1 The optical filters are calibrated to USNO-B1 and the NIR filters to 2MASS, where a single star that appears in both catalogs was used for the zeropoint calculation. These magnitudes are not corrected for foreground extinction. When these extinguished magnitudes are converted to monochromatic fluxes (using the zeropoints from Fukugita et al. 1995; Hewett et al. 2006), a single power-law with an exponent of -0.8 provides a good fit to the optical-to-NIR spectral energy distribution. My apologies for the confusion.​ //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 18555 SUBJECT: GRB 151027A: the missing GeV component DATE: 15/11/03 18:21:32 GMT FROM: Remo Rufinni at ICRA R. Ruffini, Y. Aimuratov, U. Barres, R. Belvedere, C.L. Bianco, M. Enderli, M. Kovacevic, R. Moradi, M. Muccino, A. Penacchioni, G.B. Pisani, J.A. Rueda, Y. Wang report: From its overlapping [1] with GRB 090618, the prototype of binary-driven hypernovae (BdHNe), we can assert that this GRB belongs to the class of long GRBs originating in a binary system composed of a carbon-oxygen core and a companion neutron star (Rueda & Ruffini, 2012; Fryer et al. 2014). At the redshift of z=0.81 (Perley et al, GCN 18487) the isotropic energy is Eiso ~ 4x10^(52) erg and the rest-frame spectral peak energy is Ep,i ~ 615 keV (Toelge et al., GCN 18492). A SN should appear after 13-15 days in rest-frame, namely between November 19th and November 23rd. The exceptional feature of GRB 151027A is that, even if it belongs to the BdHN class, there is no high energy emission associated as of today although it was in the Fermi-LAT field of view (Toelge et al., GCN 18492). If confirmed this can be of support to probe the angular distribution of the high energy emission. Additional data in all wavelengths are requested for this most peculiar source. [1] http://www.icranet.org/documents/GRB151027A.pdf //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 18558 SUBJECT: GRB 151027A: Mt. Terskol observatory optical observation DATE: 15/11/04 10:08:22 GMT FROM: Alexei Pozanenko at IKI, Moscow V. Kozlov (IC AMER, NASU), M. Andreev (Terskol Branch of INASAN), E. Mazaeva (IKI), A. Sergeev (Terskol Branch of INASAN), A. Volnova (IKI), A. Pozanenko (IKI) report on behalf of larger GRB follow-up collaboration: We observed the field of GRB 151027A (Maselli et al., GCN 18478) with Zeiss-600 telescope of Mt. Terskol observatory in R-filter starting on Oct. 28 (UT) 21:23:11. We obtained several images in R-filter. The afterglow (Maselli et al., GCN 18478; Zheng and Filippenko, GCN 18479) is clearly detected in a combined image. The photometry of the combined image is following Date UT start t-T0 Filter Exp. OT Err (mid, days) (s) 2015-10-28 21:23:11 1.7431 R 25*120 19.56 0.12 The photometry is based on nearby USNO-B1.0 stars USNO-B.1_id R2 1513-0237223 16.66 1513-0237170 15.58 1513-0237251 16.81 1513-0237270 16.78 //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 18559 SUBJECT: GRB 151027A: Mondy optical observations DATE: 15/11/04 17:58:29 GMT FROM: Alexei Pozanenko at IKI, Moscow E. Mazaeva (IKI), A. Volnova (IKI), E. Klunko (ISTP), I. Korobtsev (ISTP), A. Pozanenko (IKI) report on behalf of larger GRB follow-up collaboration: We observed the Swift GRB 151027A (Maselli et al., GCN 18478) with AZT-33IK telescope of Sayan observatory (Mondy) on several epochs. We obtained images in R-filter on Oct., 27-- Nov., 1 . The afterglow (Maselli et al., GCN 18478; Zheng and Filippenko, GCN 18479) is clearly detected in each epoch. Coordinates of the afterglow are (J2000) 18 09 56.66 +61 21 13.0 with uncertainties of 0.3 arcsec in each coordinate. We also detected the USNO-B1.0 source mentioned in GCN 18510 (Dichiara et al.) in a position (J2000) 18 09 56.44 +61 21 10.8 with uncertainties of 0.3 arcsec in each coordinate. Preliminary photometry of the afterglow on October-29 -- November, 1 is following Date UT start t-T0 Filter Exp. OT Err. (mid, days) (s) 2015-10-29 13:18:41 2.4082 R 55*60 19.84 0.05 2015-10-30 12:11:18 3.3736 R 78*60 20.32 0.06 2015-10-31 12:47:18 4.3958 R 41*120 21.25 0.07 2015-11-01 12:28:18 5.3694 R 19*120 21.50 0.12 The photometry is based on nearby USNO-B1.0 stars USNO-B.1_id R2 1513-0237223 16.66 1513-0237170 15.58 1513-0237251 16.81 1513-0237270 16.78 Late time photometry could be influenced by the nearby USNO-B1.0 source. The overall light curve of our observations as well as photometry reported in GCNs 18480, 18521,18558 can be found in http://grb.rssi.ru/GRB151027A/GRB151027A_lc.png //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 18567 SUBJECT: GRB 151027A: Hankasalmi optical observations DATE: 15/11/08 09:04:54 GMT FROM: Arto Oksanen at Nyrola Obs., Finland Arto Oksanen (Hankasalmi Obs., Hankasalmi, Finland) reports the following observations of GRB 151027A (Maselli et al. 2015, GCN Circular #18478; Zheng et al. 2015, GCN Circular #18479, and many subsequent Circulars) to the AAVSO High Energy Network: A. Oksanen observed the location of GRB 151027A using the Hankasalmi Observatory 0.4-m Richey-Chretien telescope using an SBIG STL-1001E camera. Time-series images were obtained with both Rc and clear filters, with fifty 60-second frames obtained in each filter. Clear filtered images were obtained between 16:27:07 UT and 22:01:23 UT on 2015 October 27, and Rc-filtered images were obtained between 18:59:58 and 21:45.04 UT. Photometry was performed using an ensemble of comparison stars with APASS photometry available from AAVSO VSP (www.aavso.org/vsp). The afterglow is detected in both Rc- and clear-filtered observations, with evidence of fading between the start and end of the observing run. Photometry of co-added groups of images yields the following: Clear filter: t-t0(d) m(CR) err(CR) 0.5235 16.872 0.030 0.5334 16.816 0.030 0.6531 17.160 0.044 0.6644 17.322 0.047 0.7468 17.575 0.065 Rc filter: t-t0(d) m(R) err(R) 0.6365 17.257 0.058 0.6848 17.544 0.074 0.7353 17.580 0.118 These magnitudes of GRB 151027A are consistent with other magnitudes obtained at similar epochs of this burst (e.g. Hentunen et al. GCN Circular #18503; Sonbas et al. #18518). //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 18575 SUBJECT: GRB 151027A: continued Mondy optical observations DATE: 15/11/10 19:10:04 GMT FROM: Alexei Pozanenko at IKI, Moscow E. Mazaeva (IKI), E. Klunko (ISTP), A. Volnova (IKI), I. Korobtsev (ISTP), A. Pozanenko (IKI) report on behalf of larger GRB follow-up collaboration: We continue observations (GCN 18559) of the Swift GRB 151027A (Maselli et al., GCN 18478) with AZT-33IK telescope of Sayan observatory (Mondy). We obtained images in R-filter on Nov., 4, 5, 7-9. In a combined image obtained on Nov. 7 we clearly detect a galaxy which coincide with the object 1513-0237216 of USNO-B1.0 catalog. The object was also mentioned in GCN 18510 (Dichiara et al.) and GCN 18559 (Mazaeva et al.) The finding chart can be found in http://grb.rssi.ru/GRB151027A/GRB151027A_20151107_AZT33IK_host.png The afterglow (Maselli et al., GCN 18478; Zheng and Filippenko, GCN 18479) is not well detected. The afterglow might overlap with North-East wing of the galaxy. The galaxy could be suggested as a host galaxy of GRB 151027A. Preliminary photometry of the galaxy is R= 20.60+/-0.04 at November, 7. The photometry is based on nearby USNO-B1.0 stars referenced in GCN 18559. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 18608 SUBJECT: GMRT radio detection of GRB 151027A DATE: 15/11/16 11:43:16 GMT FROM: Poonam Chandra at TIFR Poonam Chandra (NCRA-TIFR) and A. J. Nayana (NCRA-TIFR) reports: We carried out Giant Metrewave Radio Telescope (GMRT) observations of GRB 151027A (GCN Circ. 18478) at 1390 MHz band on 2015 Nov 15.19 UT. We detect the radio afterglow of the GRB in the Swift error circle (GCN Circ. 18482). The 1390 MHz band flux density of the afterglow is 312+/-64 uJy. Map rms is 37 uJy. Further observations are planned. We thank GMRT staff for making these observations possible. -- _________________________________________ Poonam Chandra National Centre for Radio Astrophysics Tata Institute of Fundamental Research Pune University Campus, Ganeshkhind Pune 411007, Maharashtra, INDIA Phone: +91 20 2571 9290 Fax: +91 20 2569 7257 Email: poonam@ncra.tifr.res.in Web: www.ncra.tifr.res.in:8081/~poonam/ _________________________________________ //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 18609 SUBJECT: GRB151027A; Optical observations DATE: 15/11/16 12:16:29 GMT FROM: G.C. Anupama at IIA,Bangalore We observed the field of GRB 151027A (Maselli et al., GCN 18478) using the 2m Himalayan Chandra Telescope of Indian Astronmical Observatory, Hanle, India. The GRB field was observed in Bessells R band, during 14:56 UT to 16:20 UT on 2015-10-27. We obtained 20 frames, each of 150 seconds exposure time. The optical afterglow of GRB 151027A (e.g., Maselli et al., GCN 18478; Zheng & Filippenko, GCN 18479; Elenin et al., GCN 18480; Perley & Cenko, GCN 18481) is clearly detected in each image. The measured magnitudes, calibrated using nearby USNO B1.0 (R2 magnitudes) stars are listed below. --------------------------------------------------------------------- Time (UT start) Filter Mag error 14:56 R 16.60 0.06 15:36 R 16.67 0.07 16:20 R 16.86 0.08 ----------------------------------------------------------------------- This message may be cited. D.K. Sahu and G.C. Anupama (Indian Institute of Astrophysics, Bengaluru) //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 18616 SUBJECT: GRB 151027A: SAO RAS and Mt. Terskol observations DATE: 15/11/18 12:41:05 GMT FROM: Moskvitin Alexander at SAO RAS A. S. Moskvitin (SAO RAS), I. V. Sokolov (Terskol Branch of INASAN) report on behalf of larger GRB follow-up team. We observed the field of GRB 151027A twice: with 2-m Zeiss-2000 + FLI CCD (Mt. Terskol) and 1-m Zeiss-1000 + EEV 42-40 CCD (SAO RAS) on November 6 and 12 respectively (T-T0 = 10.5 and 16.5 days). We have obtained 10x300 and 24x300 sec. frames in R band. We do not detect the GRB OT (Maselli et al., GCNC #18478) down to the limiting magnitude R_lim = 22.8 in both stacked images. As the standard stars we used USNO-B1 objects from GCNCs #18521, 18558 and 18559. We should note that nearby USNO-B1 source reported by S. Dichiara et al. (GCNC #18510) and E. Mazaeva et al. (GCNC #18559) is clearly detected in our images. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 18620 SUBJECT: 610 MHz detection of GRB 151027A with the GMRT DATE: 15/11/19 10:52:47 GMT FROM: Poonam Chandra at TIFR Poonam Chandra (NCRA-TIFR) and A. J. Nayana (NCRA-TIFR) reports: We carried out Giant Metrewave Radio Telescope (GMRT) observations of GRB 151027A (GCN Circ. 18478) at 610 MHz band on 2015 Nov 19.19 UT. We detect the radio afterglow of the GRB in the Swift error circle (GCN Circ. 18482). The 610 MHz band flux density of the afterglow is 522+/-94 uJy. Map rms is 56 uJy. Further observations are planned. We thank GMRT staff for making these observations possible. -- _________________________________________ Poonam Chandra National Centre for Radio Astrophysics Tata Institute of Fundamental Research Pune University Campus, Ganeshkhind Pune 411007, Maharashtra, INDIA Phone: +91 20 2571 9290 Fax: +91 20 2569 7257 Email: poonam@ncra.tifr.res.in Web: www.ncra.tifr.res.in:8081/~poonam/ _________________________________________ //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 18635 SUBJECT: GRB 151027A: Maidanak optical observations DATE: 15/11/22 21:48:09 GMT FROM: Alexei Pozanenko at IKI, Moscow A. Pozanenko (IKI), E. Mazaeva (IKI), A. Volnova (IKI), O. Burhonov (UBAI) report on behalf of larger GRB follow-up collaboration: We observed the Swift GRB 151027A (Maselli et al., GCN 18478) with AZT-22 telescope of Maidanak observatory equipped with SNUCAM in R filter. We obtained several images in R-filter on Oct., 30, Nov., 6 and Nov., 9 under mean FWHM of about 0.9". The afterglow (Maselli et al., GCN 18478; Zheng and Filippenko, GCN 18479) is clearly detected in each epoch. The afterglow is well separated from nearby source (Dichiara et al.GCN 18510; Mazaeva et al., GCN 18559). Preliminary photometry of the afterglow is following Date UT start t-T0 Filter Exp. OT Err. (mid, days) (s) 2015-11-06 15:04:07 10.474 R 10*300 23.30 0.24 2015-11-09 14:06:04 13.443 R 10*300 23.33 0.20 The photometry is based on nearby USNO-B1.0 stars USNO-B.1_id R2 1513-0237223 16.66 1513-0237251 16.81 1513-0237270 16.78 A preliminary light curve of the afterglow can be found in http://grb.rssi.ru/GRB151027A/GRB151027A_lc.png At this time it is unclear what is a reason of flattening of the light curve at 11-13 days. It might be SN signature or it is continuing bumps of the light curve previously seen at least on ~ 1.3 days and ~3 days.