//////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 18739 SUBJECT: GRB 151228B: Swift detection of a burst with an optical detection DATE: 15/12/28 23:03:29 GMT FROM: Scott Barthelmy at NASA/GSFC A. Y. Lien (GSFC/UMBC), S. D. Barthelmy (GSFC), D. N. Burrows (PSU), F. E. Marshall (NASA/GSFC), L. M. McCauley (PSU) and K. L. Page (U Leicester) report on behalf of the Swift Team: At 22:47:14 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 151228B (trigger=668641). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 344.441, +8.076, which is RA(J2000) = 22h 57m 46s Dec(J2000) = +08d 04' 34" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve shows FRED-like peak structure with a duration of about 40 sec. The peak count rate was ~2500 counts/sec (15-350 keV), at ~1 sec after the trigger. The XRT began observing the field at 22:48:04.4 UT, 49.6 seconds after the BAT trigger. Using promptly downlinked data we find a bright, fading, uncatalogued X-ray source with an enhanced position: RA, Dec 344.4247, 8.0816 which is equivalent to: RA(J2000) = 22h 57m 41.93s Dec(J2000) = +08d 04' 53.7" with an uncertainty of 2.7 arcseconds (radius, 90% containment). This location is 61 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. A power-law fit to a spectrum formed from promptly downlinked event data gives a column density consistent with the Galactic value of 5.74 x 10^20 cm^-2 (Willingale et al. 2013). The initial flux in the 2.5 s image was 6.74e-09 erg cm^-2 s^-1 (0.2-10 keV). UVOT took a finding chart exposure of 150 seconds with the White filter starting 57 seconds after the BAT trigger. There is a candidate afterglow in the rapidly available 2.7'x2.7' sub-image at RA(J2000) = 22:57:41.85 = 344.42437 DEC(J2000) = +08:04:54.0 = 8.08166 with a 90%-confidence error radius of about 0.80 arc sec. This position is 3.8 arc sec. from the center of the XRT error circle. The estimated magnitude is 19.74 with a 1-sigma error of about 0.17. No correction has been made for the expected extinction corresponding to E(B-V) of 0.06. Burst Advocate for this burst is A. Y. Lien (amy.y.lien AT nasa.gov). 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: 18743 SUBJECT: GRB 151228B: Enhanced Swift-XRT position DATE: 15/12/29 03:40:07 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 2601 s of XRT Photon Counting mode data and 4 UVOT images for GRB 151228B, 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 = 344.42460, +8.08148 which is equivalent to: RA (J2000): 22h 57m 41.90s Dec (J2000): +08d 04' 53.3" 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: 18749 SUBJECT: GRB 151228B: Swift-XRT refined Analysis DATE: 15/12/29 10:11:53 GMT FROM: Phil Evans at U of Leicester J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), A. D'Ai (INAF-IASFPA), A. Maselli (INAF-IASFPA), A. Melandri (INAF-OAB), J.A. Kennea (PSU), B. Sbarufatti (INAF-OAB/PSU), D.N. Burrows (PSU), C. Pagani (U. Leicester) and A.Y. Lien report on behalf of the Swift-XRT team: We have analysed 10 ks of XRT data for GRB 151228B (Lien et al. GCN Circ. 18739), from 40 s to 29.0 ks after the BAT trigger. The data comprise 194 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 Goad et al. (GCN Circ. 18743). The late-time light curve (from T0+4.7 ks) can be modelled with a power-law decay with a decay index of alpha=0.68 (+0.22, -0.21). A spectrum formed from the WT mode data can be fitted with an absorbed power-law with a photon spectral index of 2.43 (+/-0.08). The best-fitting absorption column is 1.78 (+0.21, -0.20) x 10^21 cm^-2, in excess of the Galactic value of 5.7 x 10^20 cm^-2 (Willingale et al. 2013). The PC mode spectrum has a photon index of 1.94 (+0.14, -0.12) and a best-fitting absorption column consistent with the Galactic value. The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 3.4 x 10^-11 (3.7 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 5.7 (+2.3, -0.0) x 10^20 cm^-2 Galactic foreground: 5.7 x 10^20 cm^-2 Excess significance: <1.6 sigma Photon index: 1.94 (+0.14, -0.12) If the light curve continues to decay with a power-law decay index of 0.68, the count rate at T+24 hours will be 8.8 x 10^-3 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 3.0 x 10^-13 (3.2 x 10^-13) erg cm^-2 s^-1. The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00668641. This circular is an official product of the Swift-XRT team. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 18752 SUBJECT: GRB 151228B: Swift-BAT refined analysis DATE: 15/12/29 14:29:59 GMT FROM: Scott Barthelmy at NASA/GSFC H. A. Krimm (GSFC/USRA), S. D. Barthelmy (GSFC), J. R. Cummings (GSFC/UMBC), N. Gehrels (GSFC), A. Y. Lien (GSFC/UMBC), C. B. Markwardt (GSFC), D. M. Palmer (LANL), T. Sakamoto (AGU), M. Stamatikos (OSU), T. N. Ukwatta (LANL) (i.e. the Swift-BAT team): Using the data set from T-61 to T+243 sec from the recent telemetry downlinks, we report further analysis of BAT GRB 151228B (trigger #668641) (Lien, et al., GCN Circ. 18739). The BAT ground-calculated position is RA, Dec = 344.431, 8.081 deg, which is RA(J2000) = 22h 57m 43.4s Dec(J2000) = +08d 04' 52.4" with an uncertainty of 1.0 arcmin, (radius, sys+stat, 90% containment). The partial coding was 100%. The mask-weighted light curve shows a FreD-like peak starting at ~T-10 sec, peaking at ~T+3 sec, and ending at ~T+65 sec. T90 (15-350 keV) is 48.0 +- 16.0 sec (estimated error including systematics). The time-averaged spectrum from T-12.56 to T+67.44 sec is best fit by a power law with an exponential cutoff. This fit gives a photon index 1.09 +- 0.34, and Epeak of 78.1 +- 27.0 keV (chi squared 52.3 for 56 d.o.f.). For this model the total fluence in the 15-150 keV band is 2.4 +- 0.1 x 10^-6 erg/cm2 and the 1-sec peak flux measured from T+10.94 sec in the 15-150 keV band is 1.0 +- 0.2 ph/cm2/sec. A fit to a simple power law gives a photon index of 1.66 +- 0.08 (chi squared 61.6 for 57 d.o.f.). 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/668641/BA/ //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 18755 SUBJECT: GRB 151228B: Fermi GBM observation DATE: 15/12/29 16:58:45 GMT FROM: Peter Veres at UAH P Veres (UAH) reports on behalf of the Fermi GBM Team: "At 22:47:12.59 UT on 28 December 2015, the Fermi Gamma-Ray Burst Monitor triggered and located GRB 151228B (trigger 473035636 / 151228949). which was also detected by the Swift/BAT (Lien et al. 2015, GCN 18739). The GBM on-ground location is consistent with the Swift position. The angle from the Fermi LAT boresight at the GBM trigger time is 107 degrees. The GBM light curve shows of a single pulse with a duration (T90) of about 29 s (50-300 keV). There was a Solar flare coincident with this GRB which affected the low energy channels of GBM. For this reason the spectral analysis was carried out for photon energies above 40 keV. The time-averaged spectrum from T0-6.1 s to T0+21.5 s is adequately fit by a power law function with an exponential high-energy cutoff. The power law index is -1.1 +/- 0.4 and the cutoff energy, parameterized as Epeak, is 93 +/- 9 keV. The event fluence (10-1000 keV) in this time interval is (3.6 +/- 0.4)E-6 erg/cm^2. The 1-sec peak photon flux measured starting from T0+2.3 s in the 10-1000 keV band is 7.6 +/- 0.9 ph/s/cm^2. The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog." [GCN OPS NOTE(29dec15): Per author's request, the "29A" in the Subject-line was changed to "28B", and the "2008" was changed to "2015" in the citation.] //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 18758 SUBJECT: GRB 151228B: MITSuME Akeno optical upper limits DATE: 15/12/29 21:44:48 GMT FROM: Taketoshi Yoshii at Tokyo Tech Y.Muraki, T.Fujiwara, T. Yoshii, Y. Saito, Y. Tachibana, Y.Yano, S.Harita, Y. Yatsu, and N. Kawai (Tokyo Tech) report on behalf of the MITSuME collaboration: We searched for the optical counterpart of GRB 151228B (A. Y. Lien et al., GCN Circular #18739) 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 2015-12-29 09:55:19 UT (~11.1 h after the burst). We did not find any new point source within Swift/XRT circle in all three bands. We obtained following limits for the magnitudes. T0+[sec] MID-UT T-EXP[sec] g' Rc Ic ------------------------------------------------------------- 40085 10:37:06 2507 > 20.9 > 20.6 > 19.6 ------------------------------------------------------------- T0+ : Elapsed time after the burst T-EXP: Total Exposure time We used GSC2.3 catalog for flux calibration. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 18766 SUBJECT: GRB 151228B: Swift/UVOT Detection DATE: 15/12/30 07:45:04 GMT FROM: Alice Breeveld at MSSL-UCL A.A. Breeveld (UCL-MSSL), S.W.K. Emery (UCL-MSSL) and A.Y. Lien (GSFC/UMBC) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 151228B 49 s after the BAT trigger (Lien et al., GCN Circ. 18739). A fading source consistent with the XRT position (Goad et al. GCN Circ. 18743) is detected in the initial UVOT exposures in the white filter. The preliminary UVOT position is: RA (J2000) = 22:57:41.87 = 344.42446 (deg.) Dec (J2000) = +08:04:53.7 = 8.08159 (deg.) with an estimated uncertainty of 0.58 arc sec. (radius, 90% confidence). Preliminary detections and 3-sigma upper limits 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 70 220 147 19.62 ± 0.19 v 49 6132 306 >19.2 b 537 5514 274 >20.0 u 282 5309 520 >20.1 w1 661 6373 303 >20.1 m2 6137 6337 197 >19.9 w2 1386 5927 216 >20.8 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.06 in the direction of the burst (Schlegel et al. 1998). //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 18891 SUBJECT: GRB 151228B: AbAO optical upper limit DATE: 16/01/18 21:23:00 GMT FROM: Alexei Pozanenko at IKI, Moscow E. Mazaeva (IKI), R. Inasaridze (AbAO), V. Ayvazian (AbAO), 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 151228B (Lien et al., GCN 18739) with AS-32 (0.7m) telescope of Abastumani Observatory starting on Dec. 29 (UT) 14:38:28. We do not detect any source within enhanced XRT error circle (Goad et al., GCN 18743): Date UT start t-T0 Filter Exp. UL(3 sigma) (mid, days) (s) 2015-12-29 14:38:28 0.69297 None 35*120 22.1 The photometry is based on nearby SDSS-DR9 stars: SDSS-DR9_id R_Lupton J225738.02+080336.8 18.18 J225747.18+080340.7 16.86 J225736.71+080628.4 17.72 J225752.89+080438.1 17.46 J225726.79+080540.6 16.99