//////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 17766 SUBJECT: GRB 150428B: Swift detection of a burst DATE: 15/04/28 03:37:48 GMT FROM: Kim Page at U.of Leicester K. L. Page (U Leicester), M. M. Chester (PSU), F. E. Marshall (NASA/GSFC), T. Sakamoto (AGU) and M. H. Siegel (PSU) report on behalf of the Swift Team: At 03:12:03 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 150428B (trigger=639278). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 292.654, +4.116 which is RA(J2000) = 19h 30m 37s Dec(J2000) = +04d 06' 57" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a double-peaked structure with a duration of about 30 sec. The peak count rate was ~1800 counts/sec (15-350 keV), at ~3 sec after the trigger. The XRT began observing the field at 03:13:50.9 UT, 107.5 seconds after the BAT trigger. Using promptly downlinked data we find a bright, fading, uncatalogued X-ray source located at RA, Dec 292.63764, 4.12529 which is equivalent to: RA(J2000) = 19h 30m 33.03s Dec(J2000) = +04d 07' 31.0" with an uncertainty of 3.7 arcseconds (radius, 90% containment). This location is 67 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 3.26 x 10^21 cm^-2 (Willingale et al. 2013). The initial flux in the 2.5 s image was 8.91e-09 erg cm^-2 s^-1 (0.2-10 keV). UVOT took a finding chart exposure of 150 seconds with the White filter starting 117 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. Because of the density of catalogued stars, further analysis is required to report an upper limit for any afterglow in the sub-image. The 8'x8' region for the list of sources generated on-board covers 100% of the XRT error circle. Because of the density of catalogued stars, further analysis is required to report an upper limit for any afterglow in the region. No correction has been made for the expected extinction corresponding to E(B-V) of 0.40. Burst Advocate for this burst is K. L. Page (klp5 AT leicester.ac.uk). 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: 17773 SUBJECT: GRB 150428B: Enhanced Swift-XRT position DATE: 15/04/28 11:45:22 GMT FROM: Phil Evans at U of Leicester A.P. Beardmore, P.A. Evans, M.R. Goad and J.P. Osborne (U. Leicester) report on behalf of the Swift-XRT team. Using 1321 s of XRT Photon Counting mode data and 1 UVOT images for GRB 150428B, 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 = 292.63941, +4.12505 which is equivalent to: RA (J2000): 19h 30m 33.46s Dec (J2000): +04d 07' 30.2" with an uncertainty of 1.6 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: 17776 SUBJECT: GRB 150428B: Swift-BAT refined analysis DATE: 15/04/28 13:45:43 GMT FROM: Takanori Sakamoto at AGU J. R. Cummings (GSFC/UMBC), S. D. Barthelmy (GSFC), W. H. Baumgartner (GSFC/UMBC), N. Gehrels (GSFC), H. A. Krimm (GSFC/USRA), A. Y. Lien (GSFC/UMBC), C. B. Markwardt (GSFC), K. L. Page (U Leicester), 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-239 to T+963 sec from the recent telemetry downlink, we report further analysis of BAT GRB 150428B (trigger #639278) (Page, et al., GCN Circ. 17766). The BAT ground-calculated position is RA, Dec = 292.661, 4.114 deg which is RA(J2000) = 19h 30m 38.8s Dec(J2000) = +04d 06' 52.2” with an uncertainty of 1.3 arcmin, (radius, sys+stat, 90% containment). The partial coding was 40%. The mask-weighted light curve shows three peaks. The first peak starts at T-40 sec, peaks at T-25 sec and ends at T-20 sec. The second peak starts at T-15 sec, peaks at T+5 sec and ends at T+50 sec. And the third peak starts at T+55 sec, peaks at T+65 sec and ends at T+120 sec. T90 (15-350 keV) is 130.9 +- 15.6 sec (estimated error including systematics). The time-averaged spectrum from T-40.1 to T+121.7 sec is best fit by a power law with an exponential cutoff. This fit gives a photon index 1.0 +- 0.5, and Epeak of 55 +- 10 keV (chi squared 37.44 for 56 d.o.f.). For this model the total fluence in the 15-150 keV band is 3.7 +- 0.3 x 10^-6 erg/cm2 and the 1-sec peak flux measured from T+1.36 sec in the 15-150 keV band is 1.5 +- 0.3 ph/cm2/sec. A fit to a simple power law gives a photon index of 1.87 +- 0.10 (chi squared 49.44 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/639278/BA/ //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 17780 SUBJECT: GRB 150428B: MASTER-net prompt optical observation DATE: 15/04/28 15:33:45 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs D.Buckley, S. Potter, A.Kniazev, M.Kotze South African Astronomical Observatory E. Gorbovskoy, V. Lipunov, N.Tyurina, V.Kornilov, P.Balanutsa, A.Kuznetsov, D.Kuvshinov, 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, A. Popov 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) MASTER II robotic telescope (MASTER-SAAO: http://observ.pereplet.ru) located in SAAO was pointed to the GRB150428B 24 sec after notice time and 59 sec after trigger time at 2015-04-28 03:13:03 UT in two polarizations. On our first (10s exposure) set we haven`t found optical transient within SWIFT BAT (Page et. al GCN 17766) and XRT (Beardmore et al. GCN 17773) error-boxes . We have 3x2 images during Gamma Ray activity (see Page et al., GCN 17777) in two polarizations. So our observations is prompt observations. We obtain a followin upper limits on single and coadd images: Date start T_start -T_trig T_mid-T_trig Expt. Limit Coadd 03:13:03.3 59 64 10 16.5 no 03:13:03.3 59 97 50 17.4 3 03:13:03.3 59 529 810 19.3 12 Data analysis was hampered by a high density of stars in the error box. XRT position covered by bright (~15m) star USNO B1 0941-0468603. The message may be cited. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 17781 SUBJECT: GRB 150428B: Swift-XRT refined Analysis DATE: 15/04/28 15:37:03 GMT FROM: Phil Evans at U of Leicester P. D'Avanzo (INAF-OAB), V. D'Elia (ASDC), J.A. Kennea (PSU), B. Sbarufatti (INAF-OAB/PSU), D.N. Burrows (PSU), P.A. Evans (U. Leicester), A. Amaral-Rogers (U. Leicester), J.P. Osborne (U. Leicester), M. de Pasquale (INAF-IASFPA) and K.L. Page report on behalf of the Swift-XRT team: We have analysed 8.3 ks of XRT data for GRB 150428B (Page et al. GCN Circ. 17766), from 100 s to 34.4 ks after the BAT trigger. The data comprise 187 s in Windowed Timing (WT) mode (the first 6 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 Beardmore et al. (GCN Circ. 17773). The light curve can be modelled with a series of power-law decays. The initial decay index is alpha=2.31 (+0.16, -0.20). At T+170 s the decay steepens to an alpha of 4.92 (+0.15, -0.16) before breaking again at T+618 s to a final decay with index alpha=0.29 (+/-0.07). A spectrum formed from the WT mode data can be fitted with an absorbed power-law with a photon spectral index of 1.93 (+0.06, -0.05). The best-fitting absorption column is 3.51 (+0.28, -0.25) x 10^21 cm^-2, consistent with the Galactic value of 3.3 x 10^21 cm^-2 (Willingale et al. 2013). The PC mode spectrum has a photon index of 1.90 (+0.16, -0.08) 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 3.9 x 10^-11 (5.6 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 3.3 (+0.3, -0.0) x 10^21 cm^-2 Galactic foreground: 3.3 x 10^21 cm^-2 Excess significance: <1.6 sigma Photon index: 1.90 (+0.16, -0.08) If the light curve continues to decay with a power-law decay index of 0.29, the count rate at T+24 hours will be 0.027 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.1 x 10^-12 (1.5 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/00639278. This circular is an official product of the Swift-XRT team. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 17787 SUBJECT: GRB 150428B: Swift/UVOT Upper Limits DATE: 15/04/29 13:20:58 GMT FROM: Margaret Chester at PSU M. M. Chester (PSU) and K. L. Page (U Leicester) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 150428B 117 s after the BAT trigger (Page et al., GCN Circ. 17766). No optical afterglow consistent with the enhanced XRT position (Beardmore et al., GCN Circ. 17773) 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) exposures and subsequent exposures are: Filter T_start(s) T_stop(s) Exp(s) UL (3-sigma) white_FC 117 267 146 >20.9 u_FC 329 579 246 >20.1 white 117 5414 588 >21.6 v 659 5825 313 >19.6 b 584 6598 445 >20.8 u 329 6440 717 >20.8 w1 708 6235 293 >20.0 m2 683 6030 294 >19.9 w2 634 5620 313 >20.2 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.40 in the direction of the burst (Schlegel et al. 1998). //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 17788 SUBJECT: GRB 150428B: IRSF NIR upper limits DATE: 15/04/29 23:40:11 GMT FROM: Daisuke Kuroda at OAO/NAOJ K. L. Murata (Nagoya U.), S. Nishiyama, A. Iwamatsu, I. Kawamata (Miyagi University of Education), and T. Nagayama (Kagoshima U.) We observed the field of GRB 150428B ( Page et al., GCN Circular #17766) with the near-infrared (J, H, Ks) simultaneous imaging camera SIRIUS attached to 1.4 m telescope IRSF ( InfraRed Survey Facility) in Sutherland observatory, South Africa. The observations started on 2015-04-28 03:59:59 UT (~ 48 min. after the burst). We could not detect the afterglow within the XRT error circle reported in the GCN circular in the three bands. We have obtained the following preliminary upper limits (Vega magnitude system): J > 17.4 H > 16.8 Ks > 15.3. Given magnitudes were calibrated against 2MASS point sources in this field. The upper limits were determined as the magnitudes of the faintest star within 1 arcmin from the XRT position. This observation was carried out by IRSF and OISTER collaboration.