//////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 16177 SUBJECT: GRB 140428A: Swift Detection of a Possible Burst DATE: 14/04/28 23:34:36 GMT FROM: Scott Barthelmy at NASA/GSFC D. Kocevski (NASA/GSFC/ORAU), S. D. Barthelmy (GSFC), A. Y. Lien (NASA/GSFC/ORAU), D. Malesani (DARK/NBI), C. B. Markwardt (NASA/GSFC) and D. M. Palmer (LANL) report on behalf of the Swift Team: At 22:40:50 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 140428A (trigger=597519). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 194.342, +28.357, which is RA(J2000) = 12h 57m 22s Dec(J2000) = +28d 21' 26" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). Most of the expected realtime products were not available for this trigger so we have limited information. We know that the trigger duration is 4 seconds and the image significance is 9 sigma during that exposure. A light curve is not yet available. We note that the position reported in TDRSS light curve notices are incorrect. The position reported above is correct. Because of outage in the TDRSS telemetry downlink, all but one BAT light curve notice and all of the XRT notices are missing. Only a pair of UVOT SourceList and Image notices were received on the ground. However, based on the strong detection in BAT, we believe that this is most likely a real GRB. We will issue a Circular when the full dataset is downlinked. Burst Advocate for this burst is D. Kocevski (dankocevski 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: 16178 SUBJECT: GRB 140428A: Swift-XRT detection of a source DATE: 14/04/29 05:13:35 GMT FROM: Kim Page at U.of Leicester K.L. Page (U. Leicester), D. Malesani (DARK/NBI) and D. Kocevski (NASA/GSFC/ORAU) report on behalf of the Swift-XRT team: We have analysed the initial downlinked Swift-XRT data for the possible GRB 140428A (GCN Circ. 16177) and find a fading X-ray source within the BAT field of view. Using 1124 s of XRT Photon Counting mode data and 3 UVOT images, 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 = 194.36852, 28.38490 which is equivalent to: RA (J2000): 12h 57m 28.45s Dec (J2000): +28d 23′ 05.7′′ 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). The light curve can be modelled with a power-law decay with a decay index of alpha=0.92 (+0.11,-0.10). We therefore confirm that Swift trigger number 597519 is, indeed, a real GRB. This circular is an official product of the Swift-XRT team. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 16179 SUBJECT: GRB 140428A: NOT observations DATE: 14/04/29 05:39:59 GMT FROM: Daniele Malesani at Dark Cosmology Centre, Niels Bohr Inst D. Malesani (DARK/NBI), D. Xu (DARK/NBI), H. Dahle (Univ. Oslo), E. Soto (CUA), report on behalf of the Nordic GRB collaboration: We observed the field of GRB 140428A (Kocevski et al., GCN 16177) with the NOT equipped with the ALFOSC imager. Observations started on 2014 Apr 29.223 UT (5.34 hr after the GRB) and consisted of 20 minutes in r and 12 in z. Within the X-ray error circle (Page et al., GCN 16178), we do not find any object down to a depth r > 22.5 and z > 20.5 (all AB), calibrated to the SDSS. DM thanks Thomas Kruehler (ESO) for insightful discussion. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 16180 SUBJECT: GRB 140428A: Keck detection of a red optical afterglow candidate DATE: 14/04/29 07:23:15 GMT FROM: Daniel Perley at Caltech D. A. Perley (Caltech) reports: I observed the position of GRB 140428A (Kocevski et al., GCN 16177; Page et al., GCN 16178) using LRIS on the Keck I 10-meter telescope. A single 150-second imaging exposure was acquired simultaneously in both g and i filters. An faint source is well-detected inside the XRT error circle in the i-band image at the following location (J2000): RA = 12:57:28.392 dec = +28:23:06.28 However, the object is completely absent in g-band. Photometry relative to SDSS gives magnitudes of: g > 26.42 i = 23.55 +/- 0.07 at a time of 06:09:30 UT (2014-04-29), 7.478 hours after the GRB trigger. If this corresponds to the afterglow of the GRB, the red color suggests either a (moderately) high-redshift or dust-extinguished event. Further observations are planned. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 16181 SUBJECT: GRB 140428A: Keck redshift estimate DATE: 14/04/29 08:49:50 GMT FROM: Daniel Perley at Caltech D. A. Perley (Caltech) reports: I re-observed the afterglow candidate of GRB 140428A in longslit mode using LRIS on the Keck I 10m telescope. One 940-second exposure was taken using the 400/8500 grating (red camera) and 600/4000 grism (blue camera). In a provisional reduction, the spectrum of the object shows a weak, flat continuum between 7000 Angstroms and the red limit of the wavelength range at approximately 10100 Angstroms. The flux sharply drops to zero at 7000 angstroms, though there is faint flux detected in some places slightly further to the blue. No trace is detected on the blue camera. If the drop at 7000 Angstroms is interpreted as a DLA and the onset of the Lyman-alpha forest, this would indicate a redshift for this object of approximately z=4.7. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 16182 SUBJECT: GRB 140428A: 1.5m OSN I-band detection DATE: 14/04/29 11:34:51 GMT FROM: Javier Gorosabel at IAA-CSIC F.J. Aceituno (OSN/IAA-CSIC), A.J. Castro-Tirado (IAA-CSIC/UMA), R. Sanchez-Ramirez (IAA-CSIC), J. Gorosabel (IAA-CSIC/UPV-EHU), report on behalf of a larger collaboration: “We observed the field of GRB 140428A (Kocevski et al., GCN 16177; Page et al., GCN 16178) with the 1.5m OSN telescope at Observatorio de Sierra Nevada. Three 300s images were acquired in the I-band starting on Apr 29, 00:09:39 UT (i.e. ~1.5 hours burst). A preliminary reduction clearly shows the optical afterglow reported by Perley (GCNC 16180) with a Vega magnitude of I~20.8. This magnitude must be taken with caution given the likely presence of the Lyman-alpha break in the I-band filter pass-band.” //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 16186 SUBJECT: GRB 140428A: Swift-BAT refined analysis DATE: 14/04/29 19:57:28 GMT FROM: Amy Lien at GSFC H. A. Krimm (GSFC/USRA), S. D. Barthelmy (GSFC), W. H. Baumgartner (GSFC/UMBC), J. R. Cummings (GSFC/UMBC), N. Gehrels (GSFC), D. Kocevski (NASA/GSFC/ORAU) A. Y. Lien (NASA/UMBC), C. B. Markwardt (GSFC), D. M. Palmer (LANL), T. Sakamoto (AGU), M. Stamatikos (OSU), J. Tueller (GSFC), T. N. Ukwatta (MSU) (i.e. the Swift-BAT team): Using the data set from T-240 to T+602 sec from the recent telemetry downlink, we report further analysis of BAT GRB 140428A (trigger #597519) (Kocevski et al., GCN Circ. 16177). The BAT ground-calculated position is RA, Dec = 194.365, 28.331 deg which is RA(J2000) = 12h 57m 27.5s Dec(J2000) = +28d 19' 53.4" with an uncertainty of 2.2 arcmin, (radius, sys+stat, 90% containment). The partial coding was 70%. The mask-weighted light curve shows a multi-peaked structure starts at ~T-14 s and ends at ~T+6 s. The structure contains two main peaks at ~T-4 s and ~T+2 s. T90 (15-350 keV) is 17.42 +- 5.90 sec (estimated error including systematics). The time-averaged spectrum from T-14.19 to T+5.82 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.54 +- 0.26. The fluence in the 15-150 keV band is 3.4 +- 0.6 x 10^-7 erg/cm2. The 1-sec peak photon flux measured from T+1.30 sec in the 15-150 keV band is 0.6 +- 0.2 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/597519/BA/ //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 16187 SUBJECT: GRB 140428A: Swift/UVOT Upper Limits DATE: 14/04/29 21:13:07 GMT FROM: Frank Marshall at GSFC F. E. Marshall (NASA/GSFC) and D. Kocevski (NASA/GSFC/ORAU) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 140428A 104 s after the BAT trigger (Kocevski et al., GCN Circ. 16177). No optical afterglow consistent with the optical position (Perley, GCN_Circ. 16180) 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 initial exposures are: Filter T_start(s) T_stop(s) Exp(s) Mag white 104 254 147 >21.2 v 5454 5653 197 >20.3 b 4838 5039 197 >21.4 u 264 271 7 >19.5 uw1 5864 6030 197 >20.5 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.009 in the direction of the burst (Schlegel et al. 1998). //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 16191 SUBJECT: GRB 140428A: GROND observations DATE: 14/04/30 22:02:44 GMT FROM: Karla Varela at MPE F. Knust, K. Varela, J. Greiner (MPE Garching), and D. A. Kann (TLS Tautenburg) report on behalf of the GROND team: We observed the field of GRB 140428A (Swift trigger 597519; Kocevski et al., GCN #16177) 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 La Silla Observatory (Chile). Observations started at 00:43 UT on 2014-04-29, 2 hours after the GRB trigger. They were performed at an average seeing of 1.4" and at an average airmass of 1.9. We found a single point source within the 1.7" Swift-XRT error circle reported by Page et al. (GCN #16178) at RA (J2000.0) = 12h 57m 28.39s DEC (J2000.0) = + 28d 23' 06.4" with an uncertainty of 0.5" in each coordinate. This source is consistent with the one reported by Perley (GCN #16180). Based on the first 1133 s of total exposures in g'r'i'z' and 1920 s in JHK, we estimate preliminary magnitudes (all in AB system) of g' > 24.4 mag, r' = 23.6 +/- 0.2 mag, i' = 21.7 +/- 0.1 mag, z' = 21.5 +/- 0.1 mag, J > 19.7 mag, H > 20.6 mag, and K > 19.1mag. From our data, fading can not be established. We note that our r'-band magnitude is similar to that reported by Perley (GCN #16180) at a mid-time of 7.5 hrs after the GRB. The spectral energy distribution is best-fit by a straight power-law and a sharp cut-off below the i'-band which cannot be modelled with extinction alone. If this is the GRB afterglow, the cut-off corresponds to a photometric redshift of z = 4.8 +-0.3, consistent with the Keck spectroscopy as reported by Perley (GCN #16181). Given magnitudes are calibrated against SDSS (griz) as well as 2MASS (JHK) field stars and are not corrected for the expected Galactic foreground extinction corresponding to a reddening of E_(B-V) = 0.01 mag in the direction of the burst (Schlegel et al. 1998). //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 16252 SUBJECT: GRB 140428A: GROND afterglow confirmation DATE: 14/05/12 21:05:18 GMT FROM: Karla Varela at MPE K. Varela, C. Delvaux, and J. Greiner (all MPE Garching) report on behalf of the GROND team: We re-observed the field of GRB 140428A (Swift trigger 597519; Kocevski et al., GCN #16177) 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 La Silla Observatory (Chile). A second epoch obtained on May 6th at 02:01 UT, about 7 days after the trigger, shows that the source reported by Knust et al. (GCN # 16191) has clearly faded. We find z' > 23.3, suggesting that the source has faded by at least 1.9 mag, and confirming that this was the afterglow of GRB 140428A.