//////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 10673 SUBJECT: GRB 100425A: Swift detection of a burst DATE: 10/04/25 03:03:20 GMT FROM: David Palmer at LANL D. Grupe (PSU), S. D. Barthelmy (GSFC), W. H. Baumgartner (GSFC/UMBC), J. R. Cummings (NASA/UMBC), S. T. Holland (CRESST/USRA/GSFC), C. B. Markwardt (CRESST/GSFC/UMD), F. E. Marshall (NASA/GSFC), D. M. Palmer (LANL) and M. H. Siegel (PSU) report on behalf of the Swift Team: At 02:50:45 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 100425A (trigger=420398). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 299.187, -26.441 which is RA(J2000) = 19h 56m 45s Dec(J2000) = -26d 26' 27" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed two peaks, one with a duration of about 8 sec at T0 and one of about 6 sec at T+38 sec. The peak count rate was ~500 counts/sec (15-350 keV), at ~1 sec after the trigger. The XRT began observing the field at 02:52:03.9 UT, 78.8 seconds after the BAT trigger. Using promptly downlinked data we find a bright, fading, uncatalogued X-ray source located at RA, Dec 299.19593, -26.43039 which is equivalent to: RA(J2000) = 19h 56m 47.02s Dec(J2000) = -26d 25' 49.4" with an uncertainty of 4.7 arcseconds (radius, 90% containment). This location is 47 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 8.59e+20 cm^-2 (Kalberla et al. 2005). The initial flux in the 2.5 s image was 3.11e-09 erg cm^-2 s^-1 (0.2-10 keV). UVOT took a finding chart exposure of 150 seconds with the White filter starting 88 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 0.15. Burst Advocate for this burst is D. Grupe (grupe AT astro.psu.edu). 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: 10680 SUBJECT: GRB 100425A: candidate optical afterglow from the VLT DATE: 10/04/25 08:44:36 GMT FROM: Daniele Malesani at Dark Cosmology Centre, Niels Bohr Inst D. Malesani (DARK/NBI), A. J. Levan (Univ. Warwick), N. R. Tanvir (Univ. Leicester), J. P. U. Fynbo (DARK/NBI), P. Goldoni (APC/Univ. Paris 7 and SAp/CEA), report on behalf of a larger collaboration: We are observing the field of GRB 100425A (Grupe et al., GCN 10673) with the ESO VLT equipped with the X-shooter spectrograph. In the R-band acquisition image, taken starting around 06:51 UT (approximately 4 hr after the GRB), we detect two sources within the refined XRT error circle (http://www.swift.ac.uk/sper/), at coordinates: A: RA(J2000) = 19:56:47.30, Dec(J2000) = -26:25:49.3 B: RA(J2000) = 19:56:47.13, Dec(J2000) = -26:25:50.1 Source A is visible in the DSS, and has a similar magnitude to its archival value. Source B is not readily visible in the DSS and has a magnitude R = 20.55 +- 0.2, which is at the limit of the DSS sensitivity. The large error comes mostly from calibration scatter in comparison with USNO-B1 stars. In a second image taken starting at 7:44 UT (4.9 hr after the GRB), source B has faded by 0.17 +- 0.08 mag. Given the consistency of its position with the XRT error circle and the moderate evidence for variability, we propose source B as the optical afterglow of GRB 100425A. A finding chart from the X-shooter image can be seen at the following URL: http://www.astro.ku.dk/~malesani/GRB/100425A/GRB100425A_finder.png Further observations and analysis are ongoing. We acknowledge a particularly helpful and attentive support from the ESO staff in Paranal, especially Jonathan Smoker, Lorena Faundez, Manuel Olivares and Steffen Mieske. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 10683 SUBJECT: GRB 100425A: GROND afterglow observation DATE: 10/04/25 10:46:55 GMT FROM: Thomas Kruehler at MPE/MPI F. Olivares, T. Kruehler and J. Greiner (all MPE Garching) report on behalf of the GROND team: We observed the field of GRB 100425A (Swift trigger 420398; Grupe et al., GCN 10673) simultaneously in g'r'i'z'JHK with GROND (Greiner et al. 2008, PASP 120, 405) mounted at the 2.2 m MPI/ESO telescope at La Silla Observatory (Chile). Observations started at 05:17 UT on April 25, 2.4 hours after the GRB trigger, and were initially performed through thin cloud coverage. The optical afterglow candidate reported by Malesani et al. (GCN 10680, source 'B') is found to be clearly variable. Between 2.9 and 5.9 hours after the burst, the source decayed roughly 0.5 mag in the r' band. At a midtime of 08:45 UT we measure the following preliminary magnitudes (all in the AB system) in stacked images with a total integration time of 24 min in g'r'i'z' and 20 min in JHK: g = 21.5 +- 0.2 r = 21.0 +- 0.1 i = 20.8 +- 0.1 z = 20.5 +- 0.1 J = 20.1 +- 0.2 H = 19.9 +- 0.2 K = 19.6 +- 0.2 calibrated against the GROND zeropoints and 2MASS field stars, and not corrected for the expected foreground extinction of E(B-V)=0.15 (Schlegel et al. 1998). //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 10684 SUBJECT: GRB 100425A: VLT/X-shooter redshift DATE: 10/04/25 12:27:35 GMT FROM: Daniele Malesani at Dark Cosmology Centre, Niels Bohr Inst P. Goldoni (APC/Univ. Paris 7 and SAp/CEA), H. Flores (Paris Obs.), D. Malesani (DARK/NBI), A. J. Levan (Univ. Warwick), N. R. Tanvir (Univ. Leicester), J. P. U. Fynbo (DARK/NBI), report on behalf of a larger collaboration: We observed the optical afterglow of GRB 100425A (Grupe et al., GCN 10673; Malesani et al., GCN 10680; Olivares et al., GCN 10683) with th ESO VLT equipped with the X-shooter spectrograph. Four spectra lasting 10 minutes each were obtained, covering the spectral range 3000-25000 AA, starting on 2010 April 25, at 6:53 UT (4.0 hr after the GRB). We detect the traces of both objects lying within the XRT error circle. Preliminary inspection of the spectrum of the afterglow reveals several absorption features which we interpret as due to Mg II and Fe II, at a common redshift z = 1.755. We caution that the data reduction was carried out using archival calibration files. We acknowledge a particularly helpful and attentive support from the ESO staff in Paranal, especially Jonathan Smoker, Lorena Faundez, Manuel Olivares and Steffen Mieske. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 10685 SUBJECT: GRB 100425A: Swift-BAT refined analysis DATE: 10/04/25 13:38:39 GMT FROM: Scott Barthelmy at NASA/GSFC C. B. Markwardt (GSFC/UMD), S. D. Barthelmy (GSFC), W. H. Baumgartner (GSFC/UMBC), J. R. Cummings (GSFC/UMBC), N. Gehrels (GSFC), D. Grupe (PSU), H. A. Krimm (GSFC/USRA), D. M. Palmer (LANL), T. Sakamoto (GSFC/UMBC), M. Stamatikos (GSFC/ORAU), J. Tueller (GSFC), T. N. Ukwatta (GWU) (i.e. the Swift-BAT team): Using the data set from T-61 to T+242 sec from recent telemetry downlinks, we report further analysis of BAT GRB 100425A (trigger #420398) (Grupe, et al., GCN Circ. 10673). The BAT ground-calculated position is RA, Dec = 299.161, -26.463 deg, which is RA(J2000) = 19h 56m 38.7s Dec(J2000) = -26d 27' 47.8" with an uncertainty of 2.4 arcmin, (radius, sys+stat, 90% containment). The partial coding was 48%. The mask-weighted light curve shows three peaks. A first, precursor peak at ~T-45 sec, then the main peak at T-2 sec to ~T+10 sec, and the third peak at T+35 to ~T+65 sec. T90 (15-350 keV) is 37.0 +- 2.4 sec (estimated error including systematics). The time-averaged spectrum from T-2.1 to T+39.4 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 2.42 +- 0.32. The fluence in the 15-150 keV band is 4.7 +- 0.9 x 10^-7 erg/cm2. The 1-sec peak photon flux measured from T+0.27 sec in the 15-150 keV band is 1.4 +- 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/420398/BA/ //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 10686 SUBJECT: GRB 100425A: Enhanced Swift-XRT position DATE: 10/04/25 14:13:23 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 5331 s of XRT Photon Counting mode data and 8 UVOT images for GRB 100425A, 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 = 299.19651, -26.43069 which is equivalent to: RA (J2000): 19h 56m 47.16s Dec (J2000): -26d 25' 50.5" with an uncertainty of 1.5 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: 10689 SUBJECT: GRB100425A: Swift/UVOT Upper Limits DATE: 10/04/25 18:00:55 GMT FROM: Samantha Oates at MSSL S. R. Oates (MSSL-UCL) and D. Grupe (PSU) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 100425A 88s after the BAT trigger (Grupe et al., GCN 10673). We do not detect a new source at the enhanced Swift XRT position (Goad et al. GCN 10686) and at the location of source B detected by the VLT telescope (Malesani et al. GCN 10680) and GROND telescope (Olivares et al. GCN 10683). Photometry is complicated by the prescence of the VLT source A within the source aperture. The 3-sigma upper limits for the finding chart exposures (FC) and summed images are: Filter T_start T_stop Exp(s) Mag (3-sigma upper limit) ------------------------------------------------------------- white (FC) 88 238 147 >19.37 white 88 5778 513 >19.59 u (FC) 301 551 246 >18.92 u 301 6796 650 >19.08 v 631 11961 1317 >19.76 b 556 5573 236 >19.71 uvw1 680 6600 432 >19.44 uvm2 4757 12580 997 >20.87 uvw2 606 11048 1318 >21.26 ------------------------------------------------------------- The quoted upper limits have not been corrected for the expected Galactic extinction along the line of sight of E_(B-V) = 0.15 mag. All photometry is on the UVOT photometric system described in Poole et al. (2008, MNRAS, 383, 627). //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 10691 SUBJECT: GRB 100425A: Swift XRT refined analysis DATE: 10/04/26 17:26:13 GMT FROM: Dirk Grupe at PSU/Swift-XRT D. Grupe (PSU) reports on behalf of the Swift-XRT team: We have analyzed 14.2 ks of XRT data for GRB 100425A (Grupe et al. GCN Circ. 10673), from 85 s to 81 ks after the BAT trigger. The data consist of 106s in Windowed Timing mode (WT) and 14.1 ks in Photon Counting (PC) mode. The current XRT light curve can be fit by a broken power law model with an initial decay slope of 5.3+/-0.3 with a beak at 330+/-20 s followed by a shallow decay slope of 0.55+/- 0.05. The last data point at 77 ks after the burst suggests a break at about 60ks. However, this is based on one data point. Therefore, a prediction on the future behavior of the X-ray afterglow can not be given at this point. A spectrum formed from the WT mode data can be fitted with an absorbed power-law with a photon spectral index of 4.00 (+/-0.15). The best-fitting absorption column density is 1.49 (+0.18, -0.17) x 10^22 cm^-2, at a redshift of 1.755 (Goldini et al. GCN Circ 10684), in addition to the Galactic value of 8.6 x 10^20 cm^-2 (Kalberla et al. 2005). The PC mode spectrum has a photon index of 2.30+/-0.13 and a best-fitting absorption column density consistent with the Galactic value. Based on this spectrum, the counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 3.77 x 10^-11 (5.17 x 10^-11) erg cm^-2 count^-1. Swift will continue observing the X-ray afterglow of GRB 100425A over the next few days. The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00420398. This circular is an official product of the Swift-XRT team.