//////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 15349 SUBJECT: GRB 131018A: Swift detection of a burst DATE: 13/10/18 13:01:28 GMT FROM: David Palmer at LANL A. Melandri (INAF-OAB), S. D. Barthelmy (GSFC), D. N. Burrows (PSU), P. D\'Avanzo (INAF-OAB), P. A. Evans (U Leicester), N. Gehrels (NASA/GSFC), S. T. Holland (STScI), J. A. Kennea (PSU), A. Y. Lien (NASA/GSFC/ORAU), F. E. Marshall (NASA/GSFC), A. Maselli (INAF-IASFPA), C. Pagani (U Leicester), K. L. Page (U Leicester), P. Romano (INAF-IASFPA), M. H. Siegel (PSU) and R. L. C. Starling (U Leicester) report on behalf of the Swift Team: At 12:47:48 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 131018A (trigger=574935). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 98.462, -19.882 which is RA(J2000) = 06h 33m 51s Dec(J2000) = -19d 52' 54" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a broad single peak structure with a duration of about 100 sec. The peak count rate was ~500 counts/sec (15-350 keV), at ~56 sec after the trigger. The XRT began observing the field at 12:49:41.4 UT, 112.7 seconds after the BAT trigger. Using promptly downlinked data we find a bright, fading, uncatalogued X-ray source with an enhanced position: RA, Dec 98.4716, -19.8961 which is equivalent to: RA(J2000) = 06h 33m 53.19s Dec(J2000) = -19d 53' 45.9" with an uncertainty of 2.3 arcseconds (radius, 90% containment). This location is 60 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 2.03 x 10^21 cm^-2 (Kalberla et al. 2005). The initial flux in the 2.5 s image was 4.45e-09 erg cm^-2 s^-1 (0.2-10 keV). UVOT took a finding chart exposure of 150 seconds with the White filter starting 120 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 0.26. Burst Advocate for this burst is A. Melandri (andrea.melandri AT brera.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: 15350 SUBJECT: GRB131018A, optical observations DATE: 13/10/18 13:22:50 GMT FROM: Arne A. Henden at AAVSO Arne Henden (AAVSO), as part of a larger collaboration, reports: We observed the field of GRB131018A using the Mt. John University Observatory Optical Craftsman 61cm telescope (part of AAVSOnet), with observations starting at 12:55:24 UT (7.6 minutes after the Swift trigger) under poor seeing conditions and bright moonlight. We do not see any optical afterglow at the XRT position to a limiting magnitude of R=17 (using APASS calibrations). [GCN OPS NOTE(18oct13): The "A' suffix was added to the GRB name.] //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 15352 SUBJECT: GRB 131018A: Enhanced Swift-XRT position DATE: 13/10/18 17:51:15 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 1872 s of XRT Photon Counting mode data and 1 UVOT images for GRB 131018A, 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 = 98.47133, -19.89620 which is equivalent to: RA (J2000): 06h 33m 53.12s Dec (J2000): -19d 53' 46.3" with an uncertainty of 1.9 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: 15353 SUBJECT: GRB 131018A: P60 Observations DATE: 13/10/18 21:05:59 GMT FROM: S. Bradley Cenko at Caltech S. B. Cenko (NASA/GSFC) and D. A. Perley (Caltech) report on behalf of a larger collaboration: We have observed the location of the Swift GRB131018A (Melandri et al., GCN 15349) with the robotic Palomar 60 inch telescope. Two 60 s frames were obtained before the telescope closed due to the imminent sunrise. We find no new sources within the enhanced XRT error circle (Goad et al., GCN 15352). Using nearby point sources from SDSS for photometric calibration, we the following upper limits: r' > 20.1 mag at 12:56 UT (dt = 8.6 min) i' > 19.5 mag at 12:58 (dt = 10.0 min) //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 15354 SUBJECT: GRB 131018A, Swift-BAT refined analysis DATE: 13/10/18 23:08:41 GMT FROM: Amy Lien at GSFC T. N. Ukwatta (MSU), S. D. Barthelmy (GSFC), W. H. Baumgartner (GSFC/UMBC), J. R. Cummings (GSFC/UMBC), E. E. Fenimore (LANL), N. Gehrels (GSFC), H. A. Krimm (GSFC/USRA), A. Y. Lien (NASA/GSFC/ORAU), C. B. Markwardt (GSFC), A. Melandri (INAF-OAB), D. M. Palmer (LANL), T. Sakamoto (AGU), G. Sato (ISAS), M. Stamatikos (OSU), J. Tueller (GSFC), T. N. Ukwatta (MSU) (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 131018A (trigger #574935) (Melandri, et al., GCN Circ. 15349). The BAT ground-calculated position is RA, Dec = 98.473, -19.897 deg which is RA(J2000) = 06h 33m 53.4s Dec(J2000) = -19d 53' 48.5" with an uncertainty of 1.3 arcmin, (radius, sys+stat, 90% containment). The partial coding was 100%. The mask-weighted light curve shows a single long peak starts at ~T+21 sec and ends at ~T+118 sec. T90 (15-350 keV) is 73.22 +- 18.97 sec (estimated error including systematics). The time-averaged spectrum from T+21.10 to T+117.74 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 2.24 +- 0.14. The fluence in the 15-150 keV band is 1.1 +- 0.1 x 10^-06 erg/cm2. The 1-sec peak photon flux measured from T+59.41 sec in the 15-150 keV band is 0.5 +- 0.1 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/574935/BA/ //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 15355 SUBJECT: GRB 131018A: KAIT Optical Upper Limit DATE: 13/10/18 23:16:37 GMT FROM: Weikang Zheng at UC Berkeley WeiKang Zheng, Alexei V. Filippenko, Adam Morgan (UC Berkeley), and S. B. Cenko (NASA/Goddard Space Flight Center) report on behalf of the KAIT GRB team: The 0.76-m Katzman Automatic Imaging Telescope (KAIT), located at Lick Observatory, responded to GRB 131018A (Melandri et al., GCN 15349) starting at 12:50:47 UT, 179 s after the burst. Observations were performed with an automatic sequence in the V, I, and clear(roughly R) filters, and the exposure time was 20 s per image. Comparing to the SDSS image, we do not detect new sources in our single images or in coadds of 5 images within the enhanced XRT error circle (Goad et al., GCN 15352). There is a faint stellar object (r = 22.2 mag) in the SDSS image 1.8" from the enhanced XRT position, but it is beyond our limiting magnitudes of R ~ 18.7 for single images and R ~ 19.6 for 5 coadded images. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 15356 SUBJECT: GRB 131018A: Swift-XRT refined Analysis DATE: 13/10/19 01:01:04 GMT FROM: Phil Evans at U of Leicester V. D'Elia (ASDC), A. Maselli (INAF-IASFPA), J.A. Kennea (PSU), V. Mangano (PSU), M.C. Stroh (PSU), A.P. Beardmore (U. Leicester), P.A. Evans (U. Leicester), B.P. Gompertz (U. Leicester) and A. Melandri report on behalf of the Swift-XRT team: We have analysed 11 ks of XRT data for GRB 131018A (Melandri et al. GCN Circ. 15349), from 119 s to 25.2 ks after the BAT trigger. The data comprise 171 s in Windowed Timing (WT) mode with the remainder in Photon Counting (PC) mode. The enhanced XRT position for this burst was given by Goad et al. (GCN. Circ 15352). The light curve can be modelled with an initial power-law decay with an index of alpha=4.24 (+0.17, -0.15), followed by a break at T+549 s to an alpha of 0.30 (+/-0.06). A spectrum formed from the WT mode data can be fitted with an absorbed power-law with a photon spectral index of 3.06 (+0.13, -0.12). The best-fitting absorption column is 4.3 (+/-0.3) x 10^21 cm^-2, in excess of the Galactic value of 2.0 x 10^21 cm^-2 (Kalberla et al. 2005). The PC mode spectrum has a photon index of 2.16 (+0.18, -0.17) and a best-fitting absorption column of 3.1 (+/-0.6) x 10^21 cm^-2. The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 3.8 x 10^-11 (6.7 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 3.1 (+/-0.6) x 10^21 cm^-2 Galactic foreground: 2.0 x 10^21 cm^-2 Excess significance: 2.9 sigma Photon index: 2.16 (+0.18, -0.17) If the light curve continues to decay with a power-law decay index of 0.30, the count rate at T+24 hours will be 0.040 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.5 x 10^-12 (2.7 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/00574935. This circular is an official product of the Swift-XRT team. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 15357 SUBJECT: GRB 131018B: Fermi-LAT detection of a burst DATE: 13/10/19 10:02:36 GMT FROM: Giacomo Vianello at SLAC G. Vianello (Stanford), R. Desiante (University of Udine and INFN Trieste) and F.Longo (University of Trieste and INFN Trieste) report on behalf of the Fermi-LAT team: At 16:08:39 on 2013-10-18 Fermi LAT detected high energy emission from GRB 131018B, which was also detected by Fermi-GBM ( trigger bn131018673). The best LAT on-ground location is found to be (RA, DEC) = 304.41, 23.11 (J2000) with an error radius of 0.13 deg (68% containment, statistical error only), which was 25 deg from the LAT boresight at the time of the trigger. This position is 12 deg away from the best available GBM localization. This can be explained by the large statistical error on the GBM position (4 deg) and its typical systematic error, which is of the order of few degrees. The data from the Fermi LAT show an increase in the event rate within 10 degrees of the reported position starting few seconds after the GBM trigger (a delay common to many Fermi-LAT GRBs), which behaves spatially and temporally like a new transient point source. This excess has a high significance (~6 sigma). More than 10 photons above 100 MeV are observed within 2000 seconds after the trigger. The highest energy photon is a 13 GeV event which is observed 250 seconds after the GBM trigger. A Swift ToO request for this burst has been submitted. The Fermi LAT point of contact for this burst is Rachele Desiante ( rachele.desiante@ts.infn.it). The Fermi LAT is a pair conversion telescope designed to cover the energy band from 20 MeV to greater than 300 GeV. It is the product of an international collaboration between NASA and DOE in the U.S. and many scientific institutions across France, Italy, Japan and Sweden. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 15358 SUBJECT: GRB 131018A: Swift/UVOT Upper Limits DATE: 13/10/19 17:28:41 GMT FROM: Massimiliano de Pasquale at MSSL-UCL M. De Pasquale (UCL-MSSL) and A. Melandri (INAF-OAB) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 131018A 99 s after the BAT trigger (Melandri et al., GCN Circ. 15349). No optical afterglow consistent with the XRT position (Goad et al. GCN Circ. 15352) 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 120 270 147 >21.3 u_FC 279 528 246 >20.5 white 120 13702 1588 >22.4 v 99 7600 581 >20.3 b 534 19468 2174 >22.0 u 279 18703 2368 >21.9 w1 657 17790 1382 >21.3 m2 632 7805 568 >20.5 w2 584 7395 568 >20.8 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.26 in the direction of the burst (Schlegel et al. 1998). //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 15359 SUBJECT: GRB 131018A: RATIR Optical and NIR Observations DATE: 13/10/19 18:51:08 GMT FROM: Nat Butler at Az State U Nat Butler (ASU), Alan M. Watson (UNAM), Alexander Kutyrev (GSFC), William H. Lee (UNAM), Michael G. Richer (UNAM), Chris Klein (UCB), Ori Fox (UCB), J. Xavier Prochaska (UCSC), Josh Bloom (UCB), Antonino Cucchiara (ORAU/GSFC), 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), and Harvey Moseley (GSFC) report: We observed the field of GRB 131018A (Melandri, et al., GCN 15349) 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 2013/10 19.34 to 2013/10 19.53 UTC (19.36 to 23.83 hours after the BAT trigger), obtaining a total of 2.58 hours exposure in the r and i bands and 1.09 hours exposure in the Z, Y, J, and H bands. We detect no new sources within the enhanced Swift-XRT error circle (Goad, et al., GCN 15352). In comparison with the SDSS DR9 and 2MASS, we obtain the following upper limits (3-sigma): r > 23.30 i > 23.18 Z > 22.43 Y > 22.05 J > 21.70 H > 21.27 The SDSS source present in the XRT error circle (see also, Zheng, et al., GCN 15355) is well-detected, apparently non-extended, and is measured to have the following magnitudes: r 22.06 +/- 0.11 i 20.73 +/- 0.05 Z 20.10 +/- 0.05 Y 19.63 +/- 0.05 J 19.64 +/- 0.06 H 19.18 +/- 0.06 The above magnitude 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: 15360 SUBJECT: GRB 131018B: Fermi GBM observation DATE: 13/10/19 20:28:54 GMT FROM: Binbin Zhang at UAH Bin-Bin Zhang(UAH) reports on behalf of the Fermi GBM Team: "At 16:08:39.181 UT on October 18 2013, the Fermi Gamma-Ray Burst Monitor triggered and located GRB 131018B (trigger 403805322/131018673), which is also detected by Fermi/LAT (Vianello et al. GCN 15357). The GBM on-ground location is consistent with the LAT position (Vianello et al., GCN 15357). The angle from the Fermi LAT boresight is 23 degrees. The GBM light curve consists of one FRED-shape pulse with a duration (T90) of about 38 s (50-300 keV). The time-averaged spectrum from T0+0 s to T0+30 s is well best fit with a power law function with an exponential high-energy cutoff parameterized as Epeak = 77 +/- 7 keV and an Index = -0.25 +/- 0.30. The event fluence (10-1000 keV) in this time interval is (2.14 +/- 0.16)E-06 erg/cm^2. The 1.0-sec peak photon flux measured starting from T0+1 s in the 10-1000 keV band is 2.2 +/- 0.3 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: 15361 SUBJECT: GRB 131018B: Swift-XRT observations DATE: 13/10/20 19:35:14 GMT FROM: Paolo D'Avanzo at INAF-OAB P. D'Avanzo, A. Melandri, M. G. Bernardini (INAF-OAB), P. A. Evans (U. Leicester) report on behalf of the Swift-XRT team: We have analysed 2.8 ks of XRT data for the Fermi/LAT-detected burst: GRB 131018B (Vianello et al., GCN 15357; Zhang, GCN 15360), from 83.1 ks to 95.2 ks after the Fermi/LAT trigger. The data are entirely in Photon Counting (PC) mode. An uncatalogued X-ray source is detected within the Fermi/LAT error circle. The refined XRT position is RA, Dec = 304.53693, +23.18759 which is equivalent to: RA (J2000): 20 18 08.86 Dec(J2000): +23 11 15.3 with an uncertainty of 4.9 arcsec (radius, 90% confidence). This position is 514 arcsec from the Fermi/LAT position. We cannot determine at the present time whether the source is fading. We note the presence of two further sources within the LAT error box. Source #2 has the following position RA, Dec = 304.41156, +23.16636 which is equivalent to: RA (J2000): 20 17 38.77 Dec(J2000): +23 09 58.9 with an uncertainty of 5.4 arcsec (radius, 90% confidence). Source #3 has the following position RA, Dec = 304.52361 +23.06517 which is equivalent to: RA (J2000): 20 18 05.67 Dec(J2000): +23 03 54.6 with an uncertainty of 6.0 arcsec (radius, 90% confidence). Both sources are present in the Swift-XRT point source catalogue (D'Elia et al. 2013; A&A 551, A142) and are likely not related with GRB 131018B. The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00020308. This circular is an official product of the Swift-XRT team. [GCN OPS NOTE(22oct13): Per author's reuqest, the affiliations of the authors was corrected.] //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 15362 SUBJECT: GRB 131018B: Swift/UVOT Upper Limits DATE: 13/10/20 21:17:55 GMT FROM: Samantha Oates at MSSL S. R. Oates (MSSL-UCL) and P. D'Avanzo (INAF-OAB) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 131018B 83 ks after the LAT trigger (Vianello et al., GCN Circ. 15357). No new optical candidate is detected within the LAT error circle (Vianello et al., GCN Circ. 15357) in the initial UVOT exposures. We note an optical source within the error circle of the candidate XRT position (D'Avanzo et al., GCN Circ. 15361), which is found in the USNO-B1 catalogue. 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 90363 91160 785 >21.7 v 91168 91427 255 >19.4 u 88969 95244 1300 >20.6 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.58 in the direction of the burst (Schlegel et al. 1998). //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 15431 SUBJECT: GRB 131018B: Further Swift-XRT observations. DATE: 13/11/01 13:32:42 GMT FROM: Paolo D'Avanzo at INAF-OAB P. D'Avanzo (INAF-OAB), P. A. Evans (U. Leicester) report on behalf of the Swift-XRT team: We have analysed 6.7 ks of XRT data for the Fermi/LAT-detected burst GRB 131018B (Vianello et al., GCN 15357; Zhang, GCN 15360), from 1081.2 ks to 1100.0 ks after the Fermi/LAT trigger. The data are entirely in Photon Counting (PC) mode. The uncatalogued X-ray source reported in D'Avanzo et al. (GCN 15361) is not longer detected. The source count rate changed from 5.7e-3 +/- 1.8e-3 cts/s in the first epoch (D'Avanzo et al., GCN 15361) to a 3-sigma upper limit of 1.1e-3 cts/s. We can conclude that this source is likely the X-ray afterglow of GRB 131018B. This circular is an official product of the Swift XRT team. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 15437 SUBJECT: GRB 131018B: RATIR Optical/NIR Observations DATE: 13/11/01 22:57:14 GMT FROM: Eleonora Troja at GSFC Eleonora Troja (GSFC), Nat Butler (ASU), Alan M. Watson (UNAM), Alexander Kutyrev (GSFC), William H. Lee (UNAM), Michael G. Richer (UNAM), Chris Klein (UCB), Ori Fox (UCB), J. Xavier Prochaska (UCSC), Josh Bloom (UCB), Antonino Cucchiara (ORAU/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), and Harvey Moseley (GSFC) report: We observed the field of GRB 131018B (Vianello, et al., GCN 15357; Zhang, et al., GCN 15360) 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 2013/10 20.09 to 2013/10 20.27 UTC (33.94 to 38.36 hours after the GBM trigger), and again the next night from 2013/10 21.09 to 2013/10 21.27 UTC (57.93 to 62.34 hours after the GBM trigger). We obtained a total of 2.8 hours exposure in the r and i bands and 1.3 hours exposure in the Z, Y, J, and H bands each night. During the 1st night of observations, the position of the X-ray afterglow reported by D'Avanzo et al. (GCN 15361, 15431) falls at the edge of our field of view in the Z and J bands. For a source within the Swift-XRT error circle, in comparison with 2MASS, we obtain the following upper limits (3-sigma): Z > 22.6 J > 21.6 During the 2nd night of observations, the XRT position was observed in all filters. For a source within the Swift-XRT error circle, in comparison with 2MASS and SDSS DR9, we obtain the following upper limits (3-sigma): r > 23.8 i > 23.5 Z > 22.8 Y > 22.2 J > 21.9 H > 21.4 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.