This file contains bothe GR 050820A and 050820B. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 3829 SUBJECT: GRB050820: Optical afterglow from P60 DATE: 05/08/20 07:15:30 GMT FROM: Derek Fox at PSU Derek B. Fox (Penn State) and S. Bradley Cenko (Caltech) report on behalf of a larger collaboration: "We have observed the BAT/XRT localization region of GRB050820 (Swift Trigger #151207) with the robotic Palomar 60-inch telescope (P60), in a series of automated exposures beginning at 06:37 UT, approximately 3 minutes after the burst. We identify a bright, new, variable point source within the XRT (and BAT) localization region at coordinates: R.A. 22:29:38.11, Dec +19:33:37.1 (J2000) with coordinate uncertainty <0.5 arcsec relative to USNO-B1.0 catalog astrometry. Photometry of the source relative to the USNO-B1.0 catalog indicates that in the R-band it brightens to a peak magnitude of R~14.7 mag at 7 minutes after the burst and has decayed by 0.4 mag at 12 minutes after the burst. We therefore identify the source as the optical afterglow of GRB050820." //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 3830 SUBJECT: GRB 050820: Swift detection of a GRB DATE: 05/08/20 07:29:30 GMT FROM: David Burrows at PSU/Swift M. Page (UCL-MSSL), D. Burrows (PSU), A. Beardmore (U. Leicester), D. Palmer (LANL), J, Kennea (PSU), N. Gehrels (GSFC), C. Markwardt (GSFC/UMD), K. Page (U. Leicester), T. Sakamoto (GSFC/NRC), M. Chester (PSU), P. Boyd (GSFC) report on behalf of the Swift team: At 06:34:53 BAT triggered, located, and immediately slewed to GRB 050820 (trigger=151207). The BAT on-board calculated position is RA,Dec 337.400d, +19.578d {22h 29m 36s, 19d 34' 42"} (J2000) with an uncertainty of 2 arcmin (radius, 90% containment, stat+sys). The BAT light curve shows a broad double-humped structure about 20 seconds long, with peaks around T+1s and T+14 s, with a peak count rate of ~1500 counts per second (15-350 keV) at ~1 second after the trigger. XRT began observing at 06:36:13 UT, 80s after the BAT trigger. A bright uncatalogued source was found in the field, which XRT was able to centroid on. The on-board calculated coordinates of this source are: RA(J2000): 22:29:37.8, Dec(J2000): 19:33:32.7, with an uncertainty of 7 arcseconds radius (90% containment). This position lies 73 arcseconds from the center of the BAT error circle, and 6.2 arcseconds from the P60 position (GCN 3829). The UVOT began observations at 06:36:13 UT, 80s after the BAT trigger. There is no new source detected in the preliminary UVOT data in the XRT error circle. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 3833 SUBJECT: GRB 050820: High Resolution Spectroscopy from Keck DATE: 05/08/20 09:51:16 GMT FROM: Jason Prochaska at UCO/Lick Obs J. X. Prochaska (UCO/Lick), J. S. Bloom, J. T. Wright (UC Berkeley), R. Paul Butler (DTM, Carnegie), H. W. Chen (MIT), S.S. Vogt (UCO/Lick), and G.W. Marcy (UC Berkeley) report: "Starting at 07h28m59s 20 Aug 2005 UTC, we began spectroscopic observations of the optical transient (Fox & Cenko GCN #3829) of GRB 050820 (Page et al. GCN #3830) with HIRES/Keck I. In a series of 900 sec exposures the continuum from the afterglow is well detected as are many absorption lines. Based on the identification of a damped Ly alpha feature, SiII 1304, OI 1302, and numerous fine structure lines we measure the GRB redshift to be z=2.612 +/- 0.002." We are grateful to Derek Fox for his assistance in helping us acquire this data. This message may be cited. ---------------------------------------------- Jason X. Prochaska UCO/Lick Observatory UC Santa Cruz Santa Cruz, CA 95064 xavier@ucolick.org http://www.ucolick.org/~xavier/ 831-459-2135 (Direct) 831-459-2991 (UCO/Lick Main) 831-459-5244 (Fax) //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 3834 SUBJECT: GRB 050820: P60 Temporal Decay Index DATE: 05/08/20 10:37:09 GMT FROM: S. Bradley Cenko at Caltech S. Bradley Cenko (Caltech) and Derek B. Fox (Penn State) report on behalf of a larger collaboration: We have continued to image the afterglow (GCN 3829) of GRB 050820 (GCN 3830) with the automated Palomar 60-inch telescope. Using the USNO-B1 star located at RA=22:29:39.88, Dec=+19:32:47.5 (USNO-B1 1095-0581263, R = 15.21) as a reference, we find, after rising to a peak magnitude of R = 14.7 approximately 7 minutes after the burst, the afterglow has exhibited a relatively smooth power-law decay with index alpha = -0.9. In an image taken ~ 93 minutes after the burst, the afterglow has a magnitude of R ~ 17.4. Further observations are planned. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 3835 SUBJECT: GRB 050820 Swift-BAT refined analysis DATE: 05/08/20 14:11:03 GMT FROM: Jay R. Cummings at NASA/GSFC/Swift J. Cummings (GSFC/NRC), L. Barbier (GSFC), S. Barthelmy (GSFC), J. Cannizzo (GSFC-UMBC), L. Cominsky (Sonoma State U.), D. Hullinger (GSFC/UMD), E. Fenimore (LANL), N. Gehrels (GSFC), H. Krimm (GSFC/USRA), C. Markwardt (GSFC/UMD), D. Palmer (LANL), A. Parsons (GSFC), T. Sakamoto (GSFC/NRC), G. Sato (ISAS), J. Tueller (GSFC) on behalf of the Swift-BAT team: Using the full data set from the recent telemetry downlink, we report further analysis of Swift-BAT GRB 050820 (trigger #151207) (Page, et al., GCN 3830). The ground-analysis position is RA,Dec 337.418, +19.560 (J2000) with an uncertainty of 2 arcmin (radius, 90%, stat+sys). This is 31 arcseconds from the optical transient reported by Fox et al. in GCN Circ. 3829. The light curve is multi-peaked and the spectrum clearly evolves from hard to soft within each of the two main peaks. There is a probable small precursor at ~ T-15 seconds, the largest peak at T+0 seconds, and two other peaks at T+9 and T+13 seconds. T90 is 26 +- 2 seconds. Fitting a simple power law over the interval from T-17 to T+22 seconds, the photon index is 1.7 +/- 0.1 with a fluence of 1.9 +/- 0.2 x 10^-6 erg/cm^2 in the 15-350 keV band (90% c.l). The peak flux in a 1-second wide window starting at T-0.25 seconds is 1.3 +/- 0.2 ph/cm^2/sec (15-350 keV). The isotropic-equivalent energy using the redshift of 2.612 (Prochaska, et al. GCN 3833) is 9.7 (-2.6/+3.5) x 10^51 ergs in the 4.2-41.5 keV band in the GRB rest frame (15-150 keV band in the observer's frame) using a simple power-law model. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 3836 SUBJECT: GRB 050820: Early RAPTOR detections DATE: 05/08/20 18:49:51 GMT FROM: James Wren at LANL J. Wren, W. T. Vestrand, P. Woznaik, S. Evans, R. White report on behalf of the RAPTOR team at Los Alamos National Laboratory: The RAPTOR system of robotic telescopes responded to GRB 050820 (Swift trigger 151207) beginning at 06:35:20.46 UT, 5.5 seconds after the GCN notice was sent. We detect the object reported by Fox and Cenko (GCN 3029). Our early images show the source rising rapidly to a unfiltered peak magnitude of ~14.5. We confirm the Fox and Cenko observation that the source reaches a peak brightness approximately 8 minutes after the burst and then begins a steady power law decline. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 3837 SUBJECT: GRB050820: refined XRT analysis DATE: 05/08/20 19:51:24 GMT FROM: Kim Page at U.of Leicester,Swift SDC K.L. Page, A.P. Beardmore, M.R. Goad (U. Leicester), J.A. Kennea, D.N. Burrows (PSU), F. Marshall (GSFC) and A. Smale (NASA HQ) report on behalf of the Swift/XRT team: We have analysed the first 6 orbits of XRT data for GRB050820, spanning 88 - 3e5 seconds after the burst. There is a bright, fading afterglow in the field of view, with refined coordinates of RA(J2000): 22:29:38.2 Dec(J2000): 19:33:31.1 with an uncertainty of 7 arcseconds radius (90% containment). This is 5.9 arcsec from the on-board XRT position given in GCN 3830 and 6.1 arcsec from the optical afterglow reported in GCN 3829. XRT observations began in Windowed Timing mode 88 seconds after the trigger, followed by Photon Counting (PC) data from the start of the second orbit (4660 seconds after the burst). The PC data show a smooth decline with a decay slope of alpha = 1.13 +/- 0.04. The PC spectrum can be well fitted by a power-law with Gamma = 1.94 +/- 0.07, and an excess absorbing column of ~6e21 cm^-2 in the rest-frame of the GRB (taking the redshift of 2.612 from GCN 3833). Assuming a smooth, unbroken decay, the predicted count-rate at 24 hours (06.30 UT on 2005-08-21) is 0.085 count s^-1, corresponding to an unabsorbed 0.3-10 keV flux of 3.4e-12 erg cm^-2 s^-1. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 3838 SUBJECT: Swift/UVOT photometry of GRB050820 DATE: 05/08/20 21:04:12 GMT FROM: Margaret Chester at PSU M. Chester (PSU), M. Page (UCL-MSSL), P. Roming (PSU), F. Marshall (GSFC), P. Boyd (GSFC), L. Angelini (GSFC-JHU), J. Greiner (MPE), N. Gehrels (GSFC), on behalf of the Swift UVOT team. Swift/UVOT began observing GRB050820 at 06:36:13 UT. The initial 100-second finding chart exposure in V was cut short due to entry into the SAA; it was repeated on the second orbit. The afterglow is detected in the V, B, U, and one UV band. Similar to the ground-based observations (GCN #3829), UVOT sees a rising, then falling, light curve in V. Analysis in the other bands is continuing. V-band Observations: Time-Since-Trigger V 80 s 18.2 +/- 0.3 4635 s 17.6 +/- 0.2 12238 s 18.2 +/- 0.2 Other: Time-Since-Trigger Mag Filter 5647 s 18.3 +/- 0.2 U 10423 s 19.0 +/- 0.1 B 4741 s 20.4 +/- 0.2 UVW1 11331 s >21.0 UVW2 The magnitudes have not been corrected for extinction. Upper limits are given at the 5-sigma level. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 3839 SUBJECT: GRB050820B: BAT-Swift detection of a bright GRB DATE: 05/08/21 00:23:42 GMT FROM: David Palmer at LANL M. Page (UCL-MSSL), D. Palmer (LANL), S. Barthelmy (GSFC), D. Burrows (PSU), A. Beardmore (U. Leicester). J. Kennea (PSU), M. Chester (PSU), and T. Sakamoto (GSFC/NRC) on behalf of the Swift team report At 23:50:27 BAT triggered and located GRB050820B (Trigger= 151334) at RA,Dec=135.557d, -72.668d {+09h 02m 14s, -72d 40' 03"} (J2000) with an uncertainty of 2 arcmin (radius, 90% containment, stat+sys). The BAT lightcurve shows 20 seconds of emission with a shorter softer peak at T+2 seconds, and a broader, brighter, harder interval of emission from T+6 to T+14s. The peak count rate is 10,000 counts/s (15-350 keV) at T+9s. The first peak has a maximum count rate of 2000 counts/s, with no obvious emission above 100 keV. Due to Earth limb constraints, the Swift slew is delayed until until 00:16 UT (T+26 minutes). //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 3840 SUBJECT: SUBJECT: GRB050820B: Refined analysis of the Swift-BAT burst DATE: 05/08/21 02:33:16 GMT FROM: Takanori Sakamoto at NASA/GSFC E. Fenimore (LANL), L. Barbier (GSFC), S. Barthelmy (GSFC), J. Cummings (GSFC/NRC), N. Gehrels (GSFC), D. Hullinger (GSFC/UMD), K. Hurley (Berkeley), H. Krimm (GSFC/USRA), C. Markwardt (GSFC/UMD), J. Norris (GSFC), D. Palmer (LANL), A. Parsons (GSFC), T. Sakamoto (GSFC/NRC), G. Sato (ISAS), J. Tueller (GSFC) on behalf of the Swift-BAT team: Using the full data set from the recent telemetry downlink, we report further analysis of Swift-BAT GRB 050820B (trigger #151334) (Page, et al., GCN 3839). The ground-analysis position is RA,Dec 135.594,-72.639 (J2000) with an uncertainty of 2 arcmin (radius, 90%, stat+sys). The light curve show a peak at T+1 sec and a cluster of merged peaks at T+8 sec. T90 is 13 +/-2 sec. Fitting a cutoff power law over the interval from T+0.2 to T+17.3 sec, the photon index is 0.5 +/- 0.2 and Epeak is 100 (-10/+15) keV with a fluence of 2.8 +/- 0.2 x 10^-6 erg/cm^2 in the 15-350 keV band (90% c.l.). The peak flux in a 1-sec wide window starting at T+8.7 seconds is 4.7 +/- 0.3 ph/cm^2/sec (15-350 keV). //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 3841 SUBJECT: GRB050820B: Planned XMM-Newton observation DATE: 05/08/21 03:10:44 GMT FROM: Norbert Schartel at XMM-Newton/ESA XMM-Newton will observe GRB050820B at location (RA=09h 02m 22.6s, DEC=-72d 38' 20.4", J2000), starting at 05:03 UT, on August 21, 2005, for an exposure of 59ksec seconds. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 3842 SUBJECT: GRB 050820B: Swift XRT position DATE: 05/08/21 03:26:35 GMT FROM: David Burrows at PSU/Swift D. N. Burrows (PSU) reports on behalf of the Swift XRT team: The Swift BAT instrument triggered on GRB 050820B at 23:50:27.19 UT (GCN 3839, Page et al.). At that time, the source was within the Earth limb constraint and the S/C was not able to slew immediately. Swift executed a delayed slew at 0:17:37, while the observatory was in the South Atlantic Anomaly. The XRT attempted to locate a bright source in its field of view, but was not able to do so due to the delayed slew and to the presence of many charged particle events in the image. XRT Photon-Counting mode observations began at 00:28:3.6 (2256 s after the burst trigger), following exit from the South Atlantic Anomaly and completion of pre-programmed XRT engineering data collection. In analysis of engineering format (PASS1) ground-processed data at the MOC, we find a faint, fading, uncataloged X-ray source located at: RA(J2000) = 09h 02m 24.6s Dec(J2000) = -72d 38' 43" with an estimated uncertainty of 8 arcseconds (90% containment radius). This position is 25 arcseconds from the refined BAT position reported in GCN 3840 (Fenimore et al.). Further observations are in progress. Refined analysis will become available following processing of the data through the Swift Data Center's pipeline. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 3843 SUBJECT: GRB 050820a: NIR Observations by WIRO DATE: 05/08/21 05:51:50 GMT FROM: Daryl Macomb at Boise STate U Daryl Macomb, Jessica Elias (Boise State U.), Jerry Bonnell, Alexander Kutyrev, Jay Norris (NASA/GSFC), and Ron Canterna, Mike Pierce (U. Wyoming) report: We observed the position reported by Fox and Cenko (GCN 3829) of the afterglow for GRB 050820a (Swift trigger #151207, Page et al., GCN 3830) with the 2.3-meter WIRO telescope. Starting at 08:10 UT (96 minutes after the GRB trigger) and continuing until 11:30 UT, we detected the fading afterglow in the J band in each of 120 40-s integrations. J magnitudes determined at the following times were (relative to burst trigger): Epoch T-Ttrig J mag 1 6240 s 16.0 2 9600 s 16.7 3 16020 s 16.9 Between epochs 1 and 2, the inferred average power-law decay index is -1.5, steeper than the -0.9 index reported by Cenko and Fox (GCN 3834) for the initial decay during the interval ~ 7 - 93 minutes after the burst. Between epoches 2 and 3, the average decay index flattens to -0.44, after which our observations ended due to twilight. The times of the three reported epochs are arbitrary. Detailed analysis to yield accurate break times and indices is in progress. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 3844 SUBJECT: GRB050820B XMM-Newton observation DATE: 05/08/21 06:20:24 GMT FROM: Norbert Schartel at XMM-Newton/ESA Pedro Rodriguez and Pedro Calderon report: Quick-Look-Analysis of the XMM-Newton observation of the GRB050820B field based on an exposure in the EPIC pn camera that started at 05:50 UT, shows the presence of a source within the SWIFT/XRT error circle (Burrows, GCN3842). The estimated EPIC/pn net count rate for the first 1ksec is 0.033 counts/sec. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 3845 SUBJECT: GRB050820a BVRcIc field photometry DATE: 05/08/21 16:44:01 GMT FROM: Arne A. Henden at AAVSO A. Henden (AAVSO/USNO) reports on behalf of the USNO GRB Team: We have acquired BVRcIc all-sky photometry for a 23x23arcmin field centered on the coordinates of the optical afterglow (Fox and Cenko, GCN 3829) for the Swift burst GRB050820a (Page et al., GCN 3830) with the USNOFS 1.0-m telescope on one photometric night but with bright moonlight. Stars brighter than V=12.0 are saturated and should be used with care. We have placed the photometric data on our anonymous ftp site: ftp://ftp.nofs.navy.mil/pub/outgoing/aah/grb/grb050820.dat The astrometry in this file is based on linear plate solutions with respect to UCAC2. The external errors are about 100mas. The estimated external photometric error is about 0.03mag. As always, you should check the dates on the .dat file prior to final publication to get the latest photometry. There is a README file on the ftp directory to give you information about the procedures used to calibrate these fields. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 3847 SUBJECT: GRB050820A: Radio Observation DATE: 05/08/21 19:51:46 GMT FROM: Dale A. Frail at NRAO P. B. Cameron (Caltech) and D. A. Frail (NRAO) report on behalf of a larger collaboration: "We have undertaken VLA observations at a frequency of 8.46 GHz toward GRB 050820A (GCN 3830) on August 20.39 UT and 21.20 UT, about 2.9 hrs and 22.3 hrs after the burst, respectively. On the first epoch no significant radio emission was detected at the position of the optical afterglow (GCN 3829), but on the second epoch a new radio source has appeared with a flux density of 690+/- 41 microJy. Further observations are planned. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc." //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 3848 SUBJECT: Correction to Eiso calculation in GCN 3835 on GRB 050820A DATE: 05/08/21 22:35:20 GMT FROM: Takanori Sakamoto at NASA/GSFC T. Sakamoto (GSFC/NRC) on behalf of the Swift-BAT team: The isotropic-equivalent energy of GRB050820A reported in GCN 3835 is not correctly represented. We want to correct the last paragraph of GCN 3835 to the following. "The isotropic-equivalent energy using the redshift of 2.612 (Prochaska, et al. GCN 3833) is (2.2 +- 0.13) x 10^52 ergs in the 54-542 keV band in the GRB rest frame (15-150 keV band in the observer's frame) using a simple power-law model." We would like to thank Dr. Arnon Dar for reporting about this mistake. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 3851 SUBJECT: Swift/UVOT UV Photometry of GRB 050820B DATE: 05/08/22 04:57:22 GMT FROM: Margaret Chester at PSU M. Chester (PSU), M. Page (UCL-MSSL), F. Marshall (GSFC), P. Roming (PSU), D. Hinshaw (GSFC-SPSYS), P. Meszaros (PSU), N. Gehrels (GSFC) on behalf of the Swift UVOT team. Swift/UVOT observed GRB 050820B in its UV filters only, due to the presence of a V=4.5 star in its field of view. The afterglow was not detected at the XRT position. 5-sigma upper limits are: Filter Magnitude Exp (s) T_start T_stop UVM2 >19.1 100 1987 2087 UVW1 >19.0 100 2091 2191 UVW2 >19.3 100 2198 2298 where T_start and T_stop are in seconds after the trigger (Page et al. GCN 3839). //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 3852 SUBJECT: GRB 050820a - corrections to GCN 3846 DATE: 05/08/22 11:36:41 GMT FROM: Dmitry Frederiks at Ioffe Institute V. Pal'shin and D.Frederiks on behalf of the Konus-Wind team: There were several misprints in our GCN 3846. The subject line should have read: ------------------------------------ "GRB 050820a - a long GRB like GRB041219a? (Konus-Wind observation)" ------------------------------------ The correct circular text should be: ------------------------------------ "S. Golenetskii, R.Aptekar, E. Mazets, V. Pal'shin, D. Frederiks and T. Cline on behalf of the Konus-Wind team, and A. Rau, A. von Kienlin, G. Lichti on behalf of the INTEGRAL SPI-ACS GRB team report: A long soft GRB triggered Konus-Wind at T0=23954.512s UT (06:39:14.512) on August 20. It was also detected by INTEGRAL SPI-ACS. Because the burst was soft, the SPI-ACS response was weak, and precise triangulation of this burst is not possible. But the estimated time delay is consistent with the position of GRB 050820a, detected by Swift-BAT ~260 sec before Konus-Wind trigger (Page, et al., GCN 3830; Cummings, et al., GCN 3835). The Konus-Wind GRB consists of two parts: from ~T0-35s to ~T0+29s and from ~T0+135s to ~T0+235s and is much more intense than the Swift burst (precursor?), which was weakly seen by Konus-Wind in background data. The total burst duration is ~270 s. The Konus-Wind light curve recorded in the background mode is very similar to the light curve of the famous GRB 041219a (Vestrand et al., Nature, 435, 178 (2005)): weak precursor, main pulse at ~250 sec after it, second pulse at ~150 s after main and then - weaker pulse(s). The Konus-Wind light curve of this GRB can be seen at http://www.ioffe.rssi.ru/LEA/GRBs/GRB050820_T23954/ Based on these facts, we strongly suggest that this GRB is the main part of the GRB 050820a. In this case the optical transient reported by Fox and Cenko (GCN 3829) and by Wren et al. (GCN 3836) is in fact the prompt optical emission of very long GRB 050820a (the total burst duration including Swift precursor is ~500 sec). We hope, that the further analysis of this event will clarify this issue." --------------------------------- We apologize for these misprints. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 3853 SUBJECT: GRB050820A: RTT150 optical observations DATE: 05/08/22 12:40:21 GMT FROM: Irek Khamitov at TUG I. Bikmaev, A. Galeev, N. Sakhibullin (KSU/AST), R. Burenin, M. Pavlinsky, R. Sunyaev (IKI), I. Khamitov, Z. Aslan (TUG), U. Kiziloglu (METU), E. Gogus (Sabanci Uni.), report: We have observed the OT of GRB 050820A (GCN 3829) with the Russian-Turkish 1.5-m telescope (Bakirlitepe, TUBITAK National Observatory, Turkey) in two consequative nights . We made a series of exposures in Rc between UT 18:35 - 22:15, August 20, 2005, and in BRcIc between UT 22:46-01:15, August 21/22, 2005. Moonlight produced variable background in all images for both nights. The afterglow is clearly detected in all bands. Using Henden's stars (GCN 3845) present in the frames, we estimated the magnitudes as follow: t-t0 Band mag merr exptime (hours, midtime) (sec,total) 18.05 Rc 19.48 +/- 0.01 900 41.42 Rc 20.38 +/- 0.05 1800 40.93 B 21.00 +/- 0.06 1800 41.55 Ic 19.83 +/- 0.07 1800 On the basis of our Rc data, we estimeted an alpha index of power-law decay for the observed period as ~ -1.0. The JPG-images of BRcIc and color combined image are available at: http://www.tug.tubitak.gov.tr/~irekk/grb/grb050820a/grb050820A_b.JPG http://www.tug.tubitak.gov.tr/~irekk/grb/grb050820a/grb050820A_r.JPG http://www.tug.tubitak.gov.tr/~irekk/grb/grb050820a/grb050820A_i.JPG http://www.tug.tubitak.gov.tr/~irekk/grb/grb050820a/grb050820_bri.JPG This message may be cited. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 3854 SUBJECT: GRB050820B at FRAM DATE: 05/08/22 13:22:59 GMT FROM: Martin Jelinek at Inst.Astrophys.Andalucia,Granada Martin Jelínek (IAA Granada, Spain), Michael Prouza (FZU Praha, Czech Republic), Petr Kubanek (ISDC Versiox, Switzerland and ASU AV CR, Ondrejov), Martin Nekola and Rene Hudec (ASU AV CR, Ondrejov, Czech Republic) report: Robotic telescope FRAM located near Malargue in Argentina has observed the field of GRB050820B in semi-automatic mode starting 1.31h after the GRB onset. No new optical source is detected within the uncertainity region given by GCN3840 (Fenimore et. al.). The 3-sigma limit of three coadded exposures is R=15.3. An image can be seen at http://lascaux.asu.cas.cz/~mates/050820B-fram.gif //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 3858 SUBJECT: GRB 050820A BAT observations of second, larger episode of emission DATE: 05/08/22 19:55:41 GMT FROM: Jay R. Cummings at NASA/GSFC/Swift J. Cummings (GSFC/NRC), L. Barbier (GSFC), S. Barthelmy (GSFC), D. Hullinger (GSFC/UMD), E. Fenimore (LANL), N. Gehrels (GSFC), H. Krimm (GSFC/USRA), C. Markwardt (GSFC/UMD), D. Palmer (LANL), A. Parsons (GSFC), T. Sakamoto (GSFC/NRC), G. Sato (ISAS), J. Tueller (GSFC) on behalf of the Swift-BAT team: A second, larger, harder episode of gamma rays from T+217 to T+270 sec was detected from GRB 050820A, as noted by Golenetskii et al. in GCN circ. 3846, 3852. We confirm that this larger episode of emission was from the same source as the first episode (from T-17 to T+22 sec), using BAT mask-weighting on a partial data set. Swift was entering the SAA as the first episode of emission was ending. We reported BAT refined analysis for the period covering the first episode of emission in GCN circ. 3835, 3848. The BAT entered SAA mode at T+241 sec. At this time data collection became very limited. We use mask-weighted data prior to this time, and a non-directional residual rate with a background model subtraction after this time, for the following information on the second episode: There were two peaks at T+228 and T+259 sec. T90 was 50 +/- 5 sec (for the second episode alone). In a simple power law fit, the photon index for the first part of the second episode from T+217 to T+241 was 1.06 +/- 0.03. The 1-sec peak flux is estimated to be 6 +/- 1 ph/cm^2/sec (15-350 keV) at T+259 sec. For reference, the previously reported photon index for the first episode of emission from T-17 to T+22 sec was 1.7 +/- 0.1 and the 1-sec peak flux was 1.3 +/- 0.2 ph/cm^2/sec (15-350 keV). We estimate the total fluence for the entire event including both episodes to be 8.4 +/- 0.3 x 10^-6 erg/cm^2 in the 15-150 keV band. The quoted uncertainty is statistical. Roughly 60% of the fluence is in the period lacking mask-weighted data and having a very high background rate, thus systematic errors may be large and we estimate them to be +/- 0.6 x 10^-6 erg/cm^2. The fluence estimate includes the assumption that the part of the second episode after T+241 sec had the same spectrum as it did from T+217 to T+241 sec. For the entire burst then, using the measured redshift of 2.612 (Prochaska, et al. GCN 3833), we calculate the isotropic-equivalent energy in the 54-542 keV band in the GRB rest frame (15-150 keV band in the observer's frame) as ~1.5 x 10^53 ergs. -- Jay Cummings //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 3860 SUBJECT: VLT/UVES spectroscopy of GRB050820 DATE: 05/08/23 10:29:02 GMT FROM: Paul Vreeswijk at ESO C. Ledoux, P. Vreeswijk (ESO), S. Ellison (U. Victoria), A. Jaunsen (ESO/U. Oslo), A. Smette (ESO), J. Fynbo (U. Copenhagen), P. Moller, A. Kaufer (ESO), M. Andersen (AIP), R. Wijers (U. Amsterdam) & J. Hjorth (U. Copenhagen) report: We observed the afterglow (Fox & Cenko, GCN 3829) of GRB 050820 (Page et al, GCN 3830) with UVES at VLT/UT2, starting at 7:08 UT (33 minutes after the burst trigger). The spectra cover most of the optical wavelength range (split into two observations of a total of 60min using one dichroic beam splitter and 40min using the other), with an approximate resolving power of 46,000 (6.5 km/s). We obtain a redshift of z=2.6147 (and therefore confirm the redshift reported by Prochaska et al., GCN 3833) from the detection of numerous host-galaxy metal absorption lines (e.g., CII, CIV, NI, OI, AlII, AlIII, SiII, SiIV, SII, ArI, CrII, FeII, NiII, ZnII) spread over a velocity interval of ~400 km/s. Strong fine-structure lines of CII* and SiII* are also detected. We measure a total neutral hydrogen column density of log N(HI)=21.0 and metallicities of [Si/H]=-0.6 and [Fe/H]=-1.1. In addition, an intervening metal absorption line system with log N(HI)=20.0 is observed at zabs=2.3597. We acknowlegde the excellent support from the ESO staff, and in particular the alertness of night astronomer Stefano Bagnulo. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 3863 SUBJECT: GRB050820a: PROMPT RcIc Observations DATE: 05/08/23 21:22:02 GMT FROM: Chelsea Louise MacLeod at UNC-Chapel Hill/PROMPT C. MacLeod, M. Nysewander report on behalf of the UNC team of the FUN GRB Collaboration: We have observed the position of the GRB 050820a afterglow reported by Fox et al. (GCN 3829). We detect the afterglow in RcIc: Mean Time Integration Filter Magnitude Telescope Since GRB Time 2.2 hr 39 x 40 sec Ic 17.40 +/- .08 PROMPT-3 2.2 hr 22 x 30 sec Rc 17.64 +/- .09 PROMPT-5 21.5 hr 136 x 40 sec Ic 18.42 +/- .11 PROMPT-3 21.7 hr 179 x 30 sec Rc 20.06 +/- .31 PROMPT-5 Rc and Ic calibrations were made relative to 7 calibration stars posted by Henden (GCN 3845). PROMPT is still being built and commissioned. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 3864 SUBJECT: GRB050820A: RTT150 optical observations DATE: 05/08/24 12:26:30 GMT FROM: Irek Khamitov at TUG I. Khamitov, Z. Aslan (TUG), U. Kiziloglu (METU), E. Gogus (Sabanci Uni.), I. Bikmaev, A. Galeev, N. Sakhibullin (KSU/AST), R. Burenin, M. Pavlinsky, R. Sunyaev (IKI), report: We have continued observing the OT of GRB 050820A (GCN 3829) with the Russian-Turkish 1.5-m telescope (Bakirlitepe, TUBITAK National Observatory, Turkey) on the nights of August 22 and 23 in B,Rc,Ic bands. We made a series of exposures between UT 20:23 - 01:33, August 22/23, and between UT 20:09-00:34, August 23/24, 2005. The afterglow is still clearly detected in all bands. Using Henden's stars (GCN 3845) present in the frames, we estimated the magnitudes as follow: t-t0 Band mag merr exptime (hours) (sec,total) 64.39 B 22.24 -/+ 0.06 7860 64.43 Rc 21.02 -/+ 0.03 3900 64.53 Ic 20.46 -/+ 0.05 3900 87.57 B 22.57 +/- 0.08 5400 87.72 Rc 21.30 +/- 0.04 2700 87.82 Ic 20.87 +/- 0.09 2700 We note that, on re-examining the co-added image for 21 Aug in B-band (GCN 3853), we noticed that it included a cosmic ray event close to OT. More careful calculation has resulted in a fainter value of B magnitude: 21.47 +/- 0.06 (40.93h after the trigger). This message may be cited. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 3896 SUBJECT: GRB050820A: RTT150 optical observations DATE: 05/08/28 04:19:16 GMT FROM: Irek Khamitov at TUG Z. Aslan, I. Khamitov (TUG), U. Kiziloglu (METU), E. Gogus (Sabanci Uni.), I. Bikmaev, A. Galeev, N. Sakhibullin (KSU/AST), R. Burenin, M. Pavlinsky, R. Sunyaev (IKI), report: We have continued observing the OT of GRB 050820A (GCN 3829) with the Russian-Turkish 1.5-m telescope (Bakirlitepe, TUBITAK National Observatory, Turkey) using TFOSC in R band. We made 5*300s exposures between UT 22:40 - 23:05, August 27. Using Henden's stars (GCN 3845) present in the frames, we estimated the magnitude of the co-added image as R=22.14+/-0.1 (184.25h after the trigger). The OT is fading with the same power-law decay. Using all the data obtained at the RTT150 (GCN3864, GCN3853) we estimated an alpha index of power-law decay of -1.06+/-0.03. The JPG-image is available at: http://www.tug.tubitak.gov.tr/~irekk/grb/grb050820a/grb050820A_050827r.JPG This message may be cited. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 4005 SUBJECT: GRB050820B: analysis of the XMM-Newton observation DATE: 05/09/20 16:59:46 GMT FROM: Andrea De Luca at IASF-CNR,Milano Andrea De Luca (IASF Mi) on behalf of a larger collaboraton report: We have analyzed the data from the XMM-Newton observation of GRB050820B, discovered by Swift (Page et al., GCN3839) on 2005, August 20 at 23:50:27 UT. The XMM-Newton observation started on 2005, August 21 at 05:21:30 UT (~5h 30min after the GRB) and lasted for 58.5 ks. We report here on the analysis of the data collected by the EPIC instrument. As reported by Rodriguez & Calderon (GCN3844), the afterglow of GRB050820B is detected in all the EPIC cameras. The background-subtracted, time-averaged count rate in the pn camera, estimated from a 25" radius extraction region (containing ~80% of the total counts), is 0.014+/-0.001 cts/s in the 0.2-8 keV energy range. We improved the astrometry of the XMM-Newton/EPIC images by matching X-ray sources in the field to stars in the USNO-B1 catalogue. The refined position (J2000) for the X-ray afterglow is RA: 09h 02m 25.03s Dec: -72d 38' 44.0" The 1 sigma error radius is 1.5 arcsec (including the rms error on the cross-correlation as well as systematic uncertainties in the optical catalogue). The position is consistent with the XRT coordinates reported by Burrows (GCN3842). The afterglow is clearly seen to fade along the XMM-Newton observation, spanning the time range 20-79 ks after the GRB. The background-subtracted light curve (0.3-3 keV) decays as a power law with index delta=1.55+/-0.15 (90% c.l.) (reduced chi2=1.3, 28 d.o.f.). We extracted time-averaged spectra from the three EPIC cameras and we generated ad-hoc response files. We quote here errors at 90% confidence level for a single interesting parameter. A simultaneous fit with an absorbed power law model yields a good description of the data (reduced chi2=0.90, 67 d.o.f.). The best fit value for the NH is 1.6+/-0.4x10^21 cm^-2, somewhat higher than the expected Galactic value in the burst direction (NH~8x10^20 cm^-2, Dickey & Lockman, 1990); the best fitting power law photon index is Gamma=2.3+/-0.2. The observed flux in the 0.2-10 keV range is 4.1x10^-14 erg cm^-2 s^-1, corresponding to an unabsorbed flux of 7.7x10^-14 erg cm^-2 s^-1. No significant spectral variation as a function of the time is found in the data. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 4045 SUBJECT: GRB 050820A: NIR photometry at the TNG DATE: 05/09/28 17:08:00 GMT FROM: Stefano Covino at Brera Astronomical Observatory F. Mannucci, S. Covino, D. Malesani, on behalf of the CIBO collaboration report: We observed the field of GRB 050820A (Page et al., GCN 3830) in the NIR at the TNG equipped with NICS on the 21st of August at 05:00 UT, about 22.4 hours after the high-energy event. The OT identified by Fox et al. (GCN 3829) is clearly visible with J magnitude: J = 18.48 +/- 0.08 Calibration has been derived by comparison with a suitable number of 2MASS stars in the field. This message can be cited.