GRB080928A

This page lists all entries on GRB080928A in GRBweb

Summary Fermi GBM IPN Swift GCN 8292 GCN 8293 GCN 8294 GCN 8295 GCN 8296 GCN 8297 GCN 8298 GCN 8299 GCN 8300 GCN 8301 GCN 8303 GCN 8304 GCN 8316

Summary table
Variable Value Source
GRB_name_Fermi GRB080928628
T0 15:01:32 UTC GCN_circulars,Swift Det
ra 95.0701° Swift
decl -55.1997° Swift
pos_error 6.47e-05° Swift
T90 14.336 s Fermi_GBM
T90_error 4.007 s Fermi_GBM
T90_start 15:04:54.256 UTC Fermi_GBM
fluence 1.17e-06 erg/cm² Fermi_GBM
fluence_error 3.76e-08 erg/cm² Fermi_GBM
redshift 1.6920 Swift
T100 280.0 s
GBM_located False
mjd 54737.626064814816 GCN_circulars,Swift Det
Fermi GBM table
GRB_name_Fermi GRB080928628
trigger_name bn080928628
ra 95.1000°
decl -55.2000°
pos_error 5.10e+00°
datum 2008-09-28
t_trigger 15:04:56.048 UTC
T90 14.336 s
T90_error 4.007 s
T90_start 15:04:54.256 UTC
fluence 1.17e-06 erg/cm²
fluence_error 3.76e-08 erg/cm²
flux_1024 3.19e+00 erg/cm²/s
flux_1024_error 2.25e-01 erg/cm²/s
flux_1024_time -6.40e-01 erg/cm²/s
flux_64 6.02e+00 erg/cm²/s
flux_64_error 1.27e+00 erg/cm²/s
IPN table
GRB_name GRB080928A
ra 95.0833°
decl -55.1667°
pos_error 5.00e-02°
redshift 1.6920
Swift table
GRB_name GRB080928A
t_trigger 15:01:32 UTC
ra 95.0701°
decl -55.1997°
pos_error 6.47e-05°
T90 280.0 s
fluence 2.50e-06 erg/cm²
redshift 1.6920
GCN 8292 table
GRB_name GRB080928A
GCN_number 8292
Detection_method Swift Det
t_trigger 15:01:32 UTC
ra 95.0840°
decl -55.1730°
Circular_text TITLE: GCN CIRCULAR NUMBER: 8292 SUBJECT: GRB 080928: Swift detection of a burst with an optical counterpart DATE: 08/09/28 15:16:04 GMT FROM: Scott Barthelmy at NASA/GSFC T. Sakamoto (NASA/UMBC), S. D. Barthelmy (GSFC), P. A. Evans (U Leicester), N. Gehrels (NASA/GSFC), C. Gronwall (PSU), C. Guidorzi (INAF-OAB), S. T. Holland (CRESST/USRA/GSFC), J. Mao (INAF-OAB), F. E. Marshall (NASA/GSFC), P. T. O'Brien (U Leicester), K. L. Page (U Leicester), D. M. Palmer (LANL), A. M. Parsons (GSFC) and T. N. Ukwatta (GSFC/GWU) report on behalf of the Swift Team: At 15:01:32 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 080928 (trigger=326115). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 95.084, -55.173 which is RA(J2000) = 06h 20m 20s Dec(J2000) = -55d 10' 23" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). This is an image trigger so as usual the BAT lightcurve shows nothing. The XRT began observing the field at 15:04:22.6 UT, 169.7 seconds after the BAT trigger. XRT found a bright, uncatalogued X-ray source located at RA, Dec 95.0691, -55.1997 which is equivalent to: RA(J2000) = 06h 20m 16.58s Dec(J2000) = -55d 11' 58.9" with an uncertainty of 4.8 arcseconds (radius, 90% containment). This location is 100 arcseconds from the BAT onboard position, within the BAT error circle. No event data are yet available to determine the column density using X-ray spectroscopy. The initial flux in the 2.5 s image was 5.77e-09 erg cm^-2 s^-1 (0.2-10 keV). UVOT took a finding chart exposure of 100 seconds with the White (160-650 nm) filter starting 179 seconds after the BAT trigger. There is a candidate afterglow in the rapidly available 2.7'x2.7' sub-image at RA(J2000) = 06:20:16.85 = 95.0702 DEC(J2000) = -55:11:59.3 = -55.1998 with a 1-sigma error radius of about 0.5 arc sec. This position is 2.3 arc sec. from the center of the XRT error circle. The estimated magnitude is 19.2 with a 1-sigma error of about 0.5 mag. No correction has been made for the expected extinction corresponding to E(B-V) of 0.07. Burst Advocate for this burst is T. Sakamoto (Taka.Sakamoto AT nasa.gov). 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.)
GCN 8293 table
GRB_name GRB080928A
GCN_number 8293
Detection_method Other
Circular_text TITLE: GCN CIRCULAR NUMBER: 8293 SUBJECT: GRB 080928A: ROTSE-III Confirmation of Optical Counterpart DATE: 08/09/28 15:58:35 GMT FROM: Eli Rykoff at UCSB E.S. Rykoff (UCSB), F. Yuan (U Mich), T.A. McKay (U Mich), report on behalf of the ROTSE collaboration: ROTSE-IIIa, located at Siding Spring Observatory, Australia, responded to GRB 080928A (Swift trigger 326115, GCN 8292, Sakamoto et al.). The first image was at 15:03:44.9 UT, 132.0 s after the burst (7.9 s after the GCN notice time). The unfiltered images are calibrated relative to USNO A2.0. Our initial images did not detect the UVOT counterpart to a limiting magnitude of ~17.2. However, after ~500 seconds the source brightened to 16.9 mag, and it brightened again at ~2000 s to ~16.2 mag. The coordinates of the source are consistent with the UVOT counterpart: 06:20:17.0 -55:11:58.8 (J2000), with positional uncertainty of 1" or better start UT mag mlim(of image) ---------------------------------- 15:19:02.3 16.9 16.9 This source is not visible in DSS (second epoch), 2MASS or the MPChecker database. A jpeg image is available at http://www.rotse.net/images/gsb326115_3a04_img.jpg Continuing observations are in progress.
GCN 8294 table
GRB_name GRB080928A
GCN_number 8294
Detection_method Swift-BAT Det
ra 95.0630°
decl -55.1750°
Circular_text TITLE: GCN CIRCULAR NUMBER: 8294 SUBJECT: GRB 080928, Swift-BAT initial refined analysis DATE: 08/09/28 23:18:56 GMT FROM: Scott Barthelmy at NASA/GSFC J. Cummings (GSFC/UMBC), S. D. Barthelmy (GSFC), W. Baumgartner (GSFC/UMBC), E. Fenimore (LANL), N. Gehrels (GSFC), C. Guidorzi (INAF-OAB), H. Krimm (GSFC/USRA), C. Markwardt (GSFC/UMD), K. McLean (GSFC/UMD), K. L. Page (U Leicester), D. Palmer (LANL), A. Parsons (GSFC), T. Sakamoto (GSFC/UMBC), G. Sato (ISAS), M. Stamatikos (GSFC/ORAU), J. Tueller (GSFC), T. Ukwatta (GWU) (i.e. the Swift-BAT team): Using the data set from T-239 to T+323 sec from recent telemetry downlinks, we report further analysis of BAT GRB 080928 (trigger #326115) (Sakamoto, et al., GCN Circ. 8292). The BAT ground-calculated position is RA, Dec = 95.063, -55.175 deg, which is RA(J2000) = 06h 20m 15.1s Dec(J2000) = -55d 10' 29.5" with an uncertainty of 2.3 arcmin, (radius, sys+stat, 90% containment). The partial coding was 84%. The mask-weighted light curve shows that BAT triggered on a weak blip that occurred long before the main emission of this burst. The initial peak started at ~T-10 sec, peaked at ~T_zero, and returned to baseline around T+30 sec. Then a second, slightly larger peak, started at ~T+50 and ended at ~T+130 sec. Then the main emission started at ~T+170, with a pair of peaks at ~T+205 and ~T+215 sec. We currently only have data downlinked out to T+325 sec and the mask-weighted lightcurve shows continued emission out to this time. The flight-generated mask-weighted lightcurve (lower resolution) shows no further peaks beyond T+325 sec. The main peak at ~T+210 sec coincides with the peak emission in the prompt XRT TDRSS lightcurve. The time-averaged spectrum from T+51.1 to T+255.3 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.80 +- 0.12. The fluence in the 15-150 keV band is 2.1 +- 0.1 x 10^-6 erg/cm2. The 1-sec peak photon flux measured from T+202.83 sec in the 15-150 keV band is 2.1 +- 0.1 ph/cm2/sec. All the quoted errors are at the 90% confidence level. When we get the remainder of the event-by-event data downlinked, we will issue revised spectral fit results and a T90. The results of the batgrbproduct analysis are available at http://gcn.gsfc.nasa.gov/notices_s/326115/BA/
GCN 8295 table
GRB_name GRB080928A
GCN_number 8295
Detection_method Swift-XRT Det
ra 95.0703°
decl -55.1996°
Circular_text TITLE: GCN CIRCULAR NUMBER: 8295 SUBJECT: GRB 080928: Enhanced Swift-XRT position DATE: 08/09/28 23:23:00 GMT FROM: Phil Evans at U of Leicester J.P. Osborne, A.P. Beardmore, P.A. Evans and M.R. Goad (U. Leicester) report on behalf of the Swift-XRT team. Using 5367 s of XRT Photon Counting mode data and 8 UVOT images for GRB 080928, 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 = 95.07029, -55.19958 which is equivalent to: RA (J2000): 06h 20m 16.87s Dec (J2000): -55d 11' 58.5" with an uncertainty of 1.4 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 http://www.swift.ac.uk/xrt_positions/Goad.pdf), the current algorithm is an extension of this method. This circular was automatically generated, and is an official product of the Swift-XRT team.
GCN 8296 table
GRB_name GRB080928A
GCN_number 8296
Detection_method GROND
Circular_text TITLE: GCN CIRCULAR NUMBER: 8296 SUBJECT: GRB 080928: GROND DETECTION DATE: 08/09/29 12:02:04 GMT FROM: Andrea Rossi at TLS Tautenburg A. Rossi (Tautenburg Obs.), C. Clemens, J. Greiner, A. Yoldas, T. Kruehler, R. Filgas (all MPE Garching), A. Kupcu Yoldas (ESO) and G. Szokoly (Eoetvoes Univ., Budapest) report on behalf of the GROND team: GROND (Greiner et al. 2008, PASP 120, 405), mounted at the 2.2m ESO/MPI telescope at La Silla Observatory (Chile), started observations of the field of GRB 080928 (Sakamoto et al. GCN #8292) in g'r'i'z'JHK at 04:46:00 UT on 2008-09-29, 13.5 hours after the burst trigger. We clearly detect the optical afterglow detected by UVOT (Sakamoto et al. GCN #8292) and ROTSE telescope (Rykoff et al. GCN #8293) in all optical bands, implying a redshift z<3.5. Observations continued for 90 min and were repeated at the mid-time 06:00 UT for a total 90 min. Both observations were done during strong wind and bad seeing (>2"). Calibrating the field on the SDSS standard SA95-149, we derive the following r' band observed magnitudes: midtime(s) r' err ------------------------ 50507 20.57 0.04 65807 21.36 0.06 Our data, when compared to the reported brightness of the afterglow reported by UVOT, suggest a break between the UVOT and the GROND measurements.
GCN 8297 table
GRB_name GRB080928A
GCN_number 8297
Detection_method Swift-BAT Det
ra 95.0610°
decl -55.1760°
Circular_text TITLE: GCN CIRCULAR NUMBER: 8297 SUBJECT: GRB 080928, Swift-BAT final refined analysis DATE: 08/09/29 12:41:32 GMT FROM: Scott Barthelmy at NASA/GSFC E. Fenimore (LANL), S. D. Barthelmy (GSFC), W. Baumgartner (GSFC/UMBC), J. Cummings (GSFC/UMBC), N. Gehrels (GSFC), H. Krimm (GSFC/USRA), C. Markwardt (GSFC/UMD), D. Palmer (LANL), A. Parsons (GSFC), T. Sakamoto (GSFC/UMBC), G. Sato (ISAS), M. Stamatikos (GSFC/ORAU), J. Tueller (GSFC), T. Ukwatta (GWU) (i.e. the Swift-BAT team): Using the data set from T-239 to T+494 sec from the recent telemetry downlink, we report further analysis of BAT GRB 080928 (trigger #326115) (Sakamoto, et al., GCN Circ. 8292). The BAT ground-calculated position is RA, Dec = 95.061, -55.176 deg, which is RA(J2000) = 06h 20m 14.6s Dec(J2000) = -55d 10' 34.8" with an uncertainty of 2.3 arcmin, (radius, sys+stat, 90% containment). The partial coding was 84%. With all the data downlinked, the mask-weighted light curve shows that BAT triggered on a weak blip that occurred long before the main emission of this burst. The initial peak started at ~T-10 sec, peaked at ~T_zero, and returned to baseline around T+30 sec. Then a second, slightly larger peak, started at ~T+50 and ended at ~T+130 sec. Then the main emission started at ~T+170, with a pair of peaks at ~T+205 and ~T+215 sec. The emaission tails down to almost background at T+400 sec at which time Swift started to enter the SAA and the errors on the flux become large. T90 (15-350 keV) is 280 +- 30 sec (estimated error including systematics). The time-averaged spectrum from T+51.1 to T+381.5 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.77 +- 0.12. The fluence in the 15-150 keV band is 2.5 +- 0.2 x 10^-6 erg/cm2. The 1-sec peak photon flux measured from T+202.83 sec in the 15-150 keV band is 2.1 +- 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/326115/BA/
GCN 8298 table
GRB_name GRB080928A
GCN_number 8298
Detection_method Swift-UVOT Det
ra 95.0701°
decl -55.1997°
Circular_text TITLE: GCN CIRCULAR NUMBER: 8298 SUBJECT: GRB 080928: Swift/UVOT observations DATE: 08/09/29 12:54:16 GMT FROM: Paul Kuin at MSSL N. P. M. Kuin (MSSL/UCL), T. Sakamoto (NASA/UMBC),and Stephen Holland (GSFC) report on behalf of the Swift UVOT team The Swift UltraViolet/Optical Telescope (UVOT) began observations of GRB080928 (Swift BAT trigger number 326115, Sakamoto et al., GCN Circ. 8292), on September 28, 2008, at 15:04:15 UT, 161 seconds after the trigger with a setling exposure in the UVOT v filter. We detect a new source at position : RA=06:20:16.836 Dec=-55:11:58.95 (95.07015, -55.199708 deg (J2000)), with an estimated uncertainty of 0.5 arcsec (radius, 90% confidence). The initial magnitude observed for GRB080928 is given below for the first observation in the UVOT v filters: Filter Tstart(s) Tstop(s) Exp(s) Magnitude wh(fc) 179 279 99.8 19.09 +/- 0.14 7.3-sigma v (fc) 285 479 193.7 19.07 +/- 0.43 2.5-sigma uvm2 4227 4427 196.6 >19.47 3-sigma upper limit (weak signal) uvw1 4432 4632 196.6 18.64 +/- 0.19 5.6-sigma u 4638 4838 199.8 17.96 +/- 0.09 12.1-sigma b 4843 5043 199.8 18.40 +/- 0.09 11.9-sigma uvw2 5255 5455 196.6 >19.89 3-sigma upper limit v 5460 5660 199.8 18.03 +/- 0.15 7.3-sigma The upper limits in the UV filters uvw2 and uvm2 indicate an upper limit to the redshift of z < 1.8. An initial rise is seen up to about 200s in the white filter event data. The values quoted above are on the UVOT Photometric System (Poole et al, 2008, MNRAS 383,627). They are not corrected for the expected galactic reddening of E(B-V) = 0.067 in the direction of the burst (Schlegel et al. 1998).
GCN 8299 table
GRB_name GRB080928A
GCN_number 8299
Detection_method Swift-XRT Other
Circular_text TITLE: GCN CIRCULAR NUMBER: 8299 SUBJECT: GRB 080928: Swift-XRT refined analysis DATE: 08/09/29 12:56:41 GMT FROM: Cristiano Guidorzi at INAF-OAB C. Guidorzi, R. Margutti, J. Mao (INAF-OAB) and T. Sakamoto (GSFC/UMBC) report on behalf of the Swift-XRT team: We have analysed the first 7 orbits of Swift-XRT data obtained for GRB 080928 (Sakamoto et al., GCN Circ. 8292), covering 325 s of Windowed Timing (WT) mode data and 15.3 ks of Photon Counting (PC) mode data. The UVOT-enhanced XRT position was given by Osborne et al. in GCN Circ. 8295. The light-curve can be modelled by a broken power-law, with a couple of bright flares peaking at 210 and 360 s with a FWHM duration of 55 and 35 s and a peak count rate of 420 +/- 10 and 75 +- 3 count s^-1, respectively. The power-law decay index changes from an initial value of 1.20 +- 0.03 to 1.7 +- 0.2 after a break time of (11 +- 2) ks (uncertainties at 1 sigma). The first flare coincides with the main emission seen by BAT (Fenimore et al. GCN Circ. 8297). A spectrum extracted from WT data around the first flare, from 176 to 250 s, can be modelled with an absorbed power-law, with Gamma = 1.45 +- 0.06 and NH = (1.7 +- 0.2)x1e21 cm^-2, in excess of the Galactic column in this direction of 5.6e20 cm^-2. Another spectrum extracted around the second flare, from 300 to 470 s, can be fit with the same model, with Gamma = 1.85 +- 0.06 and NH = (1.1 +- 0.2)x1e21 cm^-2. A later spectrum extracted from PC data, from 5 to 47 ks, can be fit with an absorbed power law with Gamma = 2.2 +- 0.2 and NH = (1.2 +- 0.4)x1e21 cm^-2. The observed (unabsorbed) flux over this time interval is 8.4x10^-12 (1.2x10^-11) erg cm^-2 s^-1. If the light-curve continues to decay with the current rate, the count rate 24 hours after the burst is estimated to be 5.6e-3 count s^-1, which corresponds to an observed flux of 2.5x10^-13 erg cm^-2 s^-1. This is an official product of the Swift-XRT team.
GCN 8300 table
GRB_name GRB080928A
GCN_number 8300
Detection_method Optical
redshift 2.5450
Circular_text TITLE: GCN CIRCULAR NUMBER: 8300 SUBJECT: GRB080928: Gemini-South Absorption Redshift DATE: 08/09/29 15:31:33 GMT FROM: Antonino Cucchiara at PSU A. Cucchiara, D. B. Fox (Penn State), S. B. Cenko (Berkeley) and E. Berger (Harvard) report on behalf of a larger collaboration: Starting at 06:54 UT on 2008 September 29 (T0+16h) we observed the optical counterpart of GRB 080928 (Sakamoto et al., GCN 8292, Rykoff et al., GCN 8293) using Gemini-South with the GMOS-South spectrograph (R~1200). We acquired 2x900s spectra which covered the wavelength range 4000A-8000A. Our spectrum shows a flux cut-off blueward of 4500A indicating a likely DLA associated with the GRB host galaxy, consistent with a redshift of z ~ 2.6. We also identify multiple metal absorption features including FeII(2249), FeII(2260), SiIV(1393), SiIV(1402), CIV(1548), CIV(1550), NiII(1741) and NiII(1751) at a common redshift of z = 2.49. Therefore we conclude that GRB080928 occurred in a possible DLA galaxy at z = 2.49. We thank the Gemini staff for conducting these observations. [GCN OPS NOTE(29sep08): Per author's request, the affiliation for EB was corrected to Harvard.]
GCN 8301 table
GRB_name GRB080928A
GCN_number 8301
Detection_method Swift Other
redshift 0.7360
Circular_text TITLE: GCN CIRCULAR NUMBER: 8301 SUBJECT: GRB 080928: VLT redshift DATE: 08/09/29 16:26:29 GMT FROM: Paul Vreeswijk at Dark Cosmology Centre,U.of Copenhagen Paul Vreeswijk, Daniele Malesani, Johan Fynbo (DARK/NBI), Pall Jakobsson (U. of Iceland), Christina Thoene, Jesper Sollerman, Darach Watson, Bo Milvang-Jensen (DARK/NBI) report on behalf of a larger collaboration: The afterglow of GRB 080928 detected by Swift (Sakamoto et al., GCN 8292, see also Rykoff et al., GCN 8293) was observed with FORS2 mounted on the Antu telescope of ESO's VLT on Cerro Paranal, Chile. Following an acquisition image, which was started at 6:31 UT on September 29, 2008 (15.5 hr after the GRB trigger), a single 1800 s spectrum was secured. It was taken with a 1" slit and the 300V grism, resulting in an approximate resolution of 11 A, and a useful wavelength coverage of 3800-9300 A. From the 60 s acquisition image, we measure an afterglow magnitude of R = 20.4 based on USNO-B1 magnitudes. The extracted spectrum shows a multitude of significant absorption lines, which we identify with common resonance lines of mainly MgII and FeII, originating in at least two absorption systems at z=0.735 and z=1.692. The latter redshift presumably corresponds to that of the GRB host galaxy. We do not find evidence for a spectral break due to the Lyman alpha forest down to 3800 A, setting a firm upper limit on the GRB redshift of z < 2.1. These results are consistent with the redshift limits set by GROND (Rossi et al., GCN 8296) and UVOT (Kuin et al., GCN 8298), but not with the value of z=2.49 reported by Cucchiara et al. (GCN 8300). The equivalent width of the MgII 2796 line of the z=0.735 system (EW_rest ~ 4.3 A) is much larger than that of the z=1.692 system. We note the presence of an R ~ 22 object, not covered by the slit, at 2.6" NNE of the afterglow position, which could possibly be a bright host galaxy, or the counterpart of the z=0.735 absorber. The slit serendipitously covers a galaxy 30" away from the afterglow (at R.A. 06:20:13.35, decl. -55:11:55.0), which shows an apparent emission line at 6470 A; this can be identified as [OII] 3727 at a redshift of z=0.736. At this redshift, 2.6 and 30" correspond to projected distances of 19 and 219 kpc, respectively. We are grateful for the excellent support from the Paranal observing staff, in particular Stephane Brillant, Michelle Doherty and Patricia Guajardo.
GCN 8303 table
GRB_name GRB080928A
GCN_number 8303
Detection_method Optical
Circular_text TITLE: GCN CIRCULAR NUMBER: 8303 SUBJECT: GRB 080928: Watcher observations DATE: 08/10/01 14:22:05 GMT FROM: Alejandro Ferrero at U College,Dublin Alejandro Ferrero (UCD School of Physics), John French (UCD School of Physics/ DARK/NBI), and Gary Melady (UCD School of Physics) report on behalf of a larger collaboration: We observed the field of GRB 080928 (Sakamoto et al. GCN 8292) with the Watcher robotic telescope at Boyden Observatory, South Africa. The afterglow previously reported (Sakamoto et al. GCN 8292, Rykoff et al. GCN 8293, Rossi et al. GCN 8296, Kuin et al. GCN 8298) is detected in a stacked sequence of 10 unfiltered 120s exposures with an exposure midtime of 10.56 hrs from the Swift triggger. Comparison with USNO-B1 R-band magnitudes gives a magnitude of 19.37 +/- 0.11 for the optical afterglow at this time. Comparison with later GROND observations (Rossi et al. GCN 8296) indicates a steep decay slope of approx. -3 +/- 0.4 from 10.56 hours to 18.27 hours from the trigger.
GCN 8304 table
GRB_name GRB080928A
GCN_number 8304
Detection_method retraction
redshift 2.4900
Circular_text TITLE: GCN CIRCULAR NUMBER: 8304 SUBJECT: GRB080928: redshift retraction DATE: 08/10/01 15:53:55 GMT FROM: Antonino Cucchiara at PSU A. Cucchiara and D. B. Fox (Penn State) report on behalf of a larger collaboration: We re-processed the data acquired on GRB080928 in order to reconcile our results with the redshift identification reported by Vreesvijk et al. (GCN 8301). Upon comparison of our two individual exposures, we cannot confirm the presence of the metal absorption features reported in GCN 8300. We therefore conclude that the redshift z=2.49 for GRB 080928 reported by us previously is not correct. Line misidentifications are probably the result of inaccurate sky-line and sky-fringe modeling in extraction of the 1D spectrum. We retract also the claim of a DLA system at z~2.5. We confirm the detection of strong MgII doublet and associated MgI absorption from a system at z=1.69, which - as reported by Vreeswijk et al. - represents the lower limit and most likely redshift for GRB 080928. We apologize for any confusion.
GCN 8316 table
GRB_name GRB080928A
GCN_number 8316
Detection_method Fermi GBM Det
t_trigger 15:04:56 UTC
ra 93.9000°
decl -53.1000°
Circular_text TITLE: GCN CIRCULAR NUMBER: 8316 SUBJECT: GRB 080928: Fermi GBM detection DATE: 08/10/03 16:17:37 GMT FROM: Bill Paciesas at UAH Bill Paciesas, Michael Briggs and Rob Preece (UAH), report on behalf of the Fermi Gamma-ray Burst Monitor Team: "At 15:04:56 UT on 28 September 2008, the Fermi Gamma-Ray Burst Monitor (GBM) triggered and located GRB 080928 (trigger 244307097 / 080928.628), which had triggered the Swift BAT ~204 s earlier (Sakamoto et al. GCN 8292). The on-ground calculated location, using the GBM trigger data, is RA = 93.9, Dec = -53.1 (+/- 4.9)(J2000 degrees), with an uncertainty of 4.9 degrees (radius, 1-sigma containment, statistical only; there is additionally a systematic error which is currently estimated to be 2 to 3 degrees), consistent with the Swift location (Sakamoto et al. GCN 8292; Osborne et al. 8295). The emission detected by GBM lasted about 87 s with the strongest emission in the first 20 s, and is approximately coincident with the main emission detected by Swift (Cummings et al. GCN 8294). The time-averaged spectrum from T-5 to T+24 s can be fit by a power-law with an index of -1.80 +/- 0.08. The fluence between 50 and 300 keV over these 87 seconds is (1.5 +/- .1) x 10^-6 erg/cm^2. The spectral analysis results presented above are preliminary; the final results will be published in the GBM GRB Catalog."