GRB100728A

This page lists all entries on GRB100728A in GRBweb

Summary Fermi GBM IPN Swift Fermi LAT GCN 11004 GCN 11005 GCN 11006 GCN 11007 GCN 11008 GCN 11014 GCN 11016 GCN 11018 GCN 11020 GCN 11021 GCN 11037 GCN 14500

Summary table
Variable Value Source
GRB_name_Fermi GRB100728095
T0 2:17:30 UTC Fermi_LAT
ra 88.7584° Fermi_LAT
decl -15.2557° Fermi_LAT
pos_error 1.39e-04° Fermi_LAT
T90 165.378 s Fermi_GBM
T90_error 2.896 s Fermi_GBM
T90_start 2:17:43.923 UTC Fermi_GBM
fluence 1.28e-04 erg/cm² Fermi_GBM
fluence_error 5.76e-07 erg/cm² Fermi_GBM
redshift 1.5670 GCN_circulars,Konus-Wind Det
T100 252.5 s
GBM_located False
mjd 55405.09548611111 Fermi_LAT
Fermi GBM table
GRB_name_Fermi GRB100728095
trigger_name bn100728095
ra 88.7608°
decl -15.2561°
pos_error 3.59e+00°
datum 2010-07-28
t_trigger 2:17:30.611 UTC
T90 165.378 s
T90_error 2.896 s
T90_start 2:17:43.923 UTC
fluence 1.28e-04 erg/cm²
fluence_error 5.76e-07 erg/cm²
flux_1024 1.05e+01 erg/cm²/s
flux_1024_error 2.83e-01 erg/cm²/s
flux_1024_time 8.01e+01 erg/cm²/s
flux_64 1.30e+01 erg/cm²/s
flux_64_error 1.20e+00 erg/cm²/s
IPN table
GRB_name GRB100728A
ra 77.0667°
decl -14.3333°
pos_error 5.00e-02°
redshift 1.5670
Swift table
GRB_name GRB100728A
t_trigger 2:18:24 UTC
ra 88.7583°
decl -15.2554°
pos_error 1.81e-04°
T90 198.5 s
fluence 3.80e-05 erg/cm²
redshift 1.5670
Fermi LAT table
GRB_name_Fermi GRB100728095
GRB_name GRB100728A
MET 301976252.0
datum 2010-07-28
t_trigger 2:17:30 UTC
ra 88.7584°
decl -15.2557°
pos_error 1.39e-04°
GCN 11004 table
GRB_name GRB100728A
GCN_number 11004
Detection_method Swift Det
t_trigger 2:18:24 UTC
ra 88.7430°
decl -15.2620°
Circular_text TITLE: GCN CIRCULAR NUMBER: 11004 SUBJECT: GRB 100728A: Swift detection of a burst DATE: 10/07/28 02:30:01 GMT FROM: David Palmer at LANL J. K. Cannizzo (NASA/UMBC), W. H. Baumgartner (GSFC/UMBC), P. A. Evans (U Leicester), J. M. Gelbord (PSU), S. T. Holland (CRESST/USRA/GSFC), H. A. Krimm (CRESST/GSFC/USRA), O. M. Littlejohns (U Leicester), C. B. Markwardt (CRESST/GSFC/UMD), F. E. Marshall (NASA/GSFC), C. Pagani (U Leicester), K. L. Page (U Leicester), D. M. Palmer (LANL), A. Rowlinson (U Leicester), M. H. Siegel (PSU), M. Stamatikos (OSU/NASA/GSFC) and R. L. C. Starling (U Leicester) report on behalf of the Swift Team: At 02:18:24 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 100728A (trigger=430151). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 88.743, -15.262 which is RA(J2000) = 05h 54m 58s Dec(J2000) = -15d 15' 42" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a multi-peaked structure with a duration of at least 200 sec, although the burst was already in progress when the spacecraft slewed to the original position. The peak count rate was ~11,000 counts/sec (15-350 keV), at ~25 sec after the trigger. The XRT began observing the field at 02:19:41.0 UT, 76.7 seconds after the BAT trigger. XRT found a bright, uncatalogued X-ray source located at RA, Dec 88.7610, -15.2561 which is equivalent to: RA(J2000) = 05h 55m 02.63s Dec(J2000) = -15d 15' 21.9" with an uncertainty of 5.8 arcseconds (radius, 90% containment). This location is 64 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 0.1 s image was 2.01e-08 erg cm-2 s-1 (0.2-10 keV). UVOT took a finding chart exposure of 150 seconds with the White filter starting 86 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 0.18. Burst Advocate for this burst is J. K. Cannizzo (cannizzo AT milkyway.gsfc.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 11005 table
GRB_name GRB100728A
GCN_number 11005
Detection_method Swift-XRT Det
ra 88.7584°
decl -15.2553°
Circular_text TITLE: GCN CIRCULAR NUMBER: 11005 SUBJECT: GRB 100728A: Enhanced Swift-XRT position DATE: 10/07/28 09:33:08 GMT FROM: Phil Evans at U of Leicester A.P. Beardmore, P.A. Evans, M.R. Goad and J.P. Osborne (U. Leicester) report on behalf of the Swift-XRT team. Using 5085 s of XRT Photon Counting mode data and 8 UVOT images for GRB 100728A, 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 = 88.75839, -15.25531 which is equivalent to: RA (J2000): 05h 55m 2.01s Dec (J2000): -15d 15' 19.1" 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) and Evans et al. (2009, MNRAS, 397, 1177). This circular was automatically generated, and is an official product of the Swift-XRT team.
GCN 11006 table
GRB_name GRB100728A
GCN_number 11006
Detection_method Fermi GBM Det
t_trigger 2:17:30.610 UTC
Circular_text TITLE: GCN CIRCULAR NUMBER: 11006 SUBJECT: GRB 100728A: Fermi GBM observation DATE: 10/07/28 10:06:01 GMT FROM: Andreas von Kienlin at MPE A. von Kienlin (MPE) reports on behalf of the Fermi GBM Team: "At 02:17:30.61 UT on 28 July 2010, the Fermi Gamma-Ray Burst Monitor triggered and located GRB 100728A (trigger 301976252 / 100728095), which was also detected by the Swift-BAT (Cannizzo et al. 2008, GCN 11004) The GBM on-ground location is consistent with the Swift position. The angle from the Fermi LAT boresight is 58.6 degrees. The GBM light curve shows a multi-peaked structure with a duration (T90) of about 162.9 +/- 0.9 s (50 - 300 keV). The time-averaged spectrum from T0-8.192 s to T0+191.491 s is well fit by a power law function with an exponential high energy cutoff. The power law index is -0.76 +/- 0.01 and the cutoff energy, parameterized as Epeak, is 353.7 +/- 6.7 keV (Castor C-STAT 3540 for 727 d.o.f.) . The event fluence (8-1000 keV) in this time interval is (1.291 +/- 0.008)E-04 erg/cm^2. The 1.024-sec peak photon flux measured starting from T0+80.2 s in the 8-1000 keV band is 10.8 +/- 0.2 ph/s/cm^2. A Band function fits the spectrum equally well (Castor C-STAT 3537 for 726 d.o.f.) with Epeak= 344.3 +9.1/-7.9 keV, alpha = -0.75 +/- 0.01 and beta = -3.04 +0.23/-0.57. The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog."
GCN 11007 table
GRB_name GRB100728A
GCN_number 11007
Detection_method Optical
Circular_text TITLE: GCN CIRCULAR NUMBER: 11007 SUBJECT: GRB 100728A: KAIT optical afterglow detection DATE: 10/07/28 11:30:36 GMT FROM: Daniel Perley at U.C. Berkeley D. A. Perley, C. R. Klein, A. N. Morgan, and W. Li (UC Berkeley) report on behalf of the KAIT follow-up team: The Katzman Automatic Imaging Telescope (KAIT) responded to GRB 100728A and began taking data starting less than one minute after the trigger. A moderately bright optical transient not present in DSS survey imaging is visible in the initial set of exposures at the following position: RA = 02:56:13.48 dec = +00:16:51.8 (J2000) We measure I = 18.7 +/- 0.3 mag at 10:33:51 UT (t = 95 secs after the BAT trigger) In addition, we also manually slewed the 1.0 meter Nickel telescope and began taking data starting at 6.6 minutes after the trigger; the afterglow is also well-detected and is seen to fade in subsequent exposures. Follow-up is continuing.
GCN 11008 table
GRB_name GRB100728A
GCN_number 11008
Detection_method Swift-BAT Det
Circular_text TITLE: GCN CIRCULAR NUMBER: 11008 SUBJECT: GRB 100728A: Skynet/PROMPT Detections DATE: 10/07/28 11:31:35 GMT FROM: Kevin Ivarsen at UNC/PROMPT K. Ivarsen, J. Haislip, D. Reichart, A. LaCluyze, J. Moore, A. Foster, R. Egger, A. Oza, M. Schubel, A. Trotter, J. A. Crain, and M. Nysewander report: Skynet observed the Swift/BAT localization of GRB 100728A (Swift trigger #430172) with four of the 16" PROMPT telescopes at CTIO beginning 45 seconds after the trigger in BVRI. We detect the afterglow in all filters. At 50 seconds after the trigger, its magnitude is I = 14.62 +0.08 -0.07 (calibrated to 10 SDSS stars), R = 15.24 +0.07, -0.06 (calibrated to 7 SDSS stars), V = 15.78, +0.08, -0.07 (calibrated to 8 SDSS stars), B = 16.54 +0.21, -0.17 (calibrated to 2 SDSS stars). SDSS transformations were applied using Jester et al., 2005, ApJ, 130, 873. PROMPT's BVRI light curve of the first 4.3 minutes after the trigger, calibrated to SDSS stars, can be found here: http://skynet.unc.edu/grb/grb100728a.png. Further observations were limited by morning twilight at PROMPT.
GCN 11014 table
GRB_name GRB100728A
GCN_number 11014
Detection_method Swift-XRT Other
Circular_text TITLE: GCN CIRCULAR NUMBER: 11014 SUBJECT: GRB 100728A: Swift-XRT refined analysis DATE: 10/07/28 13:35:53 GMT FROM: Phil Evans at U of Leicester P. A. Evans (U. Leicester) and J. K. Cannizzo (NASA/UMBC) report on behalf of the Swift-XRT team: We have analysed 10 ks of XRT data for GRB 100728A (Cannizzo et al. GCN Circ. 11004), from 66 s to 23.4 ks after the BAT trigger. The data comprise 1.3 ks in Windowed Timing (WT) mode (the first 9 s were taken while Swift was slewing) with the remainder in Photon Counting (PC) mode. The enhanced XRT position for this burst was given by Beardmore et al. (GCN. Circ 11005). The light curve can be modeled with a broken power-law decay, with a series of flares superimposed during the first kilosecond. The underlying decay begins with a decay index of 1.6 (+/-0.1), breaking at T+410 sec to a decay index of 1.07 (+0.03, -0.04). The decay then breaks again at T+11600 sec to a final decay of 1.82 (+/-0.2). Nine discrete flares can clearly be identified, with peak times of T+ 88, 111, 189, 252, 296, 383, 445, 516, 659 sec. These all occurred while the XRT was in Windowed Timing mode. A spectrum formed from the WT mode data can be fitted with an absorbed power-law with a photon spectral index of 2.022 (+/-0.022). The best-fitting absorption column is 3.69 (+0.09, -0.08) x 10^21 cm^-2, in excess of the Galactic value of 1.0 x 10^21 cm^-2 (Kalberla et al. 2005). The PC mode spectrum has a photon index of 2.05 (+/-0.09) and a best-fitting absorption column of 3.7 (+/-0.3) x 10^21 cm^-2. The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 4.5 x 10^-11 (7.6 x 10^-11) erg cm^-2 count^-1. If the light curve continues to decay with a power-law decay index of 1.82, the count rate at T+24 hours will be 0.024 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.1 x 10^-12 (1.8 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/00430151. This circular is an official product of the Swift-XRT team.
GCN 11016 table
GRB_name GRB100728A
GCN_number 11016
Detection_method Swift-UVOT Other
Circular_text TITLE: GCN CIRCULAR NUMBER: 11016 SUBJECT: GRB 100728A: Swift/UVOT Upper Limits DATE: 10/07/28 14:01:25 GMT FROM: Samantha Oates at MSSL S. R. Oates (MSSL-UCL) and J. K. Cannizzo (NASA/UMBC) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 100728A 86s after the BAT trigger (Cannizzo et al., GCN 11004). We do not detect a new source at the enhanced Swift XRT position (Evans et al. GCN 11005). The preliminary 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) 86 236 147 >20.54 white 578 7432 657 >21.16 u (FC) 299 548 246 >19.82 u 702 7021 490 >20.04 v 628 11695 1218 >20.06 b 554 7226 510 >20.37 uvw1 677 13337 1228 >20.62 uvm2 1255 12600 1337 >20.69 uvw2 604 7554 447 >20.19 ------------------------------------------------------------- The quoted upper limits have not been corrected for the expected Galactic extinction corresponding to a reddening along the line of sight of E_(B-V) = 0.18 mag. All photometry is on the UVOT photometric system described in Poole et al. (2008, MNRAS, 383, 627).
GCN 11018 table
GRB_name GRB100728A
GCN_number 11018
Detection_method Swift-BAT Det
ra 88.7530°
decl -15.2590°
Circular_text TITLE: GCN CIRCULAR NUMBER: 11018 SUBJECT: GRB 100728A, Swift-BAT refined analysis DATE: 10/07/28 15:22:22 GMT FROM: Hans Krimm at NASA-GSFC T. N. Ukwatta (GWU), S. D. Barthelmy (GSFC), W. H. Baumgartner (GSFC/UMBC), J. K. Cannizzo (NASA/UMBC),J. R. Cummings (GSFC/UMBC), E. E. Fenimore (LANL), N. Gehrels (GSFC), H. A. Krimm (GSFC/USRA), C. B. Markwardt (GSFC/UMD), D. M. Palmer (LANL), T. Sakamoto (GSFC/UMBC), G. Sato (ISAS), M. Stamatikos (OSU), J. Tueller (GSFC), (i.e. the Swift-BAT team): Using the data set from T-130 to T+963 sec from the recent telemetry downlink, we report further analysis of BAT GRB 100728A (trigger #430151) (Cannizzo, et al., GCN Circ. 11004). The BAT ground-calculated position is RA, Dec = 88.753, -15.259 deg which is RA(J2000) = 05h 55m 00.7s Dec(J2000) = -15d 15' 33.0" with an uncertainty of 1.0 arcmin, (radius, sys+stat, 90% containment). The partial coding was 81%. The BAT light curve is quite complex with a long series of peaks and flares extending from approximately T-100 sec to T+750 sec. Detected emission began around T-100 sec, rising to a first peak at T-40 sec. The burst continued as a series of at least ten overlapping peaks with the strongest peak centered at T+30 sec. There was a strong set of BAT peaks centered at T+120 sec, corresponding with the second flare detected by the XRT (Evans & Cannizzo, GCN Circ 11014). This was followed by a series of weaker flares out to T+750 sec, at times which appear to correspond to flares detected by the XRT. The burst triggered just after the spacecraft settled following a slew to a pre-planned target, so it is possible that there was some very early emission (before T-120 sec) which was not detected. T90 (15-350 keV) is 198.5 +- 12.7 sec (estimated error including systematics). The time-averaged spectrum from T-84.3 to T+334.0 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.18 +- 0.02. The fluence in the 15-150 keV band is 3.8 +- 0.0 x 10^-5 erg/cm2. The 1-sec peak photon flux measured from T+28.26 sec in the 15-150 keV band is 5.1 +- 0.2 ph/cm^2/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/430151/BA/
GCN 11020 table
GRB_name GRB100728A
GCN_number 11020
Detection_method GROND
ra 88.7584°
decl -15.2557°
Circular_text TITLE: GCN CIRCULAR NUMBER: 11020 SUBJECT: GRB 100728A: GROND Detection of the NIR Afterglow Candidate DATE: 10/07/28 16:55:50 GMT FROM: Robert Filgas at MPI F. Olivares, T. Kruehler, R. Filgas, J. Greiner, M. Nardini (all MPE Garching) and A. Nicuesa (TLS Tautenburg) report on behalf of the GROND team: We observed the field of GRB 100728A (Swift trigger 430151; Cannizzo et al., GCN #11004; A. von Kienlin, GCN #11006) 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 09:26 UT, 7 hours after the GRB trigger and were terminated at 10:32 UT by the GRB 100728B trigger. They were performed at an average seeing of 1.3" and at an average airmass of 2.5. We found a single, very faint point source in the H band within the enhanced Swift-XRT error circle reported by Beardmore et al. (GCN #11005) at RA (J2000) = 05:55:02.01 DEC (J2000) = -15:15:20.4 with an uncertainty of 0.5" in each coordinate. Based on 24 min of total exposures in g'r'i'z' JHK, we estimate preliminary magnitudes and upper limits (all in AB system) of g' > 23.3 r' > 23.9 i' > 23.5 z' > 23.5 J > 22.0 H = 21.2 +- 0.3 K > 20.3 Given magnitudes and upper limits are obtained by calibrating the images against GROND zeropoints as well as 2MASS field stars and are not corrected for the expected Galactic foreground extinction corresponding to a reddening of E_(B-V)=0.18 mag in the direction of the burst (Schlegel et al. 1998). These magnitudes imply very red colors of the afterglow of J-H > 0.8 and r-H > 2.7. Together with the significant excess absorption seen by the XRT (Evans & Cannizzo, GCN 11014), and the lack of prompt detections in the optical and UV filters (Oates & Cannizzo, GCN 11016), these values are suggestive of a highly extinguished optical/NIR afterglow. The K band upper limit is not constraining even for the steepest SED slopes and consistent with this hypothesis.
GCN 11021 table
GRB_name GRB100728A
GCN_number 11021
Detection_method Konus-Wind Det
t_trigger 2:18:20.008 UTC
Circular_text TITLE: GCN CIRCULAR NUMBER: 11021 SUBJECT: Konus-Wind observation of GRB 100728A DATE: 10/07/28 18:02:30 GMT FROM: Dmitry Frederiks at Ioffe Institute S. Golenetskii, R.Aptekar, D. Frederiks, E. Mazets, V. Pal'shin, P. Oleynik, M. Ulanov, D. Svinkin, and T. Cline on behalf of the Konus-Wind team, report: The long GRB 100728A (Swift/BAT trigger 430151: Canizzo et.al, GCN 11004) triggered Konus-Wind at T0=8300.008s UT (02:18:20.008) The burst light curve shows a complex structure with a total duration of ~200 s. There is a hint of a weaker emission lasting at least to T0+290 s. The emission is seen up to several MeV. The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB100728_T08300/ As observed by Konus-Wind the burst had a fluence of 1.95(+/-0.35)x10-4 erg/cm2, and a 256-ms peak flux, measured from T0+27.392s, of 4.2(+/-0.7)x10-6 erg/cm2/s (both in the 20 keV - 10 MeV energy range). The time-integrated spectrum of the burst (measured from T0 to T0+137.216 s) is best fit in the 20 keV - 10 MeV range by the GRB (Band) model, for which: the low-energy photon index alpha = -0.65 (-0.09, +0.09), the high energy photon index beta = -2.5 (-0.3, +0.2), the peak energy Ep = 305(-25, +27)keV (chi2 = 88/84 dof). The spectrum at the maximum count rate (measured from T0+24.832 to T0+31.488 s) is best fit in the 20 keV - 10 MeV range by the GRB (Band) model, for which: the low-energy photon index alpha = -0.47 (+/-0.15), the high energy photon index beta = -2.6 (-0.3, +0.2), the peak energy Ep = 390(-48, +63)keV (chi2 = 84/84 dof). All the quoted results are preliminary. All the quoted errors are at the 90% confidence level.
GCN 11037 table
GRB_name GRB100728A
GCN_number 11037
Detection_method Suzaku WAM Det
Circular_text TITLE: GCN CIRCULAR NUMBER: 11037 SUBJECT: GRB 100728A: Suzaku WAM observation of the prompt emission DATE: 10/08/02 15:27:24 GMT FROM: Yuji Urata at Nat. Central U. P. Tsai, Y. Urata, H.M. Lin (NCU), T. Uehara, Y. Hanabata, T. Takahashi, Y. Fukazawa (Hiroshima U.), N. Vasquez (Tokyo Tech.) K. Yamaoka (Aoyama Gakuin U.), S. Sugita (Nagoya U.), Y. Terada, M. Tashiro, W. Iwakiri, K. Takahara, T. Yasuda (Saitama U.), M. Ohno, M. Suzuki, M. Kokubun, T. Takahashi (ISAS/JAXA), Y. E. Nakagawa, T. Tamagawa (RIKEN), N. Ohmori, A. Daikyuji, Y. Nishioka, M. Yamauchi (Univ. of Miyazaki), K. Nakazawa, K. Makishima (Univ. of Tokyo), S. Hong (Nihon U.), on behalf of the Suzaku WAM team, report: The long GRB 100728A (Fermi/GBM trigger #301976252; von Kienlin et al., GCN #11006; Swift/BAT trigger #430151; Cannizzo et al., GCN 11004) triggered the Suzaku Wide-band All-sky Monitor (WAM) which covers an energy range of 50 keV - 5 MeV at 2010-07-28 02:17:32.68 UT (=T0). The observed light curve shows a multi-peaked structure starting at T0-5s, ending at T0+198s, with a duration (T90) of about 162 seconds. The fluence in 100 - 1000 keV was 9.09 (-1.55, +0.07) x 10^-5 ergs/cm^2. The 1-s peak flux measured from T0+80s was 4.66 (-0.78, +0.03) photons/cm^2/s in the same energy range. Preliminary result shows that the time-averaged spectrum from T0-2s to T0+180s is well fitted by a power-law with exponential cutoff model: dN/dE ~ E^{-alpha} * exp(-(2-alpha)*E/Epeak) with alpha 0.76 (+/-0.11), and Epeak 378 (-14, +13) keV (chi^2/d.o.f. = 34.4/22). All the quoted errors are at statistical 90% confidence level. The light curves for this burst are available at: http://www.astro.isas.jaxa.jp/suzaku/HXD-WAM/WAM-GRB/grb/trig/grb_table.html
GCN 14500 table
GRB_name GRB100728A
GCN_number 14500
Detection_method Konus-Wind Det
redshift 1.5670
Circular_text TITLE: GCN CIRCULAR NUMBER: 14500 SUBJECT: GRB 100728A: GROND host detection and X-shooter redshift DATE: 13/04/29 11:32:33 GMT FROM: Thomas Kruehler at Dark Cosmology Center T. Kruehler (DARK), J. Greiner (MPE) and D. A. Kann (TLS) report: We performed deep observations of the field of GRB 100728A simultaneously in g'r'i'z'JHK with GROND (Greiner et al. 2008, PASP 120, 405). GRB 100728A triggered Swift (Cannizzo et al., GCN 11004), GBM (von Kienlin, GCN 11006), Konus-Wind (Golenetskii et al., GCN 11021) and Suzaku WAM (Tsai et al., GCN 11037). Our late observations were performed on 2010-11-10, 105 days after the trigger, and consisted of dithered images with a total of 4427 s exposure in g'r'i'z' and 3600 s in JHK under clear sky conditions and a seeing of 0.8". Inside the enhanced X-ray error-circle (http://www.swift.ac.uk/xrt_positions), we detect an extended object with an r'-band AB magnitude of r' = 25.0 +/- 0.2. Its barycentric coordinates are: RA (J2000) = 05:55:01.98 Dec. (J2000) = -15:15:19.7 with uncertainties of 0.3" in each coordinate. Registering the early afterglow images (Olivares et al., GCN 11020) against the late host frame, we derive an offset between galaxy center and afterglow of approximately 0.4". A spectrum of this galaxy was taken on 2012-11-15 with the ESO VLT UT2 equipped with the X-shooter spectrograph, covering the wavelength range 3000-25000 AA. The seeing was 1.2" and the total exposure of our spectrum was 2400 s. In the VIS and NIR arm, we detect emission lines, which we interpret as being due to [O II](3729) and Halpha at a common redshift of z = 1.567. The bright X-ray emission (Evans et al., GCN 11014), coupled with the faint and red optical/NIR afterglow (Olivares et al., GCN 11020) is characteristic of dust-extinguished events. Fitting the available afterglow data with synchrotron models, the visual extinction along the GRB sightline is constrained to 1.5 mag < A_V < 3 mag at z = 1.567.