This file contains three bursts GRB 060923 'A', 'B', and 'C'. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 5583 SUBJECT: GRB 060923: Swift detection of a burst DATE: 06/09/23 05:41:32 GMT FROM: David Burrows at PSU/Swift M. Stamatikos (NASA/ORAU), D. N. Burrows (PSU), M. Capalbi (ASDC), M.L. Conciatore (ASDC), N. Gehrels (NASA/GSFC), C. Guidorzi (Univ Bicocca&INAF-OAB), S. T. Holland (GSFC/USRA), D. M. Palmer (LANL), M. Perri (ASDC), T. Sakamoto (NASA/ORAU) and D. E. Vanden Berk (PSU) report on behalf of the Swift Team: At 05:12:15 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 060923 (trigger=230662). Swift slewed immediately to the burst. The BAT on-board calculated location is RA,Dec 254.623, +12.379 {16h 58m 30s, +12d 22' 45"} (J2000) with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed at least two peaks, lasting 12 seconds. The peak count rate was ~1200 counts/sec (15-350 keV), at ~0 sec after the trigger. The XRT began taking data at 05:13:36 UT, 81 seconds after the BAT trigger. The XRT found a previously uncatalogued X-ray source in the field of view at the following coordinates: RA(J2000) = 16 58 28.27 Dec(J2000)= +12 21 43.3 with an uncertainty of 6.9 arcseconds radius (90% containment). This position lies 67 arcseconds from the center of the BAT error circle. The approximate initial flux is 1.7e-11 erg/cm2/sec (0.2-10 keV). UVOT took a finding chart exposure of 100 seconds with the White (160-650 nm) filter starting 85 seconds after the BAT trigger. No afterglow candidate has been found in the initial data products. The overlap of the sub-image and the XRT error circle is 100%. The overlap of the 8'x8' region for the list of sources generated on-board and the XRT error circle is 100%. The limiting magnitude of the finding chart image is approximately 18.5. No correction has been made for the expected extinction corresponding to E(B-V) of 0.06. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 5584 SUBJECT: GRB 060923: KAIT observations DATE: 06/09/23 06:07:28 GMT FROM: Weidong Li at UC Berkeley KAIT/LOSS W. Li, N. Butler, J. S. Bloom, and A. V. Filippenko, University of California, Berkeley, on behalf of the KAIT GRB team, report: The robotic 0.76-m Katzman Automatic Imaging Telescope (KAIT) at Lick Observatory observed GRB 060923, detected with Swift (Trigger 230662; Stamatikos et al. GCN 5583). The automatic sequence started at 05:12:33, 18 s after the burst. The first two images, however, failed due to some technical issues. In subsequent images, Our image processing pipeline did not find any new objects, and reported the following photometry limits (calibrated with USNO B1.0): ====================================================================== Start UT t(GRB) Filter Exp(s) 3sigma-limit 05:13:57 102s I 15.0 <16.9 05:14:21 126s clear 20.0 <17.9 05:14:52 157s V 45.0 <16.9 05:15:48 213s I 45.0 <17.5 05:16:43 268s clear 45.0 <18.5 05:17:39 324s V 60.0 <17.2 ======================================================================== More analyses are in progress. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 5585 SUBJECT: GRB060923 - SDSS Pre-Burst Observations DATE: 06/09/23 06:18:37 GMT FROM: Richard J. Cool at U.of AZ/Steward Obs Richard J. Cool (Arizona), Daniel J. Eisenstein (Arizona), David W. Hogg (NYU), Michael R. Blanton (NYU), David J. Schlegel (LBNL), J. Brinkmann (APO), Donald Q. Lamb (Chicago), Donald P. Schneider (PSU), and Daniel E. Vanden Berk (PSU) report: The Sloan Digital Sky Survey (SDSS) imaged the field of burst GRB060923 prior to the burst. As these data should be useful as a pre-burst comparison and for calibrating photometry, we are supplying the images and photometry measurements for this GRB field to the community. Data from the SDSS, including 5 FITS images, 3 JPGS, and 3 files of photometry and astrometry, are being placed at http://mizar.as.arizona.edu/~grb/public/GRB060923 We supply FITS images in each of the 5 SDSS bands of a 8'x8' region centered on the GRB position (ra=254.618 (16:58:28.3), dec=12.3620 (12:21:43.2); GCN 5583), as well as 3 gri color-composite JPGs (with different stretches). The units in the FITS images are nanomaggies per pixel. A pixel is 0.396 arcsec on a side. A nanomaggie is a flux-density unit equal to 10^-9 of a magnitude 0 source or, to the extent that SDSS is an AB system, 3.631e-6 Jy. The FITS images have WCS astrometric information. In the file GRB060923_sdss.calstar.dat, we report photometry and astrometry of 1668 bright stars (r<20.5) within 15' of the burst location. The magnitudes presented in this file are asinh magnitudes as are standard in the SDSS (Lupton 1999, AJ, 118, 1406). Beware that some of these stars are not well-detected in the u-band; use the errors and object flags to monitor data quality. In the files GRB060923_sdss.objects_flux.dat and GRB060923_sdss.objects_magnitudes.dat, we report photometry of 2573 objects detected within 6' of the GRB position. We have removed saturated objects and objects with model magnitudes fainter than 23.0 in the r-band. The fluxes listed in GRB060923_sdss.objects_flux.dat are in nanomaggies while the magnitudes listed in GRB060923_sdss.objects_magnitudes.dat are asinh magnitudes. All quantities reported are standard SDSS photometry, meaning that they are very close to AB zeropoints and magnitudes are quoted in asinh magnitudes. Photometric zeropoints are known to about 2% rms. None of the photometry is corrected for dust extinction. The Schlegel, Finkbeiner, and Davis (1998) predictions for this region are A_U=0.287 mag, A_g=0.211 mag, A_r = 0.153 mag, A_i=0.116 mag, and A_z=0.082 mag. There are currently no objects within 6 arcminutes of the GRB position in the SDSS spectroscopic database. SDSS astrometry is generally better than 0.1 arcsecond per coordinate. Users requiring high precision astrometry should take note that the SDSS astrometric system can differ from other systems such as those used in other notices; we have not checked the offsets in this region. More detailed information pertaining to our SDSS GRB releases can be found in our initial data release paper (Cool et al. 2006, astro-ph/0601218). See the SDSS DR4 documentation for more details: http://www.sdss.org/dr5. These data have been reduced using a slightly different pipeline than that used for SDSS public data releases. We cannot guarantee that the values here will exactly match those in the data release in which these data are included. In particular, we expect the photometric calibrations to differ by of order 0.01 mag. This note may be cited, but please also cite the SDSS data release paper, Adelman-McCarthy et al. (2006, ApJS, 162, 38), when using the data or referring to the technical documentation. grb@mizar:/home/grb/public_html/private/sdss/GRB060923 //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 5586 SUBJECT: GRB060923: Faulkes Telescope North optical observations DATE: 06/09/23 06:56:20 GMT FROM: Andreja Gomboc at LT,ARI,Liverpool JMU A. Melandri (Liverpool JMU) and A. Gomboc (University of Ljubljana) report on behalf of the RoboNet-1.0 collaboration: The 2m Faulkes North Telescope (Hawaii) automatically reacted to the Swift burst GRB060923 (trigger 230662, Stamatikos et al. GCN 5583). Observations started 2.8 min after the trigger time. In first images we do not detect any new source brighter than R~19. Further analysis are ongoing. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 5587 SUBJECT: GRB 060923: UKIRT nIR observations - candidate afterglow DATE: 06/09/23 07:57:00 GMT FROM: Nial Tanvir at IofA U.Cambridge N. Tanvir (U. Leicester), A. Levan (U. Hertfordshire), M. Jarvis (U. Oxford), T. Wold (JACH) We observed the field of GRB 060923 with UFTI on UKIRT, beginning at 06:07 (UT), approximately 55 minutes post-burst. We detect a faint source in the K-band image at approximately: 16 58 28.18 +12 21 38.9 This position (based on provisional astrometry) is only 4.6 arcsec from the reported XRT position (Stamatikos et al. GCN 5583). The source appears to have faded in another (shallower) K-band observation made 30 mins later, and therefore is likely to be the afterglow of this burst. Further analysis is ongoing. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 5588 SUBJECT: GRB 060923: Early Super-LOTIS Observations DATE: 06/09/23 08:42:34 GMT FROM: Grant Williams at Steward Observatory G. G. Williams (MMTO) and P. A. Milne (Steward Observatory), on behalf of the Super-LOTIS Collaboration, report: The robotic 0.6-m Super-LOTIS telescope began observing the error box of GRB 060923 (Swift Trigger 230662, Stamatikos et al. GCN 5583) at 05:12:56.1 UT, 41.1 seconds after the trigger. Our initial observations include 5 x 10s exposures, 5 x 20s exposures, and 30 x 60s exposures, all in the R-band. The observations began at a high airmass of 2.92. We do not detect any variable sources or afterglow candidates within the XRT error box in our earliest exposure or in the sum of our first five exposures to the following 3-sigma limiting magnitudes determined from nearby USNO-B1.0 stars: t_start (UT) exp t (s) t_start-t_0 (s) Limit -------------------------------------------------------- 05:12:56.1 10.0 41.1 R > 16.6 +/- 0.15 05:12:56.1 5 x 10.0 41.1 R > 18.3 +/- 0.15 The errors are dominated by scatter in the USNO-B1.0 stars. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 5589 SUBJECT: GRB 060923, Swift-BAT refined analysis DATE: 06/09/23 10:28:17 GMT FROM: Scott Barthelmy at NASA/GSFC J. Tueller (GSFC) L. Barbier (GSFC), S. D. Barthelmy (GSFC), J. Cummings (GSFC/UMBC), E. Fenimore (LANL), N. Gehrels (GSFC), D. Hullinger (BYU-Idaho), H. Krimm (GSFC/USRA), C. Markwardt (GSFC/UMD), D. Palmer (LANL), A. Parsons (GSFC), T. Sakamoto (GSFC/ORAU), G. Sato (GSFC/ISAS), M. Stamatikos (GSFC/ORAU) on behalf of the Swift-BAT team: Using the data set from T-240 to T+879 sec from recent telemetry downlinks, we report further analysis of BAT GRB 060923 (trigger #230662) (Stamatikos, et al., GCN Circ. 5583). The BAT ground-calculated position is RA,Dec = 254.623, 12.341 deg {16h 58m 29.6s, 12d 20' 28.1"} (J2000) +- 2.1 arcmin, (radius, sys+stat, 90% containment). The partial coding was 33%. The burst started with a 6-sec wide peak at T-42 sec. The main peak starts at T-5 sec, peaks at T+1 sec, and ends at T+20 sec. There is a possible third peak at T+19 sec. T90 (15-350 keV) is 51.7 +- 1 sec (estimated error including systematics). The time-averaged spectrum from T-42.3 to T+11.5 is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.69 +- 0.23. The fluence in the 15-150 keV band is 8.7 +- 1.3 x 10^-7 erg/cm2. The 1-sec peak photon flux measured from T+0.03 sec in the 15-150 keV band is 1.3 +- 0.3 ph/cm2/sec. All the quoted errors are at the 90% confidence level. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 5590 SUBJECT: GRB 060923B: Swift detection of a burst DATE: 06/09/23 12:02:46 GMT FROM: Scott Barthelmy at NASA/GSFC M. Stamatikos (NASA/ORAU), S. D. Barthelmy (GSFC), D. N. Burrows (PSU), M. Capalbi (ASDC), M.L. Conciatore (ASDC), N. Gehrels (NASA/GSFC), C. Guidorzi (Univ Bicocca&INAF-OAB), S. T. Holland (GSFC/USRA), J. A. Kennea (PSU), C. B. Markwardt (GSFC/UMD), D. M. Palmer (LANL), M. Perri (ASDC), T. Sakamoto (NASA/ORAU), D. E. Vanden Berk (PSU) and H. Ziaeepour (UCL-MSSL) report on behalf of the Swift Team: At 11:38:06 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 060923B (trigger=230702). Swift slewed immediately to the burst. The BAT on-board calculated location is RA,Dec 238.201, -30.907 {15h 52m 48s, -30d 54' 25"} (J2000) with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve shows a single peak with a duration of about 10 sec. The peak count rate was ~1500 counts/sec (15-350 keV), at ~4 sec after the trigger. The XRT began observing the field at 11:40:00 UT, 114 seconds after the BAT trigger. XRT centroided on a cosmic ray on-board, so the position sent out in our first, automated XRT Position Notice is incorrect. From preliminary ground analysis of photon-counting mode data, XRT did find an uncatalogued X-ray source located at RA(J2000) = 15h 52m 46.83s, Dec(J2000) = -30d 54' 12.6", with an estimated uncertainty of 6.5 arcseconds (90% confidence radius). This position was sent out via BACODINE in a second XRT Position Notice with the correct position. This location is 21 arcseconds from the BAT on-board position, within the BAT error circle. The initial flux in the 2.5s image was 2.4e-11 erg/cm2/s (0.2-10 keV). UVOT took a finding chart exposure of nominal 200 seconds with the White (160-650 nm) filter starting 122 seconds after the BAT trigger. No afterglow candidate has been found in the initial data products. Image catalog data are not available at this time. 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. The overlap of the sub-image and the XRT error circle is 100%. No source is seen in the XRT error circle to a magnitude of approximately 18.5. No correction has been made for the expected extinction corresponding to E(B-V) of 0.15. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 5591 SUBJECT: GRB 060923C: Swift detection of a burst DATE: 06/09/23 13:48:45 GMT FROM: Scott Barthelmy at NASA/GSFC M. Stamatikos (NASA/ORAU), S. D. Barthelmy (GSFC), D. N. Burrows (PSU), M. Capalbi (ASDC), M.L. Conciatore (ASDC), C. Guidorzi (Univ Bicocca&INAF-OAB), S. T. Holland (GSFC/USRA), J. A. Kennea (PSU), F. E. Marshall (NASA/GSFC), D. M. Palmer (LANL), M. Perri (ASDC), T. Sakamoto (NASA/ORAU), D. E. Vanden Berk (PSU) and H. Ziaeepour (UCL-MSSL) report on behalf of the Swift Team: At 13:33:02 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 060923C (trigger=230711). Swift slewed immediately to the burst. The BAT on-board calculated location is RA,Dec 346.127, +3.942 {23h 04m 30s, +03d 56' 32"} (J2000) with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). This is an image-trigger (88 sec), and as such, the BAT TDRSS lightcurve does not show significant activity. The XRT began observing the field at 13:36:25 UT, 203 seconds after the BAT trigger. XRT found a bright, fading, uncatalogued X-ray source located at RA(J2000) = 23h 04m 28.1s, Dec(J2000) = +03d 55' 30.3", with an estimated uncertainty of 8.1 arcseconds (90% confidence radius). This location is 70 arcseconds from the BAT on-board position, within the BAT error circle. The initial flux in the 2.5s image was 8.5e-10 erg/cm2/s (0.2-10 keV). There is a 4th magnitude star 12 arcmin from the XRT error circle. Therefore, UVOT will not and can not observe this burst. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 5592 SUBJECT: GRB 060923C: optical observation DATE: 06/09/23 14:38:23 GMT FROM: Ken ichi Torii at Osaka U K. Torii (Osaka U.) reports on behalf of the ART collaboration: The error region of GRB 060923C (Stamatikos et al. GCN 5591) was observed with the ART-3 telescopes in Toyonaka, Osaka. Preliminary analysis does not reveal an optical afterglow candidate brighter than R~15 at 6 minutes after the trigger. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 5593 SUBJECT: GRB060923C: Faulkes Telescope North optical observations DATE: 06/09/23 15:21:20 GMT FROM: Andreja Gomboc at LT,ARI,Liverpool JMU A. Gomboc (University of Ljubljana), C. Guidorzi (Univ Bicocca & INAF-OAB), A. Melandri, I.A. Steele, R.J. Smith, C.G. Mundell, A. Monfardini, D. Carter, S. Kobayashi, D. Bersier, M. Bode (Liverpool JMU), P. O'Brien, E. Rol, N. Bannister (Leicester) report: The 2m Faulkes North Telescope (Hawaii) automatically reacted to the Swift burst GRB060923C (trigger 230711, Stamatikos et al. GCN 5591). Observations started about 4.2 min after the trigger time and were performed in R and i' bands. From the stacked images we do not detect any new source down to: Filter Start(min from GRB) End(min from GRB) TotExp(s) Lim --------------------------------------------------------------------- R 4.22 20.00 220 19.0 i' 6.52 22.70 220 17.5 ---------------------------------------------------------------------- //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 5594 SUBJECT: GRB060923C : Faulkes Telescope South optical limits DATE: 06/09/23 16:08:08 GMT FROM: Andrea Melandri at Liverpool John Moores U A. Melandri (Liverpool JMU), C. Guidorzi (Univ Bicocca & INAF-OAB), A. Gomboc (University of Ljubljana), I.A. Steele, R.J. Smith, C.G. Mundell, A. Monfardini, D. Carter, S. Kobayashi, D. Bersier, M. Bode (Liverpool JMU), P. O'Brien, E. Rol, N. Bannister (Leicester) report: The 2m Faulkes Telescope South (Siding Spring, Australia) automatically reacted to the Swift burst GRB 060923C (trigger 230711, Stamatikos et al., GCN 5591). Observations were performed in the R-band. From t=19.38 min to t=20.27 min (after the burst event) a 3x10s stacked image gives a limiting magnitude R > 19.5 inside the XRT error circle (Stamatikos et al. GCN 5591). This message can be cited. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 5595 SUBJECT: GRB 060923B, Swift-BAT refined analysis DATE: 06/09/23 16:16:00 GMT FROM: Scott Barthelmy at NASA/GSFC L. Barbier (GSFC), S. D. Barthelmy (GSFC), J. Cummings (GSFC/UMBC), E. Fenimore (LANL), N. Gehrels (GSFC), D. Hullinger (BYU-Idaho), H. Krimm (GSFC/USRA), C. Markwardt (GSFC/UMD), D. Palmer (LANL), A. Parsons (GSFC), T. Sakamoto (GSFC/ORAU), G. Sato (GSFC/ISAS), M. Stamatikos (GSFC/ORAU), J. Tueller (GSFC) on behalf of the Swift-BAT team: Using the data set from T-240 to T+754 sec from recent telemetry downlinks, we report further analysis of BAT GRB 060923B (trigger #230702) (Stamitikos, et al., GCN Circ. 5590). The BAT ground-calculated position is RA,Dec = 238.193, -30.907 deg {15h 52m 46.3s, -30d 54' 25.8"} (J2000) +- 1.6 arcmin, (radius, sys+stat, 90% containment). The partial coding was 36%. The mask-weighted lightcurve has a single peak starting at T-1 sec and ending at T+10 sec. T90 (15-350 keV) is 8.8 +- 0.1 sec (estimated error including systematics). The time-averaged spectrum from T-0.1 to T+9.9 is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 2.53 +- 0.25. The fluence in the 15-150 keV band is 4.8 +- 0.6 x 10^-7 erg/cm2. The 1-sec peak photon flux measured from T+4.93 sec in the 15-150 keV band is 1.5 +- 0.3 ph/cm2/sec. All the quoted errors are at the 90% confidence level. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 5596 SUBJECT: GRB 060923C: Xinglong TNT optical observations DATE: 06/09/23 16:24:00 GMT FROM: W.K. Zheng at NAOC M.Zhai, L.P. Xing, Y.L. Qiu, J.Y. Wei, J.Y. Hu, J.S. Deng and W.K. Zheng on behalf of EAFON report: We have imaged the field of GRB 060923C with the TNT 0.8m telescope at Xinglong Observatory.The first image was taken at 13:36:37 UT, 215s after the burst. A series of White and R band images were obtained. No new source were detected in our combined images down to: Filter Mid_Time(s) 3 sigma limit --------------------------------- White 487 19.2 R 1210 20.0 This message may be cited. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 5597 SUBJECT: GRB 060923A: Keck and Gemini Observations DATE: 06/09/23 18:17:24 GMT FROM: Derek Fox at PSU D.B. Fox (Penn State), A. Rau (Caltech), & E.O. Ofek (Caltech) report on behalf of a larger collaboration: "We have imaged the Swift XRT localization region for GRB060923A (Trigger 230662; Stamatikos et al., GCN 5583) with Keck-I + LRIS (I-band) and Gemini-North + NIRI (J- and K-band). We identify the candidate afterglow of Tanvir et al. (GCN 5587) in our K-band images as the only point source consistent with the XRT localization, with a brightness estimated as follows: K-band: Ks~20.6 mag at 07:04 UT We estimate its brightness (without correcting for Galactic extinction) by reference to the 2MASS star at R.A. 16:58:31.463, Dec. +12:22:12.88 (J2000), which has J=15.175 mag, H=14.585 mag, and Ks=14.457 mag in that catalog. The position of the source by reference to NOMAD catalog sources in the vicinity is: R.A. 16:58:28.15, Dec. +12:21:38.9 (J2000) with an estimated uncertainty of less than 0.5" in each coordinate. The source is undetected in our earlier J-band and I-band images. Our upper limits on the brightness of the source in these bands are: I-band: I>23.5 mag at 06:11 UT J-band: J>23.7 mag at 06:42 UT The I-band photometry is referenced to the SDSS imaging of this field (Cool et al., GCN 5585) while the J-band zero-point is derived from the 2MASS star referenced above. Magnitudes have not been corrected for Galactic extinction. If this source is the afterglow of GRB060923A, the red colors are suggestive of a highly extinguished or high-redshift burst. In particular, correcting for the Schlegel, Finkbeiner & Davis (1998) estimate of E(B-V)=0.058 mag Galactic extinction, and assuming a temporal decay of t^(-1) and an intrinsic afterglow spectrum of F_nu ~ nu^(-1), these limits indicate suppression of the afterglow flux (relative to K-band) by a factor of >18 at 0.9 micron (I-band) and by a factor of >14 at 1.23 micron (J-band). //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 5598 SUBJECT: GRB 060923C: Keck Observations DATE: 06/09/23 18:20:56 GMT FROM: Derek Fox at PSU A. Rau (Caltech), E.O. Ofek (Caltech) and D.B. Fox (Penn State) report on behalf of a larger collaboration: We imaged the position of GRB060923C (Stamatikos et al., GCN 5591) on UT 2006 Sep 23.58 (30 minutes post trigger) with the Low Resolution Imager and Spectrograph at Keck-I. Observations were performed at high airmass (3.1). Within the XRT error circle, we detect a single point-like object, with I~21 mag, at coordinates: R.A. 23:04:28.4, Dec. +03:55:29 (J2000) We note that this source is marginally detected in the Palomar Optical Sky Survey (DSS) at a similar brightness. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 5599 SUBJECT: GRB 060923A: Swift XRT refined analysis DATE: 06/09/23 19:14:02 GMT FROM: Maria Laura Conciatore at ASDC M.L. Conciatore, M. Capalbi, M. Perri, D.N. Burrows (PSU) and M. Stamatikos (NASA/ORAU) report on behalf of the Swift XRT team: We have analysed the first five orbits of Swift XRT data from GRB 060923A (Stamatikos et al., GCN 5583). A ~2.5ks PC mode image provides a refined X-ray position of: RA(J2000) = 16h 58m 28.2s Dec(J2000) = +12d 21' 40.0" with an uncertainty of 6.0 arcseconds radius (90% containment).This is 3.4 arcseconds from the XRT position given by Stamatikos et al.(GCN 5583) and 74.8 arcsec from the refined (ground-calculated) BAT position (Tueller et al., GCN 5589). This position is 1.14 arcseconds from the detected source reported by Tanvir et al. (GCN 5587), and 1.32 arcseconds from the one reported by Fox et al. (GCN 5597) as a candidate counterpart afterglow. X-ray light curve shows an initial power-law decay with a decay index of 2.7+/-0.3. Then, after a slow rebrightening starting at ~650s, from T+4200 the source decays with a slope of 1.23 +/-0.1. An absorbed power-law fit to the X-ray spectrum from T+100s to T+960s gave a photon index of 2.1+/-0.2 and a column density of (1.2+/0.1)e21 cm**-2. We note the galactic hydrogen column density in the direction of the burst is 5.1e20 cm**-2. The 0.2-10.0 keV observed flux for this spectrum is 4.1e-11 ergs cm**-2 s**-1, which corresponds to an unabsorbed flux of 4.9e-11 ergs cm**-2 s**-1. Assuming that the X-ray emission continues to decline at the same rate, we predict a 0.2-10 keV XRT count rate of 0.006 count/s at T+24hr, which corresponds to an observed 0.2-10 keV flux of 2.4e-13 erg/cm**2/s. This circular is an official product of the Swift XRT Team. [GCN OPS NOTE(24sep06): Per author's request, the author list was added.] //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 5600 SUBJECT: GRB 060923C, Swift-BAT partial refined analysis DATE: 06/09/23 22:42:57 GMT FROM: Scott Barthelmy at NASA/GSFC S. D. Barthelmy (GSFC), L. Barbier (GSFC), J. Cummings (GSFC/UMBC), E. Fenimore (LANL), N. Gehrels (GSFC), D. Hullinger (BYU-Idaho), H. Krimm (GSFC/USRA), C. Markwardt (GSFC/UMD), D. Palmer (LANL), A. Parsons (GSFC), T. Sakamoto (GSFC/ORAU), G. Sato (GSFC/ISAS), M. Stamatikos (GSFC/ORAU), J. Tueller (GSFC) on behalf of the Swift-BAT team: Using a partial data set from T-119 to T+183 sec from recent telemetry downlinks, we report further analysis of BAT GRB 060923C (trigger #230711) (Stamatikos, et al., GCN Circ. 5591). The BAT ground-calculated position is RA,Dec = 346.123, 3.963 deg {23h 4m 29.4s, 3d 57' 47.4"} (J2000) +- 2.2 arcmin, (radius, sys+stat, 90% containment). The partial coding was 17%. With only a partial data set downlinked (there is a gap in the data between T+51 to +62 sec), the mask-weighted lightcurve has a single long emision from T+0 to T+110 sec. The lower limit to the fluence in the 15-150 keV band is 1.3 +- 0.2 x 10^-6 erg/cm2. We repeat that there is an 11-sec gap in the data in the middle of this burst used for this analysis. When the full data set is downlinked, we will report the usual numbers. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 5601 SUBJECT: GRB 060923C: Swift XRT refined analysis DATE: 06/09/24 00:14:00 GMT FROM: Matteo Perri at ISAC/ASDC M. Perri, M. Capalbi, M.L. Conciatore (ASDC), D.N. Burrows (PSU) and M. Stamatikos (NASA/ORAU) report on behalf of the Swift XRT team: We have analysed the first four orbits of Swift XRT data on the BAT GRB 060923C (Stamatikos, et al., GCN Circ. 5591). A 5.5 ks Photon Counting mode image provides a refined XRT position: RA(J2000) = 23h 04m 28.49s Dec(J2000) = +03d 55' 26.6" with an uncertainty of 5.9" (90% containment). This is 2.4' away from the center of the BAT refined position (Barthelmy et al., GCN Circ. 5600) and 6.9" away from the first XRT position quoted in GCN Circ. 5591 (Stamatikos, et al.). This position lies 2.8" from the object reported by Rau et al. (GCN Circ. 5598). The 0.3-10 keV X-ray light curve from T+212 s to T+13 ks can be fit by a broken power law model with temporal break at T+780s (+/-120s) and decay indices -3.4 (+/-0.2) and -0.6 (+/-0.2) before and after the break, respectively. The X-ray spectrum covering the time period from T+212s to T+275s is well fit by an absorbed power-law with a photon index of 1.85 (+/-0.13) and a column density consistent with the Galactic value in the direction of the burst (5.3e20 cm**-2). Assuming the X-ray emission continues to decline at the same rate, we predict a 0.3-10 keV XRT count rate of ~0.01 count/s at T+24hr, which corresponds to an observed 0.3-10 keV flux of ~5e-13 erg/cm**2/s. This circular is an official product of the Swift XRT Team. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 5602 SUBJECT: GRB 060923B: Swift XRT Refined Analysis DATE: 06/09/24 00:24:19 GMT FROM: Milvia Capalbi at ISAC/ASDC M. Capalbi, M. Perri , M.L. Conciatore (ASDC), D.N. Burrows (PSU) and M. Stamatikos (NASA/ORAU) report on behalf of the Swift XRT team: We have analysed the first 2 orbits of XRT data from GRB 060923B (Stamatikos et al., GCN Circ. 5590) with a total exposure of 2.1ks in photon counting mode. The refined position is: RA(J2000) = 15h 52m 46.83s, Dec(J2000) = -30d 54m 11.9s with an uncertainty of 6 arcsec (90% containment). This position is 0.7 arcsec from the one calculated from early downlinked data (Stamatikos et al., GCN Circ. 5590). The 0.3-10.0 keV X-ray light curve can be fit with a single power-law with a slope of -0.7+/-0.1. A power-law fit to the X-ray spectrum from T + 125s to T + 365s gives a photon index of 1.7+/-0.5, fixing the hydrogen column density to the galactic value in the direction of the burst (8.8e20cm**-2). The 0.3-10.0 keV observed flux is 8.5e-12 ergs cm**-2 s**-1, which corresponds to an unabsorbed flux of 8.9e-12 ergs cm**-2 s**-1. If the burst continues decaying at the current rate we estimate an XRT count rate of 0.014 counts/s at T + 24hr, which corresponds to an observed 0.3-10.keV flux of 5.6e-13 ergs cm**-2 s**-1. This circular is an official product of the Swift XRT Team. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 5603 SUBJECT: GRB060923B: Swift/UVOT upper limits DATE: 06/09/24 18:05:41 GMT FROM: Antonino Cucchiara at PSU S. Holland and A. Cucchiara report on behalf of the Swift/UVOT team: The Swift UVOT began observing GRB 060923B (trigger #230702), M. Stamatikos et al., GCN Circ. 5590) 122 seconds after the BAT trigger. No optical afterglow is detected in the XRT refined error circle (M. Capalbi et al., GCN Circ.5602). The 3-sigma limiting magnitudes for the finding chart and the coadded images for the UVOT filters are listed below: Finding chart: Filter T_range (s) Exposure (s) 3sigma UL White 122-220 98 19.42 White 5163-5360 197 19.79 V 225-387 162 18.52 Coadded images: Filter T_range (s) Exposure (s) 3sigma UL V 5572-5768 196 18.61 B 4959-5156 197 19.61 U 4754-4950 197 19.28 W1 4550-6170 386 19.45 M2 4345-5974 394 19.70 W2 5368-5565 197 19.92 T_range is calculated from the time of the burst. No correction has been made for the Galactic reddening of E(B-V) = 0.15 mag (Schlegel et al. 1998) along the line of sight to the burst. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 5604 SUBJECT: GRB 060923C: VLT J-band observations DATE: 06/09/24 18:11:53 GMT FROM: Daniele Malesani at SISSA-ISAS,Trieste,Italy Stefano Covino (INAF/OABr), Daniele Malesani (SISSA/ISAS), and Gianpiero Tagliaferri (INAF/OABr), report on behalf of the MISTICI collaboration: We imaged the field of GRB 060923C (Stamatikos et al., GCN 5591) on 2006 Sep 24 from 3:39 to 4:16 UT with the ESO VLT+ISAAC in the J band under good seeing conditions. Within the refined XRT error circle (Perri et al., GCN 5601) we detect three sources with the following positions (RA, DEC, J2000) and magnitudes: A: 23:04:28.40, +03:55:29.1 19.23 +- 0.03 B: 23:04:28.31, +03:55:29.0 22.87 +- 0.12 C: 23:04:28.18, +03:55:28.5 21.33 +- 0.07 Source C could be extended. Absolute magnitudes are calibrated with respect to two 2MASS stars in the field. The reported errors are only statistical; the absolute calibration error may be of the order of ~0.15 mag. At this stage, we cannot say whether any of these sources is related to GRB 060923C. A finding chart is posted at the followin URL: http://www.sissa.it/~malesani/GRB/060923C/finder_ISAAC.jpg Source A has been reported by Rau et al. (GCN 5598) and could also be marginally visible in the DSS. We acknowledge support from the ESO observing staff at Paranal, in particular Christophe Dumas and Emmanuel Jehin. This message may be cited. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 5605 SUBJECT: GRB 060923A: Gemini Second Epoch and Afterglow Confirmation DATE: 06/09/24 22:34:47 GMT FROM: Derek Fox at PSU D.B. Fox (Penn State) reports on behalf of a larger collaboration: "We have imaged the Swift XRT localization region for GRB060923A (Stamatikos et al., GCN 5583) with Gemini-North + NIRI on a second occasion. The candidate afterglow of Tanvir et al. (GCN 5587) and Fox et al. (GCN 5597) is no longer detected, and we estimate its brightness as: K-band: Ks>21.5 mag at 05:05 UT, 24 Sep (mean epoch) using the same photometric calibration as for the previous night (GCN 5597). Fading of the candidate by >~1 mag between our two epochs is separately confirmed in an image subtraction analysis. This confirms the afterglow nature of the source, and thus the highly reddened, high-redshift and/or highly-extinguished nature of the afterglow of GRB 060923A." //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 5606 SUBJECT: GRB 060923C, optical observation DATE: 06/09/25 01:20:00 GMT FROM: Shouta Maeno at U.of Miyazaki S.Maeno, E.Sonoda, M.Yamauchi (University of Miyazaki) We have observed the field covering the error circle of GRB 060923C (GCN 5591) with the unfiltered CCD camera on the 30-cm telescope at University of Miyazaki. The observation was started 15:01:30 UT on Sep. 23. We have compared our data of 30 sec exposures with the USNO-A2.0 catalog, there is no new source at the position reported by GCN 5591. The upper limit is as follows: -------------------------------------------------------------- Start(UT) End(UT) Num. of frames Limit (mag.) -------------------------------------------------------------- 15:01:30 15:32:39 17 ~17.5 --------------------------------------------------------------- //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 5607 SUBJECT: GRB 060923C: Gemini Observations and Afterglow Candidate DATE: 06/09/25 03:32:08 GMT FROM: Derek Fox at PSU D.B. Fox (Penn State) reports on behalf of a larger collaboration: "We have imaged the XRT position of GRB060923C (Stamtikos et al., GCN 5591) in the K-band with Gemini-North + NIRI on two occasions with mean epochs of 05:39 UT and 08:34 UT, respectively, on 24 Sep 2006. We detect the (I-band) source of Rau et al. (GCN 5598; hereafter source "A") as well the additional (J-band) sources "B" and "C" of Covino et al. (GCN 5604). At both epochs, these are the only sources consistent with the XRT localization. Although we lack an absolute photometric calibration at this time, we observe a relative decline of Source B by ~0.4 mag in K-band between these two epochs. The magnitudes of Sources A and C are not observed to vary, being consistent across our two epochs to within 0.1 mag. Noting as well the indication for Source A in the DSS (GCN 5598), and that Source C is clearly extended in our images, we suggest that Source B is the afterglow of GRB060923C. In this case, the absence of detectable afterglow light in the early Keck+LRIS I-band images may indicate a high-redshift origin or high line-of-sight extinction for this burst." //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 5608 SUBJECT: GRB060923C: AROMA optical obsevation DATE: 06/09/25 12:45:25 GMT FROM: Atsumasa Yoshida at Aoyama Gakuin U T.Uehara, I.Takahashi, K.Yoshida, A.Kobayashi, D.Oyamada, Y.E.Nakagawa, S.Sugita, K.Yamaoka, A.Yoshida (AGU) report: We have observed the feild of GRB060923C (Stamatikos et al. GCN 5591) from 13:35:46 (UT) with 0.3m AROMA robotic telescope with R-band filter at Aoyama Gakuin University. Although the weather condition was not good, we have taken 60 frames of image with 20s exposure each. The photometric calibration was made by first 5 and every 20 frames by comparing with USNO A2.0 stars in the same field. No new source was found. The 3 sigma limiting magnitude of each combined image is as below. number mean time since limiting magnitude of frames time (UT) GRB (s) in R (3 sigma) ======================================================================== 5 13:36:39 217 15.4 20 13:40:20 436 15.8 20 13:54:06 1264 16.8 20 14:10:26 2244 17.5 //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 5609 SUBJECT: GRB 060923C: NIR afterglow confirmed DATE: 06/09/25 17:09:07 GMT FROM: Daniele Malesani at SISSA-ISAS,Trieste,Italy Paolo D'Avanzo (INAF-OABr), Stefano Covino (INAF-OABr), Daniele Malesani (SISSA/ISAS), and Gianpiero Tagliaferri (INAF-OABr), report on behalf of the MISTICI collaboration: We imaged again the field of GRB 060923C (Stamatikos et al., GCN 5591) on 2006 Sep 25 from 0:51 to 1:36 UT with the ESO VLT+ISAAC in the J band. Seeing conditions were comparable to our previous observation (Covino et al., GCN 5604). With respect to the first epoch of imaging, we detect sources A and C, with the same brightness. Source B has faded significantly and is barely detectable. Image subtraction performed with ISIS also confirms the fading. We therefore fully confirm the identification by Fox (GCN 5607) of source B as the afterglow of GRB 060923C. We acknowledge support from the ESO observing staff at Paranal. This message may be cited. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 5610 SUBJECT: GRB 060923C: VLA Observation DATE: 06/09/25 18:46:31 GMT FROM: Poonam Chandra at U Virginia/NRAO P. Chandra (UVA/NRAO) and D. A. Frail (NRAO) report on behalf of the Caltech-NRAO-Carnegie GRB Collaboration: "We observed the field centered on the BAT position of the Swift burst GRB 060923C (GCN#5591) using the VLA at a frequency of 8.46 GHz and starting at 6.02 UT on Sept 25, about 2 days after the burst. There is no detection of the GRB with 2-sigma upper limit of 100 microJy. 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: 5611 SUBJECT: GRB 060923C, Swift-BAT refined analysis DATE: 06/09/25 19:51:01 GMT FROM: Takanori Sakamoto at NASA/GSFC T. Sakamoto (GSFC/ORAU), L. Barbier (GSFC), S. D. Barthelmy (GSFC), J. Cummings (GSFC/UMBC), E. Fenimore (LANL), N. Gehrels (GSFC), D. Hullinger (BYU-Idaho), H. Krimm (GSFC/USRA), C. Markwardt (GSFC/UMD), D. Palmer (LANL), A. Parsons (GSFC), G. Sato (GSFC/ISAS), M. Stamatikos (GSFC/ORAU), J. Tueller (GSFC) on behalf of 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 060923 (trigger #230711) (Stamatikos, et al., GCN Circ. 5591; Barthelmy, et al., GCN Circ 5600). The BAT ground-calculated position is RA,Dec = 346.122, 3.943 deg {23h 4m 29.3s, 3d 56' 33.8"} (J2000) +- 2.1 arcmin, (radius, sys+stat, 90% containment). The partial coding was 17%. The mask-weighted lightcurve has a single long emision from T+0 to T+110 sec. T90 (15-350 keV) is 76 +- 2 sec (estimated error including systematics). The long duration and smooth profile of the lightcurve suggest, but do not prove, that this is a high redshift burst. The time-averaged spectrum from T+6.8 to T+90.7 is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 2.27 +- 0.24. The fluence in the 15-150 keV band is 1.6 +- 0.2 x 10^-06 erg/cm2. The 1-sec peak photon flux measured from T+27.54 sec in the 15-150 keV band is 1.0 +- 0.4 ph/cm2/sec. All the quoted errors are at the 90% confidence level. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 5620 SUBJECT: GRB 060923A: Radio Observations DATE: 06/09/26 22:23:15 GMT FROM: Dale A. Frail at NRAO Dale A. Frail (NRAO) and P. Chandra (NRAO/UVA) report on behalf of a larger collaboration: "We used the Very Large Array to observe the field of view toward GRB060923A (GCN 5583) at a frequency of 8.46 GHz on 2006 October 26.06 UT. The peak radio brightness at the position of the afterglow of Tanvir et al. (GCN 5587) and Fox et al. (GCN 5597) is -30 uJy +/- 55 uJy. 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: 5624 SUBJECT: GRB 060923A: Schedule of Spitzer Space Telescope Observations DATE: 06/09/27 01:31:24 GMT FROM: Derek Fox at PSU D.B. Fox (Penn State) reports on behalf of a larger collaboration: "We have activated a sequence of Spitzer Space Telescope IRAC imaging observations of the afterglow of GRB 060923A (Stamatikos et al., GCN 5583). Projected start times for these observations are: Epoch 1: 10:45 UT on 27 Sep 2006 Epoch 2: 04:00 UT on 29 Sep 2006 (est.) Epoch 3: 15:15 UT on 3 Oct 2006 (est.) Observations for each epoch will last approximately 80 minutes. Observers interested in coordination with Epochs 2 and 3 should contact the author by email in advance to confirm the final schedule." //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 5648 SUBJECT: GRB060923C: optical limit DATE: 06/09/28 16:38:13 GMT FROM: Alexei Pozanenko at IKI, Moscow G. Kornienko, A. Erofeeva (UAPhO), A.Pozanenko (IKI), V.Rumyantsev (CrAO) on behalf of larger GRB follow up collaboration report: We observed the error box of GRB060923C (Stamatikos et al., GCN 5591) with 0.4m telescope of Ussuriysk Astrophysical Observatory in R-band starting Sep.23 (UT) 13:51:55. We do not detect the optical transient detected by Fox (GCN 5607). Upper limits of the first image (exposure 60 s) and combined image (exp. 10x60 s) are based on USNOA2.0: Mid time, Exposure, Limiting mag (3 sigma) (UT) (s) Sep. 23.5781 1x60 16.0 Sep. 23.5829 10x60 17.3 This message may be cited. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 5671 SUBJECT: GRB 060923A: VLA K-band Observations DATE: 06/10/01 00:58:58 GMT FROM: Poonam Chandra at U Virginia/NRAO P. Chandra (UVA/NRAO) and D. A. Frail (NRAO) report on behalf of the Caltech-NRAO-Carnegie GRB Collaboration: "We used the Very Large Array to observe the field of view toward GRB060923A (GCN 5583) at a frequency of 22.5 GHz on 2006 September 30 starting at 19.65 UT. The peak radio brightness at the position of the afterglow of Fox et al. (GCN 5597) is -200 uJy ± 260 uJy. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc." //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 5673 SUBJECT: GRB 060923A: Probable host galaxy in the R-band DATE: 06/10/01 17:32:56 GMT FROM: Andrew Levan at U.of Leicester A.J. Levan (Hertfordshire), N.R. Tanvir (Leicester), J. Gorosabel (IAA-CSIC) report for a larger collaboration: We observed the location of GRB 060923A (Tanvir et al. GCN Circ 5587; Fox et al. GCN Circ 5597) in the R-band using the VLT and FORS2. At the location of the afterglow we find a faint, extended source (angular size ~2") with R~25.5. We suggest this is likely to be the host galaxy of GRB 060923A. If this galaxy is the host of GRB 060923A then its detection in the R-band implies an upper limit for the redshift of z~5. Therefore we believe that extinction is the most likely cause for the extremely red J-K colour for the afterglow at early times. We that the staff of the VLT for their excellent support.