//////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 9854 SUBJECT: GRB 090831C: Swift detection of a burst DATE: 09/08/31 21:42:30 GMT FROM: Scott Barthelmy at NASA/GSFC P. Schady (MSSL-UCL), S. D. Barthelmy (GSFC), W. H. Baumgartner (GSFC/UMBC), A. P. Beardmore (U Leicester), J. R. Cummings (NASA/UMBC), P. A. Evans (U Leicester), C. Guidorzi (U Ferrara), S. T. Holland (CRESST/USRA/GSFC), J. A. Kennea (PSU), H. A. Krimm (CRESST/GSFC/USRA), C. B. Markwardt (CRESST/GSFC/UMD), F. E. Marshall (NASA/GSFC), C. Pagani (PSU), K. L. Page (U Leicester), D. M. Palmer (LANL), A. Rowlinson (U Leicester), M. H. Siegel (PSU), M. Stamatikos (OSU/NASA/GSFC) and M. A. Stark (PSU) report on behalf of the Swift Team: At 21:30:25 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 090831C (trigger=361489). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 108.278, -25.100 which is RA(J2000) = 07h 13m 07s Dec(J2000) = -25d 06' 00" 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 ~800 counts/sec (15-350 keV), at ~3 sec after the trigger. The XRT began observing the field at 21:32:23.5 UT, 117.5 seconds after the BAT trigger. Using promptly downlinked data we find a fading, uncatalogued X-ray source located at RA, Dec 108.29307, -25.11934 which is equivalent to: RA(J2000) = 07h 13m 10.34s Dec(J2000) = -25d 07' 09.6" with an uncertainty of 3.8 arcseconds (radius, 90% containment). This location is 85 arcseconds from the BAT onboard position, within the BAT error circle. This position may be improved as more data are received; the latest position is available at http://www.swift.ac.uk/sper. A power-law fit to a spectrum formed from promptly downlinked event data gives a column density consistent with the Galactic value of 3.24e+21 cm^-2 (Kalberla et al. 2005). UVOT took a finding chart exposure of 150 seconds with the White filter starting 120 seconds after the BAT trigger. No credible afterglow candidate has been found in the initial data products. Results from the 2.7'x2.7' sub-image are not available at this time. The coverage of the XRT error circle by the 8'x8' region for the list of sources generated on-board is uncertain because the large number of sources filled the available telemetry. No correction has been made for the expected extinction corresponding to E(B-V) of 0.38. Burst Advocate for this burst is P. Schady (ps AT mssl.ucl.ac.uk). Please contact the BA by email if you require additional information regarding Swift followup of this burst. In extremely urgent cases, after trying the Burst Advocate, you can contact the Swift PI by phone (see Swift TOO web site for information: http://www.swift.psu.edu/too.html.) //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 9855 SUBJECT: GRB 090831C: Enhanced Swift-XRT position DATE: 09/09/01 02:31:50 GMT FROM: Phil Evans at U of Leicester P.A. Evans, M.R. Goad, J.P. Osborne and A.P. Beardmore (U. Leicester) report on behalf of the Swift-XRT team. Using 3607 s of XRT Photon Counting mode data and 3 UVOT images for GRB 090831C, 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 = 108.29453, -25.11859 which is equivalent to: RA (J2000): 07h 13m 10.69s Dec (J2000): -25d 07' 06.9" with an uncertainty of 1.8 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, arXiv:0812.3662). This circular was automatically generated, and is an official product of the Swift-XRT team. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 9857 SUBJECT: GRB 090831C: Swift XRT Refined Analysis DATE: 09/09/01 07:03:06 GMT FROM: Antonia Rowlinson at U.of Leicester A. Rowlinson (U. Leicester) and P. Schady (MSSL-UCL) report on behalf of the Swift-XRT team: We have analysed 8.4 ks of XRT data for GRB 090831C (Schady et al. GCN Circ. 9854), from 121 s to 21.8 ks after the BAT trigger. The data are entirely in Photon Counting (PC) mode. The enhanced XRT position for this burst was given by Evans et al. (GCN. Circ 9855). The light curve has two flares at T+186 s and T+440 s, while the underlying decay can be modelled with a power-law decay with a decay index of alpha=0.83 (+0.17, -0.11). A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 1.84 (+0.21, -0.15). The best-fitting absorption column is 3.254 (+1.001, -0.014) x 10^21 cm^-2, consistent with the Galactic value of 3.2 x 10^21 cm^-2 (Kalberla et al. 2005). The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 4.9 x 10^-11 (7.2 x 10^-11) erg cm^-2 count^-1. If the light curve continues to decay with a power-law decay index of 0.83, the count rate at T+24 hours will be 0.0029 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.4 x 10^-13 (2.1 x 10^-13) erg cm^-2 s^-1. The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00361489. This circular is an official product of the Swift-XRT team. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 9859 SUBJECT: GRB090831C: Swift/UVOT upper limits DATE: 09/09/01 10:42:09 GMT FROM: Patricia Schady at MSSL/Swift P. Schady (MSSL-UCL) reports on behalf of the Swift/UVOT team. The Swift/UVOT began settled observations of the field of GRB 090831C 121s after the BAT trigger (Schady et al., GCN Circ 9854). No new source is detected within the XRT error circle (Evans et al., GCN Circ 9855) in any of the individual or combined UVOT filters. The 3-sigma upper limits of detecting a source at the position of the X-ray afterglow in the first white band finding chart (fc) observation and in consecutive coadded observations for each of the UVOT filters are as follows: Filter T_start(s) T_stop(s) Exp(s) Mag 3-sig UL wh (fc) 121 270 147 > 20.78 wh 561 1183 206 > 20.73 vv 610 1060 58 > 18.47 bb 536 1159 58 > 19.30 uu 279 1134 285 > 19.95 w1 660 1109 58 > 18.74 m2 635 1084 58 > 18.48 w2 586 1209 78 > 18.95 The values quoted above are not corrected for the Galactic extinction due to the large reddening of E(B-V) = 0.38 in the direction of the burst (Schlegel et al., 1998). The photometry is on the UVOT photometric system described in Poole et al. (2008, MNRAS, 383, 627). //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 9862 SUBJECT: GRB 090831C: GROND upper limits DATE: 09/09/01 18:45:16 GMT FROM: Thomas Kruehler at MPE/MPI F. Olivares, T. Kruehler and J. Greiner (all MPE Garching) report on behalf of the GROND team: We observed the field of GRB 090831C (Swift trigger #361489; Schady et al., GCN #9854) simultaneously in g'r'i'z'JHK with GROND (Greiner et al. 2008, PASP 120, 405) mounted at the 2.2 m ESO/MPI telescope at LaSilla Observatory (Chile). Observations started at 08:07 UT on September 1st, 2009, 10.6 hr after the burst. At this time the position of the burst was becoming visible above the pointing constraints of the telescope. Observations suffer from high airmass and large seeing of around 2". In stacked images of 74 min total integration time in griz and 60 min in JHK, we do not detect any object within the enhanced XRT error circle (Evans et al., GCN #9855), down to the following limiting magnitudes (all in the AB system): g' > 23.5 r' > 24.0 i' > 23.3 z' > 22.9 J > 21.4 H > 21.1 K > 20.0 These upper limits were derived using the GROND zeropoints and 2MASS field stars as reference and are not corrected for significant Galactic foreground extinction corresponding to a reddening of E(B-V)=0.38 mag (Schlegel et al., 1998). //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 9863 SUBJECT: GRB 090831C BAT refined analysis DATE: 09/09/02 01:30:11 GMT FROM: Jay R. Cummings at NASA/GSFC/Swift C. B. Markwardt (GSFC/UMD), S. D. Barthelmy (GSFC), W. H. Baumgartner (GSFC/UMBC), J. R. Cummings (GSFC/UMBC), E. E. Fenimore (LANL), N. Gehrels (GSFC), H. A. Krimm (GSFC/USRA), D. M. Palmer (LANL), A. M. Parsons (GSFC), T. Sakamoto (GSFC/UMBC), G. Sato (ISAS), P. Schady (MSSL-UCL), M. Stamatikos (OSU), J. Tueller (GSFC), T. N. Ukwatta (GWU) (i.e. the Swift-BAT team): Using the data set from T-61 to T+242 sec from the recent telemetry downlink, we report further analysis of BAT GRB 090831 (trigger #361489) (Schady, et al., GCN Circ. 9854). The BAT ground-calculated position is RA, Dec = 108.294, -25.112 deg which is RA(J2000) = 07h 13m 10.6s Dec(J2000) = -25d 06' 44.0" with an uncertainty of 2.1 arcmin, (radius, sys+stat, 90% containment). The partial coding was 84%. The mask-weighted light curve shows a single roughly symmetrical peak. T90 (15-350 keV) is 3.3 +- 1.0 sec (estimated error including systematics). The time-averaged spectrum from T+0.6 to T+4.9 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.33 +- 0.29. The fluence in the 15-150 keV band is 1.5 +- 0.3 x 10^-07 erg/cm2. The 1-sec peak photon flux measured from T+1.94 sec in the 15-150 keV band is 0.5 +- 0.1 ph/cm2/sec. All the quoted errors are at the 90% confidence level. The results of the batgrbproduct analysis are available at http://gcn.gsfc.nasa.gov/notices_s/361489/BA/