Gamma-ray Burst 081105

(All information courtesy of the instrument teams.)

Previous IAU Circulars

• none

• GCN Circular #8484
  J. Cummings, S. Barthelmy, N. Gehrels, H. Krimm, and D. Palmer, on behalf of the Swift-BAT team
  S. Golenetskii, R.Aptekar, E. Mazets, V. Pal'shin, D. Frederiks, K. Hurley, and T. Cline on behalf of the Konus-Wind team,
  K. Yamaoka, M. Ohno, Y. Fukazawa, T. Takahashi, M. Tashiro, Y. Terada, T. Murakami, and K. Makishima on behalf of the Suzaku WAM team
  A. von Kienlin, G. Lichti, and A. Rau, on behalf of the INTEGRAL SPI-ACS GRB team,
  and M. Marisaldi, F. Fuschino, M. Galli, C. Labanti, E. Del Monte, F. Lazzarotto, L. Pacciani, and P. Soffitta on behalf of the AGILE team
  At 2008-11-05 T0=48372.403 s UT (13:26:12.403), a long soft GRB, GRB 081105 triggered Konus/Wind. The IPN was informed, and Swift/BAT, AGILE-MCAL, Suzaku/WAM, and INTEGRAL/SPI-ACS reported coincident rate increases. Ground analysis of BAT data (trigger #333811) yielded a significant image peak that was found to be coincident with the IPN timing triangulation annulus. The location of the burst was RA, Dec 3.966, 3.454, uncertainty radius of 2.5 arcmin, which is

     RA(J2000)  = 00h 15m 51.8s
     Dec(J2000) = +03d 27' 14"
  

  The source was found onboard, but not with high enough significance to trigger an automatic burst response. The partial coding was only 2.5%.
  The burst was a single peak, about 10 seconds long.
  A Swift TOO has been requested and approved. The Swift narrow-field instruments should begin observing the burst at about 04:30 UT, 15 hours after the burst.
• GCN Circular #8487
  A.P. Beardmore (U. Leicester) and J. Cummings (GSFC/UMBC) report on behalf of the Swift-XRT team.
  The Swift-XRT started observing the field of the Swift-BAT and IPN localization GRB 081105 (Cummings et al., GCN 8484) at 2008-11-06 05:18:07(UT), 15.8 hours after the trigger.
  In an exposure of 5ks we detect an X-ray source within the BAT error circle at RA, Dec = 3.95224, 3.47098, which is

  RA  (J2000) =  00:15:48.5
  Dec (J2000) = +03:28:15.5
  

  with an uncertainty of 4.8 arcsec (radius, 90 percent confidence).
  The observed count rate is (7.6+/-2.0)e-3 count/s. At this stage we cannot tell whether the source is fading. Further Swift observations are planned.
  This circular is an official product of the Swift-XRT team.
• GCN Circular #8488
  P.A. Curran (UCL-MSSL), P. Schady (UCL-MSSL) and J. Cummings (GSFC/UMBC), on behalf of the Swift/UVOT team.
  The Swift Ultra-Violet/Optical Telescope (UVOT) began settled observations of the Swift-BAT and IPN localization GRB 081105 (#333811; Cummings et al., GCN 8484) ~16 hours after the BAT trigger. No afterglow is detected at the XRT position (Beardmore et al., GCN 8487) in any filter. The 3-sigma limiting magnitudes in each of the observed UVOT filters are as follows:

  Filter  T_start(dys) Exp(s)  Mag UL (3sig)
  
  white     0.67        159     > 20.76
  v         0.81        630     > 19.92
  b         0.66        885     > 21.05
  u         0.74        224     > 19.92
  uvw1      0.73        886     > 20.75
  uvw2      0.89        886     > 21.02
  

  The values quoted above are in the UVOT photometric system (Poole et al. 2008, MNRAS, 383, 627). They are not corrected for the expected Galactic extinction corresponding to a reddening of E(B-V)=0.03 mag in the direction of the burst (Schlegel et al. 1998).
• GCN Circular #8489
  A. de Ugarte Postigo (ESO, Santiago), F. Aceituno & A. J. Castro-Tirado (IAA-CSIC, Granada) report on behalf of a larger collaboration:
  We have observed the field of GRB 081105 (Cummings et al. GCNC 8484) with the 1.5m OSN telescope in R and I bands. We do not detect any source within the XRT error box (Beardmore et al. GCNC 8487). The mean times and 3-sigma limits of the observations are the following:

  t-t0(days)    Band     Limit
  1.2454        R        > 21.3
  1.2499        I        > 20.7
  

  Photometry is based on the star 0934-0003777 of USNO-B1.0 catalogue (R.A.: 3.953112, Dec.: +3.463859), assuming R=17.11 and I=16.54.
• GCN Circular #8492
  C. Clemens, R. Filgas, J. Greiner, T. Kruehler, A. Yoldas (all MPE Garching), A. Kupcu Yoldas (ESO) and G. Szokoly (Eoetvoes Univ., Budapest) report on behalf of the GROND team:
  We observed the field of GRB 081105 (Swift trigger #333811; Cummings et al., GCN #8484) 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 La Silla Observatory (Chile).
  Observations started at 02:01 UT on November 6th, 2008, 12.6 hr after the GRB trigger with 23.0 min of total exposures in g'r'i'z' and 24.0 min in JHK. They were performed at an average seeing of 1.4" and at an average airmass of 1.2.
  As Ugarte Postigo et al. (GCN #8489), we do not detect any object within the 4.8'' Swift-XRT error circle reported by Beardmore et al. (GCN #8487) down to the following upper limits (all in AB system) of:

  g' > 23.3 mag,
  r' > 23.2 mag,
  i' > 22.5 mag,
  z' > 22.3 mag,
  J > 21.6 mag,
  H > 21.0 mag and
  K > 20.0 mag.
  

  These upper limits are derived based on calibrating the images against the GROND zeropoints as well as 2MASS field stars.
• GCN Circular #8522
  A.P. Beardmore (U. Leicester), D.N. Burrows (PSU), J.R. Cummings (NASA/UMBC) report on behalf of the Swift-XRT team.
  The Swift-XRT reobserved the field of the Swift-BAT and IPN localisation GRB 081105 (Cummings et al., GCN 8484) for a further 9.8 ks starting at 2008-11-12T04:15:51(UT), 6.62 days after the trigger.
  Using a 10 pixel radius extraction region we detect 9 counts at the position of the XRT source reported in GCN 8487 (Beardmore & Cummings) compared with 1.28+/-0.20 estimated background counts. The Bayesian method of Kraft et al. (1991 ApJ 374 344) produces a 3 sigma confidence level on the expected source counts of S_min = 1.40 to S_max = 20.08, suggesting the source is detected. (The lower limit on the expected source counts, S_min, approaches zero when the confidence level reaches 4.4 sigma.) The estimated source count rate is (1.07+/-0.40)e-3 count/s (where the quoted error is 1 sigma), compared with a value of 0.0065 +/-0.0015 count/s from the earlier observation.
  By fitting the low counts per bin data using Cash statistics, we find the source has faded with a decay slope of 1.01 +0.38-0.32. Both the source intensity and decay is comparable to those seen in other long GRBs at this stage of their outburst (e.g. see http://www.swift.ac.uk/xrt_curves/allcurves.php).
  We suggest the X-ray source reported in GCN 8487 was the counterpart to the BAT/IPN localisation and its decaying nature gives further weight to a GRB interpretation.
  This circular is an official product of the Swift-XRT team.