Gamma-ray Burst 090827

(All information courtesy of the instrument teams.)

Previous IAU Circulars

• none

• GCN Circular #9846
  J. R. Cummings (GSFC/UMBC), H. A. Krimm (GSFC/USRA), C. B. Markwardt (GSFC/UMD), and D. M. Palmer (LANL), on behalf of the Swift-BAT team
  At 19:06:26 on 2009-08-27, GRB 090827 triggered Swift-BAT (trigger #361029). No source was found onboard. A source was found in ground analysis of BAT event data. The burst consisted of a single pulse of 7 seconds. This burst also triggered Konus-Wind and INTEGRAL-SPI-ACS (V. Pal'shin, private communication).
  The BAT position is RA, Dec 18.435, -50.899, which is equivalent to: RA, Dec (J2000): 01:13:44.4, -50d 53' 58" with an uncertainty radius of 2.8 arcmin (estimated 90% containment, stat+sys). The source was 3% coded.
  Because of the extreme partial coding, the spectral parameters can be defined only poorly. The spectrum is best fit by a simple powerlaw relation. The photon index is 1.0 +/- 0.3. The fluence was (4 +/- 2) x 10^-6 ergs/cm2. The errors are estimated 1-sigma.
  A Swift TOO has been requested and will take place starting approximately 26 hours after the burst.
• GCN Circular #9847
  P.A. Evans (U. Leicester) and S.R. Oates (MSSL-UCL) report on behalf of the Swift team:
  The Swift-XRT observed the field of GRB 090827 (Cummings et al. GCN Circ. 9846), gathering 7.1 ks of Photon Counting (PC) mode data from T0+92 ks to T0+122 ks. Inside the BAT error circle we find a single, uncatalogued source at a location of RA,Dec = 18.4495, -50.8957 which is equivalent to:

  RA (J2000)  = 01h 13m 47.88s
  Dec (J2000) = -50d 53' 44.0"
  

  with an uncertainty of 6.4 arcsec (radius, 90% condfidence). There are only 14 counts detected from this source, giving it a count rate of (3+/-1) x 10^-3 ct/sec. It is impossible to say whether this source is fading.
  A spectrum formed from all available data can be well fitted using an absorbed power law, with a photon index of 1.6 (+0.9, -0.8) and an absorption column density consistent with the Galactic value of 1.6 x 10^20 cm^-2 (Kalberla et al. 2005).
  The Swift-UVOT began settled observations of the field 91.6 ks after the BAT trigger. We do not detect any source at the XRT position.
  The 3-sigma upper limits for the finding chart exposure is:

  Filter   T_start(s)   T_stop(s)   Exp(s)  Mag (3-sigma upper limit)
  -------------------------------------------------------------
  U         91644        120333      5671        > 21.94
  -------------------------------------------------------------
  

  The quoted upper limits have not been corrected for the expected Galactic extinction along the line of sight of E_(B-V) = 0.01 mag. All photometry is on the UVOT photometric system described in Poole et al. (2008, MNRAS, 383, 627).
  This circular is an official product of the Swift team.
• GCN Circular #9848
  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 090827 (Cummings et al., GCN 9846) triggered Konus-Wind at T0=68787.702 s UT (19:06:27.702)
  The burst time profile had a FRED-like structure with a duration of ~8 s. The Konus-Wind light curves of this GRB are available at http://www.ioffe.ru/LEA/GRBs/GRB090827_T68787/
  As observed by Konus-Wind the burst had a fluence of 3.0(-0.5,+0.6)x10-6 erg/cm2, and a 256-ms peak flux, measured from T0-0.256, of 1.7(-0.5,+0.7)x10-6 erg/cm2/s (both in the 20 keV - 2 MeV energy range).
  The time-integrated spectrum of the burst (from T0 to T0+8.848 s) is well fitted (in the 20 keV - 2 MeV range) by a power law with exponential cutoff model: dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep) with alpha = -0.6(-0.45,+0.58), and Ep = 200(-39,+69)keV (chi2 = 62/57 dof).
  Fitting by the GRB (Band) model yields the same alpha and Ep values with the high energy photon index Beta of -9 (< -2.3)
  All the quoted values are preliminary. All the quoted errors are at the 90% confidence level.
• GCN Circular #9911
  P.A. Evans, K.L. Page (U. Leicester) and S.R. Oates (MSSL-UCL) report on behalf of the Swift-XRT team:
  Swift reobserved the field of GRB 090827 (Cummings et al. GCN Circ. 9846) on 2009 September 9th and 13th, 13 and 17 days after the trigger, respectively. The XRT gathered 14 ks of Photon Counting mode data in this time.
  The source reported by Evans & Oates (GCN Circ. 9847) is not detected, with a 3-sigma upper limit of 8.6 x 10^-4 count s^-1, significantly below the level of the previous detection. We thus conclude that this source was the afterglow of GRB 090827.
  This circular is an official product of the Swift-XRT team.
• GCN Report 244.1
  GCN_Report 244.1 has been posted: http://gcn.gsfc.nasa.gov/reports/report_244_1.pdf by S.R. Oates at MSSL-UCL titled: "Final Results on Swift GRB 090827"