Gamma-ray Burst 151122A

(All information courtesy of the instrument teams.)

Previous IAU Circulars

• none

• GCN Circular #18637
  David Palmer reports on behalf of the Swift team:
  On November 22, at 17:00:40 UT, BAT rate-triggered and detected a 6.0 sigma peak in an image. Because this was below the nominal 6.5 sigma threshold, BAT did not trigger a burst response. However, ground analysis leads us to believe that this is a real burst, GRB 151122A (trigger #664653) with an onboard-calculated location RA,dec =3D 299.704, -19.899, which is

  RA(J2000) = 19h 58m 49s
  dec(J2000) =-19d 53' 56"
  

  with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The lightcurve shows a slow-rise, fast decay peak from T-5 s to T+12 s, following by a possible second lower peak extending to T+45 s. The peak count rate was ~1500 counts/sec (15-350 keV), at ~6 sec after the trigger.
  The peak of this burst was after a pre-planned slew had started, thus only the initial rise of this burst was imaged on board. However, the burst was also seen by Fermi GBM (trigger #469904449) which gave a final ground-calculated position of RA,dec =3D 292.950, -21.350 with an 11.1 degree statistical error radius and a 1-sigma location contour that contains the BAT location. The GBM lightcurve is also consistent with the BAT lightcurve. Therefore we believe that both of these triggers are the same astrophysical GRB at the location found by BAT
  A Target Of Opportunity Swift observation has been accepted for this GRB.
• GCN Circular #18638
  P. A. Evans (U. Leicester) reports on behalf of the Swift team:
  Swift has initiated a ToO observation of the Swift/BAT GRB 151122A. Automated analysis of the XRT data will be presented online at http://www.swift.ac.uk/ToO_GRBs/00020560
  Any uncatalogued X-ray sources detected in this analysis will be reported on this website and via GCN COUNTERPART notices. These are not necessarily related to the Swift/BAT event. Any X-ray source considered to be a probable afterglow candidate will be reported via a GCN Circular after manual consideration.
  Details of the XRT automated analysis methods are detailed in Evans et al. (2007, A&A, 469, 379; 2009, MNRAS, 397, 1177 and 2014, ApJS, 210, 8).
  This circular is an official product of the Swift-XRT team.
• GCN Circular #18639
  Matthew Stanbro (UAH) reports on behalf of the Fermi GBM Team:
  "At 17:00:45.01 UT on 22 November 2015, the Fermi Gamma-Ray Burst Monitor triggered and located GRB 151122A (trigger 469904449 / 151122709) which was also detected by the Swift/BAT (Palmer et al. 2015, GCN 18637). The GBM on-ground location is consistent with the Swift position.
  The angle from the Fermi LAT boresight at the GBM trigger time is 51 degrees.
  The GBM light curve consists of several episodes with a duration (T90) of about 30 s (50-300 keV). The time-averaged spectrum from T0-4.10 s to T0+29.70 s is best fit by a simple power law function with index -2.23 +/- 0.06.
  The event fluence (10-1000 keV) in this time interval is (2.18 +/- 0.15)E-06 erg/cm^2. The 1-sec peak photon flux measured starting from T0+0.77 s in the 8-1000 keV band is 1.97 +/- 0.26 ph/s/cm^2.
  The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog."
• GCN Circular #18640
  A. Melandri (INAF-OAB), P. D'Avanzo (INAF-OAB), V. D'Elia (ASDC), D.N. Burrows (PSU), T.G.R. Roegiers (PSU), L.M. McCauley (PSU), S.L. Gibson (U. Leicester), J.P. Osborne (U. Leicester) and P.A. Evans (U. Leicester) report on behalf of the Swift-XRT team:
  Swift-XRT has performed follow-up observations of the Swift/BAT-detected burst GRB 151122A (David Palmer et al. GCN Circ. 18637), collecting 3.0 ks of Photon Counting (PC) mode data between T0+102.9 ks and T0+114.0 ks.
  Two uncatalogued X-ray sources have been detected inside or close to the Swift/BAT error region, however none of them is above the RASS limit or shows definitive signs of fading. Therefore, at the present time we cannot identify which, if any, is the afterglow. Details of these sources are given below:
  Source 1:

     RA (J2000.0):  299.6973  =3D  19:58:47.35
     Dec (J2000.0): -19.9063  =3D  -19:54:22.8
     Error: 4.7 arcsec (radius, 90% conf.)
     Count-rate: 0.0100 =B1 0.0023 ct s^-1
     Flux: (4.24 =B1 0.95)e-13 erg cm^-2 s^-1 (observed, 0.3-10 keV)
  

  This source is 5.8" away from PMN J1958-1954, classified in SIMBAD as a=20 radio source.
  Source 2:

     RA (J2000.0):  299.6668  =3D  19:58:40.03
     Dec (J2000.0): -19.9360  =3D  -19:56:09.5
     Error: 4.9 arcsec (radius, 90% conf.)
     Count-rate: (3.9 =B1 1.6)e-3 ct s^-1
     Flux: (1.57 =B1 0.64)e-13 erg cm^-2 s^-1 (observed, 0.3-10 keV)
  

  This source is 2.1" from HD 189004, a high proper-motion, K star.
  Another uncatalogued was also detected, however this was too far from the GRB position to be the afterglow.
  The results of the XRT-team automatic analysis of the XRT observations, including a position-specific upper limit calculator, are available at http://www.swift.ac.uk/ToO_GRBs/00020560.
  This circular is an official product of the Swift-XRT team.
• GCN Circular #18641
  M. H. Siegel (PSU) and P. A. Evans (U.Leicester) report on behalf of the Swift/UVOT team:
  The Swift/UVOT began settled observations of the field of GRB 151122A 102884 s after the BAT trigger (Palmer et al., GCN Circ. 18637). No optical afterglow consistent with either of the XRT positions given by Evans et al. (GCN Circ 18640) is detected in the initial UVOT exposures. For source 1, we do not detect any new source down to the detection limit. For source 2, we only detect the bright high proper motion star HD 189004.
  Preliminary 3-sigma upper limits using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the initial exposures are:

  Filter         T_start(s)   T_stop(s)      Exp(s)         Mag
  
  w2              102884       113997         2933         >21.1
  

  The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.20 in the direction of the burst (Schlegel et al. 1998).
• GCN Circular #18652
  P.A. Evans (U. Leicester) reports on behalf of the Swift-XRT team.
  Swift-XRT has performed repeat observations of the field of GRB 151122A (Palmer et al., GCN Cric. 18637), collecting 4 ks of data from T0+373 ks to T0+442 ks.
  Both of the X-ray sources reported by Melandri et al (GCN Circ. 18640) are still detected, with neither showing evidence of fading. We therefore conclude that these are unrelated to the GRB, and XRT did not detect the afterglow of GRB 151122A.
  The 3-sigma upper limit from the initial observations (3 ks, from T0+102.9 ks and T0+114.0 ks) is 5e-3 ct/sec, which corresponds to a 0.3-10 keV flux of approximately 2e-13 erg cm^-2 s^-1.
  This circular is an official product of the Swift-XRT team.