Gamma-ray Burst 131018B

(All information courtesy of the instrument teams.)

Previous IAU Circulars

• none

• GCN Circular #15357
  G. Vianello (Stanford), R. Desiante (University of Udine and INFN Trieste) and F.Longo (University of Trieste and INFN Trieste) report on behalf of the Fermi-LAT team:
  At 16:08:39 on 2013-10-18 Fermi LAT detected high energy emission from GRB 131018B, which was also detected by Fermi-GBM ( trigger bn131018673).
  The best LAT on-ground location is found to be (RA, DEC) = 304.41, 23.11 (J2000) with an error radius of 0.13 deg (68% containment, statistical error only), which was 25 deg from the LAT boresight at the time of the trigger. This position is 12 deg away from the best available GBM localization. This can be explained by the large statistical error on the GBM position (4 deg) and its typical systematic error, which is of the order of few degrees.
  The data from the Fermi LAT show an increase in the event rate within 10 degrees of the reported position starting few seconds after the GBM trigger (a delay common to many Fermi-LAT GRBs), which behaves spatially and temporally like a new transient point source. This excess has a high significance (~6 sigma).
  More than 10 photons above 100 MeV are observed within 2000 seconds after the trigger. The highest energy photon is a 13 GeV event which is observed 250 seconds after the GBM trigger.
  A Swift ToO request for this burst has been submitted.
  The Fermi LAT point of contact for this burst is Rachele Desiante ( rachele.desiante@ts.infn.it).
  The Fermi LAT is a pair conversion telescope designed to cover the energy band from 20 MeV to greater than 300 GeV. It is the product of an international collaboration between NASA and DOE in the U.S. and many scientific institutions across France, Italy, Japan and Sweden.
• GCN Circular #15360
  Bin-Bin Zhang(UAH) reports on behalf of the Fermi GBM Team:
  "At 16:08:39.181 UT on October 18 2013, the Fermi Gamma-Ray Burst Monitor triggered and located GRB 131018B (trigger 403805322/131018673), which is also detected by Fermi/LAT (Vianello et al. GCN 15357). The GBM on-ground location is consistent with the LAT position (Vianello et al., GCN 15357). The angle from the Fermi LAT boresight is 23 degrees.
  The GBM light curve consists of one FRED-shape pulse with a duration (T90) of about 38 s (50-300 keV). The time-averaged spectrum from T0+0 s to T0+30 s is well best fit with a power law function with an exponential high-energy cutoff parameterized as Epeak = 77 +/- 7 keV and an Index = -0.25 +/- 0.30. The event fluence (10-1000 keV) in this time interval is (2.14 +/- 0.16)E-06 erg/cm^2. The 1.0-sec peak photon flux measured starting from T0+1 s in the 10-1000 keV band is 2.2 +/- 0.3 ph/s/cm^2.
  The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog."
• GCN Circular #15361
  P. D'Avanzo, A. Melandri, M. G. Bernardini, P. A. Evans (U. Leicester) report on behalf of the Swift-XRT team:
  We have analysed 2.8 ks of XRT data for the Fermi/LAT-detected burst: GRB 131018B (Vianello et al., GCN 15357; Zhang, GCN 15360), from 83.1 ks to 95.2 ks after the Fermi/LAT trigger. The data are entirely in Photon Counting (PC) mode. An uncatalogued X-ray source is detected within the Fermi/LAT error circle. The refined XRT position is RA, Dec = 304.53693, +23.18759 which is equivalent to:

  RA (J2000): 20 18 08.86
  Dec(J2000): +23 11 15.3
  

  with an uncertainty of 4.9 arcsec (radius, 90% confidence). This position is 514 arcsec from the Fermi/LAT position. We cannot determine at the present time whether the source is fading.
  We note the presence of two further sources within the LAT error box.
  Source #2 has the following position RA, Dec = 304.41156, +23.16636 which is equivalent to:

  RA (J2000): 20 17 38.77
  Dec(J2000): +23 09 58.9
  

  with an uncertainty of 5.4 arcsec (radius, 90% confidence).
  Source #3 has the following position RA, Dec = 304.52361 +23.06517 which is equivalent to:

  RA (J2000): 20 18 05.67
  Dec(J2000): +23 03 54.6
  

  with an uncertainty of 6.0 arcsec (radius, 90% confidence).
  Both sources are present in the Swift-XRT point source catalogue (D'Elia et al. 2013; A&A 551, A142) and are likely not related with GRB 131018B.
  The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00020308.
  This circular is an official product of the Swift-XRT team.
• GCN Circular #15362
  S. R. Oates (MSSL-UCL) and P. D'Avanzo (INAF-OAB) report on behalf of the Swift/UVOT team:
  The Swift/UVOT began settled observations of the field of GRB 131018B 83 ks after the LAT trigger (Vianello et al., GCN Circ. 15357). No new optical candidate is detected within the LAT error circle (Vianello et al., GCN Circ. 15357) in the initial UVOT exposures. We note an optical source within the error circle of the candidate XRT position (D'Avanzo et al., GCN Circ. 15361), which is found in the USNO-B1 catalogue.
  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
  
  white          90363	    91160          785         >21.7
  v              91168	    91427          255         >19.4
  u              88969	    95244         1300         >20.6
  

  The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.58 in the direction of the burst (Schlegel et al. 1998).
• GCN Circular #15431
  P. D'Avanzo (INAF-OAB), P. A. Evans (U. Leicester) report on behalf of the Swift-XRT team:
  We have analysed 6.7 ks of XRT data for the Fermi/LAT-detected burst GRB 131018B (Vianello et al., GCN 15357; Zhang, GCN 15360), from 1081.2 ks to 1100.0 ks after the Fermi/LAT trigger. The data are entirely in Photon Counting (PC) mode. The uncatalogued X-ray source reported in D'Avanzo et al. (GCN 15361) is not longer detected. The source count rate changed from 5.7e-3 +/- 1.8e-3 cts/s in the first epoch (D'Avanzo et al., GCN 15361) to a 3-sigma upper limit of 1.1e-3 cts/s. We can conclude that this source is likely the X-ray afterglow of GRB 131018B.
  This circular is an official product of the Swift XRT team.
• GCN Circular #15437
  Eleonora Troja (GSFC), Nat Butler (ASU), Alan M. Watson (UNAM), Alexander Kutyrev (GSFC), William H. Lee (UNAM), Michael G. Richer (UNAM), Chris Klein (UCB), Ori Fox (UCB), J. Xavier Prochaska (UCSC), Josh Bloom (UCB), Antonino Cucchiara (ORAU/GSFC), Owen Littlejohns (ASU), Enrico Ramirez-Ruiz (UCSC), Jos=E9 A. de Diego (UNAM), Leonid Georgiev (UNAM), Jes=FAs Gonz=E1lez (UNAM), Carlos Rom=E1n-Z=FA=F1= iga (UNAM), Neil Gehrels (GSFC), and Harvey Moseley (GSFC) report:
  We observed the field of GRB 131018B (Vianello, et al., GCN 15357;=20 Zhang, et al., GCN 15360) with the Reionization and Transients Infrared Camera=20 (RATIR; www.ratir.org) on the 1.5m Harold Johnson Telescope at the Observatorio Astron=F3mico Nacional on Sierra San Pedro M=E1rtir from 2013/10 20.09 to 2013/10 20.27 UTC (33.94 to 38.36 hours after the GBM trigger), and agai= n the next night from 2013/10 21.09 to 2013/10 21.27 UTC (57.93 to 62.34 hours after the GBM trigger). We obtained a total of 2.8 hours exposure=20 in the r and i bands and 1.3 hours exposure in the Z, Y, J, and H bands each=20 night.
  During the 1st night of observations, the position of the X-ray afterglow reported by D'Avanzo et al. (GCN 15361, 15431) falls at the edge of our=20 field of view in the Z and J bands. For a source within the Swift-XRT error=20 circle, in comparison with 2MASS, we obtain the following upper limits (3-sigma):

     Z   > 22.6
     J    > 21.6
  

  During the 2nd night of observations, the XRT position was observed in al= l filters. For a source within the Swift-XRT error circle, in comparison=20 with 2MASS and SDSS DR9, we obtain the following upper limits (3-sigma):

     r   > 23.8
     i   > 23.5
     Z  > 22.8
     Y  > 22.2
     J   > 21.9
     H  > 21.4
  

  These magnitudes are in the AB system and are not corrected for Galactic extinction in the direction of the GRB.
  We thank the staff of the Observatorio Astron=F3mico Nacional in San Pedr= o M=E1rtir.