GRB 131028A

A. von Kienlin (MPE) reports on behalf of the Fermi GBM Team:

"At 01:49:02.35 UT on 28 October 2013, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 131028A (trigger 404617745 / 131028076).

The on-ground calculated location, using the GBM trigger
data, is RA = 57.0, DEC = +72.2 (J2000 degrees,
equivalent to 03 h 48 m, 72 d 12 '), with an uncertainty
of 1.2 degrees (radius, 1-sigma containment,
statistical only; there is additionally a systematic
error which is currently estimated to be 2 to 3 degrees).

The angle from the Fermi LAT boresight is 123 degrees.

This burst was also independently detected by INTEGRAL SPI-ACS.

The GBM light curve consists of a single pulse
with a duration (T90) of about 17 s (50-300 keV).
The time-averaged spectrum from T0-1.28 s to T0+22.27 s is
best fit by a Band function with Epeak = 888 +/-18 keV,
alpha = -0.71 +/- 0.01, and beta = -3.4 +/-0.2. 

The event fluence (10-1000 keV) in this time interval is
(1.62 +/- 0.02)E-04 erg/cm^2. The 1.024-sec peak photon flux measured
starting from T0+8.13 s in the 10-1000 keV band is 62 +/- 1 ph/s/cm^2.

The spectral analysis results presented above are preliminary;
final results will be published in the GBM GRB Catalog."

K. Hurley and J. Goldsten, on behalf of the MESSENGER NS GRB team,

S. Golenetskii, R. Aptekar, V. Pal'shin, D. Frederiks, D. Svinkin, and 
T. Cline on behalf of the Konus-Wind team,

V. Connaughton, M. S. Briggs, C. Meegan, and V. Pelassa, on behalf of 
the Fermi GBM team,

A. von Kienlin, X. Zhang, A. Rau, V. Savchenko, E. Bozzo, and C.
Ferrigno, on behalf of the INTEGRAL SPI-ACS GRB team,

S. Barthelmy, J. Cummings, N. Gehrels, H. Krimm, and D. Palmer, on 
behalf of the Swift-BAT team, and

G. Di Cocco, F. Fuschino, M. Galli, C. Labanti, and M. Marisaldi, on
behalf of the AGILE MCAL team, report:

The long, bright GRB 131028A was observed by Konus-Wind, Fermi (GCN 
15396
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 ), INTEGRAL (SPI-ACS), Swift (BAT), AGILE (MCAL), and MESSENGER 
(GRNS) at about 6542 s UT (01:49:02). The burst was outside the coded 
field of view of the BAT.

We have triangulated it to a 3 sigma error box whose
coordinates are:
---------------------------------------------
   RA(2000), deg                 Dec(2000), deg
  ---------------------------------------------
  Center:
    61.225 (04h 04m 54s) +71.595 (+71d 35' 41")
  Corners:
    69.087 (04h 36m 21s) +70.098 (+70d 05' 51")
    66.215 (04h 24m 52s) +70.982 (+70d 58' 56")
    52.752 (03h 31m 00s) +72.570 (+72d 34' 14")
    56.127 (03h 44m 30s) +72.015 (+72d 00' 52")
  ---------------------------------------------
The error box area is 1.3 sq. deg, and its maximum dimension is
5.8 deg (the minimum one is 1.2 deg).

A triangulation map is posted at
http://www.ioffe.ru/LEA/GRBs/GRB131028_T06546/IPN/

Some improvement in this triangulation is possible.

S. Golenetskii, R.Aptekar, D. Frederiks, V. Pal'shin,
P. Oleynik, M. Ulanov, D. Svinkin, and T. Cline on behalf
of the Konus-Wind team, report:

The bright, long-duration, hard-spectrum GRB 131028A
(Fermi GBM detection: von Kienlin, GCN 15396
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 ;
IPN triangulation: Hurley at al., GCN 15397
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 )
triggered Konus-Wind at T0=6546.966 s UT (01:49:06.966).

The burst light curve shows a bright, hard pulse from ~T0 to ~T0+20 s,
followed by a tail of softer emission in next ~50 s.
The emission in the main pulse is seen up to ~10 MeV.

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB131028_T06546/

As observed by Konus-Wind, the burst
had a fluence of (2.41 � 0.05)x10-4 erg/cm2,
and a 64-ms peak flux, measured from T0+5.760 s,
of (6.6 � 0.3)x10-5 erg/cm2/s
(both in the 20 keV - 10 MeV energy range).

The time-averaged spectrum (measured from T0 to T0+20.736 s)
is best fit in the 50 keV - 15 MeV range
by the GRB (Band) function with the following model parameters:
the low-energy photon index alpha = -0.82 � 0.02,
the high energy photon index beta = -3.07 � 0.17,
the peak energy Ep = 901 � 25 keV,
chi2 = 97.2/93 dof.

The spectrum near the maximum count rate
(measured from T0+5.376 s to T0+6.400 s)
is best fit in the 50 keV - 15 MeV range
by the GRB (Band) function with the following model parameters:
the low-energy photon index alpha = -0.56 � 0.06,
the high energy photon index beta = -3.18 � 0.42,
the peak energy Ep = 1277 � 91 keV,
chi2 = 119/86 dof.

All the quoted values are preliminary.