GRB 130804A

Subject: GRB 130804A: Fermi GBM observation

Hoi-Fung Yu (MPE), Adam Goldstein (ORAU/NASA MSFC) and Veronique Pelassa (UAH)
report on behalf of the Fermi GBM Team:

"At 00:33:15.53 UT on 04 August 2013, the Fermi Gamma-Ray Burst
Monitor triggered and located GRB 130804A (trigger 397269198 / 130804023).

High peak flux from the GRB caused GBM to issue a repoint request
that reoriented the satellite to place the GRB near the LAT boresight
for 2.5 hours, subject to Earth limb contraints.

The on-ground calculated location, using the GBM trigger data, is
RA = 280.0, DEC = -76.2 (J2000 degrees, equivalent to 18h 40m,
-76d 09'), with an uncertainty of 2.3 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 21 degrees.

The GBM light curve consists of two main pulses with sub-structures,
with a duration (T90) of about 0.96 s (50-300 keV).
The time-averaged spectrum from T0-0.064 s to T0+1.024 s is
adequately fit by a Band function with Epeak = 545 +/- 110 keV,
alpha = -0.77 +/- 0.09, and beta = -2.22 +/- 0.31.

The event fluence (10-1000 keV) in this time interval is
(1.89 +/- 0.10)E-6 erg/cm^2. The 64 ms peak photon flux measured
starting from T0-0.064 s in the 10-1000 keV band
is 42.0 +/- 1.7 ph/s/cm^2.

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

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

K. Hurley on behalf of the IPN,

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

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

K. Yamaoka, M. Ohno, Y. Hanabata, Y. Fukazawa, T. Takahashi, M. Tashiro,
Y. Terada, T. Murakami, and K. Makishima, on behalf of the Suzaku WAM
team,

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

D. M. Smith, J. McTiernan, and W. Hajdas, on behalf of the RHESSI team, 
  report:

The short-duration, hard spectrum, intense GRB 130804A (Yu, Goldstein, 
and Pelassa , GCN Circ. 15070
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 ) was observed by Fermi (GBM), Suzaku 
(WAM), Swift (BAT), AGILE (MCAL), Konus-Wind, and RHESSI at about 1995 s 
UT (00:33:15.353). The burst was outside the coded field of view of the BAT.

We have triangulated this burst to a narrow Konus-GBM annulus centered 
at RA(2000)=324.539 deg (21h 38m 09s)  Dec(2000)=-9.265 deg (-9d 15' 
53"), whose radius is 71.038 � 0.041 deg (3 sigma) and to a wide GBM-WAM 
annulus centered at RA(2000)=RA(2000)=102.159 deg (06h 48m 38s) 
Dec(2000)=-31.166 deg (-31d 09' 56"), whose radius is 68.583 � 5.163 deg 
(3 sigma).

These annuli intersect to form a long arc, whose
coordinates are:
  ---------------------------------------------
   RA(2000), deg                 Dec(2000), deg
  ---------------------------------------------
  Center:
   303.653 (20h 14m 37s) -79.591 (-79d 35' 28")
  Corners:
   276.360 (18h 25m 26s) -75.021 (-75d 01' 15")
   275.920 (18h 23m 41s) -75.010 (-75d 00' 37")
   349.555 (23h 18m 13s) -79.299 (-79d 17' 56")
   349.905 (23h 19m 37s) -79.175 (-79d 10' 29")
  ---------------------------------------------
The arc area is 1.29 sq. arcmin, and its maximum
dimension is 15.8 deg (the minimum one is 2.9 arcmin).
The Sun distance was ~117 deg.


The center of the GBM location (Yu, Goldstein, and Pelassa , GCN Circ. 
15070
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 ) is 5.9 deg from the center of the IPN arc.

A triangulation map is posted at
http://www.ioffe.ru/LEA/GRBs/GRB130804_T01995/IPN/

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, short-duration GRB 130804A
(Fermi-GBM detection: Yu, Goldstein, and Pelassa, GCN 15070
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 ;
IPN triangulation: Golenetskii at al., GCN 15075
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 )
triggered Konus-Wind at T0=1997.053 s UT (00:33:17.053).

The burst light curve from ~T0-0.2 s to ~T0+1 s shows three major pulses
with the brightest, hard-spectrum pulse peaked at ~T0.

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB130804_T01997/

As observed by Konus-Wind, the burst
had a fluence of (1.8 � 0.2)x10-6 erg/cm2,
and a 16-ms peak flux, measured from T0,
of (3.4 � 0.3)x10-5 erg/cm2/s
(both in the 20 keV - 10 MeV energy range).

The 3-channel time-integrated spectrum
(measured from T0-0.256 to T0+1.024 s)
can be modeled, in the 25 keV - 1.5 MeV range,
by the cutoff power law with the following model parameters:
the photon index alpha = -0.94 � 0.06,
and the peak energy Ep = 434 � 37 keV.

All the quoted results are preliminary.