GRB 120913A

E. A. Helder (PSU), S. D. Barthelmy (GSFC),
W. H. Baumgartner (GSFC/UMBC), N. Gehrels (NASA/GSFC),
C. Gronwall (PSU), D. Grupe (PSU), J. A. Kennea (PSU),
H. A. Krimm (CRESST/GSFC/USRA), C. B. Markwardt (NASA/GSFC),
D. M. Palmer (LANL), B. Sbarufatti (INAF-OAB/PSU) and
B.-B. Zhang (PSU) report on behalf of the Swift Team:

At 20:18:21 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 120913A (trigger=533568).  Swift did not slew because
of the Sun observing constraint. 
The BAT on-board calculated location is 
RA, Dec 146.437, +26.977 which is 
   RA(J2000)  =  09h 45m 45s
   Dec(J2000) = +26d 58' 36"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve shows several peaks
with a total duration of at least 40 sec.  (At T+30s, Swift
executed a pre-planned slew that moved the GRB outside of the BAT FOV)
The peak count rate was ~2600 counts/sec (15-350 keV), at ~23 sec 
after the trigger. 

Due to a Sun observing constraint, Swift cannot slew to the BAT
position until 22:34 UT on 2012 September 27. There will thus be no XRT
or UVOT data for this trigger before this time. 

Burst Advocate for this burst is E. A. Helder (helder AT psu.edu). 
Please contact the BA by email if you require additional information
regarding Swift followup of this burst. In extremely urgent cases, after
trying the Burst Advocate, you can contact the Swift PI by phone (see
Swift TOO web site for information: http://www.swift.psu.edu/too.html.)

W. H. Baumgartner (GSFC/UMBC), S. D. Barthelmy (GSFC), J. R. Cummings (GSFC/UMBC),
E. E. Fenimore (LANL), N. Gehrels (GSFC), E. A. Helder (PSU),
H. A. Krimm (GSFC/USRA), C. B. Markwardt (GSFC), D. M. Palmer (LANL),
T. Sakamoto (GSFC/UMBC), G. Sato (ISAS), M. Stamatikos (OSU),
J. Tueller (GSFC), T. N. Ukwatta (MSU)
(i.e. the Swift-BAT team):
 
Using the data set from T-240 to T+962 sec from recent telemetry downlinks,
we report further analysis of BAT GRB 120913A (trigger #533568)
(Helder, et al., GCN Circ. 13762
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 ).  The BAT ground-calculated position is
RA, Dec = 146.400, 26.959 deg, which is 
   RA(J2000)  =  09h 45m 36.1s 
   Dec(J2000) = +26d 57' 32.4" 
with an uncertainty of 1.2 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 71%.
 
The mask-weighted light curve shows three slightly overlapping FRED peaks
starting at ~T-5 sec, peaking at ~T+1, ~T+23, & ~T+40 sec, and ending at ~T+42 sec.
Due to a slew, the burst location left the BAT FoV at ~T+115 sec.
T90 (15-350 keV) is 30.1 +- 4.8 sec (estimated error including systematics).
 
The time-averaged spectrum from T-0.72 to T+39.80 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
2.18 +- 0.15.  The fluence in the 15-150 keV band is 8.7 +- 0.8 x 10^-7 erg/cm2.
The 1-sec peak photon flux measured from T+22.45 sec in the 15-150 keV band
is 2.3 +- 0.2 ph/cm2/sec.  All the quoted errors are at the 90% confidence
level. 
 
The results of the batgrbproduct analysis are available at
http://gcn.gsfc.nasa.gov/notices_s/533568/BA/

V. Pelassa and V. Connaughton (UAH) report on behalf of the Fermi GBM Team:

"At 20:18:22.89 UT on 13 spetember 2012, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 120913A (trigger369260305  / 120913846), which was
also detected by the Swift/BAT (E.A. Helder et al. 2008, GCN 13762
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 ).
The GBM on-ground location is consistent with the Swift position.
The angle from the Fermi LAT boresight is 97 degrees.

The GBM light curve consists of 2 peaks at T0 and T0+20s with a duration (T90)
of about 41s (50-300 keV).

The event fluence (10-1000keV) from T0-3.584 s to T0+33.280 s is
(1.8 +/- 0.3)E-06 erg/cm^2. The 1.024-sec peak photon flux measured starting
from T0+21.568 s in the 10-1000 keV band is 3.8 +/- 0.2 ph/s/cm^2.

The first peak is harder but fainter than the second peak, which is
best fit by a
power law function with an exponential high-energy cutoff. The power law
index is -1.25 +/- 0.38 and the cutoff energy, parameterized as Epeak, is
26 +/- 4 keV (C-stat 372 for 366 d.o.f.).

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