GRB 100924A

V. Mangano (INAF-IASFPA), W. H. Baumgartner (GSFC/UMBC),
J. R. Cummings (NASA/UMBC), N. Gehrels (NASA/GSFC),
E. A. Hoversten (PSU), C. B. Markwardt (NASA/GSFC) and
B. Sbarufatti (INAF-OAB/IASFPA) report on behalf of the Swift Team:

At 03:58:08 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 100924A (trigger=434843).  Swift did not slew to the burst. 
The BAT on-board calculated location is 
RA, Dec 0.671, +7.015 which is 
   RA(J2000) = 00h 02m 41s
   Dec(J2000) = +07d 00' 54"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a multi-peaked
structure with a duration of about 90 sec.  The peak count rate
was ~5457 counts/sec (15-350 keV), at ~0 sec after the trigger. 

Due to an Moon observing constraint, Swift cannot slew to the BAT
position until 13:21 UT on 2010 September 25. There will thus be no XRT
or UVOT data for this trigger before this time. 

Burst Advocate for this burst is V. Mangano (vanessa AT ifc.inaf.it). 
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.)

S. D. Barthelmy (GSFC), W. H. Baumgartner (GSFC/UMBC), J. R. Cummings (GSFC/UMBC),
N. Gehrels (GSFC), H. A. Krimm (GSFC/USRA), V. Mangano (INAF-IASFPA),
C. B. Markwardt (GSFC), D. M. Palmer (LANL), T. Sakamoto (GSFC/UMBC),
M. Stamatikos (OSU), J. Tueller (GSFC), T. N. Ukwatta (GWU)
(i.e. the Swift-BAT team):
 
Using the data set from T-239 to T+963 sec from recent telemetry downlinks,
we report further analysis of BAT GRB 100924A (trigger #434843)
(Mangano, et al., GCN Circ. 11294
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 ).  The BAT ground-calculated position is
RA, Dec = 0.672, 7.004 deg which is 
   RA(J2000)  =  00h 02m 41.3s 
   Dec(J2000) = +07d 00' 15.0" 
with an uncertainty of 1.0 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 25%.
 
The mask-weighted light curve shows an initial cluster of two peaks starting
at ~T-4 sec, peaking at ~T_zero, and returning to essentially background at ~T+20 sec.
The second cluster has approximately 8 peakis starting at ~T+20 sec, with
main peaks at ~T+35, +45, +52, +60, amd +68, and returning to background
around T+120 sec.  T90 (15-350 keV) is 96.0 +- 16.0 sec (estimated error
including systematics).
 
The time-averaged spectrum from T-15.1 to T+128.9 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.53 +- 0.06.  The fluence in the 15-150 keV band is 8.3 +- 0.3 x 10^-6 erg/cm2.
The 1-sec peak photon flux measured from T+56.40 sec in the 15-150 keV band
is 1.5 +- 0.3 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/434843/BA/

P. Schady, T. Kruehler, and J. Greiner (all MPE Garching) report on
behalf of the GROND team:

We observed the field of GRB 100924A (Mangano et al., GCN 11294
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 )
simultaneously in g'r'i'z'JHK with GROND (Greiner et al. 2008, PASP 120,
405) mounted at the 2.2 m MPI/ESO telescope at La Silla Observatory (Chile).

Observations started at 04:32 UT on September 24, 0.57 hours after the
GRB and were performed under very challenging observing conditions, in
particular a full moon at close distance. A second epoch of imaging was
performed starting at 00:36 UT on September 25.

In the first epoch we detect a bright point source in all channels at:

RA = 00:02:42.26
Dec = 07:00:02.8

inside the refined BAT error circle (Barthelmy et al., GCN 11295
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 ) and
with a preliminary magnitude of r' = 17.19. Both, photometry and
astrometry have been tied to the SDSS catalog. The object faded below r'
 > 20 in the second epoch and is not present in the much deeper archival
SDSS frames. We hence conclude that this is the optical/NIR afterglow of
GRB 100924A.

David Gruber (MPE) reports on behalf of the Fermi GBM Team: 

"At 03:58:08.32 UT on 24 September 2010, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 100924A (trigger 306993490 / 100924165).
which was also detected by the Swift-BAT (Mangano et al. 2010, GCN 11294
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 ).
The GBM on-ground location is consistent with the Swift position.
 
The angle from the Fermi LAT boresight is 57 degrees.

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

The GBM light curve shows a bright initial peak
with a duration (T90) of about 9.0 +/- 0.4 s (50-300 keV). 
Fermi entered the SAA ~ 35 s after the trigger.
Thus, the observation of additional emission episodes,
as reported in Mangano et al. 2010, GCN 11294
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 , was not possible.

The time-averaged spectrum from T0+0.003 s to T0+9.088 s is 
best fit by a simple power law function with index -1.59 +0.02/-0.02
(Castor C-STAT 1767 for 725 d.o.f.).

The event fluence (10-1000 keV) in this time interval is 
(3.33 +/- 0.04)E-06 erg/cm^2. The 1-sec peak photon flux measured 
starting from T0+0.384 s in the 10-1000 keV band 
is 7.3 +/- 0.2 ph/s/cm^2.

S. Sugita (Nagoya U.), T. Uehara, Y. Hanabata,
T. Takahashi, Y. Fukazawa (Hiroshima U.),
N. Vasquez (Tokyo Tech.) K. Yamaoka (Aoyama Gakuin U.),
Y. Terada, M. Tashiro, W. Iwakiri, K. Takahara, T. Yasuda (Saitama U.),
M. Ohno, M. Suzuki, M. Kokubun, T. Takahashi (ISAS/JAXA),
Y. E. Nakagawa, T. Tamagawa (RIKEN), N. Ohmori, A. Daikyuji, Y. Nishioka,
M. Yamauchi (Univ. of Miyazaki), Y. Urata, P. Tsai (NCU),
K. Nakazawa, K. Makishima (Univ. of Tokyo),
S. Hong (Nihon U.), on behalf of the Suzaku WAM team, report:


The multi-spiked long GRB 100924A (Swift/BAT trigger #434843, GCN
11294
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 ; Mangano et al.,)
triggered the Suzaku Wide-band  All-sky Monitor (WAM) which covers an
energy range of 50 keV - 5 MeV at 03:58:09.027 UT (=T0).

The observed light curve shows a multi-peaked structure starting at T0-1s,
ending at T0+65s with a duration (T90) of about 60 seconds.
The fluence in 100 - 1000 keV was 5.90 (+0.86/-0.84) x 10^-6 erg/cm^2.
The 1-s peak flux measured from T0s was 1.44 (+-0.23) photons/cm^2/s
in the same energy range.

Preliminary result shows that the time-averaged spectrum from T0-1s to
T0+65s is well fitted by a single power-law with a photon index
of 2.55 (+0.38/-0.29) (chi^2/d.o.f = 25.1/15).
All the quoted errors are at statistical 90% confidence level.

The light curves for this burst are available at:
http://www.astro.isas.jaxa.jp/suzaku/HXD-WAM/WAM-GRB/grb/trig/grb_table.html