GRB 120908A

M. Morii (Tokyo Tech), K. Yamaoka (Waseda U.), H. Negoro (Nihon U.),
S. Ueno, H. Tomida, S. Nakahira, M. Ishikawa (JAXA),
T. Mihara, M. Sugizaki, M. Serino, T. Yamamoto, J. Sugimoto, M. Matsuoka (RIKEN), 
N. Kawai, R. Usui, K. Ishikawa, T. Yoshii (Tokyo Tech),
A. Yoshida (AGU), H. Tsunemi, M. Kimura (Osaka U.),
M. Nakajima, M. Asada, N. Serita (Nihon U.),
Y. Ueda, K. Hiroi, M. Shidatsu, R. Sato (Kyoto U.),
Y. Tsuboi, M. Higa (Chuo U.),
M. Yamauchi, Y. Nishimura, T. Hanayama, K. Yoshidome (Miyazaki U.), 
report on behalf of the MAXI team:

MAXI/GSC triggered a bright uncatalogued X-ray transient source at UT 2012-09-08T22:35:13.
Assuming that the source flux was constant over the transit,
we obtain the source position at 

(R.A., Dec) = (230.64 deg, -25.79 deg) = (15 22 32, -25 47 42) (J2000)

with a statistical 90% C.L. elliptical error region
with long and short radii of 0.46 deg and 0.31 deg, respectively.
The position angle of long axis is -30 deg.
There is an additional systematic uncertainty of 0.1 deg (90% containment radius).

The preliminary flux of the transient source was 78 +- 19 mCrab (4 - 10 keV).
There was no significant detection at the transit location in the
previous and the next orbit (92 min before and after the detection)
with an upper limit of 20 mCrab.
There is no known bright X-ray source at the detected position.

Follow-up observations are encouraged.

S. Immler (CRESST/GSFC/UMD), C. Pagani (U. Leicester), and
A. A. Breeveld (MSSL-UCL) report on behalf of the Swift team:

Swift began a Target of Opportunity observation of the MAXI/GSC
discovered burst GRB 120908A (Morii et al. GCN 13731
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 ) at 2012-09-09
13:41:43 UT.

We have analyzed 3.7 ks of XRT data, starting ~54 ks after the MAXI
trigger. The data are entirely in Photon Counting mode, centered on
the MAXI position and partially covering the MAXI error region.
No new source is detected in the XRT data. The 3-sigma upper limit
is 0.004 counts/sec which is 2.4e-13 erg cm^-2 s^-1 for a typical GRB
spectrum.

The Swift/UVOT began settled observations of the field 54.4 ks after
the MAXI trigger (Morii et al., GCN Circ. 13731
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 ). No optical afterglow
consistent with the MAXI position given in that circular is detected
in the initial UVOT exposures. 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            54383        66117         2345         >21.7

The magnitude in the table is not corrected for the Galactic
extinction due to the reddening of E(B-V) = 0.23 in the direction of
the burst (Schlegel et al. 1998).

Sinead McGlynn (MPE/TUM)
reports on behalf of the Fermi GBM Team:

"At 22:31:00.02  UT on 08 September 2012, the Fermi Gamma-Ray Burst Monitor triggered and located GRB 120908A (trigger 368836263/120908938). GBM was triggered over 4 minutes earlier than the bright X-ray source reported as a MAXI/GSC detection by Morii et al. (GCN 13731
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 ). 

The on-ground GBM location is consistent with the MAXI/GSC reported location. As a result, and due to the presence of extended soft emission in the GBM data at the time of the MAXI/GSC detection, we associate the GBM trigger with GRB 120908A.

The angle from the Fermi LAT boresight is 87 degrees.

The GBM light curve consists of two spiky pulses with a duration (T90) of about 66  s (50-300 keV).
The time-averaged spectrum from T0-5.38 s to T0+15.1 s is best fit by a power law function with an exponential
high-energy cutoff.  The power law index is -1.21 +/- 0.11 and the cutoff energy, parameterized as Epeak, is 205.9 +/- 43.1 keV. In addition, weak longer-lived soft emission is observed close to the MAXI trigger time (200-300s post GBM trigger) up to approximately 50 keV.

The event fluence (10-1000 keV) in this time interval is (1.7 +/- 0.2)E-05 erg/cm^2. The 1-sec peak photon flux measured starting from T0+6 s in the 10-1000 keV band is 2.7 +/- 0.2 ph/s/cm^2.

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

Weikang Zheng and Carl Akerlof (Umich), report on behalf of the ROTSE
collaboration:

We analyzed Fermi/LAT data of GRB 120908A (Morii et al., GCN 13731
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 )
and GRB 120909A (Immler et al., GCN 13727
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 )
as a follow-up of routine search in Swift trigger catalogs in our LAT
data processing pipeline using both the matched filter technique
(Akerlof et al. 2010, ApJ, 725, L15; 2011 ApJ, 726, 22; 2012,
arXiv:1205.3066; Zheng et al. 2012, ApJ 745,72; ApJ, 756, 64)
and likelihood method. We do NOT detect high energy photon emission
from both methods in the two GRBs.

A standard data selection method is applied when extracting the LAT
photon data with energy E > 100 MeV, and a duration of T0 - T0+47.5s
after the trigger. A zenith angle cut of <105 degree is applied to
all photons.

For GRB 120908A, the burst location was about 72 degrees from the
LAT boresight, and the zenith angle was about 64 degrees at trigger time.
Using the likelihood method, we estimated the upper limit in LAT energy
range (0.1 - 10 GeV) is 8.3e-09 (photons cm^-2 s^-1) by assuming a
spectral index of -2.2.
The pipeline result of GRB 120908A is given in the following link:
http://www.rotse.net/LAT/SwiftTriggers/368836516/

For GRB 120909A, the burst location was about 65 degrees from the
LAT boresight, and the zenith angle was about 98 degrees at trigger time.
Using the likelihood method, we estimated the upper limit in LAT energy
range (0.1 - 10 GeV) is 2.0e-08 (photons cm^-2 s^-1) by assuming a
spectral index of -2.2.
The pipeline result of GRB 120909A is given in the following link:
http://www.rotse.net/LAT/SwiftTriggers/368847726/