GRB 091117A

J. R. Cummings (GSFC/CRESST),
V. Pal'shin (Ioffe Inst.),
K. Yamaoka (Aoyama Gakuin U.),
P. Evans (U. Leicester)
on behalf of the Swift-BAT, Konus-Wind, and Suzaku-WAM teams


The Suzaku WAM alerted the IPN to a short hard burst that occurred at
17:44:29 UT on November 17th.  The burst was seen in detector rates
with Suzaku, Konus-Wind, INTEGRAL SPI ACS, and Swift-BAT.  A source
was found in ground analysis of BAT data (trigger 376211) at 12% coding.
The BAT ground position was RA, Dec 30.945, -16.944, which is

RA (J2000) 02h 03m 46.9s
Dec (J2000) -16d 56' 38.0"

with an estimated 90% containment radius of 2.6 arcmin.

As seen in BAT, the burst had a weak precursor at T0, and the main spike
at T+2.7 sec. The precursor was about 0.12 sec and the main spike was
about 0.4 seconds long. The BAT peak count rate was about
700 counts/0.064 sec in the 15-350 keV band.

There is an AGN 2.5 arcmin from this position, 2MASX J02035665-1656585
at z = 0.092.

The BAT position is inside the error box of a triangulation performed
using Konus-Wind, BAT, Suzaku-WAM, and INTEGRAL-SPI-ACS data.

A Swift TOO observation has been requested and approved.

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

The short hard GRB 091117A (localized by Swift-BAT and IPN,
Cummings et al., GCN 10171
Loading...
 
 ) triggered Konus-Wind
at T0=63869.513 s UT (17:44:29.513).

The burst light curve consists of a single peak with a total
duration of ~0.3 s. The Konus-Wind light curve of this GRB
is available at http://www.ioffe.ru/LEA/GRBs/GRB091117_T63869/

As observed by Konus-Wind the burst
had a fluence of 1.9(-0.5, +0.7)x10-6 erg/cm2,
and a 16-ms peak flux measured from T0
of 1.4(-0.4. +0.7)x10-5 erg/cm2/s
(both in the 20 keV - 2 MeV energy range).

The time-integrated spectrum of the burst
(from T0 to T0+0.256 s) can be fitted
(in the 20 keV - 5 MeV range) by a power law
with exponential cutoff model:
dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep)
with alpha = -0.42(-0.41, +0.64),
and Ep = 663(-225, +396) keV (chi2 = 29/23 dof).

Fitting by GRB (Band) model yields the same alpha
and Ep values with the high energy photon index
beta = -9.4 (< -1.9).

All the quoted results are preliminary.
All the quoted errors are at the 90% confidence level.

A. Breeveld (MSSL/UCL), M. De Pasquale (MSSL/UCL) and J. R. Cummings 
(GSFC/UMBC) report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 091117A 
96767s (~27 hours) after the BAT trigger (Cummings et al., GCN Circ. 
10171
Loading...
 
 ). The galaxy described by Berger and Mulchaey (GCN Circ. 10174
Loading...
 
 ) 
as being a possible host, is clearly seen as an extended object in the 
UVOT data. There is no evidence of a fading source at either of the 
two XRT source positions (D'Elia et al., GCN Circ. 10177
Loading...
 
 ) when 
compared with data taken ~47 hours after the burst. In the case of 
source 1, which is coincident with the spiral galaxy, we checked for 
fading using an aperture of 2" at the refined XRT position as well as 
using an aperture of 8" to contain the whole galaxy.

Magnitudes measured with a non-standard 8" aperture to include the 
whole galaxy, using the UVOT photometric system (Poole et al. 2008, 
MNRAS, 383, 627), for the initial summed exposures are:

Filter         T_start(s)   T_stop(s)      Exp(s)         Mag

white            97197       113850          875         17.56 � 0.01
v               109296       109642          340         17.05 � 0.06
u                96767       119064         2614         17.60 � 0.02

Upper limits (3 sigma) obtained at the position of source 2 (D'Elia et 
al., GCN Circ. 10181
Loading...
 
 ) are as follows:

white            97197       113850          875         21.89 (UL)
v               109296       109642          340         19.72 (UL)
u                96767       119064         2614         21.52 (UL)


None of the values quoted above are corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.03 in the direction of the burst
(Schlegel et al. 1998).

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

The short GRB 091117A (Swift/BAT Detected in ground analysis ; Cummings et al.,
GCN 10171
Loading...
 
 ) triggered the Suzaku Wide-band  All-sky Monitor (WAM) which covers an 
energy range of 50 keV - 5 MeV at 2009-11-17 17:44:25.253 UT (=T0). 

The observed light curve shows a single peak starting at T0 s, ending 
at T0+1 s with a duration (T90) of about 0.4 seconds.
The fluence in 100 - 1000 keV was 1.54 (-0.26/+0.25) x10^-6 erg/cm^2. 
The 1-s peak flux measured from T0 s was 2.78 (-0.30,+0.37) photons/cm^2/s 
in the same energy range.

Preliminary result shows that the time-averaged spectrum from T0 s to 
T0+1 s is well fitted by a single power-law with a photon index 
of 1.29 (-0.13,+0.13) (chi^2/d.o.f. = 42/33).

All the quoted errors are at statistical 90% confidence level,
in which the systematic uncertainties are not included.

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