GRB 091003A

Arne Rau (MPE) reports on behalf of the Fermi GBM Team:

"At 04:35:45.58 UT on 03 September 2009, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 091003A (trigger 276237347 / 091003191).

The on-ground calculated location, using the GBM trigger
data, is RA = 251.1, DEC = 37.2 (J2000 degrees,
equivalent to 16h 44m, 37d 12'), with an uncertainty
of 1.0 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 13 degrees.

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

The GBM light curve consists of multiple peaks
with a duration (T90) of about 21.1 +/- 0.5s (8-1000 keV).
The time-averaged spectrum from T0-0.384s to T0+23.168s is
best fit by a Band function with Epeak = 486.2 +/- 23.6 keV,
alpha = -1.13 +/- 0.01, and beta = -2.64 +/- 0.24
(chi squared 851 for 611 d.o.f.).

The event fluence (8-1000 keV) in this time interval is
(3.76 +/- 0.04)E-05 erg/cm^2. The 1.024-sec peak photon flux measured
starting from T0+18.048 s in the 8-1000 keV band
is 31.8 +/- 0.4 ph/s/cm^2.

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

Julie McEnery (NASA/GSFC), Jim Chiang (SLAC) and Yoshitaka Hanabata  (Hiroshima) report on behalf of the Fermi LAT team:

At 04:35:45 (UT) on 03 Oct 2009, the Fermi Large Area Telescope (LAT) detected gamma rays from the long GRB 091003, which was triggered and located by the Fermi Gamma-ray Burst Monitor (GBM) (trigger 2756237347 / 091003191, GCN9983
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 ). The angle of the GBM best position (RA, Dec= 251.1, 37.2) with respect to the LAT boresight was ~13 degrees at the time of the trigger, which is close to the center of our field of view.

This burst was bright enough to initiate a Fermi spacecraft repointing maneuver resulting in 5 hours of pointed observations of the burst  position following the GBM trigger.

The data from the Fermi LAT shows a significant increase in the event rate after the GBM trigger that is spatially and temporally correlated with the GBM emission with high significance (>10 sigma).

The best LAT on-ground localization is found to be (RA, Dec = 251.39, 36.58) with a 90% containment radius of 0.21 deg (statistical; 68% containment radius: 0.15 deg, preliminary systematic error is less than 0.1 deg) which is consistent with the GBM localization.

A Swift TOO request has been issued.

Further analysis is ongoing.

The point of contact for this burst is

Julie McEnery : julie.mcenery@nasa.gov

The Fermi LAT is a pair conversion telescope designed to cover the energy band from 20 MeV to greater than 300 GeV. It is the product of an international collaboration between NASA and DOE in the U.S. and many scientific institutions across France, Italy, Japan and Sweden.

This message can be cited.

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

The long bright GRB 091003A (Fermi-GBM trigger 276237347 / 091003191:
Rau, GCN 9983
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 ) localized by Fermi-LAT (McEnery et al., GCN 9985
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 )
triggered Konus-Wind at T0=16543.801 s UT (04:35:43.801).

The burst light curve shows a multipeaked structure with a total
duration of ~23 s.

As observed by Konus-Wind the burst
had a fluence of 3.44(-0.19, +0.20)x10^-5 erg/cm2,
and a 16-ms peak flux measured from T0+18.592 s
of (1.68 +/- 0.32)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+26.880 s) is well fitted (in the 20 keV - 2 MeV
range) by a power law with exponential cutoff model:
dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep), with
alpha = -1.04 +/- 0.06,  and
Ep = 381(-36, +44) keV (chi2 = 58.4/61 dof).
Fitting by GRB (Band) model yields the same alpha and Ep,
and only an upper limit on the high energy
photon index: beta < -2.22 (chi2 = 56.2/60 dof).

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

The Konus-Wind light curve of this GRB is available
at http://www.ioffe.ru/LEA/GRBs/GRB091003_T16543/

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

The long GRB 091003A
(Fermi-GBM trigger 276237347 / 091003191 ; A. Rau et al., GCN 9983
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  ; J.
McEnery et al., GCN 9985
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 )
triggered the Suzaku Wide-band All-sky Monitor (WAM) which covers an
energy range of 50 keV - 5 MeV at 04:35:45.586 UT (=T0).

The observed light curve shows a multi-peaked structure
starting at T0-2 s and ending at T0+23 s, with a total duration (T90) of
about 21 s.

The fluence in 100 - 1000 keV was 1.98(-0.14, +0.08)x10-5 erg/cm2.
The 1-s peak flux measured from T0+18 s was 7.53(-1.28, +0.39)
photons/cm2/s in the same energy range.

Preliminary result shows that the time-averaged spectrum from
T0-2 s to T0+23 s is well fitted by a power-law with exponential cutoff
model:
dN/dE ~ E^{-alpha} * exp(-(2-alpha)*E/Epeak) with
alpha 1.19(-0.36, +0.29), and
Epeak 576(-72, +106) keV (chi2/d.o.f. = 21.5/24).

Due to the brightness of this burst, a 3% systematic error
was added for low energy channels.
All the quoted errors are at 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