GRB 090820

Valerie Connaughton (UAH) reports on behalf of the Fermi GBM Team:

"At 00:38:16.19 UT on 20 August 2009, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 090820027 (trigger 272421498 / 090820027).

The on-ground calculated location, using the GBM trigger
data, is RA = 87.7, DEC = 27.0 (J2000 degrees,
equivalent to 05h 51 m, 27 d 00 '), 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 108 degrees.

Although this burst was bright enough to result in a Fermi spacecraft
repointing maneuver and ensuing pointed observations of the burst
position, Earth avoidance constraints prevented such a maneuver
until 3100 sec after the burst trigger.

The light curve shows GBM triggered on a weak precursor,
followed by a bright pulse beginning 30 s later and lasting a
further 30 s.  The time-averaged spectrum from T0+28 s to T0+60 s
is best fit by a Band function with Epeak = 215 +/- 3 keV,
alpha = -0.69  +/- 0.01, and beta = -2.61 - 0.05.

The event fluence (8-1000 keV) in this time interval is
(6.6 +/- 0.1)E-5 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+34 s in the 8-1000 keV band
is about 58 ph/s/cm^2.

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

E. Gorbovskoy, V. Lipunov, V.Kornilov, A.Belinski, N.Shatskiy, N.Tyurina,
D.Kuvshinov, P.Balanutsa, V.V.Chazov, P.V.Kortunov, A.Kuznetsov
Sternberg Astronomical Institute, Moscow State University

K.Ivanov, S.Yazev
Irkutsk State University

A. Tlatov, A.V. Parhomenko,
Kislovodsk Solar Station of the Pulkovo Observatory

V.Krushinski, I.Zalognih, T.Kopytova
Ural State University, Kourovka


There are 6 MASTER Very Wide Field cameras located at Kislovodsk and Irkutsk 
with common FOW = 2000 + 1680 square degrees (http://observ.pereplet.ru/).

Four   MASTER Very Wide Field Cameras located at Kislovodsk
(4 Carl Zeiss Planar T* 85/1.4 ZF, 4x420 square degrees, 11 Mpx, 22" per 
pix  with 4 polarizers) responded to 
the bright  GRB 090820 (Fermi TRIGGER_NUM:272421498, V. Connaughton, GCN 
9829
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 ), producing images beginning 9 s after the GRB Time (first alert notice).

We took 1300 images with 5 sec exposition in different polarizations.
Individual images have limiting magnitudes~11.

Our unfiltered images are calibrated relative to Tycho stars (V) and very close 
to V band.
Other observations are required for independ error box elaboration.

The reduction is continued.

The message may be cited.

mailto: lipunov@sai.msu.ru

GRB 090820: RT-2 detection of a strong burst


S. K. Chakrabarti, A. Nandi, D. Debnath, T. C. Kotoch (ICSP, Kolkata, 
India), A. R. Rao, J. P. Malkar, M. K. Hingar, V. K. Agrawal (TIFR, Mumbai, 
India),  T. R. Chidambaram, P. Vinod, S. Sreekumar (VSSC, 
Thiruvananthapuram, India), Y. D. Kotov, A. S. Buslov, V. N. Yurov, V. G. 
Tyshkevich, A. I. Arkhangelskij, R. A.Zyatkov (MephI, Moscow, Russia) report:

The RT-2 Experiment onboard the CORONAS-PHOTON satellite has detected GRB 
090820 (FERMI, Trigger No.- 272421498, V. Connaughton, GCN 9829
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 ) which 
is     triggered at T0 = 00h 38m 16s (UT) (Onboard processor switch/toggle 
to Flare mode from Quiet mode). The satellite was in the GOOD/LIGHT mode  
with Earth latitude = -64.09 and longitude = 169.11. with GOOD time 
observation of 600 sec starting at 00h 29m 16sec (UT) and ending at 00h 39m 
16sec (UT). After 30 sec, the satellite completely entered into BAD mode of 
high charge particle region.

The GRB light curve shows a simple profile of a strong emission peak at 
T0+34 sec with a weak precursor (T0). The time duration of the brightest 
emission is around 19 sec with ~1100 cts/sec.
 
Both RT-2/S and RT-2/G detectors have registered this burst profile in the 
energy band of 15 - 1000 keV with strongest emission in the energy range of 
above 100 keV to 330 keV. It is also noted that the burst width decreases 
with the increase in the energy band, a quite natural phenomena of GRB burst 
profile. 

This analysis is preliminary. Analysis of time resolved spectral data is 
going on, however
the light curve is available at the web-site: 
http://csp.res.in/rt2_files/grb090820-lc.html