GRB 120821A

S.Mereghetti (IASF-Milano), D.Gotz (CEA, Saclay), C.Ferrigno, R.Boissay 
(ISDC, Versoix), and J.Borkowski (CAMK, Torun) on behalf of the IBAS 
Localization Team report:

a long gamma ray burst lasting about 12 s has been detected by IBAS in the 
IBIS/ISGRI data at 13:23:45 UT of August 21

Its refined   coordinates (J2000) are:

RA:   255.2692    [degrees]
DEC:  -40.5212   [degrees]

with an uncertainty of 2 arcmin (90% c.l.).

The burst has a fluence of about  3e-7 erg/cm2  (20-200 keV)

A plot of the light curve will be  posted at
http://ibas.iasf-milano.inaf.it/IBAS_Results.html








=====================================================================
Sandro Mereghetti        INAF - Istituto di Astrofisica Spaziale
                                 e Fisica Cosmica - Milano
Tel. +39-02-23699323
Fax  +39-02-2666017       via Bassini 15, I-20133 Milano, ITALY

sandro@iasf-milano.inaf.it 
http://www.iasf-milano.inaf.it/~sandro/personal.html
===========================================================================

P. Schady (MPE Garching), S. Klose (TLS Tautenburg) and J. Greiner (MPE
Garching) report on behalf of the GROND team:

We observed the field of GRB 120821A (INTEGRAL trigger #6266; Mereghetti
et al., GCN #13696
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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 MPG/ESO telescope at La
Silla Observatory (Chile).

Observations started at 23:47 UT, 10.4 hours after the GRB trigger. They
were performed at an average seeing of 1.1" and at an average airmass of
1.0.

The GROND JHK observations fully covered the INTEGRAL error circle,
whereas the g'r'i'z observations covered ~60% of the error circle. We do
not detect any obvious new source brighter than the detection limits of
DSS2 and 2MASS within the area covered by the 2arcmin INTEGRAL error
circle.

S. R. Oates (MSSL-UCL) and P. D'Avanzo (INAF-OAB)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 120821A
15ks after the INTEGRAL trigger (Mereghetti et al., GCN Circ. 13696
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 ).
No optical afterglow consistent with the INTEGRAL position
(Mereghetti et al., GCN Circ. 13696
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 ) 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

u                17059        17241          179         >20.92
w1               16153        17053          886         >21.7
m2               15246        16146          886         >21.6

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 25.4 in the direction of the burst
(Schlegel et al. 1998).

P. D'Avanzo, A. Melandri, S. Campana (INAF-OAB) report on behalf of the
Swift team:

The Swift XRT observed the error circle of the INTEGRAL-detected GRB
120821A (Mereghetti et al, GCN Circ. 13696
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 ) from 15.2 to 17.2 ks after the
trigger. The data comprise 2.0 ks of Photon Counting (PC) mode data. No
clear afterglow candidate is detected. We note however the presence of a
very faint and low-significance source within the INTEGRAL error circle
(Mereghetti et al, GCN Circ. 13696
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 ) at the following position: RA, Dec
=255.25762, -40.51365 which is equivalent to:

RA (J2000): 17h 01m 01.83s
Dec (J2000): -40d 30' 49.1"

with an uncertainty of 6.7 arcsec (radius, 90% confidence).

The source has a count rate of (4.5 +/- 2.1) x 10^-3 cts/s. This
corresponds to an observed 0.3-10 keV flux of (2.7 +/- 1.2) x 10^-13
erg/cm2/s (assuming a typical GRB spectrum with photon spectral index of
2). If we consider the Galactic absorption in this direction (1.1 x 10^22
cm^-2; Kalberla et al. 2005) this corresponds to an unabsorbed flux of
(5.5 +/- 2.5) x 10^-12 erg/cm2/s. Given the limited statistics, it is not
possible to determine whether the source is fading.