GRB 080825B

Y. Evangelista, P. Soffitta, E. Del Monte, I. Donnarumma, M. Feroci, 
F. Lazzarotto, L. Pacciani, E. Costa, I. Lapshov, M. Rapisarda
(INAF/IASF Rome), A. Giuliani, S. Vercellone, A. Chen,
S. Mereghetti, A. Pellizzoni, F. Perotti, F. Fornari, P. 
Caraveo (INAF/IASF Milan), A. Bulgarelli, F. Gianotti,
M. Trifoglio, G. Di Cocco, C. Labanti, F. Fuschino, M. Marisaldi,
M. Galli, (INAF/IASF Bologna), M. Tavani, G. Pucella, F. D'Ammando, V. 
Vittorini, A. Argan, A. Trois (INAF/IASF Rome), G. Barbiellini,
F. Longo (INFN Trieste), P. Picozza, A. Morselli (INFN Roma-2),
M. Prest, E. Vallazza (Universita` dell'Insubria), P. Lipari,
D. Zanello (INFN Roma-1), and  P. Giommi, C. Pittori, B. Preger,
P. Santolamazza, F. Verrecchia (ASDC) and L. Salotti (ASI), 
on behalf of the AGILE Team, report:

"SuperAGILE detected a gamma ray burst on 25 August 2008, at 17:46:40 UT. 
The event was approximately 10 degrees off-axis, with a duration of about 
50 s in the 20-60 keV energy range, with a multi-peaked structure.
The burst position was reconstructed  as (RA, Dec) 
(209.281 deg, -68.943 deg), which is:

RA(J2000)  = 13h 57m 07.42s
Dec(J2000) = -68d 56' 34.0"

with an uncertainty of 3' radius. The given uncertainty accounts
for both the statistical and systematic errors.

An analysis of the AGILE Gamma Ray Imager (GRID) data is in progress."

This message may be cited.

Christina C. Thoene (DARK/NBI), Antonio de Ugarte Postigo (ESO) and Davide
Ricci (Univ. of Liege) report:

We observed the complete 3' error box of the SuperAGILE GRB 080825B
(Evangelista et al., GCN 8133
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 ) using the Danish 1.54m + DFOSC at La
Silla (Chile) starting Aug. 25 at 23:18:31 UT (5.53 hours after the
burst). In the first I-band frame we detect a new source not present
in the DSS-2 catalogue at the following coordinates (J2000.0 +/-
0.7"):

RA: 13:56:48.22
DEC: -68:57:18.5

for which we measure an I-band magnitude of 17.4 +/- 0.2 as compared
to several USNO-B1 stars.

A finding chart can be found at:
http://www.sc.eso.org/~adeugart/GRB/080825/080825.jpg

Further observations and analysis are ongoing to establish the connection
to the GRB and the fading of the object.

C. Pagani reports on behalf of the Swift-XRT team:

We have analyzed the Swift XRT data on the field of the AGILE detected GRB
080825B (Evangelista et al., GCN Circ. 8133
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 ), consisting of 7.5 ks of Photon
Counting data collected from T0+44 ks to T0+78 ks.

We detect a point source at the position of the optical afterglow (Thoene et
al., GCN Circ. 8135
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 ). During the XRT observations the source faded from an
initial count rate of 0.05 counts/s to a later count rate of 0.01 counts/s.

The spectrum from the PC data can be fitted by an absorbed power law model with
photon index of 2.1 and the absorption consistent with the Galactic value along
the line of sight (2.10e21 cm^-2, Kalberla et al. 2005).  The average observed
(unabsorbed) flux of the PC mode data is 5.8e-13 (9.0e-13) ergs cm^-2 s^-1.

This Circular is an official product of the Swift-XRT team.

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

The most intense part of the GRB 080825B localized by SuperAGILE 
(Evangelista et al., GCN 8133
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 ) triggered Konus-Wind
at T0=64012.487 s UT (17:46:52.487).

The burst light curve shows a weak emission starting at ~T0-70s,
the main multipeaked part (from ~T0-5s to ~T0+15s), and an extended 
emission seen up to ~T0+40s.

As observed by Konus-Wind the burst
had a fluence of 7.81(-0.70, +0.83)x10^-6 erg/cm2,
and a 256-ms peak flux measured from T0-0.080 s
of 1.21(-0.31, +0.32)x10^-6 erg/cm2/s
(both in the 20 keV - 1 MeV energy range).

The spectrum of the most intense part
(from T0 to T0+16.640 s) is well fitted (in the 20 keV-1 MeV range)
by a power law with exponential cutoff model:
dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep)
with alpha = -1.13(-0.36, +0.40),
and Ep = 72(-9, +11) keV (chi2 = 40.0/51 dof).
Fitting by GRBM (Band) model yields:
the low-energy photon index is alpha = -1.05(-0.38, +0.56),
the high energy photon index beta < -2.52,
the peak energy Ep = 71(-9, +11) keV (chi2 = 38.8/50 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.rssi.ru/LEA/GRBs/GRB080825_T64012/

We used the spectral parameters of GRB 080825B
provided by Golenetskii et al. (GCNC 8142) to compute
the spectral pseudo-redshift(**) of this burst localized
by SuperAGILE (Evangelista et al., GCN 8133
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 ).

We find a pseudo-redshift pz= 0.83 � 0.30


(**) cf. http://www.ast.obs-mip.fr/grb/pz

P. J. Brown (PSU) reports on behalf of the Swift/UVOT team:

The Swift/UVOT observed the field of GRB 080825B
starting about 45 ks after the SuperAGILE detection
(Evangelista et al., GCN Circ. 8133
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 ).  We do not detect
the optical afterglow seen by Thoene et al. (GCN Circ. 8135
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 )
in any of the UVOT filters down to the following 3 sigma
upper limits.

Filter  T_start(s) T_stop  Exp(s)   MagLimit
white   49916      50823   885      >22.1
uvw2    44237      78448   1903     >21.5
uvm2    61477      67242   988      >20.8
uvw1    67248      73020   1036     >20.9
u       73027      73522   483      >20.8
b       49004      49911   885      >21.2
v       45144      61472   1234     >20.5

The above magnitudes are not corrected for the Galactic extinction
corresponding to a reddening of E(B-V) ~ 0.25 mag (Schlegel et al.,
1998, ApJS, 500, 525).  The photometry is on the UVOT photometric
system described in Poole et al. (2008, MNRAS, 383,627).