GRB 100331B

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

"SuperAGILE detected a gamma ray burst on 31 March 2010, at 21:08:38 UT.
The event had a duration of about 30 s in the 20-60 keV energy range,
with a multi-peak structure. AGILE is currently operating in a  
spinning mode and the reported duration may be a lower limit to the  
GRB duration.

The burst position was reconstructed as (RA, Dec)
(302.987, -11.067) deg, which is:

RA(J2000)  = 20h 11m 56.95s
Dec(J2000) = -11d 04' 02.04"

with an uncertainty of 6' radius to account for possible systematics  
error due to the spinning mode.

The GRB is not detected by the AGILE/MCAL (above 350 keV) nor AGILE/GRID
(30 MeV - 30 GeV)."

This message may be cited.

V. D'Elia and G. Stratta (ASDC) report on behalf of the Swift Team:

Swift began a target of opportunity observation of the SuperAGILE detected
GRB 100331B (Del Monte et al., GCN #10560
Loading...
 
 ), at 14:38UT on April 1st, 2010,
about 17.5 hours after the SuperAgile detection.

We have analysed 2.1 ks of XRT data, �from 63152 s to 69.7 ks after  
the� � � � BAT trigger.
The data are entirely in Photon Counting (PC) mode. Using 1839 s of PC
mode data and 2 UVOT images, we find an enhanced XRT position (using
the XRT-UVOT alignment and matching UVOT field sources to the USNO-B1
catalogue): RA, Dec = 303.02160, -11.10810 which is equivalent to:

RA (J2000): 20 12 5.18
Dec(J2000): -11 06 29.0

with an uncertainty of 2.0 arcsec (radius, 90% confidence). This�
position lies 3.2 arcmins from the SuperAGILE reported position. We�
currently cannot confirm if this source is fading.

This circular is an official product of the Swift/XRT team.

----------------------------------------------------------------
This message was sent using IMP, the Internet Messaging Program.

M. A. Stark (PSU), G. Stratta (ASDC), E. A. Hoversten (PSU), and
M. H. Siegel (PSU) report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of the
SuperAGILE detected GRB 100331B about 17.5 hours after the SuperAGILE
detection (Del Monte et al., GCN #10560
Loading...
 
 ).  No optical afterglow
consistent with the XRT enhanced position reported by D'Elia & Stratta
(GCN #10562
Loading...
 
 ) is detected in the initial UVOT exposure.  Observations
were conducted using only the UVOT white filter, with a preliminary
3-sigma upper limit using the UVOT photometric system (Poole et
al. 2008, MNRAS, 383, 627) for the initial exposure of:

Filter         T_start(s)   T_stop(s)      Exp(s)         Mag
---------------------------------------------------------------
white            63371        64517          650         >21.21

The value quoted above is not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.12 in the direction of the burst
(Schlegel et al. 1998).

A. de Ugarte Postigo (INAF-OAB),  A.J. Castro-Tirado, J. Gorosabel,
M. Jelinek (IAA-CSIC), P. Kubanek (IPL UV, IAA-CSIC),
R. Cunniffe, S. Guziy (IAA-CSIC), P. Yock  (Auckland Univ.),
W.H. Allen (Vintage  Lane Obs.), I. Bond (Massey Univ.), G. Christie
(Stardome Obs.), report on behalf of a larger collaboration, report:

We have observed the field of the AGILE GRB 100331B
(Del Monte et al. GCN 10560
Loading...
 
 ) using the 0.6m Yock-Allen robotic
telescope (BOOTES-3) located in Blenheim, New Zealand.
A combined 36x60s unfiltered exposure with mean epoch 1st
April 2010 at 16:30 UT (19.2 hours after the burst) obtained through
cirrus does not show any source within the Swift/XRT error circle
(D'Elia et al. GCN 10562
Loading...
 
 ) down to a 3-sigma limiting magnitude
of R~18.5 using USNO-B1.0 as photometric reference.

Adria Updike (Clemson University), Paulo Afonso, and Jochen Greiner (both
MPE Garching) report on behalf of the GROND team:

We observed the field of GRB 100331B (SuperAGILE; Del Monte et al., GCN
#10560
Loading...
 
 ) simultaneously in g'r'i'z'JHK with GROND (Greiner et al. 2008,
PASP 120, 405) mounted at the 2.2 m MPI/ESO telescope at La Silla Observatory 
(Chile). Observations started at 09:31 UT on April 1, 2010, 12.37 hours after 
the GRB trigger, and a second epoch was taken beginning at 08:50 UT on April
2. They were performed at an average seeing of 1.0" and at an average
airmass of 1.3.

We do not detect a source within the Swift-XRT error circle reported by
D'Elia et al. (GCN #10562
Loading...
 
 ).  Upper limits from the first epoch are limited
to the NIR bands; the GROND observation was executed prior to the Swift/XRT
observation, and the XRT position turned out to be outside the FOV of our
optical channels.

On April 1, our upper limits were:
J > 21.5,
H > 21.0,
K > 20.2
from a total of 960 seconds of exposure time.

On April 2, our upper limits were:
g' > 24.6,
r' > 25.1,
i' > 24.5,
z' > 24.4,
J  > 22.6,
H  > 22.1 and
K  > 20.9
from a total of 2952 seconds of exposure in the optical bands and 2320
seconds in the NIR.

These limits are derived based on calibrating the images against GROND
zeropoints and 2MASS field stars and are not corrected for the Galactic
foreground extinction corresponding to a reddening of E_(B-V)= 0.12 in the
direction of the burst (Schlegel et al. 1998).