GRB 071104

GRB 071104: Gamma Ray Burst Localization by SuperAGILE

I. Donnarumma, Y. Evangelista, M. Feroci, E. Costa, E. Del Monte, 
I. Lapshov, F. Lazzarotto, L. Pacciani, M. Rapisarda, P. Soffitta
(INAF/IASF Rome), A. Giuliani, S. Vercellone, A. Chen, S. Mereghetti, A. 
Pellizzoni, F. Perotti, F. Fornari, M. Fiorini, P. Caraveo, 
A. Zambra (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), F. Mauri (INFN Pavia) and  P. Giommi, 
C. Pittori, L. A. Antonelli (ASDC) and L. Salotti (ASI),
on bhealf of the AGILE Team, report:

"SuperAGILE detected and localized a gamma ray burst 
on November 4th, at 11:41:23 UT. The event was approximately 
22 degrees off-axis. The observed duration in the 20-60 keV
energy range is about 12 seconds, with a time structure composed
of two main peaks. The burst was triggered and localized during
on ground data processing, since the onboard localization procedure
is not active yet.
The burst position was reconstructed as (RA, Dec) (295.600 deg, 
14.645 deg), which is:

RA(J2000) = 19h 42m 23.9s
Dec(J2000) = +14d 38' 42"

with an uncertainty of 8' 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.
The Minicalorimeter also detected the event up to the energy range 0.7-1.4 
MeV."

This message may be cited.

Swift-XRT started observing the field of view of the SuperAGILE burst GRB 
071104 (Donnarumma et al., GCN Circ. 7042
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 ), ~20.6 ks after the AGILE 
trigger. In the first 10 ks of data, we detect a clear, fading X-ray 
source at a position of RA, Dec (J2000) = 295.6117, +14.6104, which is 
equivalent to

RA(J2000)  = 19 42 26.81 
Dec(J2000) = 14 36 37.4

with an uncertainty radius of 4.2 arcsec (90% containment, including 
boresight uncertainties). This is 131 arcsec from the AGILE position, 
within their error circle.

Further analysis of these XRT data will be reported in a subsequent 
circular.

S. Immler (NASA/CRESST/GSFC) reports on behalf of the Swift
UVOT team:

Swift UVOT started observing the field of the SuperAGILE burst GRB
071104 (Donnarumma et al., GCN Circ. 7042
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 ), 20.6 ks after the AGILE
trigger. In the first 120-s and co-added 5037-s of data obtained in the 
white
filter, a possible UVOT afterglow candidate is found consistent with the
XRT position (Page, GCN 7043
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 ), with a magnitude of 20.6+/-0.1 mag,
overlaying the coincidence-loss structure of a nearby bright star.

The value quoted above is not corrected for the expected Galactic
extinction corresponding to a reddening of E_{B-V} = 0.54 mag in the
direction of the burst (Schlegel et al. 1998).

Further analysis is required due to possible contamination with the
coincidence-loss structure of the nearby star and the high source
density of the field in the Galactic plane.

K.L. Page (U Leicester) reports on behalf of the Swift-XRT Team:

Seven orbits (15.6 ks) of Swift-XRT data have now been obtained and 
analysed for the SuperAGILE burst GRB 071104 (Donnarumma et al., GCN Circ 
7042
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 ), all in Photon Counting mode. The XRT position was given in GCN 
Circ. 7043
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  and has not been further improved.

Although the X-ray light-curve can, to first order, be fitted by a single 
power-law, there is an indication that the decay has broken (around 43 ks 
after the trigger) from an initial slope of alpha ~ 0.6 to a steeper 
value of ~2.9, although this decay slope is not well-constrained because 
of the limited data after the break time (a 90% range of alpha = 0.5 - 5.3 
is estimated).

A spectrum formed from all the data (20.5 - 50.9 ks after the trigger) can 
be modelled with a power-law of Gamma = 1.9 +/- 0.3 absorbed by the 
Galactic column density of 2.69e21 cm^-2. (The 90% upper limit on this 
absorption is 4.9e21 cm^-2.) Over this period, the 0.3-10 keV observed 
flux is 1.1e-12 erg cm^-2 s^-1, with the unabsorbed value being 1.5e-12 
erg cm^-2 s^-1.

Using the range of possible decay slopes, the count-rate is expected to be 
between 0.018 and 7e-4 count s^-1 at 24 hours, corresponding to an 
observed flux range of between 1.0e-12 and 4.0e-14 erg cm^-2 s^-1 over 
0.3-10 keV (1.4e-12 - 5.4e-14 erg cm^-2 s^-1 unabsorbed).

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

L. A. Antonelli (INAF-OAR), E. Maiorano (INAF-IASF Bo), M. Pedani, L. 
Di Fabrizio, S. Marinoni (TNG) report on behalf the CIBO collaboration:

"We observed the field of the GRB 071104 detected by SuperAGILE 
(Donnarumma et al., GCN 7042
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 ) with the Telescopio Nazionale Galileo 
(TNG) [La Palma (Canary Islands)] equipped with NICS in the J and H 
bands. The observations were performed on 2 different epochs, Nov. 04 
and Nov 09 2007, just after the twilight in good seeing condition 
(<0.9").

First epoch observation started Nov 04 at 19:28 UT (about 7.8 hrs after 
the burst) and filters were  exposed for a total time of about 1200 s 
each. Two sources are clearly detected  within the XRT error circle 
(Page, GCN 7043
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 ) in both filters:

	Source	RA(J2000)	Dec.(J2000)    Jmag
	   S1         19:42:26.72	+14:36:36.9    18.8+/-0.2
	   S2	        19:42:26.82	+14:36:37.2    20.5+/-0.5

Calibrated against the 2MASS.

Second epoch observation started on Nov. 09 at 19:00 UT and the same 
filters were exposed for the same time under better seeing condition. 
The source S1 is still well detected at the same mag. On the contrary, 
source S2 is not detected down to a limiting magnitude of J > 21.7 (3 
sigma) strongly suggesting that this is the afterglow of GRB 071104.

This message may be cited.