GRB 070309

S.D. Vergani (Dunsink observatory-DIAS, DCU), P. Romano
(INAF-OAB, Univ. Bicocca), C. Guidorzi (INAF-OAB, Univ. Bicocca)
report on behalf of the Swift-XRT team:

XRT observed again the field of INTEGRAL GRB 070309 (Paizis, et
al. 2007, GCN Circ. 6182
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 ) between 26 and 27 April (about 50
days after the trigger) for a total exposure time of about 17ks
to verify the nature of the afterglow candidate reported
by Vergani et al. in GCN Circ.'s 6187 and 6200.
There is no source detected at the afterglow candidate position
(RA(J2000) = 17h 34m 39.1s  Dec(J2000) = -37d 55' 48.2")
down to a count rate of 1.43E-3 counts/s (3 sigma).
We therefore confirm that the candidate suggested in GCN
Circ. 6187
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  is the afterglow of GRB 070309.

This Circular is an official product of the Swift XRT Team.

S.D. Vergani (Dunsink observatory-DIAS, DCU), P. Romano (INAF-OAB, Univ. 
Bicocca),
C. Guidorzi (INAF-OAB, Univ. Bicocca), A. Moretti (INAF-OAB) report on 
behalf
of the Swift-XRT team:

We continued to analyse the XRT data regarding the source reported by
Vergani et al. in GCN Circ. 6187
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 .
We collected a total of 21 counts for a total exposure time of about
17ks. It is not possible to extract a proper light curve or spectrum.
We divided the observations in two consecutive blocks, with exposures
of 7672 s and of 9623 s, collecting 16 and 5 counts, respectively.
In the assumption of a constant rate source, the probability of having
equally or less uniformly distributed counts is estimated to be smaller 
than 1%.
We conclude that this seems to be a varying source but at the present
time we cannot confirm that this is the X-ray afterglow of GRB070309.

This Circular is an official product of the Swift XRT Team.

S.D. Vergani (Dunsink observatory-DIAS, DCU),
P. Romano (INAF-OAB, Univ. Bicocca),
C. Guidorzi (INAF-OAB, Univ. Bicocca) report on behalf
of the Swift-XRT team:

We have analyzed the Swift XRT data from the first 11ks observations
of INTEGRAL GRB 070309 (Paizis, et al. 2007, GCN Circ. 6182
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 ).
Inside the INTEGRAL error circle we find one source at the position

RA(J2000) = 17h 34m 39.1s
Dec(J2000) = -37d 55' 48.2"

with an estimated error radius of ~5 arcsec (90% confidence).
This is 81 arcseconds from the INTEGRAL position.
The source has a count rate of (2.0+-0.6)E-3 counts/s and, assuming
a crab spectrum, a flux of 5E-14 erg/cm2/s. We collected a total of
15 counts. More data are being collected that will be used to determine
whether the source is fading and to perform a spectral analysis.

This Circular is an official product of the Swift XRT Team.

S. T. Holland (CRESST/USRA/GSFC) and Cucchiara A. (PSU) report on the
behalf of the Swift UVOT team:

     Swift/UVOT observed the field of GRB 070309 (Paizis, et al. 2007,
GCN Circ. 6182
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 ) starting 13,906 s after the INTEGRAL/IBAS trigger.
UVOT did not detect any source inside the INTEGRAL error circle,
relative to the DSS, down to the following 3 sigma upper limits.

Filter  t_start(s)  t_stop(s)  Exp(s)  Mag 3-sig UL

    V      14,525     14,868      274      19.3
    B      14,215     14,365      147      20.0
    U      14,061     14,211      147      19.7
  UVW1     13,906     14,056      147      19.6
  UVM2     14,930     15,080      147      19.5
  UVW2     14,371     14,446      147      19.8

These upper limits are not corrected for the Galactic extinction,
corresponding to a reddening of E_{B-V} = 1.46 mag (Schlegel et
al. 1998), in the direction of this burst.  We note that this
burst lies in the Galactic plane towards the Galactic centre and
the field is very crowded.

P. Roming (PSU) reporting on behalf of the Swift UVOT team:

The Swift UVOT team is currently uploading enhancements to the UVOT 
software. Due to the fact that the code load has not been completed, the 
UVOT generated finding charts in all the UVOT color filters for GRB 
070309 (GCN 6182
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 ). Although this is not normal operating procedure for 
the UVOT, we want to make the community aware that the finding charts 
are valid data for the field of the GRB. We apologize for any confusion 
the code load has created.

A.Paizis, S.Mereghetti (IASF-Milano), D.Gotz (CEA-Saclay), I.Kreykenbohm, 
N.Mowlavi, M. Beck (ISDC, Versoix), and J. Borkowski (CAMK, Torun) on 
behalf of the IBAS Localization Team report:

A GRB lasting about 40 s has been detected by IBAS in IBIS/ISGRI data on 
March 9 at 10:01:03 UT

The coordinates (J2000)  are:
RA:  263.6848 [degrees]
DEC: -37.9446 [degrees]

with an uncertainty of 2.5 arcmin (90% c.l.).

Preliminary analysis of the IBIS data indicates a peak flux of 0.2 
photons/cmq s (20-200 keV, 1 s integration time) and a fluence of 5x10e-7 
erg/cmq


A plot of the light curve will be posted at

http://ibas.mi.iasf.cnr.it/IBAS_Results.html

This message can be cited.