GRB 090625B

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

A long GRB with duration of about 11 s has been detected by IBAS in 
IBIS/ISGRI data at 13:26:21 UT on June 25th.

The refined coordinates (J2000)  are:

 RA:    2.2626 [degrees]
 DEC: -65.7816 [degrees]

with an uncertainty of 1.7 arcmin (90% c.l.).

A preliminary analysis gives a peak flux in the 20-200 keV range of  
about 2 ph/cmq/s (1 s integration time) and a fluence over the same energy
range of about  1.5e-6 erg/cmq.

A plot of the light curve will be posted at

http://ibas.iasf-milano.inaf.it/IBAS_Results.html

This message can be cited.

J. Mao (INAF-OAB), D. N. Burrows (PSU), E. A. Hoversten (PSU),
J. A. Kennea (PSU), K. L. Page (U Leicester), M. A. Stark (PSU) and
R. L. C. Starling (U Leicester) report on behalf of the Swift Team:

Swift executed a Target of Opportunity observation 
of the INTEGRAL GRB 090625B, slewing to the 
burst at 14:24 UT. 

XRT observations began at 14:30:13.  The observation begins too late 
after the burst for us to determine whether any sources in the field 
of view are fading.  However, we find a faint X-ray source located at
RA,Dec = 2.2618, -65.7803 which is equivalent to:

RA  (J2000.0) =  00 09 2.83
DEC (J2000.0) =  -65 46 49.2

with an uncertainty of 4.1 arcsec (radius, 90% containment). 

UVOT observations are being made, but data will not be available until
a ground downlink. 

Burst Advocate for this burst is J. Mao (jirong.mao AT brera.inaf.it). 
Please contact the BA by email if you require additional information
regarding Swift followup of this burst. In extremely urgent cases, after
trying the Burst Advocate, you can contact the Swift PI by phone (see
Swift TOO web site for information: http://www.swift.psu.edu/too.html.)

C. Guidorzi (U. Ferrara), D. Bersier (Liverpool JMU), P. O'Brien,
N. Tanvir (U. Leicester) on behalf of a large collaboration report:

On 2009 June 25 at 13:28:21 UT the 2-m Faulkes Telescope South
automatically began observing the INTEGRAL GRB 090625B
(Gotz et al., GCN Circ. 9572
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 ).

Observations started 120 seconds after the IBAS trigger time and
were performed using the B, V, R and i' filters. We could not find any
uncatalogued object inside the XRT error circle (Mao et al., GCN Circ.
9573
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 ) down to the following limiting magnitudes:

For single frames:

Mid Time   Exposure  Filter   Limit
  (s)       (s)              (mag)
-------------------------------------
141         3x10      R       > 19.3
526           10      i'      > 18.5
-------------------------------------

For coadded frames:

Time Range Exposure  Filter   Limit
  (min)     (s)               (mag)
-------------------------------------
22.5-45.2    420      R       > 21.0
25.4-48.2    420      i'      > 20.3
-------------------------------------

Calibration was performed using a few USNOB1 nearby stars, adopting
R2 and I values.

T. Kruehler, F. Olivares, and J. Greiner (all MPE Garching) report on behalf
of the GROND team:

We observed the field of GRB 090625B (Gotz et al., GCN #9572
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 )
simultaneously in g'r'i'z'JHK with GROND (Greiner et al. 2008, PASP 120,
405) mounted at the 2.2m MPI/ESO telescope at La Silla Observatory
(Chile).

Observations started on 26 June 2009 at 03:58 UT, 14.5 hours after the
burst, continued until 05:58 UT and were performed under variable sky
conditions. In stacked images of 75 min total integration time in griz and
60 min in JHK, we do not detect any object within the XRT error circle
(Mao et al., GCN #9573
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 ), down to the following limiting magnitudes (all in
the AB system):

g' > 23.6
r' > 23.8
i' > 23.1
z' > 22.7
J  > 21.5
H  > 21.0
K  > 20.5

These upper limits were derived using USNO-B1 and 2MASS field stars as
reference. No correction has been made for the Galactic foreground
extinction corresponding to E(B-V) of 0.02 mag (Schlegel et al., 1998).

J. Mao, R. Margutti (INAF-OAB) and C. Guidorzi (U. Ferrara) report
on behalf of the Swift-XRT team:

We have analyzed the first three orbit data (6.9 ks exposure) of the
Swift ToO observation of the INTEGRAL burst GRB 090625B (Gotz, GCN
Circ. 9572
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 ).

Swift-XRT observations started at 14:30:13 UT (Mao et al. GCN Circ. 9573
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 ),
4ks from trigger.

The source is fading with a best fit simple power law model index
of alpha= 0.6+/- 0.3, confirming its nature of X-ray afterglow.

A spectrum extracted from PC mode data can be modelled with an
absorbed power-law, with Gamma = 3.3 +1.1/-0.8 and NH = (3.7
+2.2/-1.7)x1021 cm^-2. The Galactic column in this direction is
2.1 x 1020 cm-2 (Kalberla et al. 2005).

The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor
deduced from this spectrum is 2.8 x 10-11 (1.8 x 10-10) erg cm-2 count-1.

If the light curve continues to decay with a power-law decay index of 0.6,
the count rate at T+24 hours will be 6.3x10-3 count s-1, corresponding to
an observed (unabsorbed) 0.3-10 keV flux of 1.8x10-13 (1.1x10-12) erg 
cm-2 s-1.

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

[GCN OPS NOTE(26jun09): Per author's request, "Cristiano" was replaced
with "Guidorzi".]

S. T. Holland (CRESST/GSFC/USRA) and J. Mao (INAF-OAB)
report on the behalf of the Swift UVOT team:

       The Swift/UVOT observed the field of GRB 090625B starting 3679 s
after the INTEGRAL/IBAS detection (Gotz, et al., 2009, GCN
Circ. 9572
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 ).  We do not find any new source, relative to the DSS,
USNO-B1.0, or 2MASS at the position of the XRT afterglow (Mao, et
al. 2009, GCN Circ. 9573
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 ).  Preliminary 3-sigma upper limits for
detecting a source in the co-added images are

Filter   T_start    T_stop   Exp(s)      Mag
--------------------------------------------
v           3679      5007       318   >20.0
b           4192    11,398       413   >20.8
u           3987    67,218      6439   >21.7
uvw1        5218    17,045      1781   >21.5
uvm2        5012    16,139      1082   >21.0
uvw2        4602      4802       197   >20.1
white       3828      4596       344   >21.8
--------------------------------------------

The quoted upper limits have not been corrected for the expected
Galactic extinction along the line of sight corresponding to a
reddening of E_{B-V} = 0.02 mag (Schlegel, et al., 1998, ApJS, 500,
525).  All photometry is on the UVOT photometry system described in
Poole et al. (2008, MNRAS, 383, 627).

Arne Rau (MPE) reports on behalf of the Fermi GBM Team:

"At 13:26:22.51  UT on 25 June 2009, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 090625B (trigger 267629184 / 090625560)
which was also detected by the INTEGRAL (Goetz et al. 2009, GCN 9572
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 ).
The GBM on-ground location is consistent with the INTEGRAL position.
 
The angle from the Fermi LAT boresight is 125 degrees.

The GBM light curve consists of a single pulse
with a duration (T90) of about 13.6 s (8-1000 keV).
The time-averaged spectrum from T0-2.048 s to T0+6.144 s is
well fit  by a power law function with an exponential
high energy cutoff.  The power law index is -0.9 +/- 0.2 and
the cutoff energy, parameterized as Epeak, is 165 +/- 28 keV
(chi squared 429 for 453 d.o.f.).

The event fluence (8-1000 keV) in this time interval is
(1.04 +/- 0.13)E-06 erg/cm^2. The 1.024-sec peak photon flux measured
starting from T0+3.072 s in the 8-1000 keV band
is 1.87 +/- 0.09 ph/s/cm^2.

A Band function fits the spectrum equally well (chi squared 424 for 454 
d.o.f.)
with Epeak= 100 +/- 32 keV, alpha = -0.4 +/- 0.5, and beta -2.0 +/- 0.2.

The spectral analysis results presented above are preliminary;
final results will be published in the GBM GRB Catalog."