GRB 100725B

W. H. Baumgartner (GSFC/UMBC), M. M. Chester (PSU), V. D'Elia (ASDC),
J. M. Gelbord (PSU), S. T. Holland (CRESST/USRA/GSFC),
N. P. M. Kuin (UCL-MSSL), V. Mangano (INAF-IASFPA),
F. E. Marshall (NASA/GSFC), K. L. Page (U Leicester),
T. A. Pritchard (PSU), J. L. Racusin (NASA/GSFC),
B. Sbarufatti (INAF-OAB/IASFPA) and T. N. Ukwatta (GSFC/GWU) report on
behalf of the Swift Team:

At 11:24:34 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 100725B (trigger=429969).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 290.026, +76.955 which is 
   RA(J2000) = 19h 20m 06s
   Dec(J2000) = +76d 57' 17"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a multi-peaked
structure with a duration of about 160 sec.  The peak count rate
was ~3500 counts/sec (15-350 keV), at ~140 sec after the trigger. 

The XRT began observing the field at 11:25:52.4 UT, 77.9 seconds after
the BAT trigger. Using promptly downlinked data we find a bright,
uncatalogued X-ray source located at RA, Dec 290.03471, 76.95639 which
is equivalent to:
   RA(J2000)  = 19h 20m 8.33s
   Dec(J2000) = +76d 57' 23.0"
with an uncertainty of 4.3 arcseconds (radius, 90% containment). This
location is 9.1 arcseconds from the BAT onboard position, within the
BAT error circle. This position may be improved as more data are
received; the latest position is available at
http://www.swift.ac.uk/sper.  We cannot determine whether the source is
fading at the present time. 

A power-law fit to a spectrum formed from promptly downlinked event
data gives a column density in excess of the Galactic value (5.43e+20
cm^-2, Kalberla et al. 2005), with an excess column of 2.7
(+3.09/-2.62) x 10^21 cm^-2 (90% confidence). 

The initial flux in the 2.5 s image was 8.20e-09 erg cm^-2 s^-1 (0.2-10
keV). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 87 seconds after the BAT trigger. No credible afterglow candidate has
been found in the initial data products. The 2.7'x2.7' sub-image covers 100% of
the XRT error circle. The typical 3-sigma upper limit has been about 19.6 mag. 
The 8'x8' region for the list of sources generated on-board covers 100% of the
XRT error circle. The list of sources is typically complete to about 18 mag. No
correction has been made for the expected extinction corresponding to E(B-V) of
0.09. 

Burst Advocate for this burst is W. H. Baumgartner (wayne AT milkyway.gsfc.nasa.gov). 
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.)

D. Bersier, Z. Cano report on behalf of a larger collaboration:

The Faulkes Telescope North located in Hawaii automatically
responded to Swift trigger 429969 (GCN 10983
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 ) 104 seconds
after trigger, in poor seeing conditions. We do not detect
any source inside the XRT error circle to the following limits:

delta_T    exp time  lim mag   filter
1.75 min   10 sec    17.5      R
11 min     30 sec    18.0      R
17 min     60 sec    18.5      R
27 min     120 sec   18.0      i

M.R. Goad, J.P. Osborne, A.P. Beardmore and P.A. Evans (U. Leicester) 
report on behalf of the Swift-XRT team.

Using 702 s of XRT Photon Counting mode data and 1 UVOT
images for GRB 100725B, we find an astrometrically corrected X-ray
position (using the XRT-UVOT alignment and matching UVOT field sources
to the USNO-B1 catalogue): RA, Dec = 290.03298, +76.95643 which is equivalent
to:

RA (J2000): 19h 20m 7.92s
Dec (J2000): +76d 57' 23.1"

with an uncertainty of 1.8 arcsec (radius, 90% confidence).

This position may be improved as more data are received. The latest
position can be viewed at http://www.swift.ac.uk/xrt_positions. Position
enhancement is described by Goad et al. (2007, A&A, 476, 1401) and Evans
et al. (2009, MNRAS, 397, 1177).

This circular was automatically generated, and is an official product of the
Swift-XRT team.

GRB 100725B: Swift/UVOT Upper Limits

T. A. Pritchard (PSU) and W. H. Baumgartner (GSFC/UMBC)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 100725B
87 s after the BAT trigger (Baumgartner et al., GCN Circ. 10983
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 ).
No optical afterglow consistent with the XRT position
(Goad et al., GCN Circ. 10986
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 ) is detected in the initial UVOT
exposures.  Preliminary 3-sigma upper limits using the UVOT
photometric system (Poole et al. 2008, MNRAS, 383, 627) for the
first finding chart (FC) exposure and subsequent exposures are:

Filter         T_start(s)   T_stop(s)      Exp(s)         Mag

white(FC)           87          237          147 >20.8
u(FC)              300          549          246 >20.4
white               87         6844          664 >21.4
v                  629         5882          244 >19.6
b                  555         6703          432 >20.5
u                  300         6498          659 >20.2
w1                 678         6293          432 >20.3
m2                 653         6088          432 >20.1
w2                 605         5677          255 >20.1

The values quoted above are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.09 in the direction of the burst
(Schlegel et al. 1998).

V. Mangano (INAF IASF-PA), B. Sbarufatti (INAF OAB/INAF IASF-PA)
and W. H. Baumgartner (GSFC/UMBC) report on behalf of the Swift-XRT team:

We have analysed 10 ks of XRT data for GRB 100725B (Baumgartner et al.
GCN Circ. 10983
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 ), from 68 s to 58.8 ks after the BAT trigger. The data
comprise 288 s in Windowed Timing (WT) mode (the first 8 s were taken
while Swift was slewing) with the remainder in Photon Counting (PC)
mode. The light curve shows flaring activity for the initial 300 s (i.e. the
WT observation), then can be modeled with a series of power-law decays
and a small Gaussian flare.
The initial decay index is alpha=4.66 (+0.4 -0.2). The Gaussian flare peaks
at T+780 (+/-37) s with a sigma of 145 (+/- 30) s.
At T+770 s the decay change in a possible slow rise with an alpha of
0.30 (+/- 0.27) before breaking again at T+8660 s to a final
decay with index alpha=1.3 (+/- 0.2).

A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index    of 1.75 (+/-0.06). The
best-fitting absorption column is  4.7 (+0.4, -0.3) x 10^21 cm^-2,
in excess of the Galactic value of 5.4 x 10^20 cm^-2 (Kalberla et al.
2005). The PC mode spectrum (extracted from T+359 s to T+6761 s, 2.9 ks
exposure) has a photon index of 2.5 (+/-0.2) and a best-fitting absorption
column of 5.1 (+0.7, -0.6) x 10^21 cm^-2. The counts to observed (unabsorbed)
0.3-10 keV flux conversion factor deduced from this spectrum is
4.1 x 10^-11 (1.1 x 10^-10) erg cm^-2 count^-1.

If the light curve continues to decay with a power-law decay index of
1.3, the count rate at T+48 hours will be 4.3 x 10^-3 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of
1.8 x 10-13 (4.7 x 10-13) erg cm^-2 s^-1.

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00429969.

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

T. Sakamoto (GSFC/UMBC), S. D. Barthelmy (GSFC), W. H. Baumgartner (GSFC/UMBC),
J. R. Cummings (GSFC/UMBC), N. Gehrels (GSFC), H. A. Krimm (GSFC/USRA),
C. B. Markwardt (GSFC/UMD), D. M. Palmer (LANL), M. Stamatikos (GSFC/ORAU),
J. Tueller (GSFC), T. N. Ukwatta (GWU)
(i.e. the Swift-BAT team):
 
Using the data set from T-240 to T+609 sec from recent telemetry downlinks,
we report further analysis of BAT GRB 100725B (trigger #429969)
(Baumgartner, et al., GCN Circ. 10983
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 ).  The BAT ground-calculated position is
RA, Dec = 290.029, 76.955 deg, which is 
   RA(J2000)  =  19h 20m 07.0s 
   Dec(J2000) = +76d 57' 17.6" 
with an uncertainty of 1.2 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 28%.
 
The mask-weighted light curve shows several peaks starting at ~T-10 sec, peaking
at ~T+10, T+60, T+90, T+130, and T+220 sec, and ending at ~T+240 sec.
T90 (15-350 keV) is 200 +- 30 sec (estimated error including systematics).
 
The time-averaged spectrum from T-4.8 to T+226.1 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.89 +- 0.06.  The fluence in the 15-150 keV band is 6.8 +- 0.2 x 10^-6 erg/cm2.
The 1-sec peak photon flux measured from T+132.41 sec in the 15-150 keV band
is 2.4 +- 0.1 ph/cm2/sec.  All the quoted errors are at the 90% confidence
level. 
 
The results of the batgrbproduct analysis are available at
http://gcn.gsfc.nasa.gov/notices_s/429969/BA/

D. Kuroda, K. Yanagisawa, Y. Shimizu, H. Toda (OAO, NAOJ),
S. Nagayama (NAOJ), M. Yoshida (Hiroshima), K. Ohta (Kyoto)
and N. Kawai(Tokyo Tech)
report on behalf of the MITSuME collaboration:

We observed the field of GRB 100725B (Baumgartner et al. GCNC 10983)
with the optical three color (g', Rc and Ic) CCD camera attached
to the MITSuME 50cm telescope of Okayama Astrophysical Observatory.
The observation started on 2010-07-25 14:05:46 UT (~2.7 h after
the burst). We did not find any new point source within the XRT
error circle (Goad et al., GCNC 10986) in all the three bands.

Three sigma upper limits of the OT are listed below. We used SDSS
catalog for flux calibration.


T0+[day]   MID-UT   T-EXP[sec]    g'     Rc     Ic
------------------------------------------------------
0.13892    14:44:37  7620.0     >19.7  >19.3  >18.7
------------------------------------------------------
T0+ : Elapsed time after the burst [day]
T-EXP: Total Exposure time [sec]

J. C. Tello, R. S��nchez, M. Jel��nek, P. Kub��nek, S. Guziy,
A. J. Castro-Tirado (IAA-CSIC Granada) on behalf of a
larger collaboration report:

"Following the detection of GRB 100725B by Swift (Baumgartner et al.
GCNC 10983), we have obtained optical images with the 0.6m TELMA robotic
telescope at the BOOTES-2 station located in Southern Spain.

At the position of the X-ray afterglow detected by SWIFT/XRT (Goad et
al. GCNC 10986) we do not detect any optical source down to i' < 19 in
the co-added 187 images (60-s each, using an i' band filter, at 20:41 UT,
i.e. 9.3-hr after the onset of the burst).

This message can be quoted.

A. Volnova (SAI MSU), A. Pozanenko (IKI), B. Satovski (Astrotel), M.
Ibrahimov (MAO) report on behalf of  larger GRB  follow-up
collaboration:

We observed the field of the Swift GRB 100725B (Baumgartner et al.,
GCN 10983
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 ) with AZT-22 telescope of  Maidanak observatory in R-band on
Jul.25 between (UT) 16:36:55 - 17:51:54 under good waether conditions
(seeing 0.7"). We took 9 images with exposure 300 seconds. We do not
detect any sources in enhanced XRT error circle (Goad et al. GCN
10986
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 ). The upper limit (3 sigma) of stacked image is based on
SDSS-DR7 is the following:

t-t0,d	filter	exp., 	uplim
0.24295	R	9x300	22.7

E. Klunko (ISTP), A. Volnova(SAI MSU), A. Pozanenko (IKI) report on
behalf of larger GRB follow-up collaboration:

We observed the field of the Swift GRB 100725B (Baumgartner et al.,
GCN 10983
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 ) with AZT-33IK telescope of Sayan observatory (Mondy) on
Jul.25 between (UT) 16:36 - 20:18 under variable weather conditions
and mean seeing ~2.0". In the stacked image of the best of 36 images
we do not detect any sources in enhanced XRT error circle (Goad et al.
GCN 10986
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 ). The upper limit (3 sigma) of the stacked image based on
SDSS-DR7 field stars is the following:

t-t0,d	filter	exp.,s	uplim
0.31128	R	36*90	21.3