GRB 100725A

C. B. Markwardt (CRESST/GSFC/UMD), J. M. Gelbord (PSU),
V. Mangano (INAF-IASFPA), K. L. Page (U Leicester),
D. M. Palmer (LANL), T. A. Pritchard (PSU) and
B. Sbarufatti (INAF-OAB/IASFPA) report on behalf of the Swift Team:

At 07:12:52 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 100725A (trigger=429954).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is RA, Dec 166.515, -26.688 which is 
   RA(J2000) = 11h 06m 04s
   Dec(J2000) = -26d 41' 14"
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 at least 40 sec.  The peak count rate
was ~3000 counts/sec (15-350 keV), at ~0 sec after the trigger. 

The XRT began observing the field at 07:14:09.1 UT, 76.7 seconds after
the BAT trigger. XRT found a bright, uncatalogued X-ray source located
at RA, Dec 166.4839, -26.6716 which is equivalent to:
   RA(J2000)  = 11h 05m 56.13s
   Dec(J2000) = -26d 40' 17.7"
with an uncertainty of 5.4 arcseconds (radius, 90% containment). This
location is 115 arcseconds from the BAT onboard position, within the
BAT error circle. No event data are yet available to determine the
column density using X-ray spectroscopy. 

The initial flux in the 2.5 s image was 1.32e-09 erg cm^-2 s^-1 (0.2-10
keV). 


UVOT took a finding chart exposure of nominal 150 seconds with the White filter
starting 84 seconds after the BAT trigger. No credible afterglow candidate has
been found in the initial data products. Data from the 2.7'x2.7' sub-image are
not available at this time. 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 0.05. 




Burst Advocate for this burst is C. B. Markwardt (Craig.Markwardt AT 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.)

P.A. Evans (U. Leicester) reports on behalf of the Swift-XRT team:

Using  promptly downlinked XRT event data for GRB 100725A, we find an
enhanced XRT position of the afterglow: RA, Dec: 166.4815, -26.6703
which is equivalent to:
   RA (J2000)  = 11 05 55.57
   Dec (J2000) = -26 40 12.9
with an uncertainty of 2.2 arc sec (radius, 90% confidence). Analysis
of the promptly available data is online at
http://www.swift.ac.uk/sper/429954.

Position enhancement is is described by Goad et al. (2007, A&A, 476,
1401) and Evans et al. (2009, MNRAS, 397, 1177).

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

D. Bersier, C. Guidorzi, Z. Cano, S. Kobayashi report on behalf of a 
larger collaboration:

We observed the location of GRB100725A (GCN 10979
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 ) with the Faulkes 
Telescope South,
starting at the beginning of the night (1.7 hour after trigger). In a 5 
minutes R-band
exposure, we do not detect any source not present on the DSS inside the 
enhanced XRT error
circle (GCN 10980
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 ). Any source at m=20.0 would have been clearly 
detected. The same holds
for a 6x5minutes exposure at a magnitude m=21.3.

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

Using 1441 s of XRT Photon Counting mode data and 1 UVOT
images for GRB 100725A, 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 = 166.48153, -26.67025 which is equivalent
to:

RA (J2000): 11h 05m 55.57s
Dec (J2000): -26d 40' 12.9"

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.

B. Sbarufatti (INAF OAB/INAF IASF-PA) , V. Mangano (INAF/IASF_PA)
and C. B. Markwardt (CRESST/GSFC/UMD) report on behalf of the
Swift-XRT team:

We have analysed 4.3 ks of XRT data for GRB 100725A (Markwardt	et al.
GCN Circ. 10979
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 ), from 82 s to 11.0 ks after the  BAT trigger. The data
comprise 177 s in Windowed Timing (WT) mode with the remainder in
Photon Counting (PC) mode. The light curve can be modelled with an
initial power-law decay with an index of alpha=1.1 (+/-0.1), followed
by a break at T+270 s to an alpha of 6.5 (+/-0.5). After a second break
at T+590 s the decay follows an index of alpha=0.9 (+0.3 -0.4).

The spectrum formed from the WT mode data can be fitted with an
absorbed power-law with a photon spectral index of 1.18 (+/-0.08).
The best-fitting absorption column is  1.2 (+/-0.3) x 10^21 cm^-2,
in excess of the Galactic value of 4.6 x 10^20 cm^-2 (Kalberla et al.
2005). The spectrum formed from the PC mode data can be fitted with
an absorbed power-law with a photon spectral index of 1.20 (+/-0.09).
The best-fitting absorption column is 8.9 (+10.0 -0.8) x 10^20 cm^-2,
marginally in excess of the Galactic value. The counts to observed
(unabsorbed) 0.3-10 keV flux conversion factor is 6.2 x 10^-11
(6.7 x 10^-11) ergcm^-2 count^-1.

If the light curve continues to decay with a power-law decay index of
0.9, the count rate at T+24 hours will be 2.4 x 10^-4 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.4 x
10^-14 (1.6 x 10^-14) erg cm^-2 s^-1.

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00429954.

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

D. M. Palmer (LANL), 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), T. Sakamoto (GSFC/UMBC), M. Stamatikos (GSFC/ORAU),
J. Tueller (GSFC), T. N. Ukwatta (GWU)
(i.e. the Swift-BAT team):
 
Using the data set from T-239 to T+903 sec from recent telemetry downlinks,
we report further analysis of BAT GRB 100725A (trigger #429954)
(Markwardt, et al., GCN Circ. 10979
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 ).  The BAT ground-calculated position is
RA, Dec = 166.468, -26.667 deg, which is 
   RA(J2000)  =  11h 05m 52.2s 
   Dec(J2000) = -26d 39' 59.9" 
with an uncertainty of 1.2 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 82%.
 
The mask-weighted light curve shows many overlapping peaks starting
at ~T-3 sec, with the highest peak at ~T+9 sec, and ending at ~T+200 sec.
T90 (15-350 keV) is 141 +- 27 sec (estimated error including systematics).
 
The time-averaged spectrum from T-4.8 to T+172.0 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.23 +- 0.12.  The fluence in the 15-150 keV band is 2.0 +- 0.1 x 10^-6 erg/cm2.
The 1-sec peak photon flux measured from T+8.58 sec in the 15-150 keV band
is 0.7 +- 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/429954/BA/

GRB 100725A: Swift/UVOT Upper Limits

T. A. Pritchard (PSU) and C. B. Markwardt (CRESST/GSFC/UMD)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 100725A
85 s after the BAT trigger (Markwardt et al., GCN Circ. 10979
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 ).
No optical afterglow consistent with the XRT position
(Evans et al., GCN Circ. 10985
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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            85          234          147 >20.7
u_FC               297          547          246 >20.3
white               85        11646         1486 >21.8
v                  626        13269         1202 >20.2
b                  552         7488          440 >20.6
u                  297         7353          736 >20.5
w1                 675         7148          510 >20.4
m2                 651         6942          510 >20.3
w2                 602        12552         1396 >21.2

The values quoted above are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.05 in the direction of the burst
(Schlegel et al. 1998).

F. Olivares E. (MPE Garching), S. Klose (Tautenburg), and J. Greiner
(MPE Garching) report on behalf of the GROND team:

GROND (Greiner et al. 2008, PASP 120, 405), the 7-channel imager
mounted at the 2.2m ESO/MPI telescope on La Silla, started follow-up
observations of GRB 100725A (Markwardt et al. 2010, GCN 10979
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 ) on July
25 at 23:05 UT (about 16 hrs after the trigger).

With a total integration time of 24.4 min in the optical and 20 min in
the nIR, we do not detect any source within the 1.8-arcsec XRT error
circle (Evans et al. 2010, GCN 10985
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 ) down to the following upper
limits (AB system):

g' > 22.8
r' > 23.3
i' > 23.1
z' > 22.9
J �> 21.7
H �> 21.1
K �> 20.4,

The given limits are calibrated againt GROND zeropoints and 2MASS
field stars and are not corrected for the Galactic foreground
extinction corresponding to a reddening of E(B-V)= 0.052 in the
direction of the burst (Schlegel et al. 1998).