GRB 070810

J. R. Cummings (NASA/UMBC), S. D. Barthelmy (GSFC),
M. M. Chester (PSU), N. Gehrels (NASA/GSFC),
S. T. Holland (CRESST/GSFC/USRA), J. A. Kennea (PSU),
C. B. Markwardt (CRESST/GSFC/UMD), D. M. Palmer (LANL) and
M. Stamatikos (NASA/ORAU) report on behalf of the Swift Team:

At 02:11:52 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 070810 (trigger=287364).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 189.939, +10.744 which is 
   RA(J2000)  =  12h 39m 45s
   Dec(J2000) = +10d 44' 40"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a single peak
structure with a duration of about 20 sec.  The peak count rate
was ~2500 counts/sec (15-350 keV), at T+0 sec after the trigger. 

The XRT began taking data at 02:13:20 UT, 88 seconds after the BAT
trigger.  The XRT on-board centroid algorithm did not find a source in the
image. Using prompt downlinked data, we find a fading, X-ray source
located at RA, Dec 189.9629, 10.7513  which is
   RA(J2000)  =  12 39 51.10
   Dec(J2000) = +10 45 04.7
with an uncertainty of 3.9 arcsec (radius, 90% containment). This position
is 89 arcminutes from the BAT position. 

UVOT took a finding chart exposure of 100 seconds with the White
(160-650 nm) filter starting 92 seconds after the BAT trigger, and a
finding chart exposure of a nominal 400 seconds starting 198 seconds. 
A possible candidate has been identified visually in the initial data
products, but processing is still underway so no position or
significance is available at this time. The 2.7' x 2.7' sub-image
does not cover the XRT error circle; the 8' x 8' list of sources
covers 100% of the XRT error circle.  The typical 3-sigma upper limit
has been about 18.5 mag. 

No BAT_Position Notice was distributed, because none was received
from the TDRSS system.  This burst occurred during a 24-sec gap
in TDRSS coverage due to a hand-off from one TDRSS satellite to
the next satellite, so none of the initial notices were available
(BAT_Position, FOM, and SC_Slew). 

Burst Advocate for this burst is J. R. Cummings (jayc 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.)

H. Swan (U Mich), B. E. Schaefer (Louisiana State), E.S. Rykoff (U 
Mich), report on behalf of the ROTSE collaboration:

ROTSE-IIIb, located at McDonald Observatory, Texas, responded to GRB 
070810 (Swift trigger 287364). The first image was at 02:34:02.5 UT, 
1330.5 s after the burst. The unfiltered images are calibrated relative 
to USNO A2.0. We detect a 16.7 magnitude, fading source with coordinates:

      12:39:51.48      +10:45:00.90    (J2000).

The source is blended with a nearby USNO star visible in the DSS, and 
thus our initial positional uncertainty is ~3".

start UT    	mag     mlim(of image)
----------------------------------
02:29:53.4     16.7     18.5


This source is not visible in DSS (second epoch), 2MASS or the MPChecker 
database.

A jpeg image is available at 
http://www.rotse.net/images/gsb0174_3b01_img.jpg

Continuing observations are in progress.

M.M. Chester (PSU), F.E. Marshall (NASA/GSFC), and J.R. Cummings
(NASA/UMBC) report on behalf of the Swift UVOT team:

The Swift/UVOT observed the field of GRB 070810 (Cummings et al., GCN
Circ. 6733
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 ) beginning 02:13:24 UT, 92 seconds after the BAT trigger.

We find an uncatalogued source inside the Swift/XRT error circle in the
initial 2.7' x 2.7' subimage in the White filter at:

    RA(J2000)  = 12:39:51.22 = 189.9634
    DEC(J2000) = +10:45:04.3  = 10.7512

with a 1-sigma error radius of about 0.6 arc sec. This position is 1.9
arcsec from the center of the XRT error circle, and 5.0 arcsec from the
position reported by ROTSE (Swan et al. GCN Circ. 6734
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 ).  The
counterpart is not blended in the Swift/UVOT images.  The estimated
magnitudes (1-sigma error is about 1 mag) are:

Filter   Tstart    Exp     Magnitude
            (s)     (s)
White      92      100       17.4
v         198      306       17.1

The values quoted above are not corrected for the expected Galactic
extinction corresponding to a reddening of E_{B-V} = 0.02 mag in the
direction of the burst (Schlegel et al. 1998).

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

Using 505 s of overlapping XRT Photon Counting mode and UVOT
V-band data for GRB 070810, 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 = 189.96368, +10.75080 which is equivalent
to:

RA (J2000): 12d 39' 51.28"
Dec (J2000): +10h 45m 02.9s

with an uncertainty of 1.9 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, astro-ph/0708.0986
http://www.swift.ac.uk/xrt_positions/Goad.pdf).

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

K.L. Page, P.A. Evans (U. Leicester), M.M Chester (PSU) and J.R. Cummings 
(NASA/UMBC) report on behalf of the Swift-XRT team:

We have analysed the first four orbits of Swift-XRT data obtained for GRB 
070810 (Cummings et al., GCN Circ. 6733
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 ), totalling 7.9 ks of Photon 
Counting (PC) mode data. The enhanced XRT position was given by Evans et 
al. in GCN Circ. 6736
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 , and is 1.7 arcsec from the fading UVOT source 
(Chester et al., GCN Circ. 6735
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 ).

The X-ray light-curve is almost flat for the first orbit of PC data, with 
alpha = 0.30 +0.18/-0.20. About 1.1 ks after the trigger, the decay 
steepened to a slope of 1.1 +/- 0.2.

Fitting the PC data from the second to fourth orbits (i.e. after the 
break; 3.8-17.8 ks after the trigger), the spectrum can be modelled by an 
absorbed power-law with Gamma = 2.3 +/- 0.3 and NH = (1.3 +/- 0.5)e21 
cm^-2, in excess of the Galactic value of 1.75e20 cm^-2. The 0.3-10 keV 
observed (unabsorbed) flux during this time is 2.17e-12 (3.34e-12) erg 
cm^-2 s^-1.

If the decay continues with a slope of alpha ~ 1.1, the predicted count 
rate at 24 hours is 4.1e-3 count s^-1. Using a flux conversion factor 
(determined from the post-break spectrum described above) of 1 count s^-1 
~ 4e-11 erg cm^-2 s^-1 (observed) and 5.8e-11 erg cm^-2 s^-1 (unabsorbed), 
this corresponds to an observed (unabsorbed) flux of 1.6e-13 (2.4e-13) erg 
cm^-2 s^-1.

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

C. C. Thoene (DARK, UC Berkeley), D. A. Perley (UCB), J. Cooke (UC
Irvine), J. S. Bloom (UC Berkeley), H.-W. Chen (Univ. Chicago) and E.
Barton (UCI) report:

We took 2x10min spectra of the afterglow of GRB 070810 (GCN 6734
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 , Swan et
al.; GCN 6735
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 , Chester et al.) with Keck I + LRIS on Aug. 10, starting
05:46:32 UT (3.58h after the burst) in twilight. From a DLA and several
absorption lines including Fe II, OI, SiII and CII, we infer a redshift of
z=2.17 for that burst.

In addition, we obtained 2x120 s imaging in R band and 2x150 s in g band,
starting at 06:13:26 UT.
Calibrating relative to five USNO-B1.0 stars, we measure a magnitude of
R=20.45 +/- 0.5, dominated by the systematic uncertainty relative to the
catalog.

V. Lipunov, V.Kornilov, D.Kuvshinov,  A.Belinski, E.Gorbovskoy,
A.Krylov, N.Shatskiy, N.Tyurina,G.Borisov, A.Sankovich, V.Vladimirov, 
O.S.Shvartsman
Sternberg Astronomical Institute, Moscow Union 'Optic'

I.Zalozhnih
Ural State University


Sternberg Astronomical Institute, Moscow Union 'Optic'
MASTER  robotic system (http://observ.pereplet.ru) responded to 
GRB070810.8
(GRB_TIME is 2007-08-10 19:54:05.85).
The first image was at 2007-08-10 19:56:11 UT, 125.15  after the GRB
time
The unfiltered image is calibrated relative to USNO A2.0 (0.8 R + 0.2 B).
The robot not find OT-candidate in error box brighter then  14.8 (s/n=10).
The JPG-image will be  available at
http://observ.pereplet.ru/images/GRB070810.8/img/i12.jpg
The reduction is continuing.
This work is supported by RFFI  04-02-16411 grant.
This message can be cited.



Mailto: lipunov@sai.msu.ru