GRB 070808

J. R. Cummings (NASA/UMBC), S. D. Barthelmy (GSFC),
P. A. Evans (U Leicester), N. Gehrels (NASA/GSFC),
S. T. Holland (CRESST/GSFC/USRA), J. A. Kennea (PSU),
H. A. Krimm (GSFC/USRA), V. Mangano (INAF-IASFPA),
F. E. Marshall (NASA/GSFC), K. L. Page (U Leicester),
D. M. Palmer (LANL), P. Romano (Univ. Bicocca & INAF-OAB),
G. Sato (GSFC/ISAS), M. Stamatikos (NASA/ORAU),
R. L. C. Starling (U Leicester), E. Troja (INAF-IASFPA),
T. N. Ukwatta (GSFC/GWU) and D. E. Vanden Berk (PSU) report on behalf
of the Swift Team:

At 18:28:00 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 070808 (trigger=287260).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 6.766, +1.166 which is 
   RA(J2000)  =  00h 27m 04s
   Dec(J2000) = +01d 09' 59"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a single FRED peak
structure with a duration of about 10 sec.  The peak count rate
was ~2000 counts/sec (15-350 keV), at ~0 sec after the trigger. 

The XRT began taking data at 18:29:54 UT, 114 seconds after the BAT
trigger. Using prompt downlinked data, we find a fading, uncatalogued
X-ray source located at RA, Dec: 6.7628, 1.1758 which is
   RA(J2000)  = 00 27 03.08
   Dec(J2000) = +01 10 32.7
with an uncertainty of 4.5 arcsec (radius, 90% containment). 
This location is 36 arcseconds from the BAT on-board position, within 
the BAT error circle. 

UVOT took a finding chart exposure of 100 seconds with the White (160-650 nm)
filter starting 118 seconds after the BAT trigger. No afterglow candidate has
been found in the initial data products. The 2.7' x 2.7' sub-image covers 100%
of the XRT error circle. The typical 3-sigma upper limit has been about 18.5 mag. 
No correction has been made for the expected extinction corresponding
to E(B-V) of 0.02 mag. 

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.)

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

ROTSE-IIIa, located at Siding Spring Observatory, Australia, responded to
GRB 070808 (Swift trigger 287260; J. R. Cummings et al., GCN 6718
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 ),
producing images beginning 7.6 s after the GCN notice time. An automated
response took the first image at 18:28:29.6 UT, 29.0 s after the burst,
under excellent conditions. We took 10 5-sec, 10 20-sec and 10 60-sec
exposures, with further exposures ongoing. These unfiltered images are
calibrated relative to USNO A2.0 (R). Imaging is on going.

Comparison to the DSS (second epoch) reveals no new sources within the 
3-sigma Swift/BAT error circle or the XRT error circle; the field is not 
crowded. Individual images have limiting magnitudes ranging from 
16.2-17.6; we set the following specific limits.

start UT       end UT      t_exp(s)   mlim   t_start-tGRB(s)  Coadd?
--------------------------------------------------------------------
18:28:29.6   18:28:34.6         5     16.2           29.0       N

Richard J. Cool (Arizona), Daniel J. Eisenstein (Arizona), David W. Hogg
(NYU), Michael R. Blanton (NYU), David J. Schlegel (LBNL), J. Brinkmann
(APO),
Donald Q. Lamb (Chicago), Donald P. Schneider (PSU), and Daniel E. Vanden
Berk
(PSU) report:

The Sloan Digital Sky Survey (SDSS) imaged the field of burst GRB070808
prior to the burst.  As these data should be useful as a pre-burst comparison
and for calibrating photometry, we are supplying the images and photometry
measurements for this GRB field to the community.

Data from the SDSS, including 5 FITS images, 3 JPGS, and
3 files of photometry and astrometry, are being placed at
http://mizar.as.arizona.edu/~grb/public/GRB070808

We supply FITS images in each of the 5 SDSS bands of a 8'x8' region centered
on the GRB position (ra=6.76600 (00:27:03.8), dec=1.16600 (01:09:57.6);
Swift-BAT TRIGGER 287260), as well as 3 gri color-composite JPGs (with
different stretches). The units in the FITS images are nanomaggies per pixel.
A pixel is 0.396 arcsec on a side. A nanomaggie is a flux-density unit equal
to 10^-9 of a magnitude 0 source or, to the extent that SDSS is an AB system,
3.631e-6 Jy.  The FITS images have WCS astrometric information.

In the file GRB070808_sdss.calstar.dat, we report photometry and astrometry
of 148 bright stars (r<20.5) within 15' of the burst location.  The
magnitudes
presented in this file are asinh magnitudes as are standard in the SDSS
(Lupton
1999, AJ, 118, 1406). Beware that some of these stars are not well-detected
in the u-band; use the errors and object flags to monitor data quality.

In the files GRB070808_sdss.objects_flux.dat and
GRB070808_sdss.objects_magnitudes.dat, we report photometry of 1167
objects detected within 6' of the GRB position.  We have removed saturated
objects and objects with model magnitudes fainter than 23.0 in the r-band.
The fluxes listed in GRB070808_sdss.objects_flux.dat are in nanomaggies
while the magnitudes listed in GRB070808_sdss.objects_magnitudes.dat are
asinh magnitudes.

All quantities reported are standard SDSS photometry, meaning that they are
very close to AB zeropoints and magnitudes are quoted in asinh magnitudes.
Photometric zeropoints are known to about 2% rms.  None of the photometry
is corrected for dust extinction.  The Schlegel, Finkbeiner, and Davis
(1998) predictions for this region are A_U=0.134 mag, A_g=0.098 mag, A_r =
0.071 mag, A_i=0.054 mag, and A_z=0.038 mag.

The file GRB070808_sdss.spectro.dat contains a list of the 21 objects with
SDSS spectroscopy within 6 arcminutes of the GRB position.  In addition to
the redshift and 1-sigma error for each object, this file also lists the
object spectroscopic classification.

SDSS astrometry is generally better than 0.1 arcsecond per coordinate.
Users requiring high precision astrometry should take note that the SDSS
astrometric system can differ from other systems such as those used in other
notices; we have not checked the offsets in this region.

More detailed information pertaining to our SDSS GRB releases can be found
in our initial data release paper (Cool et al. 2006, PASP 118, 733).  See the
SDSS DR4 documentation for more details: http://www.sdss.org/dr5.

These data have been reduced using a slightly different pipeline than that
used for SDSS public data releases.  We cannot guarantee that the values here
will exactly match those in the data release in which these data are
included.
In particular, we expect the photometric calibrations to differ by of order
0.01 mag.

This note may be cited, but please also cite the SDSS data release paper,
Adelman-McCarthy et al. (2006, ApJS, 162, 38), when using the data or
referring to the technical documentation.

M. Uemura, A. Arai, M. Sasada, M. Isogai, T. Uehara (Hiroshima Univ.),
and D. Nogami (Kyoto Univ.) report on behalf of the KANATA GRB team:

  We started optical imaging of the field of GRB070808 (GCN 6718
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 ) 
at 18:29:38 UT 8 Aug. using TRISPEC attached to the KANATA 
1.5-m telescope at Higashi-Hiroshima Observatory, Japan.  
Exposure times for Rc-band images are 30 sec.  

No new object was significantly detected.  
In our first image, a limit magnitude was estimated from 
neighbour USNO A2.0 stars as below:

18:29:53 UT 8 Aug.  20.5  Rc  

Follow-up observations are ongoing.

Y.Q. Lou, X.F. Wang, L.P. Xin, M.Zhai, Y.L. Qiu, J.Y. Wei, J.Y. Hu,
J.S. Deng, Y. Urata, and W.K. Zheng on behalf of EAFON report:

We have imaged the field of GRB 070808 (Cummings  et al., GCN 6718
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with the Xinglong TNT 80cm telescope. Observation started from
18:29:55, 115s after the burst with White and R band. No new
object was seen in our combined image within XRT error circle.
The 3 sigam limit is ~19.7 in our co-added White image derived
from USNO-A2.0, with mean time ~330s after the burst. Observation
is on going. 

This message may be cited.

A. Stefanescu (1), S. Duscha (1), G. Kanbach (1), F. Schrey (1), A.
Slowikowska (2)(3), H. Steinle (1) ((1)=MPE Garching, (2)=FORTH,
Heraklion (3)=NCAC, Torun) of the OPTIMA-Burst Team report the following:

OPTIMA-Burst at the 1.3m Skinakas Observatory, of the University of
Crete, Greece observed the location of the XRT error-circle of GRB
070808 (GCN Circ 6718
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 , J. R. Cummings et al.), starting at 2007-08-08
21:45:35 UT (3.3h after the burst).

We did not detect any source inside the XRT error-circle in 3 co-added
900s exposures in R-filter.

Our limit is as follows:

t-t_0 (mid-exp)       t_exp     R-limit
13229s (i.e. 3.7h)    2700s     22.0

E. Fenimore (LANL), L. Barbier (GSFC), S. D. Barthelmy (GSFC),
J. Cummings (GSFC/UMBC), N. Gehrels (GSFC), H. Krimm (GSFC/USRA), 
C. Markwardt (GSFC/UMD), D. Palmer (LANL), A. Parsons (GSFC),
T. Sakamoto (GSFC/ORAU), G. Sato (GSFC/ISAS), M. Stamatikos (GSFC/ORAU),
J. Tueller (GSFC), T. Ukwatta (GWU)
 
Using the data set from T-120 to T+218 sec from the recent telemetry 
downlink, we report further analysis of BAT GRB 070808 (trigger #287260)
(Cummings, et al., GCN Circ. 6718
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 ).  The BAT ground-calculated position 
is RA, Dec = 6.761, 1.180 deg which is 
   RA(J2000) = 0h 27m 2.6s 
   Dec(J2000) = 1d 10' 47" 
with an uncertainty of 1.2 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 47%.
 
The burst had a single FRED peak. T90 (15-350 keV) was 32 +- 3 sec 
(estimated error including systematics).
 
The time-averaged spectrum from T-0.7 to T+41.4 sec is best fit by a 
simple power-law model.  The power law index of the time-averaged 
spectrum is 1.47 +- 0.14.  The fluence in the 15-150 keV band was 
1.2 +- 0.1 x 10^-06 erg/cm2. The 1-sec peak photon flux measured from 
T+0.73 sec in the 15-150 keV band was 2.0 +- 0.2 ph/cm2/sec.  All the 
quoted errors are at the 90% confidence level.

R. Starling (U. Leicester) and J.R. Cummings (NASA/UMBC) report on behalf of 
the Swift XRT team:

We have analysed the first orbit and part of the second orbit of Swift XRT
data for GRB 070808 (trigger=287260; Cummings et al., GCN Circ. 6718
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 ),
covering 114-7500 s since BAT trigger.

Using 799 s of overlapping XRT Photon Counting mode and UVOT V-band
data, 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 (J2000) = 6.76402, 1.17635 deg, which is equivalent to:
RA (J2000):  00h 27m 3.36s
Dec (J2000): +01d 10' 34.8''
with an uncertainty of 1.9 arcsec (radius, 90% confidence).
This is 4.7 arcsec from the initial XRT position (GCN Circ. 6718
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 ) and 16.7 
arcsec from the BAT refined position (Fenimore et al. 2007, GCN Circ. 6724
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 ).

The 0.3-10 keV lightcurve shows a smooth and somewhat curved decay, which can
be modelled with a broken power law with alpha_1=3.5 +0.7/-0.2, T_bk=234 
+13/-20 s and alpha_2=1.06 +0.1/-0.08.

The PC mode spectrum from 500-7500 s since trigger can be modelled with an
absorbed power law with photon index Gamma=2.8 +/-0.5, and 
nH=(1.2 +0.5/-0.3)E22 cm^-2 in excess of the Galactic column of 3E20 
cm^-2. The 0.3-10 keV observed (unabsorbed) flux is 2.4E-12 (1.0E-11) 
erg/cm^2/s corresponding to a count rate of 4.5E-2 count/s and a count 
rate to flux conversion of 1 count/s = 5E-11 erg/cm^2/s.

Assuming the X-ray emission continues to decay with alpha=1.06, we predict a
count rate at T+24h of 9E-4 count/s.

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

A. Melandri, (Liverpool JMU), C. Guidorzi (Uni-Bicocca/INAF-OAB),
R.J. Smith, I.A. Steele, C.G. Mundell, M.J. Burgdorf, C.J. Mottram,
M.F. Bode, S.N. Fraser, S. Kobayashi, D.F. Bersier (Liverpool JMU),
A. Gomboc (Ljubljana), P. O'Brien, E. Rol, N. Bannister, N. Tanvir
(U. Leicester) report on behalf of larger GRB collaboration :


On 2007 Aug 08 at 18:30:21 UT the Faulkes Telescope South automatically
observed the field of GRB 070808 (trigger=287260, Cummings et al.,
GCN 6718
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 ).

On our coadded frames we do not detect any source inside the refined
XRT error circle (Starling et al., GCN 6725
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 ) down to a limiting
magnitude of


Filter  Tstart(min)  Tstop(min)    Exposure(s)   M_lim
---------------------------------------------------------
   R       2.35          62.9          960         20.6
   i'      5.55          53.4          700         20.5
---------------------------------------------------------

Magnitudes are calibrated with respect to USNOB1 R2 in the R filter.
For the SDSS-i' filter we used the magnitude derived from the
pre-burst calibration field of Cool et al. (GCN 6720
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 ).

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 070808 starting 119 s after
the BAT trigger (Cummings et al., GCN Circ. 6718
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 ).  We do not find a source
in any of the UVOT observations inside the refined XRT error circle
(Starling and Cummings, GCN Circ. 6725
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 ). The 3-sigma upper limits for detecting
a source in the first finding chart (FC) exposure and co-added frames are:

Filter            T_start(s)   T_stop(s)     Exp(s)     Mag (3-sigma UL)

white (FC)        119          218           98         >20.6
white             119          7539          628        >20.9
v                 225          6515          1051       >20.4
b                 704          7334          461        >20.5
u                 680          7129          490        >20.6
uvw1              655          6925          490        >20.3
uvm2              783          6720          452        >20.9
uvw2              734          7625          353        >20.8

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).