GRB 070517

S. D. Vergani (DIAS-DCU), S. D. Barthelmy (GSFC),
A. P. Beardmore (U Leicester), D. N. Burrows (PSU),
S. Campana (INAF-OAB), M. M. Chester (PSU),
G. Cusumano (INAF-IASFPA), P. A. Evans (U Leicester),
N. Gehrels (NASA/GSFC), J. A. Kennea (PSU), H. A. Krimm (GSFC/USRA),
W. B. Landsman (NASA/GSFC), V. Mangano (INAF-IASFPA),
A. Moretti (INAF-OAB), P. T. O'Brien (U Leicester),
J. P. Osborne (U Leicester), K. L. Page (U Leicester),
D. M. Palmer (LANL), P. Romano (Univ. Bicocca & INAF-OAB),
G. Sato (GSFC/ISAS), B. Sbarufatti (INAF-IASFPA),
M. Stamatikos (NASA/ORAU), R. L. C. Starling (U Leicester),
G. Tagliaferri (INAF-OAB), E. Troja (INAF-IASFPA) and
H. Ziaeepour (UCL-MSSL) report on behalf of the Swift Team:

At 11:20:58 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 070517 (trigger=279494).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 277.579, -62.333 which is 
   RA(J2000)  =  18h 30m 19s
   Dec(J2000) = -62d 19' 56"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve shows two peaks
with a duration of about 10 sec.  The peak count rate
was ~1000 counts/sec (15-350 keV), at ~1 sec after the trigger. 

The XRT began taking data at 11:22:43 UT, 105 seconds after the BAT
trigger. The XRT on-board centroid algorithm did not find a source in
the image, but analysis of down-linked data yields a position:  
  RA(J2000) = 18h 30m 29.4s   
  Dec(J2000) = -62d 17' 50.8" 
with an uncertainty of 5.2 arcsec (radius, 90% containment). 
This position is  2.4 arcmin from the BAT position. 

The UVOT is unable to observe the field of GRB070517 due to the
presence of a 4th magnitude star 8 arcmin from the burst's location. 
The Galactic reddening in the direction of the burst is E(B-V) =
0.15.

A. C. Gilmore (Mt John Observatory of the University of Canterbury) reports:

A total of 1200 seconds clear CCD exposures of the GRB 070517 region were taken 
with the 1-m f/7.7 reflector at Mt John Observatory in poor (3.5") seeing . The 
exposure set was centred on May 17 14:01 UT, 2.7 hours after the burst. 
No new object was seen to the limit of DSS-2 infrared in a 5' x 5' region 
approximately centred on the revised position of Vergani et al at (J2000) RA 18h 
30m 30s  Dec -62d 17' 50".

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), S. D. Vergani (DIAS-DCU), on behalf of the Swift-BAT team:

Using the data set from T-239.4 to T+302.8 sec from the recent telemetry
downlink, we report further analysis of BAT GRB 070517
(trigger #279494)  (Vergani, et al., GCN Circ. 6411
Loading...
 
 ).  The BAT
ground-calculated position is RA, Dec = 277.603, -62.297 deg which is
    RA(J2000) = 18h 30m 24.7s
    Dec(J2000) = -62d 17' 49.8"
with an uncertainty of 1.9 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 67%. The mask-weighted light curve shows a
single peak lasting from approximately T+0 to T+10 seconds.
T90 (15-350 keV) is 9.0 +- 1 sec (estimated error including systematics).

The time-averaged spectrum from T-0.4 to T+10.6 is best fit by
a simple power-law model.  The power law index of the time-averaged
spectrum is 1.81 +- 0.24. The fluence in the 15-150 keV band is
2.6 +- 0.4 x 10^-07 erg/cm2. The 1-sec peak photon flux measured
from T+1.65 sec in the 15-150 keV band is 0.8 +- 0.2 ph/cm2/sec.
All the quoted errors are at the 90% confidence level.

S.D. Vergani (DIAS-DCU) and P. Romano (INAF-OAB) report
on behalf of the Swift Team:

We have analysed the first four orbits of Swift XRT data from GRB070517
(trigger number 279494, GCN Circ. 6411
Loading...
 
 ) for a total of 8.9ks.
The refined XRT position is

RA/Dec(J2000) = 18h 30m 29.0s   -62d 17' 51.7"  which is
RA/Dec(J2000) = 277.6207   -62.2977

with an uncertainty of 3.7 arcsec (radius, 90% containment).
This position lies 3.5 arcsec from the XRT position and 2.4 arcmin from
the BAT position given in GCN Circ. 6411
Loading...
 
  (Vergani et al.).

The XRT PC light curve of the firts four orbits presents a flaring behaviour.
A tentative fit with a power law gives a decay index alpha=0.4 +/- 0.1

The X-ray spectrum of the PC data can be fitted using an
absorbed power law (photon index = 1.95 +/-0.07) with an absorbed column
density fixed to the Galactic value (8.6e20 cm^-2; Dickey & Lockman,
1990). The absorbed (unabsorbed) 0.3-10.0keV flux for this spectrum
was 1.9E-12 (2.3E-12) ergs cm^-2 s^-1.

Assuming the source continues to decay at the same rate, we predict
an XRT count rate of 1.8E-2 counts/s at T+24 hours, which corresponds
to an observed flux of about 9E-13 ergs cm^-2 s^-1.

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

D.B. Fox (Penn State), P.A. Price (Hawaii), and E. Berger (Carnegie
Observatories) report:

"We observed the refined XRT localization (Vergani & Romano, GCN 6414
Loading...
 
 )
of GRB 070517 (Vergani et al., GCN 6411
Loading...
 
 ) with the Gemini South
telescope + GMOS-S, in a series of exposures beginning 03:23 UT on May
18, 2007.

Within the refined XRT localization we identify a point-like source at
coordinates R.A. 18:30:29.12, Dec -62:17:50.7 (uncertainty of <0.75"
in each coordinate).  This source is not present in DSS images of the
region, although at an estimated brightness of r'=22.1 mag, i'=22.0
mag it lies beyond the depth of that survey.  The source is detected
in all of our imaged filters, g', r', i', and z'.

We also identify a possible point-like source at coordinates
R.A. 18:30:29.07, Dec -62:17:52.3 (uncertainty of <1.0" in each
coordinate).  This source is detected in the i' and z' bands only,
with brightness i'~24.5 mag.

Further observations will be necessary to assess the variable /
afterglow nature of these sources."