GRB 080413

GRB 080413: ROTSE-III Detection of Optical Counterpart

E.S. Rykoff (UCSB), W. Rujopakarn (Steward), report on behalf of the ROTSE
collaboration:

ROTSE-IIIc, located at the H.E.S.S. site at Mt. Gamsberg, Namibia,
responded to GRB 080413A (Swift trigger 309096). The first image was at
02:54:39.7 UT, 20.4 s after the burst (6.7 s after the GCN notice time).
The unfiltered images are calibrated relative to USNO A2.0. We detect a
12.8 magnitude, fading source with coordinates:

19:09:11.8 -27:40:41.6 (J2000), with positional uncertainty of 1' or better

start UT mag mlim(of image)
----------------------------------
02:54:39.7 12.8 15.3


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/gsb309096_3c00_img.jpg Note that the object
marked 7 is the candidate in question.

Continuing observations are in progress.

A. P. Beardmore (U Leicester), D. N. Burrows (PSU),
P. A. Evans (U Leicester), N. Gehrels (NASA/GSFC),
S. T. Holland (CRESST/USRA/GSFC), S. D. Hunsberger (PSU),
J. A. Kennea (PSU), C. B. Markwardt (CRESST/GSFC/UMD),
K. L. Page (U Leicester), D. M. Palmer (LANL),
T. Sakamoto (NASA/UMBC), M. Stamatikos (NASA/ORAU) and
E. Troja (U Leicester/INAF-IASFPA) report on behalf of the Swift
Team:

At 02:54:19 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 080413 (trigger=309096).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 287.290, -27.679 which is 
   RA(J2000) = 19h 09m 10s
   Dec(J2000) = -27d 40' 44"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a triple-peaked
structure with a duration of about 55 sec.  The peak count rate
was ~10000 counts/sec (15-350 keV), at ~1 sec after the trigger. 

The XRT began observing the field at 02:55:20.0 UT, 60.7 seconds after
the BAT trigger. XRT found a bright, fading uncatalogued X-ray source
located at RA, Dec 287.2978, -27.6779 which is equivalent to:
   RA(J2000)  = 19h 09m 11.4s
   Dec(J2000) = -27d 40' 40.4"
with an uncertainty of 4.7 arcseconds (radius, 90% containment). This
location is 25 arcseconds from the BAT onboard position, within the BAT
error circle. No event data are yet available to assess possible
redshift constraints using X-ray spectroscopy and the nH-z relation
from Grupe et al. (2007). 


UVOT took a finding chart exposure of 100 seconds with the White (160-650 nm)
filter starting 76 seconds after the BAT trigger. There is a candidate
afterglow in the rapidly available 2.7'x2.7' sub-image at
  RA(J2000)  =	19:09:11.76 = 287.2990
  DEC(J2000) = -27:40:40.1  = -27.6778
with a 1-sigma error radius of about 0.6 arc sec. This position is 3.9 arc sec. 
from the center of the XRT error circle. The estimated magnitude is 15.2 with a
1-sigma error of about 0.5 mag. No correction has been made for the expected
extinction corresponding to E(B-V) of 0.16.

Klotz, A. (CESR-OMP), Boer M. (OHP), Atteia J.L. (LATT-OMP) report:

We imaged the field of GRB 080413 detected by SWIFT
(trigger 309096) with the TAROT robotic telescope (D=25cm)
located at the Calern observatory, France.

The observations started 21.8s after the GRB trigger
(8.3s after the notice). The elevation of the field increased from
from 11 degrees above horizon and weather conditions
were poor at the beginning of observations. The first
image showing stars started 480s after the trigger.

We detected the candidate couterpart mentioned by Rykoff
et al. (GCNC 7593) at the following position (+/- 2 arcsec):

RA(J2000.0) = 19h 09m 11.85s
DEC(J2000.0) -27d 40' 43.0"

Unfiltered magnitudes are:
t0+480s to t0+570s : R > 12.5
t0+1174s to t0+1263s : R = 15.0 +/- 0.2
t0+1470s to t0+1650s : R = 15.3 +/- 0.2
t0+2035s to t0+2215s : R = 15.5 +/- 0.2


Magnitudes were estimated with the nearby USNO-B1 stars
and are not corrected for galactic dust extinction.

N.B. Galactic coordinates are lon=  9.5236 lat=-15.8249
and the galactic extinction in R band is 2.4 magnitudes
estimated from D. Schlegel et al. 1998ApJ...500..525S.

This message may be cited.

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

Using 176 s of overlapping XRT Photon Counting mode and UVOT
data for GRB 080413, 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 = 287.29829, -27.67807 which is equivalent
to:

RA (J2000): 19h 09m 11.59s
Dec (J2000): -27d 40' 41.1"

with an uncertainty of 2.3 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
http://www.swift.ac.uk/xrt_positions/Goad.pdf), the current algorithm is an
extension of this method.

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