[vsnet-grb-info 6466] GRB 080723B: XMM-Newton observation

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  8078
SUBJECT: GRB 080723B: XMM-Newton observation
DATE:    08/08/08 20:16:55 GMT
FROM:    Jochen Greiner at MPI  <jcg at mpe.mpg.de>

G. Sala, J. Greiner, S. McBreen, T. Kruehler, P.M. Esquej (all MPE Garching, 
Germany) report:


XMM-Newton observed GRB 080723B detected by INTEGRAL (Gotz et al. 2008, 
#GCN 8002) and AGILE (Del Monte et al. 2008, GCN #8003), starting at
18:47:41 UT, on July 23, 2008, for an exposure of 62.5 ks (Schartel 2008, 
GCN 8005). The observation was affected by background radiation flaring, 
reducing the good exposure time to 54 ks. 
GRB 080723B is detected with an average count rate of 0.9, 0.3 and 0.01 cts/s 
in the EPIC-pn, MOS1/2 and RGS instruments, respectively. Here we report
on a refined position and the X-ray spectrum of the afterglow of GRB 080723B.

By identifying four X-ray sources in the FOV of the EPIC camera with 
counterparts from the 2MASS catalogue, we are able to register the X-ray
coordinate system, and obtain a best-fit  X-ray position of the afterglow
of GRB 080723B of RA = 176.83317, Decl. = -60.24096, equivalent to

RA  (2000.0) =  11 47 20.09
Dec (2000.0) = -60 14 28.6
  
with an uncertainty of 2.0 arcsec. This coincides perfectly with the X-ray 
position reported by Swift/XRT (Page 2008, GCN #8008), but reduces the
error circle by nearly a factor of two.
  
The X-ray flux during the XMM-Newton observation decays gradually, with no
noticable deviations from a power law of slope 1.50 +/-0.05, compatible
within the error with the flatter Swift/XRT decay (Page 2008, GCN #8009).
The spectrum averaged over the full observation (25.7 - 65.7 ks after the
GRB trigger) can be fitted by an absorbed power-law with photon index 
Gamma = 1.79 +/-0.02, and an equivalent hydrogen column of 
1.22(+/-0.02)*10^22 cm^-2, in excess of the catalogued Galactic column 
in this direction, 7.4*10^21 cm^-2 (Kalberla et al. 2005, AA 440, 775; 
Dickey & Lockman 1990, ARAA 28, 215).  Being at a Galactic latitude of 
1.6 deg, this difference may be due to clumpiness of foreground material 
relative to the spacing of the above HI surveys, rather than necessarily 
due to intrinsic extinction in the GRB host galaxy. The observed 0.3-10 keV 
flux during the XMM-Newton observation decreases from about 
1*10^-11 erg/cm^2/s (26 ks after burst trigger) to  
2.5*10^-12 erg/cm^2/s (65 ks post-burst). 

We thank Ignacio de la Calle, Nora Loiseau and Norbert Schartel from the 
XMM-Newton SOC (Villafranca, Spain) for scheduling and executing this 
observation.