GRB 081016A, GRB 081016

P.A. Evans (U. Leicester) reports on behalf of the Swift-XRT team:

Swift-XRT reobserved the field of the INTEGRAL GRB 081016A (Gotz  et al.
GCN Circ. 8377
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 ) 5.2 days after the trigger, obtaining 3.8 ks of data in
Photon Counting (PC) mode. The source seen in the earlier XRT
observation (Evans, GCN Circ. 8379
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 ) was no longer detected. A
three-sigma upper limit on the count rate is 4.7e-3 counts/sec,
significantly below the level of the previous detection (0.03
counts/sec). We therefore confirm that this was the afterglow of
GRB 081016A.

A spectrum formed from the first XRT observation, totalling 2 ks in PC
mode, can be modelled with an absorbed power law with photon index
2.60 (+0.94, -0.81). The absorption column is consistent with the
Galactic value of 1.7e21 cm^-2 (Kalberla et al 2005). The counts to
observed (unabsorbed) flux conversion factor is 1.1e-12 (3.0e-12) erg
cm^-2 ct^-1.

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

P.A. Evans (U. Leicester) reports on behalf of the Swift-XRT Team

We have obtained 2 ks of XRT Photon Counting mode data of GRB 081016 (Gotz 
et al. GCN Circ. 8377
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 ), beginning 20.4 ks after the INTEGRAL trigger. We 
find an uncatalogued X-ray source at RA,Dec, 255.57032, -23.33556 which is 
equvialent to:

RA (J2000.0):  17 02 16.88
Dec (J2000.0): -23:20:08.0

with an estimated uncertainty of 3.6" (radius, 90% confidence). This 
position is 21" from the INTEGRAL position, within the INTEGRAL error 
circle. It is not currently possible to determine whether this source is 
fading. Further observations are planned.

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

D.Gotz (CEA-Saclay), S.Mereghetti, A.Paizis (IASF-Milano), S. Soldi, 
V.Beckmann, M. Beck, M. Tuerler (ISDC, Versoix), and J. Borkowski (CAMK, 
Torun) on behalf of the IBAS Localization Team report:

A GRB lasting about 34 s has been detected by IBAS in IBIS/ISGRI data at 
06:51:31 UT of October 16. 

The coordinates (J2000) are:

RA = 255.5725 [degrees]
DEC= -23.3301 [degrees]

with an uncertainty of 1.5 arcmin (90% c.l.).

The burst is composed by two distinct peaks, and a preliminary spectral 
analysis gives a peak flux in the 20-200 keV range of about 2.4 
ph/cmsq/s (1-s integration time) and a fluence over the same energy range 
of about 1.8x10e-6 erg/cmsq. Due to data gaps caused by telemetry 
saturation these values should be considered as lower limits.

A plot of the light curve will be posted at

http://ibas.iasf-milano.inaf.it/IBAS_Results.html

This message can be cited.