[vsnet-grb-info 8561] GRB 091024: Swift-XRT team refined analysis
GCN Circulars
gcncirc at capella.gsfc.nasa.gov
Sat Oct 24 23:51:25 JST 2009
TITLE: GCN CIRCULAR
NUMBER: 10069
SUBJECT: GRB 091024: Swift-XRT team refined analysis
DATE: 09/10/24 14:51:19 GMT
FROM: Kim Page at U.of Leicester <kpa at star.le.ac.uk>
K.L. Page (U. Leicester) and F.E. Marshall (NASA/GSFC) report on behalf of
the Swift-XRT team:
Following an Earth-limb constraint, Swift-XRT began observing the field of
GRB 091024 at 09:49:13, about 53 minutes after the BAT trigger. We detect
a bright, uncatalogued X-ray source at a position of RA, Dec = 339.25167,
56.88928, which is equivalent to
RA (J2000): 22 37 00.40
Dec (J2000): 56 53 21.4
with an uncertainty of 6 arcsec (radius, 90% confidence). This is 6.1
arcsec from the optical afterglow candidate given by Mundell et al. (GCN
Circ. 10063) and 6.0 arcsec from the position given by Nissinen & Hentunen
(GCN Circ. 10064).
Only one orbit of data has been collected thus far (spanning 3.2-5.4 ks
after the burst), but the source does appear to be fading, albeit with a
relatively large uncertainty: alpha = 1.2 +/- 0.4.
The spectrum of the source, extracted from the 2.2 ks of Photon Counting
mode data, can be fitted by an absorbed power-law with Gamma = 1.70 +/-
0.17, the Galactic column of NH = 4.86 x 10^21 cm^-2 and an intrinsic
column of (2.3 +1.0/-0.9) x 10^22 at a redshift of 1.092 (Cucchiara, Fox &
Tanvir, GCN Circ. 10065). The observed (unabsorbed) flux over this time is
7.23 x 10^-11 (1.15 x 10^-10) erg cm^-2 s^-1, corresponding to a counts to
observed (unabsorbed) flux conversion of 7.5 x 10^-11 (1.2 x 10^-10) erg
cm^-2 count^-1.
If the source continues to fade with alpha ~ 1.2, the predicted count rate
at 24 hours will be 0.034 count s^-1, corresponding to an observed
(unabsorbed) flux of 2.6x10^-12 (4.1x10^-12) erg cm^-2 s^-1.
The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00373674.
This circular is an official product of the Swift-XRT team.
More information about the vsnet-grb-info
mailing list