GCN Circular 37746
Subject
GRB 241002B: Swift-XRT afterglow detection
Date
2024-10-09T09:51:52Z (5 months ago)
From
Phil Evans at U of Leicester <pae9@star.le.ac.uk>
Via
email
V. D'Elia (SSDC & INAF-OAR), B. Sbarufatti (INAF-OAB), J.A. Kennea
(PSU), D.N. Burrows (PSU), M. A. Williams (PSU), A.P. Beardmore (U.
Leicester), J.P. Osborne (U. Leicester), C. Salvaggio (INAF-OAB) and
P.A. Evans (U. Leicester) reports on behalf of the Swift-XRT team:
Swift-XRT has conducted further observations of the field of the
Fermi/GBM-detected burst GRB 241002B (GCN Circs. 37668 and 37711), also
detected by Swift-BAT GUANO (GCN Circ. 37704). The observations now
extend from T0+134.5 ks to T0+600.2 ks. The source previously reported,
"Source 4", is fading with 2.8 sigma significance and thus is believed
to be the GRB afterglow. Using 2711 s of PC mode data and 3 UVOT
images, we find an enhanced XRT position (using the XRT-UVOT alignment
and matching UVOT field sources to the USNO-B1 catalogue): RA, Dec =
328.32006, -58.94706 which is equivalent to:
RA (J2000): 21h 53m 16.81s
Dec(J2000): -58d 56' 49.4"
with an uncertainty of 3.2 arcsec (radius, 90% confidence). This
position is 3.2 arcsec from the position of candidate optical
counterpart GOTO24gpc/AT 2024xbg (GCN Circs. 37676 and 37694).
The light curve can be modelled with a power-law decay with a decay
index of alpha=0.9 (+0.6, -0.4).
A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.7 (+0.9, -0.7). The
best-fitting absorption column is 1.3 (+2.8, -0.9) x 10^21 cm^-2,
consistent with the Galactic value of 3.0 x 10^20 cm^-2 (Willingale et
al. 2013). The counts to observed (unabsorbed) 0.3-10 keV flux
conversion factor deduced from this spectrum is 4.6 x 10^-11 (5.3 x
10^-11) erg cm^-2 count^-1.
A summary of the PC-mode spectrum is thus:
Total column: 1.3 (+2.8, -0.9) x 10^21 cm^-2
Galactic foreground: 3.0 x 10^20 cm^-2
Excess significance: <1.6 sigma
Photon index: 1.7 (+0.9, -0.7)
The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00021721.
The results of the full analysis of the XRT observations are available
at https://www.swift.ac.uk/ToO_GRBs/00021721.
This circular is an official product of the Swift-XRT team.