Skip to main content
New Swift-BAT/GUANO and IceCube Notice Types Available! See news and announcements

GCN Circular 35064

Subject
GRB 231115A: Swift-XRT and Swift-UVOT observations
Date
2023-11-16T14:39:58Z (4 months ago)
From
Phil Evans at U of Leicester <pae9@star.le.ac.uk>
Via
email
J.P. Osborne (U. Leicester), B. Sbarufatti (INAF-OAB), A. D'Ai
(INAF-IASFPA), A. Melandri (INAF-OAR), J. D. Gropp (PSU), S. Dichiara
(PSU), J.A. Kennea (PSU), K.L. Page (U. Leicester), A.P. Beardmore (U.
Leicester) and P.A. Evans (U. Leicester) and S. R. Oates (Lancaster U.)
report on behalf of the Swift-XRT and the Swift-UVOT teams:

Swift-XRT has performed follow-up observations of the INTEGRAL-detected
burst GRB 231115A, which is likely not a GRB, but it is likely a MGF
(Burns GCN Circular 35038) and whose position is consistent with M82
galaxy (D'Avanzo et al. GCN Circ. 35036; Mereghetti et al. GCN Circ.
35037), collecting 4.4 ks of Photon Counting (PC) mode data between
T0+9.0 ks and T0+39.2 ks.

No uncatalogued X-ray sources have been detected consistent with being
within 303 arcsec of the INTEGRAL position. The 3-sigma upper limit in
the field ranges from ~0.002 to ~0.003 ct s^-1, corresponding to a
0.3-10 keV observed flux of 8.2e-14 to 1.2e-13 erg cm^-2 s^-1 (assuming
a typical GRB spectrum).

Six previously-catalogued X-ray sources have been detected consistent
with being within 303 arcsec of the INTEGRAL position, however their
status as catalogued objects makes them unlikely to be the X-ray
counterpart.

An uncatalogued object was detected, however this was too far from the
GRB position to be the	X-ray counterpart.

We note that the diffuse X-ray emission from the M82 galaxy affects a
significant fraction of the INTEGRAL error circle. This likely reduces
the sensitivity for source detection.

The results of the XRT-team automatic analysis of the XRT observations,
including a position specific upper limit calculator, are available at
https://www.swift.ac.uk/ToO_GRBs/00021625.

No optical counterpart consistent with the INTEGRAL position
(Mereghetti et al., GCN Circ. 35037) is detected in the initial UVOT
exposures.

Preliminary 3-sigma upper limits using the UVOT photometric system
(Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) are:

Filter	       T_start(s)   T_stop(s)	   Exp(s)	  Mag

w1		   9253
       39224	    4283	>17.4

The magnitude in the table is not corrected for the Galactic extinction

due to the reddening of E(B-V) = 0.155 in the direction of the burst
(Schlegel et al. 1998).



This circular is an official product of the Swift team.



Looking for U.S. government information and services? Visit USA.gov