V. D'Elia (SSDC & INAF-OAR), A. D'Ai (INAF-IASFPA), B. Sbarufatti
(PSU), D.N. Burrows (PSU), J. D. Gropp (PSU), K.L. Page (U. Leicester),
A.P. Beardmore (U. Leicester), A. Melandri (INAF-OAB) and P.A. Evans
(U. Leicester) report on behalf of the Swift-XRT team:
Swift-XRT has performed follow-up observations of the INTEGRAL-detected
burst GRB 210406A (Mereghetti et al. GCN Circ. 29767), collecting 5.1
ks of Photon Counting (PC) mode data between T0+169.5 and T0+244.5 ks.
One uncatalogued X-ray source has been detected consistent with being
within 148 arcsec of the INTEGRAL position, it is below the RASS limit
and shows no definitive signs of fading. Therefore, at the present time
we cannot confirm this as the afterglow. Details of this source are
RA (J2000.0): 132.4988 = 08:49:59.72
Dec (J2000.0): +76.5289 = +76:31:44.0
Error: 6.4 arcsec (radius, 90% conf.)
Count-rate: (1.28 [+0.75, -0.56])e-3 ct s^-1
Distance: 35 arcsec from INTEGRAL position.
Flux: (1.46 [+0.86, -0.64])e-13 erg cm^-2 s^-1 (observed, 0.3-10 keV)
An uncatalogued source was also detected, however this was too far from
the GRB position to be the afterglow.
No X-ray source is detected at the position of the optical afterglow
candidate reported by Belkin et al. (GCN Circ. 29775) down to a 3sigma
upper limit of 1.4e-3 ct s^-1.
The results of the XRT-team automatic analysis of the XRT observations,
including a position-specific upper limit calculator, are available at
This circular is an official product of the Swift-XRT team.