P. D'Avanzo (INAF-OAB), J.A. Kennea (PSU), B. Sbarufatti
(INAF-OAB/PSU), D.N. Burrows (PSU), J.P. Osborne (U. Leicester), K.L.
Page (U. Leicester), A.P. Beardmore (U. Leicester), V. D'Elia (ASDC),
A. D'Ai (INAF-IASFPA) and P.A. Evans (U. Leicester) report on behalf of
the Swift-XRT team:
Swift-XRT has performed follow-up observations of the MAXI-detected
burst GRB 190404C (Yamada et al. 2019, GCN circ. 24049)in a series of
observations tiled on the sky. The total exposure time is 4.9 ks,
distributed over 4 tiles; the maximum exposure at a single sky location
was 3.4 ks. The data were collected between T0+7.4 ks and T0+19.1 ks,
and are entirely in Photon Counting (PC) mode.
Three uncatalogued X-ray sources have been detected, however none of
them is above the RASS limit. No source shows definitive signs of
fading, despite Source 3, which is the brightest, marginally weakened
(at the 2.7 sigma level) during the observation. Therefore, at the
present time we cannot safely identify the afterglow. Details of these
sources are given below:
RA (J2000.0): 221.0760 = 14:44:18.23
Dec (J2000.0): -22.6488 = -22:38:55.5
Error: 6.1 arcsec (radius, 90% conf.)
Count-rate: (6.3 [+3.2, -2.4])e-3 ct s^-1
Distance: 1015 arcsec from MAXI position.
Flux: (3.0 [+1.5, -1.1])e-13 erg cm^-2 s^-1 (observed, 0.3-10 keV)
RA (J2000.0): 221.0110 = 14:44:2.63
Dec (J2000.0): -22.5140 = -22:30:50.3
Error: 13.5 arcsec (radius, 90% conf.)
Count-rate: (6.8 [+3.8, -2.8])e-3 ct s^-1
Distance: 1006 arcsec from MAXI position.
Flux: (5.4 [+3.0, -2.2])e-13 erg cm^-2 s^-1 (observed, 0.3-10 keV)
RA (J2000.0): 220.84256 = 14:43:22.21
Dec (J2000.0): -22.66386 = -22:39:49.9
Error: 2.8 arcsec (radius, 90% conf. [Enhanced position])
Count-rate: 0.0236 [+0.0041, -0.0038] ct s^-1
Distance: 245 arcsec from MAXI position.
Flux: (5.99 [+1.03, -0.98])e-13 erg cm^-2 s^-1 (observed, 0.3-10 keV)
We do not find any X-ray object at the position of the optical
candidate reported by Waratkar et al. 2019 (GCN circ. 24051), the
closest source being Source 1 at a distance of 4.3 arcmin. The XRT
upper limit at the position of the GROWTH candidate is ~7e-3 ct s^-1.
The UVOT upper limit at the same position is ~ 21 mag in the U band.
The results of the XRT-team automatic analysis of the tiled XRT
observations, including a position-specific upper limit calculator, are
available at http://www.swift.ac.uk/xrt_products/TILED_GRB00079.
This circular is an official product of the Swift-XRT team.