GCN Circular 24093
Subject
GRB 190409A: ground analysis reveals a likely spurious event
Date
2019-04-10T14:55:51Z (5 years ago)
From
Antonino D'Ai at IASF-PA <antonino.dai@ifc.inaf.it>
A. D'Ai (INAF-IASFPA), A. Y. Lien (GSFC/UMBC), A. A. Breeveld (MSSL-UCL)
report on behalf of the Swift team:
Using Swift/BAT data set from T-60 to T+243 sec from
the recent telemetry downlink, we report further
analysis of the possible GRB 190409A (trigger #897653,
D'Ai et al. GCN 24081). The BAT image significance has
decreased to 3.7 sigma, and thus is consistent with
a noise fluctuation.
We have analysed 2.8 ks of Photon Counting (PC) mode
XRT data, collected between T0+3.0 ks and T0+10.2 ks.
One uncatalogued X-ray source has been detected but
outside the BAT error circle at 4.3 arcmin from the Swift/BAT
position reported in GCN 24081. The source is below the RASS
limit and shows no definitive signs of fading. Details of this source
are given below:
Source 1:
RA (J2000.0): 325.0326 = 21:40:7.82
Dec (J2000.0): -46.6064 = -46:36:23.0
Error: 7.7 arcsec (radius, 90% conf.)
Count-rate: (4.3 [+1.8, -1.4])e-3 ct s^-1
Distance: 276 arcsec from Swift/BAT position.
The Swift/UVOT began settled observations of the field of GRB 190409A
with the white filter 2950 s after the BAT trigger (D'Ai et al., GCN Circ. 24081).
No optical afterglow is detected in the initial UVOT exposure.
Given the lowered significance of the BAT trigger from the ground
analysis, the lack of a clear X-ray/UVOT counterpart within the
BAT error circle, we believe that GRB 190409A was most likely
a spurious event.