[vsnet-grb-info 21994] GRB 190409A: ground analysis reveals a likely spurious event

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  24093
SUBJECT: GRB 190409A: ground analysis reveals a likely spurious event
DATE:    19/04/10 14:55:51 GMT
FROM:    Antonino D'Ai at IASF-PA  <antonino.dai at 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.