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GRB 190409A

GCN Circular 24081

Subject
GRB 190409A: Swift detection of a possible burst
Date
2019-04-09T14:16:59Z (6 years ago)
From
Scott Barthelmy at NASA/GSFC <scott@milkyway.gsfc.nasa.gov>
A. D'Ai (INAF-IASFPA), S. D. Barthelmy (GSFC),
M. G. Bernardini (INAF-OAB), D. N. Burrows (PSU), V. D'Elia (SSDC),
P. A. Evans (U Leicester), J.D. Gropp (PSU), J. A. Kennea (PSU),
N. J. Klingler (PSU), N. P. M. Kuin (UCL-MSSL),
K. L. Page (U Leicester), D. M. Palmer (LANL), B. Sbarufatti (PSU),
M. H. Siegel (PSU) and A. Tohuvavohu (PSU) report on behalf of the
Neil Gehrels Swift Observatory Team:

At 13:01:21 UT, the Swift Burst Alert Telescope (BAT) triggered and
located possible GRB 190409A (trigger=897653).  Swift did not immediately slew
due to an observing constraint.  The BAT on-board calculated location is 
RA, Dec 324.921, -46.607, which is 
   RA(J2000)  =  21h 39m 41s
   Dec(J2000) = -46d 36' 25"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  As is typical for image triggers, the real-time
light curve does not show anything significant. 

The XRT began observing the field at 13:50:28.1 UT, 2946.9 seconds
after the BAT trigger. No source was detected in 1.2 ks of promptly
downlinked data, which covered 55% of the BAT error circle. We are
waiting for the full dataset to detect and localise the XRT
counterpart. 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 2950 seconds after the BAT trigger. No credible afterglow candidate
has been found in the initial data products. Results from the 2.7'x2.7'
sub-image are not available at this time. The 8'x8' region for the list of
sources generated on-board covers 100% of the BAT error circle. The list of
sources is typically complete to about 18 mag. No correction has been made for
the expected extinction corresponding to E(B-V) of 0.02. 

Burst Advocate for this burst is A. D'Ai (antonino.dai AT gmail.com). 
Please contact the BA by email if you require additional information
regarding Swift followup of this burst. In extremely urgent cases, after
trying the Burst Advocate, you can contact the Swift PI by phone (see
Swift TOO web site for information: http://www.swift.psu.edu/)

GCN Circular 24093

Subject
GRB 190409A: ground analysis reveals a likely spurious event
Date
2019-04-10T14:55:51Z (6 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.

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