[vsnet-grb-info 19289] GRB 170405A: Swift detection of a burst with an optical counterpart

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  20984
SUBJECT: GRB 170405A: Swift detection of a burst with an optical counterpart
DATE:    17/04/05 18:50:16 GMT
FROM:    Scott Barthelmy at NASA/GSFC  <scott at milkyway.gsfc.nasa.gov>

E. Troja (NASA/GSFC/UMCP), S. D. Barthelmy (GSFC),
D. N. Burrows (PSU), S. B. Cenko (GSFC), A. Cholden-Brown (PSU),
A. D'Ai (INAF-IASFPA), F. E. Marshall (NASA/GSFC) and
M. H. Siegel (PSU) report on behalf of the Swift Team:

At 18:39:48 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 170405A (trigger=745797).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 219.810, -25.244, which is 
   RA(J2000)  =  14h 39m 14s
   Dec(J2000) = -25d 14' 36"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve shows multiple peaks
with a duration of about 180 sec.  The peak count rate
was ~4500 counts/sec (15-350 keV), at ~4 sec after the trigger. 

The XRT began observing the field at 18:41:49.0 UT, 120.6 seconds after
the BAT trigger. XRT found a bright, uncatalogued X-ray source located
at RA, Dec 219.8290, -25.2438 which is equivalent to:
   RA(J2000)  = +14h 39m 18.96s
   Dec(J2000) = -25d 14' 37.7"
with an uncertainty of 4.7 arcseconds (radius, 90% containment). This
location is 61 arcseconds from the BAT onboard position, within the BAT
error circle. No event data are yet available to determine the column
density using X-ray spectroscopy. 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 128 seconds after the BAT trigger. There is a candidate afterglow in
the rapidly available 2.7'x2.7' sub-image at
  RA(J2000)  =	14:39:18.72 = 219.82800
  DEC(J2000) = -25:14:35.3  = -25.24315
with a 90%-confidence error radius of about 0.61 arc sec. This position is 3.7
arc sec. from the center of the XRT error circle. The estimated magnitude is
16.18 with a 1-sigma error of about  0.14. No correction has been made for the
expected extinction corresponding to E(B-V) of 0.09. 

Burst Advocate for this burst is E. Troja (eleonora.troja AT nasa.gov). 
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/too.html.)