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TITLE:   GCN CIRCULAR
NUMBER:  23554
SUBJECT: GRB 181224A: Swift detection of a burst
DATE:    18/12/24 13:47:41 GMT
FROM:    Scott Barthelmy at NASA/GSFC  <scott@milkyway.gsfc.nasa.gov>

A. Melandri (INAF-OAB), S. D. Barthelmy (GSFC),
M. G. Bernardini (INAF-OAB), P. D'Avanzo (INAF-OAB),
A. Y. Lien (GSFC/UMBC) and B. Sbarufatti (PSU) report on behalf of the
Neil Gehrels Swift Observatory Team:

At 13:36:51 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 181224A (trigger=878911).  Swift did not slew to the burst
because of the Moon constraint.  The BAT on-board calculated location is 
RA, Dec 125.931, +6.206, which is 
   RA(J2000)  =  08h 23m 43s
   Dec(J2000) = +06d 12' 20"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curves one peak with a total
duration of about 15 sec.  The peak count rate
was ~1000 counts/sec (15-350 keV), at ~1 sec after the trigger. 

Due to a Moon observing constraint, Swift cannot slew to the BAT
position until 08:10 UT on 2018 December 26. There will thus be no XRT
or UVOT data for this trigger before this time. 

Burst Advocate for this burst is A. Melandri (andrea.melandri AT brera.inaf.it). 
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.)

////////////////////////////////////////////////////////////////////////
TITLE:   GCN CIRCULAR
NUMBER:  23555
SUBJECT: GRB 181224A: Swift-BAT refined analysis
DATE:    18/12/25 03:17:55 GMT
FROM:    Amy Lien at GSFC  <amy.y.lien@nasa.gov>

H. A. Krimm (NSF/USRA), S. D. Barthelmy (GSFC),
J. R. Cummings (CPI), A. Y. Lien (GSFC/UMBC),
C. B. Markwardt (GSFC), A. Melandri (INAF-OAB),
D. M. Palmer (LANL), T. Sakamoto (AGU),
M. Stamatikos (OSU), T. N. Ukwatta (LANL)
(i.e. the Swift-BAT team):

Using the data set from T-240 to T+450 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 181224A (trigger #878911)
(Melandri et al., GCN Circ. 23554).  The BAT ground-calculated position is
RA, Dec = 125.949, 6.194 deg which is
  RA(J2000)  =  08h 23m 47.7s
  Dec(J2000) = +06d 11' 39.9"
with an uncertainty of 1.9 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 80%.

The mask-weighted light curve shows a single-peaked structure that starts at
~ T-12 s, peaks at ~ T+1 s, one ends at ~ T+4 s. T90 (15-350 keV) is
12.5 +- 4.2 sec (estimated error including systematics).

The time-averaged spectrum from T-12.04 to T+3.30 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.27 +- 0.20.  The fluence in the 15-150 keV band is 4.9 +- 0.6 x 10^-7 erg/cm2.
The 1-sec peak photon flux measured from T+0.48 sec in the 15-150 keV band
is 1.0 +- 0.2 ph/cm2/sec.  All the quoted errors are at the 90% confidence
level.

The results of the batgrbproduct analysis are available at
http://gcn.gsfc.nasa.gov/notices_s/878911/BA/