GRB 180329A

J. L. Racusin (NASA/GSFC), A. Deich (PSU), J. A. Kennea (PSU),
H. A. Krimm (NSF/USRA), K. L. Page (U Leicester), D. M. Palmer (LANL)
and A. Tohuvavohu (PSU) report on behalf of the Neil Gehrels Swift
Observatory Team:

At 00:58:00 UT, the Swift Burst Alert Telescope (BAT) triggered and
located a marginal-significance (6.9 sigma) image peak that may be 
GRB 180329A (trigger=819301).  Swift could not slew to the location 
due to an observing constraint. 
The BAT on-board calculated location is 
RA, Dec 329.298, -15.071 which is 
   RA(J2000) = 21h 57m 11s
   Dec(J2000) = -15d 04' 14"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve shows some variation
consistent with a ~8 second long GRB, however this variation
is also consistent with the presence of the currently-active black hole
transient MAXI J1820+070 in the FOV.  The peak count rate
was ~1400 counts/sec (15-350 keV), at ~5 sec after the trigger. 

Due to a Sun observing constraint, Swift cannot slew to the BAT
position until 23:07 UT on 2018 April 02. There will thus be no XRT or
UVOT data for this trigger before this time. 

Due to the low significance of this detection, the presence of
a bright variable X-ray source in the BAT Field of View, and the lack
of follow-up observations from the XRT and UVOT, we cannot determine
whether this is a GRB at this time.  Further analysis of the
full downlinked data will be required to decide if this is a
GRB or a statistical fluctuation in the image plane. 

Burst Advocate for this burst is J. L. Racusin (judith.racusin 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.)

C. B. Markwardt (GSFC), S. D. Barthelmy (GSFC),
J. R. Cummings (CPI), H. A. Krimm (NSF/USRA),
A. Y. Lien (GSFC/UMBC), D. M. Palmer (LANL),
J. L. Racusin (NASA/GSFC), 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+963 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 180329A (trigger #819301)
(Racusin et al., GCN Circ. 22556
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 ).  The BAT ground-calculated position is
RA, Dec = 329.314, -15.043 deg which is
  RA(J2000)  =  21h 57m 15.3s
  Dec(J2000) = -15d 02' 36.0"
with an uncertainty of 2.3 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 80%.

The mask-weighted light curve shows a weak pulse that starts at ~T0, peaks
at ~T+1 s, and ends at ~T+10 s. T90 (15-350 keV) is 9.1 +- 1.8 sec (estimated
error including systematics).

The time-averaged spectrum from T-0.30 to T+9.69 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.39 +- 0.31.  The fluence in the 15-150 keV band is 2.3 +- 0.4 x 10^-7 erg/cm2.
The 1-sec peak photon flux measured from T+1.14 sec in the 15-150 keV band
is 0.5 +- 0.2 ph/cm2/sec.  All the quoted errors are at the 90% confidence
level.

Due to an observing constraint, there are no observations of this source with the
Swift XRT or UVOT, and hence no confirmation of the nature of the source.
However, because the image significance from the ground analysis of the BAT
data is ~ 9 sigma, and the temporal and spectral properties are consistent with
those from a BAT GRB, we conclude that this source is likely a real GRB.

The results of the batgrbproduct analysis are available at
http://gcn.gsfc.nasa.gov/notices_s/819301/BA/