GRB 190331A

K. L. Page (U Leicester), S. D. Barthelmy (GSFC), J. A. Kennea (PSU),
N. J. Klingler (PSU), A. Y. Lien (GSFC/UMBC), D. M. Palmer (LANL) and
A. Tohuvavohu (PSU) report on behalf of the Neil Gehrels Swift
Observatory Team:

At 02:14:37.50 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 190331A (trigger=895813).  Swift did not slew immediately 
due to an observing constraint. 
The BAT on-board calculated location is 
RA, Dec 28.576, +27.619 which is 
   RA(J2000) = 01h 54m 18s
   Dec(J2000) = +27d 37' 10"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a bright multi-peaked 
structure with a duration of about 5 sec.  The peak count rate was ~6000 
counts/sec (15-350 keV), at ~0 sec after the trigger. 

Due to a Sun observing constraint, Swift cannot slew to the BAT
position until 18:15 UT on 2019 June 12. There will thus be no XRT or
UVOT data for this trigger before this time. 

Burst Advocate for this burst is K. L. Page (klp5 AT leicester.ac.uk). 
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/)

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

Using the data set from T-599 to T+986 sec from the recent telemetry
downlink,
we report further analysis of BAT GRB 190331A (trigger #895813)
(Page et al., GCN Circ. 24027
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 ).  The BAT ground-calculated position is
RA, Dec = 28.573, 27.635 deg which is
   RA(J2000)  =  01h 54m 17.4s
   Dec(J2000) = +27d 38' 06.8"
with an uncertainty of 1.4 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 82%.

The mask-weighted light curve shows a multi-peaked structure that starts
at ~T0 and ends at ~T+4.5. The main peak occurs at ~T0.
T90 (15-350 keV) is 4.3 +- 0.2 sec (estimated error including systematics).

The time-averaged spectrum from T-0.1 to T+4.5 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.24 +- 0.15.  The fluence in the 15-150 keV band is 4.5 +- 0.4 x 10^-7
erg/cm2.
The 1-sec peak photon flux measured from T-0.06 sec in the 15-150 keV band
is 2.8 +- 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/895813/BA/

S. Poolakkil (UAH) and C. Meegan (UAH)
report on behalf of the Fermi GBM Team:

"At 02:14:37.57 UT on 31 March 2019, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 190331A (trigger 575691282/ 190331093),
which was also detected by the Swift/BAT (Page et al. 2019, GCN 24027
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 ).
The GBM on-ground location is consistent with the Swift position.

The angle from the Fermi LAT boresight
at the GBM trigger time is 40 degrees.

The GBM light curve shows multiple peaks
with a duration (T90) of about 4.8 s (50-300 keV).
The time-averaged spectrum from T0-1.0 s to T0+6.1 s is
best fit by a power law function with an exponential
high-energy cutoff.  The power law index is -0.74 +/- 0.19 and
the cutoff energy, parameterized as Epeak, is 214 +/- 47 keV.

The event fluence (10-1000 keV) in this time interval is
(1.343 +/- 0.179)E-06 erg/cm^2. The 1-sec peak photon flux
measured starting from T-0.06 s in the 10-1000 keV band
is 4.6 +/- 0.2 ph/s/cm^2.

The spectral analysis results presented above are preliminary;
final results will be published in the GBM GRB Catalog."

Q. Luo, C. K. Li, X. B. Li, G. Li, J. Y. Liao, S. L. Xiong, 
C. Z. Liu, X. F. Li, Z. W. Li, Z. Chang, X. F. Lu,
A. M. Zhang, Y. F. Zhang, C. L. Zou (IHEP), Y. J. Jin, 
Z. Zhang (THU), T. P. Li (IHEP/THU), F. J. Lu, L. M. Song, 
M. Wu, Y. P. Xu, S. N. Zhang (IHEP),
report on behalf of the Insight-HXMT team:

At 2019-03-31T02:14:38.000 (T0), the Insight-HXMT/HE detected
GRB 190331A(trigger ID: HEB190331093) in a routine search of the data,
which was also triggered by Swift/BAT(K. L. Page et al. ,GCN 24027)
and Fermi/GBM (M. Niwano et al. ,GCN 24032).

The Insight-HXMT/HE light curve mainly consists of one 
pulse with a duration (T90) of 7.65 s measured from T0+0.13 s.
The 1-ms peak rate, measured from T0+0.271 s, is 1552 cnts/sec.
The total counts from this burst is 1691 counts.
URL_LC: http://www.hxmt.org/images/GRB/HEB190331093_lc.jpg

All measurements above are made with the CsI detectors operating in the
regular mode with the energy range of about 80-800 keV (record energy).
Only gamma-rays with energy greater than about 200 keV can penetrate
the spacecraft and leave signals in the CsI detectors installed inside
of the telescope.

Insight-HXMT is the first Chinese space X-ray telescope, which was
fundedjointly by the China National Space Administration (CNSA) and
the Chinese Academy of Sciences (CAS).
More information about it could be found at:
http://www.hxmt.org.