GRB 090401

P. Schady (MSSL-UCL), S. D. Barthelmy (GSFC), N. Gehrels (NASA/GSFC),
S. T. Holland (CRESST/USRA/GSFC), H. A. Krimm (CRESST/GSFC/USRA),
C. B. Markwardt (CRESST/GSFC/UMD), F. E. Marshall (NASA/GSFC),
K. L. Page (U Leicester), D. M. Palmer (LANL), A. M. Parsons (GSFC),
B. A. Rowlinson (U Leicester) and L. Vetere (PSU) report on behalf of
the Swift Team:

At 00:00:59 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 090401 (trigger=348128).  The BAT on-board calculated 
location is RA, Dec 350.909, +29.767 which is 
   RA(J2000)  =  23h 23m 38s
   Dec(J2000) = +29d 46' 00"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve shows a small peak at
~T+30 sec and then two large peaks at ~T+100 and ~T+120 sec. 
The peak count rate was ~4000 counts/sec (15-350 keV), at ~120 sec
after the trigger. 

Due to an observing constraint, Swift cannot slew to
the BAT position. It will not be possible to observe
until 2nd May due to a sun constraint. There will thus 
be no XRT or UVOT data for this trigger. 

Burst Advocate for this burst is P. Schady (ps AT mssl.ucl.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/too.html.)

G. Sato (ISAS), S. D. Barthelmy (GSFC), W. H. Baumgartner (GSFC/UMBC),
J. R. Cummings (GSFC/UMBC), E. E. Fenimore (LANL), N. Gehrels (GSFC),
H. A. Krimm (GSFC/USRA), C. B. Markwardt (GSFC/UMD), D. M. Palmer (LANL),
A. M. Parsons (GSFC), T. Sakamoto (GSFC/UMBC), P. Schady (MSSL-UCL),
M. Stamatikos (GSFC/ORAU), J. Tueller (GSFC), T. N. Ukwatta (GWU)
(i.e. the Swift-BAT team):
 
Using the data set from T-239 to T+713 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 090401 (trigger #348128)
(Schady, et al., GCN Circ. 9062
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 ).  The BAT ground-calculated position is
RA, Dec = 350.920, 29.762 deg, which is 
   RA(J2000)  =  23h 23m 40.8s 
   Dec(J2000) = +29d 45' 44.1" 
with an uncertainty of 1.0 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 38%.
 
The mask-weighted light curve starts out at T-20 sec when the burst location
first came into the BAT FOV during a planned-target slew maneuver.  There is
evidence for emission starting prior to burst coming to the FOV.  There are
two small peaks at T+0 and T+30 sec. Then comes the main emission
with a series of at least 7 overlapping peaks starting at ~T+95 sec and
returning to background at ~T+190 sec.  T90 (15-350 keV) is 112 +- 15 sec
(estimated error including systematics).
 
The time-averaged spectrum from T-9.4 to T+160.0 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.70 +- 0.05.  The fluence in the 15-150 keV band is 1.1 +- 0.0 x 10^-5 erg/cm2.
The 1-sec peak photon flux measured from T+122.05 sec in the 15-150 keV band
is 10.9 +- 0.5 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/348128/BA/