GRB 120402A

S. D. Barthelmy (GSFC), A. P. Beardmore (U Leicester),
V. D'Elia (ASDC), S. T. Holland (STScI), J. A. Kennea (PSU),
N. P. M. Kuin (UCL-MSSL), O. M. Littlejohns (U Leicester),
V. Mangano (INAF-IASFPA), F. E. Marshall (NASA/GSFC),
C. J. Mountford (U Leicester), K. L. Page (U Leicester),
T. Sakamoto (NASA/UMBC), R. L. C. Starling (U Leicester) and
C. A. Swenson (PSU) report on behalf of the Swift Team:

At 22:49:22 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 120402A (trigger=519207).  Swift slewed immediately to the location. 
The BAT on-board calculated location is 
RA, Dec 314.326, +19.258, which is 
   RA(J2000)  =  20h 57m 18s
   Dec(J2000) = +19d 15' 28"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve shows a single pulse
with a duration of about 5 sec.  The peak count rate
was ~1300 counts/sec (15-350 keV), at ~1 sec after the trigger. 

The XRT began observing the field at 22:51:08.6 UT, 105.8 seconds after
the BAT trigger. No source was detected in 451 s of promptly downlinked
data. We are waiting for the full dataset to detect and localise the
XRT counterpart. 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 109 seconds after the BAT trigger. No credible afterglow candidate has
been found in the initial data products. The 2.7'x2.7' sub-image covers 25% of
the BAT error circle. The typical 3-sigma upper limit has been about 19.6 mag. 
The 8'x8' region for the list of sources generated on-board covers 100% of the
BAT error circle. The list of sources is typically complete to about 18 mag. No
correction has been made for the expected extinction corresponding to E(B-V) of
0.12. 

Given that the BAT image significance is only 6.6 sigma
and that the XRT and UVOT do not detect anything, it is 
unlikely that this is a real GRB.  It is possible that
this is a noisy detector in the BAT array.  We will have 
to wait for the full data set to downlink to resolve
this uncertainty.

E. Gorbovskoy, V. Lipunov, V.Kornilov, D.Kuvshinov, A.Belinski, N.Tyurina,
N.Shatskiy, P.Balanutsa, D.Zimnukhov, A.Kuznetsov,  V.V.Chazov, A.Kuznetsov,
A.Sankovich
Moscow Lomonosov State University, Sternberg Astronomical Institute,

K.Ivanov, S.Yazev, N.M.Budnev, O.Gres, O.Chuvalaev, V.A.Poleshchuk
Irkutsk State University

V.Yurkov, Yu.Sergienko, D.Varda, E.Sinyakov
Blagoveschensk Educational State University, Blagoveschensk

A. Tlatov, A.V. Parhomenko, D. Dormidontov, V.Sennik
Kislovodsk Solar Station of the Pulkovo Observatory

V.Krushinski, I.Zalozhnich,  A. Popov, A. Bourdanov, A. Punanova
Ural Federal University

Hugo Levato and Carlos Saffe
Instituto de Ciencias Astronomicas, de la Tierra y del Espacio (ICATE)

Claudio Mallamaci, Carlos Lopez and Federico Podest
Observatorio Astronomico Felix Aguilar (OAFA)


MASTER II  robotic telescope (MASTER-Net: http://observ.pereplet.ru) 
located in Kislovodsk was pointed to the  GRB120402B 10651 sec s after 
notice time and 10700 sec after GRB time at 2012-04-03 01:47:42.444 UT. On 
our first (180s exposure) set we haven`t found optical transient  within 
SWIFT error-box (ra=20 57 19 dec=+19 15 36 ).
The 5-sigma upper limit has been about 17.4mag
The long delay  was due to the weather conditions.

The message may be cited.

A. Volnova (SAI MSU), E. Litvinenko (UBAI), I. Molotov (KIAM), A.
Pozanenko (IKI) on behalf of �larger GRB follow up collaboration
report:

We observed the field of the possible GRB 120402A (Swift
trigger=519207; Barthelmy et al., �GCN 13190) with ORI-40 telescope of
Kitab ISON observatory on Apr. 02 starting �(UT) 22:55:14, i.e. ~6 min
after burst trigger. We obtained several �unfiltered images with
exposure of 60 seconds. Within BAT error circle of 3 arcmin, radius
(Barthelmy et al., �GCN 13190) we do not detect apparently new source
in comparison with DSS2-red. �The �photometry is based on �USNO-B1.0
reference star 1092-0548647 �(20:57:27.42 +19:17:47.2) assuming R =
14.41.

Tstart UT, � T0+, � � � �Filter, Exposure, OT, �UL (3 sigma)
� � � � � � � �(mid, d) � � � � � � � (s)

22:55:14 � �0.01449 � �none � 2800 � � �n/d � � 19.8

J. R. Cummings (GSFC/UMBC), C. B. Markwardt (GSFC), and
T. Sakamoto (NASA/UMBC) on behalf of the Swift-BAT team

The BAT trigger# 519207 (Barthelmy et al, GCN Circ# 13190) has been
identified as due to a flare from Cyg X-1, not a GRB.  The maskweighted
BAT lightcurve for Cyg X-1 shows a single symmetric pulse in the
15-50 keV band, about 4 seconds long at the same time as the BAT
trigger.  The BAT triggered on the Cyg X-1 flare.  While the on-board
processing ignores known bright sources, a portion of the Cyg X-1 flare
appeared in a spatially separate side-lobe, which the BAT did
trigger on.