GRB 120510A

N. Serita, H. Negoro, M. Nakajima, M. Asada, H. Sakakibara (Nihon U.), 
M. Serino, T. Mihara, M. Sugizaki, T. Yamamoto, M. Matsuoka (RIKEN), 
S. Nakahira, S. Ueno, H. Tomida, M. Ishikawa (JAXA),
N. Kawai, M. Morii, R. Usui, K. Ishikawa (Tokyo Tech),
A. Yoshida (AGU),
H. Tsunemi, M. Kimura (Osaka U.), 
Y. Ueda, K. Hiroi, M. Shidatsu, R. Sato (Kyoto U.),
Y. Tsuboi, M. Higa (Chuo U.)
M. Yamauchi, Y. Nishimura, T. Hanayama, K. Yoshidome (Miyazaki U.), 
K. Yamaoka (Waseda U.)
report on behalf of the MAXI team:

During a scan transit centered at UT 2012-05-10T08:47:44,
MAXI/GSC detected a short X-ray transient lasting about 27 seconds 
within the 42 seconds triangular transit response of MAXI/GSC.
Judging from its hardness ratio, 
this transient is probably a gamma-ray burst.

Assuming that the source flux was constant over the transit, 
we obtain the source position at

(R.A., Dec) = (+44.285 deg, +72.850deg) = ( 02 57 08.60, +72 51 00.8 )(J2000)

which has a statistical uncertainty of 10 arcmin at the 90% confidence limit 
and an additional systematic uncertainty of 6 arcmin (90% containment radius).
Due to a short burst duration, the uncertainty for the scan direction is possibly larger than this estimation.
Without assuming a constant flux of the source,
a rectangular sky region of 90% confidence
is 0.4 degrees by 1.4 degrees with the following corners:

(R.A., Dec) = (+41.76 deg, +72.60 deg) = (02 47  2, +72 36 12)(J2000)
(R.A., Dec) = (+41.77 deg, +73.02 deg) = (02 47  4, +73 01 20)(J2000)
(R.A., Dec) = (+46.50 deg, +72.97 deg) = (03 06  0, +72 58  4)(J2000)
(R.A., Dec) = (+46.40 deg, +72.55 deg) = (03 05 36, +72 32 59)(J2000).

The preliminary flux estimate (4-10 keV) of the source was 330+-40 mCrab.

There was no significant detection at the transit location in the
previous and the following orbits (92 min before and after the detection) 
with an upper limit of 20 mCrab.

Follow-up observations are encouraged.

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

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

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 Blagoveschensk was pointed to the  120510A 24146 sec after 
GRB time at 2012-05-10 15:30:10.64 UT. On our first (180s exposure) set we 
haven`t found optical transient  within MAXI/GSC error-box (Serita 
et al., GCN Circ 13282
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 ).
The 5-sigma upper limit has been about 18.6 mag

  The message may be cited.

P. D'Avanzo, A. Melandri (INAF-OAB), K. L. Page, P. A. Evans (U
Leicester), M. Perri (ASDC), S. T. Holland (NASA/GSFC) report on behalf of
the Swift team:

The Swift XRT and UVOT instruments observed the centre of the error circle
for the MAXI-detected GRB 120510A (Serita et al., GCN Circ. 13282
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 ) from
21.4 to 33.0 ks after the trigger.

The XRT data comprise 2.0 ks of Photon Counting (PC) mode data. A faint
source is detected RA, Dec = 44.04666, +72.88692 which is equivalent to:

RA (J2000):        02h 56m 11.20s
Dec (J2000):        +72d 53' 12.9"

with an uncertainty of 4.8 arcsec (radius, 90% confidence). The observed
count rate is (3.3 +/- 1.3) x 10^-3 cts/s. This corresponds to an observed
0.3-10 keV flux of (1.4 +/- 0.5) x 10^-13 erg/cm2/s (assuming a typical
GRB spectrum with photon spectral index of 2). If we consider the Galactic
absorption in this direction (2.3 x 10^21 cm^-2; Kalberla et al. 2005)
this corresponds to an unabsorbed flux of (2.0 +/- 0.8) x 10^-12
erg/cm2/s. Given the limited statistics, it is not possible to determine
whether the source is fading. We note that the XRT position lies 15.6
arcsec from the ROSAT source 1RXS J025613.2+725300 (RA(J2000), Dec(J2000)=
02h 56m 13.2s, +72d 52' 59", with an error radius of 11 arcsec). We also
note that the XRT field of view covers only about 69% of the reported 16
arcmin radius error circle GRB 120510A (Serita et al., GCN Circ. 13282
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 ).

The XRT coordinates correspond to the bright, catalogued ultraviolet
source HD 17785 with a magnitude of uvw2 = 11.85 +/- 0.02 mag.  There is
very weak evidence in the UVOT data that the source may have increased in
brightness by about 0.2 mag between 28 ks and 33 ks after the burst.

S. Golenetskii, R.Aptekar, E. Mazets, V. Pal'shin, D. Frederiks, P.
Oleynik, M. Ulanov, D. Svinkin, and T. Cline on behalf of the Konus-Wind
team report:

The long GRB 120510A localized by MAXI/GSC (Serita et al., GCN
13282
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 ) was detected by Konus-Wind in the waiting mode.

The burst light curve shows several pulses with a total duration of ~130 s.

As observed by Konus-Wind, the burst had a fluence of (3.82 +/- 
0.26)x10^-6 erg/cm2 (in the 20 - 1200 keV energy range).

Fitting the K-W 3-channel time-integrated spectrum (from T0(MAXI)+5 s to 
T0(MAXI)+135 s) by a simple power-law model yields a power law index of 
2.05 +/- 0.24.

All the quoted errors are estimated at the 1 sigma confidence level.

The K-W light curve of this burst is available at
http://www.ioffe.rssi.ru/LEA/GRBs/GRB120510A/