TITLE:   GCN CIRCULAR
NUMBER:  20780
SUBJECT: LIGO/Virgo G274296 and G275404 : MAXI/GSC observations
DATE:    17/03/01 06:37:30 GMT
FROM:    Satoshi Sugita at Tokyo Inst. of Tech.  <sugita@hp.phys.titech.ac.jp>

S. Sugita, N. Kawai (Tokyo Tech), M. Serino (RIKEN), H. Negoro (Nihon U.),
S. Ueno, H. Tomida, S. Nakahira, M. Ishikawa, Y. Sugawara (JAXA),
Y. E. Nakagawa (JAMSTEC),
T. Mihara, M. Sugizaki, W. Iwakiri, M. Shidatsu, J. Sugimoto, T.
Takagi, M. Matsuoka (RIKEN),
N.Isobe, T. Yoshii, Y. Tachibana, Y. Ono, T. Fujiwara, S. Harita, Y.
Muraki (Tokyo Tech),
A. Yoshida, T. Sakamoto, Y. Kawakubo, Y. Kitaoka (AGU),
H. Tsunemi, R. Shomura (Osaka U.),
M. Nakajima, K. Tanaka, T. Masumitsu, T. Kawase (Nihon U.),
Y. Ueda, T. Kawamuro, T. Hori, A. Tanimoto, S. Oda (Kyoto U.),
Y. Tsuboi, Y. Nakamura, R. Sasaki (Chuo U.),
M. Yamauchi, K. Furuya (Miyazaki U.),
K. Yamaoka (Nagoya U.)
report on behalf of the MAXI team:

We examined the MAXI/GSC all-sky X-ray images (2-20 keV) obtained
in the orbit and the day after the LVC trigger
G274296 at 2017-02-17 06:05:55.050 UTC (GCN 20689) and
G275404 at 2017-02-25 18:30:21.374 UTC (GCN 20738).

MAXI/GSC did not observe (HV off) at the trigger time of G274296,
and observed from T0+843 sec.
MAXI/GSC scanned more than 87%
of the whole sky in the 92-min orbit, which includes 77.4% of the
90% regions in the skyprobcc_cWB skymap.
One day image covers 89.7% of the 90% regions
in the skyprobcc_cWB skymap.
No significant new source was found in these images.
The upper limits for the X-ray flux are different depending
on the part of the sky.
For instance, typical 2-20 keV 1-sigma (3-sigma) upper limits obtained
from the one-orbit and one-day images are
40 (120) mCrab and 15 (35) mCrab, respectively,
which was larger than the typical upper limits of GSC
because anti-coincidence function of one of the GSC cameras was disabled.

In G275404 observation,
MAXI/GSC did not observe at the trigger time
and observed from T0+1246 sec.
MAXI/GSC scanned more than 62%
of the whole sky in the one orbit, which includes 55.0% of the
90% regions in the bayestar skymap.
One day image covers 96.3% of the 90% regions
in the bayestar skymap.
No significant new source was found in these images.
For instance, typical 2-20 keV 1-sigma (3-sigma) upper limits obtained
from the one-orbit and one-day images are
12 (36) mCrab and 3 (9) mCrab, respectively.

MAXI/GSC also observed the position of the possible gamma-ray
transient (GCN 20754),
but it was difficult to estimate upper limits because the effect of stray photon
from bright GRS 1915+105 near by the localized position of the transient
was large.