Short X-ray Transient Detection by MAXI/GSC

ATel #2321; M. Nakajima, S. Miyoshi (Nihon U.), M. Morii, K. Sugimori, N. Kawai (Tokyo Tech), H. Negoro, H. Ozawa, R. Ishiwata (Nihon U.), M. Suzuki, M. Matsuoka, K. Kawasaki, S. Ueno, H. Tomida, M. Ishikawa (JAXA), S. Eguchi, Y. Ueda, N. Isobe, K. Hiroi (Kyoto U.), S. Nakahira, A. Yoshida, K. Yamaoka (AGU), T. Mihara, M. Kohama, Y. E. Nakagawa, M. Sugizaki, T. Yamamoto (RIKEN), H. Tsunemi, M. Kimura (Osaka U.), A. Daikyuji (Miyazaki U.) on behalf of the MAXI team
on 2 Dec 2009; 15:45 UT
Distributed as an Instant Email Notice Transients
Credential Certification: Nobuyuki Kawai (nkawai@phys.titech.ac.jp)

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At the scan transit centered at UT 2009-12-01T21:48:36, MAXI/GSC detected an X-ray source, which was detectable at least for 20 seconds within the 67 seconds triangular transit response of MAXI/GSC. With the current statistics we cannot distinguish whether the source was constant over the scan transit.

Assuming that the source flux was constant over the transit, the source location is determined as

(R.A., Dec)=(118.6 deg, 16.6 deg) = (07 54 24, +16 36 36) (J2000)

with a systematic uncertainty of 0.4 degrees.

If the source was highly variable, as is the case for a GRB/XRF, the uncertainty along the scan direction becomes large, as we cannot fit the light curve to the triangular transit response. Without assumptions on the source constancy, we obtain a rectangular error box with the following corners:

(R.A., Dec)=(116.27 deg, 14.59 deg) = (07 45 04.80, +14 35 24.0) (J2000)
(R.A., Dec)=(116.96 deg, 14.14 deg) = (07 47 50.40, +14 08 24.0) (J2000)
(R.A., Dec)=(120.22 deg, 19.33 deg) = (08 00 52.80, +19 19 48.0) (J2000)
(R.A., Dec)=(120.96 deg, 18.95 deg) = (08 03 50.40, +18 57 00.0) (J2000)

The preliminary flux (2-10 keV) of the source was 120 mCrab. There was no significant detection at the transit location in the previous and following orbits (92 min before or after the detection) with an upper limit of 20 mCrab.
There is no known bright X-ray source at the detected position. At the galactic coordinates (l,b)=(204.6, 21.2), the source can be either a Galactic object (e.g. flare stars, compact objects) or an extragalactic object (e.g. GRB/XRF, AGN, SN). Follow-up observations are encouraged.
MAXI is currently in the commissioning phase.