MAXI/GSC detection of a new soft X-ray transient MAXI J0545+043 and Swift/XRT observation

ATel #6066; Y. Morooka (Miyazaki U.), S. Nakahira (JAXA), Y. Tsuboi, A Kawagoe (Chuo U.), M. Serino, T. Mihara, M. Sugizaki, M. Morii, J. Sugimoto, T. Takagi, A. Yoshikawa, M. Matsuoka (RIKEN), S. Ueno, H. Tomida, M. Kimura, M. Ishikawa, Y. E. Nakagawa (JAXA), N. Kawai, T. Yoshii, Y. Tachibana (Tokyo Tech), A. Yoshida, T. Sakamoto, Y. Kawakubo, H. Ohtsuki (AGU), H. Tsunemi, D. Uchida (Osaka U.), H. Negoro, M. Nakajima, K. Fukushima, T. Onodera, K. Suzuki (Nihon U.), Y. Ueda, M. Shidatsu, T. Kawamuro, T. Hori (Kyoto U.), M. Yamauchi, (Miyazaki U.), K. Yamaoka (Nagoya U.) report on behalf of the MAXI team
on 13 Apr 2014; 14:34 UT
Credential Certification: Satoshi NAKAHIRA (nakahira@crab.riken.jp)

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On 2014-04-12T00:25:54 UT (=MJD 56759.018), the MAXI/GSC transient alert system triggered ( trigger ID=6759029967) on enhanced X-ray emission at (R.A., Dec) = (86.190 deg, + 4.497 deg). This event is initially identified as a stellar flare from V1149 Ori. Then with the refined data we obtain a new source position at,
(R.A., Dec) = (86.44 deg, +4.32 deg) = (05 45 45.60, +04 19 12.0) (J2000)
with an estimated error of 0.5 degrees radius. The position is not consistent with any known bright X-ray sources, so we tentatively name the source MAXI J0545+043.

The MAXI/GSC spectrum can be modeled with a blackbody function with a temperature of 0.8±0.2 keV. The 2-4 keV flux averaged over the triangular transit corrected for the Galactic absorption was 117⁺³³_-35 mCrab (90% error), and that of the 4-10 keV was 56⁺³⁷_-26 mCrab. The flux decayed to an upper limit of about 20 mCrab at the next scan performed 92 minutes later.

We proposed a Swift ToO observation with 7-point tiling to cover the MAXI error circle with the Swift XRT. The observation was performed from 2014-04-13T02:17 with 250 sec exposure for each tiling. As a result, no obvious X-ray source was found. Hence, nature of this transient is still unclear.

We thank the Swift team for performing the observation.