MAXI/GSC observations of the gamma-ray/X-ray transient Fermi J1544-0649

ATel #10495; T. Kawase, H. Negoro, (Nihon U.), S. Ueno, H. Tomida, N. Isobe, M. Ishikawa, Y. Sugawara (JAXA), T. Mihara, M. Sugizaki, M. Serino, S. Nakahira, W. Iwakiri, M. Shidatsu, K. Makishima, M. Matsuoka (RIKEN), N. Kawai, S. Sugita, T. Yoshii, Y. Tachibana, S. Harita, K. Morita, Y. Muraki (Tokyo Tech), A. Yoshida, T. Sakamoto, Y. Kawakubo, Y. Kitaoka (AGU), H. Tsunemi, T. Yoneyama (Osaka U.), M. Nakajima, A. Sakamaki (Nihon U.), Y. Ueda, T. Hori, A. Tanimoto, S. Oda (Kyoto U.), Y. Tsuboi, Y. Nakamura, R. Sasaki (Chuo U.), M. Yamauchi, C. Hanyu, K. Hidaka (Miyazaki U.), K. Yamaoka (Nagoya U.), T. Kawamuro (NAOJ)
on 15 Jun 2017; 14:15 UT
Credential Certification: Hitoshi Negoro (negoro@phys.cst.nihon-u.ac.jp)

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We report MAXI/GSC observations of the newly discovered high energy transient source Fermi J1544-0649 (Ciprini et al. ATel. #10482; Chornock & Margutti ATel. #10491). We investigating 2-4 keV and 4-10 keV X-ray light curves at the source position, obtained by applying the image fitting method (Morii et al. 2016, PASJ, 68, S11) to MAXI/GSC data since 2009 August 15.
No significant variations were found before 2017 May 11 (MJD 57884). Slight enhancement was, however, once recognized around May 12-13. The 2-4 keV and 4-10 keV fluxes (Crab count ratios) averaged over 4-days from May 11 to May 14 were 3.8 +/- 1.3 mCrab and 3.2 +/- 1.4 mCrab, respectively. From May 21 (MJD 57894), the X-ray flux increased again, and the 4-10 keV flux peaked at 8.8 +/- 2.1 mCrab in the period from May 21 to May 25, and decayed to 2.8 +/- 1.1 mCrab from May 26 to June 4. On the other hand, the 2-4 keV flux was almost stable at 4.6 +/- 1.2 mCrab in the period from May 21 to June 4. Since June 5, no significant emission was detected in both energy bands.

These observational properties are consistent with those of Fermi and Swift observations reported by Ciprini et al. (#10482) except for the slight enhancement before the Fermi/LAT detection from May 15. They considered that this flaring event was a BL Lac origin, but a possibility of a tidal disruption event (TDE) was also pointed out. No rapid and violent flares were observed in the MAXI data as were observed in Swift J164449.3+573451 (Burrows et al. 2011, Nature, 476, 421). This, however, does not exclude the possibility of the TDE (for TDE examples MAXI detected, see Kawamuro et al. 2016, PASJ, 68, 58).

Finally, we note that MAXI so far detected similar flaring events from (not so bright) BL Lac objects 1ES 0033+595 (ATel. #4877), 2FGL J1931.1+0938 (ATel. #5943), and BZB J0244-5819 (ATel. #6012) just around the detection limit for 4 day data (8-10 mCrab, see Negoro et al. 2016, PASJ, 68, S1), implying that BL Lac objects sometimes exhibit very bright flares.