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MAXI/GSC detection of short intense flare from GRS 1915+105

ATel #12787; W. Iwakiri (Chuo U.), H. Negoro (Nihon U.), N. Kawai, M. Sugizaki(Tokyo Tech),K. Yamaoka (Nagoya U.), Y. Ueda(Kyoto U.), M. Nakajima, W. Maruyama, M. Aoki, K. Kobayashi (Nihon U.), S. Nakahira, T. Mihara, T. Tamagawa, M. Matsuoka (RIKEN), T. Sakamoto, M. Serino, S. Sugita, H. Nishida, A. Yoshida (AGU), Y. Tsuboi, R. Sasaki, H. Kawai, T. Sato (Chuo U.), M. Shidatsu (Ehime U.), M. Oeda, K. Shiraishi (Tokyo Tech), S. Ueno, H. Tomida, M. Ishikawa, Y. Sugawara, N. Isobe, R. Shimomukai, M. Tominaga (JAXA), A. Tanimoto, S. Yamada, S. Ogawa, K. Setoguchi, T. Yoshitake (Kyoto U.), H. Tsunemi, T. Yoneyama, K. Asakura, S. Ide (Osaka U.), M. Yamauchi, S. Iwahori, Y. Kurihara, K. Kurogi, K. Miike (Miyazaki U.), T. Kawamuro (NAOJ), Y. Kawakubo (LSU) report on behalf of the MAXI team:
on 21 May 2019; 07:53 UT
Credential Certification: Wataru Iwakiri (wataru.iwakiri@riken.jp)

Subjects: X-ray, Binary, Black Hole, Transient, Variables

Referred to by ATel #: 12818, 12839, 12848, 13478, 13652, 15968

The MAXI/GSC nova alert system triggered on the X-ray flare from GRS 1915+105 at 2019-05-21 00:16 (UT). The spectrum is well reproduced by absorbed powerlaw model with a photon index of 1.8 +/- 0.3 and the hydrogen column density of 8.0 (+2.9, -2.3) x 1022 cm-2. The estimated absorbed X-ray flux in the 2-20 keV is 3.9 (+0.3, -1.5) x 10-8 ergs/cm2/s. Assuming the distance of 8.6 kpc (Reid et al, 2014 ApJ,796,2), the absorbed luminosity is 3.5 (+0.2, -0.9) x 1038 erg/s (2-20 keV). All errors are at 90% confidence level. There are no significant X-ray signal at the preceding and following scan transits of MAXI that occured 92 minutes before and after the trigger. The 3 sigma upper limits for the both preceding and following scan transits in the 2 - 10 keV band are 2 x 10-9 ergs/cm2/s. This is the second X-ray flare after the previous one reported in ATel #12761, with an interval of 7 days, which was followed by activities in NIR (ATel #12769), radio (ATel #12773), X-ray halo (Atel #12770) and dimming (Atel #12772). These short intense flares suggests that GRS 1915+105 is in a new activity state characterized by sporadic massive accretion and/or ejection overlaid on a very low persistent emission. We strongly encourage multi-wavelength observations of GRS 1915+105.

MAXI lightcurve of GRS 1915+105