MAXI/GSC detection of an intense hard X-ray flare from GRS 1915+105
ATel #13478; R. Takagi, K. Kobayashi, H. Negoro, M. Nakajima, W. Maruyama, M. Aoki (Nihon U.), T. Mihara, C. Guo, Y. Zhou, T. Tamagawa, M. Matsuoka (RIKEN), T. Sakamoto, M. Serino, S. Sugita, H. Nishida, A. Yoshida (AGU), Y. Tsuboi, W. Iwakiri, R. Sasaki, H. Kawai, T. Sato (Chuo U.), M. Shidatsu (Ehime U.), N. Kawai, M. Oeda, K. Shiraishi (Tokyo Tech), S. Nakahira, Y. Sugawara, S. Ueno, H. Tomida, M. Ishikawa, R. Shimomukai, M. Tominaga (JAXA), Y. Ueda, 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), K. Yamaoka (Nagoya U.), Y. Kawakubo (LSU), M. Sugizaki (NAOC) report on behalf of the MAXI team
on 14 Feb 2020; 03:45 UT
Credential Certification: Hitoshi Negoro (negoro@phys.cst.nihon-u.ac.jp)
Subjects: X-ray, Black Hole
MAXI/GSC detected a very bright hard flare from GRS 1915+105 in a scan transit at 12:38 UT on 2020 February 13. The average count rates during the scan at 2-20 keV, 2-4 keV, 4-10 keV, and 10-20 keV are 2.63 +/- 0.13 ph/cm^2/s (~0.82 Crab), 0.68 +/- 0.08 ph/cm^2/s (~0.41 Crab), 1.19 +/- 0.08 ph/cm^2/s (~1.03 Crab), and 0.44 +/- 0.05 ph/cm^2/s (~1.22 Crab), respectively. We also note that MAXI/GSC detected a gradual increase in X-ray flux from February 12 (MAXI ML x-ray-star:749), and that further enhancement (~60-100 mCrab) was recognized in two or three scan transits before and after this intense flare.
A flare spectrum is represented by an absorbed power-law with a photon index of 2.0+/-0.2 and a column density N_H of (8.7+/-1.9)e22. The absorbed and unabsorbed 2-10 keV fluxes are 1.6e-8 erg/cm^2/s and 3.1e-8 erg/cm^2/s, respectively.
Such intense flares were often observed after the decay of the flux in the last year with MAXI (ATel #12787), NICER (ATel #12793, #13308), AstroSAT (ATel #12805), and Konus-Wind (ATel #12818, #13316). MAXI, however, had not detected any bright X-ray flare since 2019 June 2. The brightest radio flare detected with the RATAN-600 radio telescope on February 2 (ATel #13442) may indicate that GRS 1915+105 enters a new active phase.
Multi-wavelength observations are encouraged to understand the nature of the sporadic intense flares from this source.
MAXI GSC data of GRS 1915+105