MAXI/GSC detection of the historically brightest flares from the Sy2 galaxy NGC 2992
ATel #9155; H. Negoro (Nihon U.), S. Ueno, H. Tomida, S. Nakahira, M. Ishikawa, Y. E. Nakagawa, Y. Sugawara (JAXA), T. Mihara, M. Sugizaki , M. Serino, W. Iwakiri, M. Shidatsu, J. Sugimoto, T. Takagi, M. Matsuoka (RIKEN), N. Kawai, N. Isobe, S. Sugita, T. Yoshii, Y. Tachibana, Y. Ono, T. Fujiwara (Tokyo Tech), A. Yoshida, T. Sakamoto, Y. Kawakubo, Y. Kitaoka (AGU), H. Tsunemi, R. Shomura (Osaka U.), M. Nakajima, K. Tanaka, T. Masumitsu, T. Kawase (Nihon U.), Y. Ueda, T. Kawamuro, T. Hori, A. Tanimoto (Kyoto U.), Y. Tsuboi, Y. Nakamura, R. Sasaki (Chuo U.), M. Yamauchi, K. Furuya (Miyazaki U.), K. Yamaoka (Nagoya U.)
on 15 Jun 2016; 10:28 UT
Credential Certification: Hitoshi Negoro (negoro@phys.cst.nihon-u.ac.jp)
At 10:02 UT on 2016 June 2, the MAXI/GSC nova-alert system (Negoro et al. 2016, PASJ, 68, SP1, A1) triggered on faint X-ray enhancement positionally consistent with a nearby Seyfert 1.9 galaxy NGC 2992.
A long-term GSC light curve of this source obtained by the on-demand analysis shows that the 2-10 keV flux has gradually increased since the MAXI launch in 2009, and that the latest 1-month averaged flux was approximately 0.016 +/- 0.002 photons/s/cm2 (~4.7 mCrab). We note that the average flux for the first 37 months was about 0.8 mCrab (see Hiroi et al. 2013, ApJS, 207, 36).
The largest flare was observed on 2016 June 2-3, and the 2-10 keV flux was 0.052 +/- 0.012 photons/s/cm2 (~15 mCrab) in scan observations from 20:50 on June 2 to 10:45 on June 3 (MJD 57541.8681-57542.4481), and its peak flux was 0.065 +/- 0.022 photons/s/cm2 (~19 mCrab) from 01:28 on June 3 to 04:34 on June 3 (MJD 57542.0611-57542.1908). We also found that a bright flare with similar flux was observed on 2014 April 14.
Historically, NGC 2992 exhibited large X-ray variations, and the 2-10 keV flux changed from 9e-11 erg/s/cm2 (~ 4 mCrab) to below 1e-11 erg/s/cm2 (e.g., Murphy et al. 2007, ApJ, 666, 96; Shu et al. 2010, ApJ, 713, 1256). Thus, the source is currently in a highest flux state.
The MAXI/GSC products of NGC 2992 are publicly available (see below).
MAXI public archival data of NGC 2992
