Title: Near-infrared variations of GRS 1915+105 in an unusual state

ATel #12769; K. L. Murata, N. Kawai (Tokyo Tech), M. Yamagishi (ISAS/JAXA), K. Morihana (Nagoya U), K. Shiraishi, R. Adachi, M. Oeda, K. Iida, S. Niwano, Y. Yatsu (Tokyo Tech), F. Imazato, M. Sasada, H. Akitaya, T. Nakaoka (Hiroshima U), N. Katoh, J. Takahashi (U of Hyogo)
on 16 May 2019; 15:36 UT
Credential Certification: Mahito Sasada (sasadam@hiroshima-u.ac.jp)

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The microquasar GRS 1915+105 has been in an unusual low-flux state in X-ray wavelength (ATel #11828, #12742, #12743, #12755), and then shows the rebrightening on 14th May 2019 (ATel #12761). Imazato et al. (ATel #12765, #12766) reported the Ks-band brightening from 6th April 2019 to 12th May 2019. We observed GRS 1915+105 with the near-infrared (J, H, Ks) simultaneous imaging camera SIRIUS attached to 1.4 m telescope IRSF (InfraRed Survey Facility) in Sutherland observatory, South Africa. During the 0.68 hour window starting at MJD ~ 58618.168, the Ks-band flux decreased from ~10 mJy down to 7 mJy at MJD ~ 58618.177, and then increased to 10 mJy at MJD ~ 58618.197. Similar trend was seen in the H band with a smaller amplitude, and also seen in the J band with marginal significance. Thus the amplitudes of the flux variations is larger toward longer wavelengths in the near-infrared. The Ks-band magnitude is 13.7-14.3 mag in the AB system, which suggests that the day-scale increase trend in Ks band from 6th April 2019 to 12th May 2019 (ATel #12765, #12766) still continues on 15th May 2019. Given fluxes and magnitudes are calibrated against 2MASS point sources near GRS 1915+105. This report is based on a part of the results of the ToO observation for GRS 1915+105 by Optical and Infrared Synergetic Telescopes for Education and Research (OISTER) in Japan. We will perform further analysis and observations.

Light curves of GRS 1915+105