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  • Origins of the Long-term Va...
    Imazato, Fumiya; Sasada, Mahito; Uemura, Makoto; Fukazawa, Yasushi; Takahashi, Hiromitsu; Nakaoka, Tatsuya; Akitaya, Hiroshi; Kawabata, Koji S.; Akimoto, Masanori; Fujisawa, Kenta

    Astrophysical journal/˜The œAstrophysical journal, 08/2021, Letnik: 916, Številka: 2
    Journal Article

    Abstract Since 2018 July, the black hole X-ray binary GRS 1915+105 has been in an X-ray low luminous state (XLLS), which is the faintest period ever observed in a soft X-ray band. We present here the results of near-infrared (NIR) observations from 2019 April–December in the XLLS using HONIR attached to the Kanata telescope, together with radio data obtained by the Yamaguchi Interferometer and archival X-ray data. We found the historical NIR brightening in the XLLS. For several tens of days in the XLLS, NIR flux showed a positive correlation with radio flux and negative correlation with X-ray flux. This result suggests that at least a jet contributes to the NIR bands in the NIR-bright XLLS period. An accretion disk is not likely a candidate for the NIR emission because of the decrease of X-ray flux. In contrast to the NIR band, there was no historical radio brightening in the XLLS. This implies that the NIR emission in the NIR-bright period cannot be explained by the jet alone. The X-ray obscuration suggested by X-ray data is another possible candidate for the nonjet emission component in the NIR band.