Insight-Hxmt Observations Of A Possible Fast Transition From The Jet- To Wind-Dominated State During A Huge Flare Of Grs 1915+105

We present the analysis of the brightest flare that was recorded in the Insight-HMXT data set in a broad energy range (2-200 keV) from the microquasar GRS 1915+105 during an unusual low-luminosity state. This flare was detected by Insight-HXMT among a series of flares during 2019 June 2 UTC 16:37:06-20:11:36 with a 2-200 keV luminosity of 3.4-7.27 x 10(38) erg s(-1). Basing on the broadband spectral analysis, we find that the flare spectrum shows different behaviors during bright and faint epochs. The spectrum of the flare can be fitted with a model dominated by a power-law component. Additional components show up in the bright epoch with a hard tail and in the faint epoch with an absorption line of similar to 6.78 keV. The reflection component of the latter is consistent with an inner disk radius similar to five times larger than that of the former. These results on the giant flare during the "unusual" low-luminosity state of GRS 1915+105 may suggest that the source experiences a possible fast transition from a jet-dominated state to a wind-dominated state. We speculate that the evolving accretion disk and the large-scale magnetic field may play important roles in this peculiar huge flare.