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arXiv · 2202.01401

Discovery and Long-term Broadband X-ray monitoring of Galactic Black Hole Candidate MAXI J1803-298

Megumi Shidatsu·Kohei Kobayashi·Hitoshi Negoro·Wataru Iwakiri·Satoshi Nakahira·Yoshihiro Ueda·Tatehiro Mihara·Teruaki Enoto·Keith Gendreau·Zaven Arzoumanian·John Pope·Bruce Trout·Takashi Okajima·Yang Soong
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Abstract

We report the results from the broad-band X-ray monitoring of the new Galactic black hole candidate MAXI J1803$-$298 with the MAXI/GSC and Swift/BAT during its outburst. After the discovery on 2021 May 1, the soft X-ray flux below 10 keV rapidly increased for $\sim 10$ days and then have been gradually decreasing over 5 months. At the brightest phase, the source exhibited the state transition from the low/hard state to the high/soft state via the intermediate state. The broad-band X-ray spectrum during the outburst was well described with a disk blackbody plus its thermal or non-thermal Comptonization. Before the transition the source spectrum was described by a thermal Comptonization component with a photon index of $\sim 1.7$ and an electron temperature of $\sim 30$ keV, whereas a strong disk blackbody component was observed after the transition. The spectral properties in these periods are consistent with the low/hard state and the high/soft state, respectively. A sudden flux drop with a few days duration, unassociated with a significant change in the hardness ratio, was found in the intermediate state. A possible cause of this variation is that the mass accretion rate rapidly increased at the disk transition, which induced a strong Compton-thick outflow and scattered out the X-ray flux. Assuming a non-spinning black hole, we estimated a black hole mass of MAXI J1803$-$298 as $5.8 \pm 0.4~(\cos i/\cos 70^\circ)^{-1/2} (D/8~\mathrm{kpc})~M_\odot$ (where $i$ and $D$ are the inclination angle and the distance) from the inner disk radius obtained in the high/soft state.

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Megumi Shidatsu, Kohei Kobayashi, Hitoshi Negoro, Wataru Iwakiri, Satoshi Nakahira, Yoshihiro Ueda, Tatehiro Mihara, Teruaki Enoto, Keith Gendreau, Zaven Arzoumanian, John Pope, Bruce Trout, Takashi Okajima, Yang Soong. 2022-02-03. Discovery and Long-term Broadband X-ray monitoring of Galactic Black Hole Candidate MAXI J1803-298. https://doi.org/10.3847/1538-4357%2Fac517b

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