标题： 银河系黑洞候选体MAXI J1803-298的发现和长期宽波段X射线监测 显示英文标题

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

摘要： 我们报告了在爆发期间使用MAXI/GSC和Swift/BAT对新的银河系黑洞候选体MAXI J1803$-$298进行的宽波段X射线监测结果。在2021年5月1日发现之后，低于10 keV的软X射线通量在$\sim 10$天内迅速增加，然后逐渐减少持续了5个月。在最亮阶段，该源经历了从低/硬态到高/软态的态转变，通过中间态。爆发期间的宽波段X射线谱可以用一个盘黑体加上其热或非热康普顿化来很好地描述。在转变之前，源谱由一个光子指数为$\sim 1.7$的热康普顿化成分和电子温度为$\sim 30$keV 的成分描述，而在转变之后观察到了一个强烈的盘黑体成分。这些时期的光谱特性分别与低/硬态和高/软态一致。在中间态中发现了一次持续几天的通量突然下降，这与硬度比没有显著变化无关。这种变化的可能原因是，在盘转变时质量吸积率迅速增加，导致强烈的康普顿厚外流并散射出X射线通量。 假设一个非自转黑洞，我们从高/软态中获得的内盘半径估计了MAXI J1803$-$298的黑洞质量为$5.8 \pm 0.4~(\cos i/\cos 70^\circ)^{-1/2} (D/8~\mathrm{kpc})~M_\odot$（其中$i$和$D$分别为倾斜角度和距离）。 显示英文摘要

摘要： 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.