Search

Recently, the system parameters of Cygnus X-1, i.e., the black hole mass M, the orbital inclination i and the source distance D, have been updated. As the input constraints of the continuum-fitting method, it is necessary to refine the spin with these new parameters. The Hard X-ray Modulation Telescope (HXMT, also named Insight) was successfully launched on June 15th, 2017 in China. In this work, we analyzed spectra obtained by the Insight-HXMT during 2017-2018 and re-estimated the spin via the continuum-fitting method. We first re-estimated the spin using old parameters and found the dimensionless spin parameter to be a ⁎ > 0.934 (3σ), which is consistent with previous measurements both from the continuum-fitting and iron-line fitting methods ( Gou et al. 2011 , Gou et al. 2014 ; Fabian et al. 2012 , Walton et al. 2016 , Tomsick et al. 2018 ). Then, when the new parameters were applied, we obtained an increased spin: a ⁎ > 0.967 (3σ), which is also consistent with the recent measurement (Zhao et al. 2020, submitted to ApJ) and also confirms an extreme Kerr black hole lying in this system.

The Einstein Probe is a small mission dedicated to time-domain astronomy to monitor the sky in the soft X-ray band (0.5–4 keV). It will carry out systematic survey and characterisation of high-energy transients at unprecedented sensitivity, spatial resolution, Grasp and monitoring cadence. Its wide-field imaging capability, as provided by an X-ray monitor with a field of view of 3600 square degrees, is enabled by using established technology of micro-pore lobster-eye focusing optics. Complementary to this wide-field instrument is a follow-up X-ray telescope with a large effective area and a narrow field of view. It is also capable of real time triggering and downlink of transient alerts on the fly, in order to activate multi-wavelength follow-up observations by other astronomical facilities worldwide. Its scientific goals are concerned with discovering new or rare types of transients, particularly tidal disruption events, supernova shock breakouts, high-redshift gamma-ray bursts and, particularly, electromagnetic sources associated with gravitational wave events. The mission is planned for launch around end of 2022, with a lifetime of three years and five years as a goal.

Gamma-ray bursts (GRBs) with long durations originate from collapse of massive stars, and this is the present popular idea about the mechanism of energy source of GRBs. Massive stars are unavoidably surrounded by stellar winds. It is also commonly believed that jets exist in GRBs. On the basis of these two viewpoints, the authors performed detailed calculations of the evolution of jets in the stellar wind environment. Because in the transition from relativistic to non-relativistic phase there are serious problems in the traditional formulae for the description of jets, some revised formulae are used. Finally, the authors' results on the evolution in the stellar wind environment are compared with those in the homogeneous medium environment, and with the results of Livio and Waxman. The following conclusions are drawn: (1) In the stellar wind environment, even for calculations up to 109s, the flux density does not show any clear tendency of levelling off. (2) In the vicinity of γ = 1/θ0 there is no break in the light curve. (Here θ0 is the initial half aperture angle.) (3) When the shock wave changes from a relativistic to a non-relativistic phase, there is a break in the light curve. (4) In comparison with the homogeneous medium, the flux density in the stellar wind environment is comparatively small.