The launch of NuSTAR and the increasing number of binary black hole (BBH) mergers detected through gravitational wave observations have exponentially advanced our understanding of BHs. Despite the simplicity owed to being fully described by their mass and angular momentum, BHs have remained mysterious laboratories that probe the most extreme environments in the universe. While significant progress has been made in the recent decade, the distribution of spin in BHs has not yet been understood. In this work, we provide a systematic analysis of all known BHs in X-ray binary systems (XBs) that have previously been observed by NuSTAR, but have not yet had a spin measurement made using the “relativistic reflection” method obtained from those data. By looking at all the available archival NuSTAR data of these sources, we measure 10 new BH spins: IGR J17454-2919 − a=0.97−0.17+0.03; GRS 1758-258 − a=0.991−0.019+0.007; MAXI J1727-203 − a=0.986−0.159+0.012; MAXI J0637-430 − a = 0.97 ± 0.02; Swift J1753.5-0127 − a=0.997−0.003+0.001; V4641 Sgr − a=0.86−0.06+0.04; 4U 1543-47 − a=0.98−0.02+0.01; 4U 1957+11 − a=0.95−0.04+0.02; H 1743-322 − a=0.98−0.02+0.01; and MAXI J1820+070 − a=0.988−0.028+0.006 (all uncertainties are at the 1σ confidence level). We discuss the implications of our measurements on the entire distribution of stellar-mass BH spins in XBs, and we compare them with the spin distribution in BBHs, finding that the two distributions are clearly in disagreement. Additionally, we discuss the implications of this work on our understanding of how the “relativistic reflection” spin measurement technique works, and discuss possible sources of systematic uncertainty that can bias our measurements.

https://iopscience.iop.org/article/10.3847/1538-4357/acafe7/pdf

A Systematic View of Ten New Black Hole Spins


 We report results on the joint-fit of the NuSTAR and HXMT data for the black hole X-ray binary candidate MAXI J1535-571. The observations were obtained in 2017 when the source evolved through the hard, hard-intermediate and soft-intermediate states over the rising phase of the outburst. After subtracting continuum components, X-ray reflection signatures are clearly showed in those observations. By modeling the relativistic reflection in detail, we find that the inner radius Rin is relatively stable with Rin ≲ 1.55Rg during the three states, which implies that the inner radius likely extends to the innermost stable circular orbit even in the bright hard state. When adopting Rin = RISCO, the spin parameter is constrained to be $0.985_{-0.004}^{+0.002}$ at 90 per cent confidence (statistical only). The best-fitting results reveal that the inclination of the inner accretion disc is ∼70 − 74 degrees, which notably conflicts with the apparent orientation of the ballistic jet (≤45 degrees). In addition, both the photon index and the electron temperature increase during the transition from hard to soft state. It seems that the corona evolves from dense low-temperature in the LHS to tenuous high-temperature after the state transition, which indicates that the state transition is accompanied by the evolution of the coronal properties.

/pdf/analysis-of-the-reflection-spectra-of-maxi-j1535-571-in-the-17ajx4hc.pdf

Analysis of the reflection spectra of MAXI J1535-571 in the hard and intermediate states

The power-law emission and reflection component provide valuable insights into the accretion process around a black hole. In this work, thanks to the broadband spectra coverage of the Nuclear Spectroscopic Telescope Array, we study the spectral properties for a sample of low-mass black hole X-ray binaries (BHXRBs). We find that there is a positive correlation between the photon index Γ and the reflection fraction R (the ratio of the coronal intensity that illuminates the disk to the coronal intensity that reaches the observer), consistent with previous studies, but except for MAXI J1820+070. It is quite interesting that this source also deviates from the well-known “V”-shaped correlation between the photon index Γ and the X-ray luminosity logLX , when it is in the bright hard state. More specifically, the Λ-shaped correlation between Γ and logL X is observed, as the luminosity decreases by a factor of 3 in a narrow range from ∼1038 to 1037.5 erg s−1. Furthermore, we discover a strong positive correlation between R and the X-ray luminosity for BHXRBs in the hard state, which puts a constraint on the disk-corona coupling and the evolution.

https://iopscience.iop.org/article/10.3847/1538-4357/acba11/pdf

X-Ray Spectral Correlations in a Sample of Low-mass Black Hole X-Ray Binaries in the Hard State

AT2019wey is a new galactic X-ray binary that was first discovered as an optical transient by the Australia Telescope Large Area Survey (ATLAS) on December 7, 2019. AT2019wey consists of a black hole candidate as well as a low-mass companion star ($M_{\text {star }} \lesssim 0.8 M_{\odot}$) and is likely to have a short orbital period ($P_{\text {orb }} \lesssim 8$ h). Although AT2019wey began activation in the X-ray band during almost the entire outburst on March 8, 2020, it did not enter the soft state during the entire outburst. In this study, we present a detailed spectral analysis of AT2019wey in the low/hard state during its X-ray outburst on the basis of Nuclear Spectroscopic Telescope Array \emph observations. We obtain tight constraints on several of its important physical parameters by applying the State-of-art \texttt{relxill} relativistic reflection model family. In particular, we determine that the measured inner radius of the accretion disk is most likely to have extended to the innermost stable circular orbit (ISCO) radius, i.e., $R_{\text{in}}=1.38^{+0.23}_{-0.16}~R_{\text{ISCO}}$. Hence, assuming $R_{\text{in}}$=$R_{\text{ISCO}}$, we find the spin of AT2019wey to be $a_{*}\sim$$0.97$, which is close to the extreme and an inner disk inclination angle of ~$i\sim$$22 ^{\circ}$. Additionally, according to our adopted models, AT2019wey tends to have a relatively high iron abundance of $A_{\mathrm{Fe}}\sim$ 5 $A_{\mathrm{Fe}, \odot}$ and a high disk ionization state of $\log \xi\sim$ 3.4.

Spectral Analysis of New Black Hole Candidate AT2019wey Observed by NuSTAR

AT2019wey is a new galactic X-ray binary that was first discovered as an optical transient by the Australia Telescope Large Area Survey (ATLAS) on December 7, 2019. AT2019wey consists of a black hole candidate as well as a low-mass companion star ($M_{\text {star }} \lesssim 0.8 M_{\odot}$) and is likely to have a short orbital period ($P_{\text {orb }} \lesssim 8$ h). Although AT2019wey began activation in the X-ray band during almost the entire outburst on March 8, 2020, it did not enter the soft state during the entire outburst. In this study, we present a detailed spectral analysis of AT2019wey in the low/hard state during its X-ray outburst on the basis of Nuclear Spectroscopic Telescope Array \emph observations. We obtain tight constraints on several of its important physical parameters by applying the State-of-art \texttt{relxill} relativistic reflection model family. In particular, we determine that the measured inner radius of the accretion disk is most likely to have extended to the innermost stable circular orbit (ISCO) radius, i.e., $R_{\text{in}}=1.38^{+0.23}_{-0.16}~R_{\text{ISCO}}$. Hence, assuming $R_{\text{in}}$=$R_{\text{ISCO}}$, we find the spin of AT2019wey to be $a_{*}\sim$ $0.97$, which is close to the extreme and an inner disk inclination angle of ~$i\sim$ $22 ^{\circ}$. Additionally, according to our adopted models, AT2019wey tends to have a relatively high iron abundance of $A_{\mathrm{Fe}}\sim$ 5 $A_{\mathrm{Fe}, \odot}$ and a high disk ionization state of $\log \xi\sim$ 3.4.

Huixian Li

Papers

Spectral Analysis of New Black Hole Candidate AT2019wey Observed by NuSTAR

Spectral Analysis of New Black Hole Candidate AT2019wey Observed by NuSTAR