Joint analysis of energy and RMS spectra from MAXI J1535-571 with Insight-HXMT

Abstract

A new black hole X-ray binary (BHXRB) MAXI J1535-571 was discovered by MAXI during its outburst in 2017. Using observations taken by the first Chinese X-ray satellite, the Hard X-ray Modulation Telescope (dubbed as Insight -HXMT), we perform a joint spectral analysis (2-150 keV) in both energy and time domains. The energy spectra provide the essential input for probing the intrinsic Quasi-Periodic Oscillation (QPO) fractional rms spectra (FRS). Our results show that during the intermediate state, the energy spectra are in general consistent with those reported by Swift/XRT and NuSTAR. However, the QPO FRS become harder and the FRS residuals may suggest the presence of either an additional power-law component in the energy spectrum or a turn-over in the intrinsic QPO FRS at high energies.

State transitions of GX 339-4 during its outburst rising phase

“…However, the QPO RMS from different outbursts share the same slope once replace the nonthermal flux with the ratio of non-thermal flux to the total (see Figure 10b), i.e. the RMS is plotted in its definition of what follows: RMS = 𝜎 × 𝐹 c /𝐹 total where 𝐹 total is the time-averaged total flux, 𝜎 denotes the intrinsic RMS, and 𝐹 c represents the flux that contributes to QPO RMS (Kong et al 2020). This is the first observational evidence that GX 339-4 has a same intrinsic QPO RMS during different outbursts.…”

“…𝑃 × [(𝑆 + 𝐵)/𝑆], where 𝑆 is the source average rate, 𝐵 the background average rate, and 𝑃 the power calculated with integration of the QPO Lorentzian function (see Bu et al 2015 andKong et al 2020). The results derived from PDS fitting are listed in Table A2.…”

The spins of the Galactic black holes in MAXI J1535-571 and 4U 1630-472 from Insight-HXMT

“…For GRS 1915+105, an estimate of the black hole spin has been inferred using QPOs, but there is not yet a common consensus on the exact mechanism responsible for QPOs, so that measurement should be taken with caution even if it agrees with previous measurements obtained from the continuum-fitting and the iron line methods. For MAXI J1535-571, Kong et al (2020) analyze only one of the 8 Insight-HXMT observations of MAXI J1535-571, so they have a very low statistics.…”

“…From the analysis of AstroSat data, Sridhar et al ( 2019) find a * = 0.67 +0.16 −0.04 employing the lamppost From the spectral analysis of the Insight-HXMT observation P011453500107 (one of the five observations in our obs 1 of MAXI J1535-571, see Tab. 3), Kong et al (2020) infer the black hole spin parameter a * = 0.7 +0.2 −0.3 (90% C.L.) employing the lamppost version of relxillCp.…”

“…employing the lamppost version of relxillCp. However, Kong et al (2020) is mainly devoted to the timing analysis of the Insight-HXMT observations of MAXI J1535-571 and the measurement of the black hole spin is inferred from a short observation with a low number of photon counts.…”