A detailed study on the reflection component for the black hole candidate MAXI J1836−194

Abstract

We present a detailed spectral analysis of the black hole candidate MAXI J1836-194. The source was caught in the intermediate state during its 2011 outburst by Suzaku and RXTE. We jointly fit the X-ray data from these two missions using the relxill model to study the reflection component, and a steep inner emissivity profile indicating a compact corona as the primary source is required in order to achieve a good fit. In addition, a reflection model with a lamp-post configuration (relxilllp), which is normally invoked to explain the steep emissivity profile, gives a worse fit and is excluded at 99% confidence level compared to relxill. We also explore the effect of the ionization gradient on the emissivity profile by fitting the data with two relativistic reflection components, and it is found that the inner emissivity flattens. These results may indicate that the ionization state of the disc is not constant. All the models above require a supersolar iron abundance higher than ∼ 4.5. However, we find that the high-density version of reflionx can describe the same spectra even with solar iron abundance well. A moderate rotating black hole (a * = 0.84-0.94) is consistently obtained by our models, which is in agreement with previously reported values.2 Yanting Dong et al. INTRODUCTIONGalactic X-ray binaries are believed to be powered by accretion onto stellar-mass black holes or neutron stars. The gases in accretion disc emit thermal radiation in UV/X-ray band (Shakura & Sunyaev 1973). Some fraction of the thermal photons from the disc are then inverse Compton scattered by energetic electrons in the hypothetically hot corona, producing a hard X-ray spectrum in the form of power-law, i.e. N(E) ∝ E −Γ . A fraction of the high-energy photons will irradiate the cold accretion disc, generating the so-called X-ray reflection component (Fabian et al. 1989). The main features of the reflection spectrum are the fluorescent Fe Kα emission line at energies of 6.4-6.97 keV (depend upon the ionization state of the disc) and the Compton hump at 20-30 keV (Young et al. 1999).The profile of the reflection spectrum will be smeared due to the effects of Doppler shift, special relativity, and general relativity if it comes from the inner region of the accretion disc (Fabian et al. 2000). Observationally, the most prominent effect is that the intrinsically narrow Fe Kα line is broadened and skewed to an asymmetric shape. The profile of the broad line, especially the red wing of the line, is directly linked to the inner radius of the accretion disc which is thought to be at the innermost stable circular orbit (ISCO), i.e. R in = R ISCO . Thus, by modelling the broad iron line, we can deduce the spin of the black hole based on the relation between the spin and the ISCO (Bardeen et al. 1972). However, the line profile is readily affected by the subtraction of continuum and other components. Therefore, Reynolds (2014) pointed out that a more accurate measurement of the spin can be achieved by modelling the full reflection spectrum. The spin...

Correlating spectral and timing properties in the evolving jet of the micro blazar MAXI J1836-194

“…We stress that the goal of these phenomenological spectral fits is simply to constrain the location of the X-ray emitting region by quantifying the presence or absences of reflection features. These phenomenological spectral fits favour the inverse Compton scenario, as the reflection features are very strong, particularly near the peak of the outburst, in agreement with other works (Reis et al 2012, Dong et al 2020). This picture is further strengthened by our tentative detection of a hard lag in the X-ray lightcurves.…”

“…MAXI J1836−194 is a low mass BHXB that went in outburst during late August 2011; it was quickly identified as a black hole candidate (Negoro et al 2011, Strohmayer & Smith 2011, Miller-Jones et al 2011, Russell et al 2011. Later studies of the source's X-ray spectra found that the black hole spin is likely high (≈ 0.9), and that the hard X-rays show a very prominent reflection component (Reis et al 2012, Dong et al 2020. Rather than undergoing a full outburst, the source reached a hard-intermediate state (HIMS) before going back into the HS and fading into quiescence (Ferrigno et al 2012).…”

Plasma environment effects on K lines of astrophysical interest

“…Supersolar abundances have been inferred from K lines of different elements observed in the X-ray spectra of X-ray binaries (XRB) and active galactic nuclei (AGN) (see e.g., Kallman et al (2009); Dong et al (2020); Walton et al (2020); Fukumura et al (2021)). These absorption and emission features can occur in the inner regions of the black-hole accretion disks where the plasma densities are predicted to range from 10 15 to 10 22 cm −3 (Schnittman et al 2013).…”

Plasma environment effects on K lines of astrophysical interest. V. Universal formulae for ionization potential and K-threshold shifts

“…Supersolar abundances have been inferred from K lines of different elements observed in the X-ray spectra of X-ray binaries (XRB) and active galactic nuclei (AGN) (see e.g., Kallman et al (2009); Dong et al (2020); Walton et al (2020); Fukumura et al (2021)). These absorption and emission features can occur in the inner regions of the black-hole accretion disks where the plasma densities are predicted to range from 10 15 to 10 22 cm −3 (Schnittman et al 2013).…”