The reflection component in the average and heartbeat spectra of the black hole candidate IGR J17091-3642 during the 2016 outburst

Abstract

We present simultaneous NuSTAR and Swift observations of the black hole transient IGR J17091-3642 during its 2016 outburst. By jointly fitting six NuSTAR and four Swift spectra, we found that during this outburst the source evolves from the hard to the hard/soft intermediate and back to the hard state, similar to the 2011 outburst. Unlike in the previous outburst, in this case we observed both a broad emission and an moderately broad absorption line in our observations. Our fits favour an accretion disc with an inclination angle of ∼45 • with respect to the line of sight and a high iron abundance of 3.5 ± 0.3 in units of the solar abundance. We also observed heartbeat variability in one NuSTAR observation. We fitted the phase-resolved spectra of this observation and found that the reflected emission varies independently from the direct emission, whereas in the fits to the average spectra these two quantities are strongly correlated. Assuming that in IGR J17091-3642 the inner radius of the disc both in the average and the phase-resolved spectra is located at the radius of the innermost stable circular orbit, with 90% confidence the spin parameter of the black hole in this system is −0.13 ≤ a * ≤ 0.27.

Simultaneous detection of an intrinsic absorber and a compact jet emission in the X-ray binary IGR J17091−3624 during a hard accretion state

“…We note that during the 2016 outburst multiple NuS-TAR observations of IGR J17091-3624 were taken, however we note that they were not simultaneous with respect to the XMM-Newton observations and therefore cannot be used to model the high-energy band. We find in the XMM-Newton spectra signatures of reflection via the presence of a broad Fe line, similar to those present in the NuSTAR data (Xu et al 2017;Wang et al 2018). However, in this paper, due to the lack of simultaneous hard X-ray observations, we use a simple Gaussian model to fit the line rather than a reflection component (see Section 3) and focus for the search of absorbers in the spectra.…”

“…Their best-fit model indicates an inclination angle of the accretion disc of ∼ 30 • − 40 • . Wang et al (2018) support these conclusions in their analysis of the same data, although their reflection model requires an abundance of Fe=(3.5 ± 0.3) compared to (1.77<Fe<2.95) reported by Xu et al (2017). However, they pointed out that model assumptions, such as the photon-index of the incident continuum spectrum and the density profile, strongly affect the iron abundance.…”

A Variable Ionized Disk Wind in the Black Hole Candidate EXO 1846–031

“…Apart from the thermal and nonthermal components, emissionand absorption-line features have also been widely observed in BHXBs, especially the broad emission line centered at 6.4-7 keV (e.g., Laor 1991;Miller 2007;García et al 2015;Wang et al 2018). As the most prominent feature of disk reflection, such emission line is produced when the nonthermal/hard emission illuminates the accretion disk (Lightman & White 1988;George & Fabian 1991;García et al 2014;Dauser et al 2014), though the illuminating source has also been attributed to the surface emission or the boundary layer in neutron star X-ray binaries (e.g., Ross & Fabian 2005;Cackett et al 2010;Miller et al 2015;Wang et al 2019).…”

NuSTAR monitoring of MAXI J1348-630: evidence of high density disc reflection

“…The mass of MAXI J1348-630 has been reported to be 9.1 +1.6 −1.2 M by Jana et al ( 2020) and 13 ± 2 M by Tominaga et al (2020), further rectified to be 11 ± 2 M by Lamer et al (2020). Using equation 3 from Wang et al (2018) and the correction factor from Kubota et al (1998) for the soft state diskbb normalisation, we find the black hole mass to be ∼ 11.6 − 19.4 M . We note that the calculated mass from the NuSTAR diskbb normalisation is likely to be incorrect, due to lack of <3 keV spectra in NuSTAR.…”