On the assessment of the disk truncation and detection of type-II-like bursts from the accreting millisecond X-ray Pulsar IGR J17062-6143

Abstract

We present a spectral analysis of the NuSTAR and NICER observations of the accreting millisecond X-ray pulsar IGR J17062-6143, performed in 2022. The source remained in the hard spectral state during these observations, with a luminosity of about $\sim$0.13-0.14 percent of the Eddington luminosity. The continuum emission of the NuSTAR spectrum is entirely dominated by a power-law component or by Comptonized emission of disc photons by a plasma with a high electron temperature ($\gtrsim 100$ keV). The NuSTAR spectrum also reveals clear evidence of disc reflection, a broad Fe K line around 6-8 keV, and a Compton hump peaking at 20 keV, irrespective of the choice of the continuum models. Our spectral studies suggest a disk extending close to the neutron star surface ($\sim$6-20 $R_{\mathrm{g}}$) at low inclination angle ($\sim 41$ degrees), as revealed by the self-consistent relativistic reflection model, relxill. In addition, we detected type-II-like bursts for the first time in the NICER observation of this source. Light curve profiles of type-II-like bursts exhibit different patterns, mostly associated with the so-called mode-0 and transition from mode-0 to mode-1 type-II bursts. The energy spectra of the persistent (pre-burst) and burst emission are well described by an absorbed Comptonization component, scattering disk- and blackbody-distributed photons, respectively, by a corona with a temperature of 1-3 keV. Although the origin of the type-II-like burst is not very clear, it has been possibly linked to disk-magnetosphere interaction of the accretion flow.

arXiv comment30 pages, 8 figures and 6 tables, accepted for publication in JHEAP