Orbital parameters of V 0332+53 from 2015 giant outburst data

We present the updated orbital solution for the transient Be X-ray binary V 0332+53 comple- menting historical measurements with the data from the gamma-ray burst monitor onboard Fermi obtained during the outburst in June-October 2015. We model the observed changes in the spin- frequency of the pulsar and deduce the orbital parameters of the system. We significantly improve existing constrains and show that contrary to the previous findings no change in orbital parameters is required to explain the spin evolution of the source during the outbursts in 1983, 2005 and 2015. The reconstructed intrinsic spin-up of the neutron star during the latest outburst is found to be comparable with previosly observed values and predictions of the accretion torque theory.Comment: 3 pages, 2 figures, submitted to A&

An upper limit on nickel overabundance in the supercritical accretion disk wind of SS 433 from X-ray spectroscopy

We take advantage of a long (with a total exposure time of 120 ks) X-ray observation of the unique Galactic microquasar SS 433, carried out with the XMM-Newton space observatory, to search for a fluorescent line of neutral (or weakly ionized) nickel at the energy 7.5 keV. We consider two models of the formation of fluorescent lines in the spectrum of SS 433: 1) due to reflection of hard X-ray radiation from a putative central source on the optically thick walls of the accretion disk "funnel"; and 2) due to scattering of the radiation coming from the hottest parts of the jets in the optically thin wind of the system. It is shown, that for these cases, the photon flux of Ni I K$_{\alpha}$ fluorescent line is expected to be 0.45 of the flux of Fe I K$_{\alpha}$ fluorescent line at 6.4 keV, for the relative nickel overabundance $Z_{Ni}/Z = 10$, as observed in the jets of SS 433. For the continuum model without the absorption edge of neutral iron, we set a 90 per cent upper limit on the flux of the narrow Ni I K$_{\alpha}$ line at the level of $0.9 \times 10^{-5}$ ph s$^{-1}$ cm$^{-2}$. For the continuum model with the absorption edge, the corresponding upper limit is $2.5 \times 10^{-5}$ ph s$^{-1}$ cm$^{-2}$. At the same time, for the Fe I K$_{\alpha}$ line, we measure the flux of $9.9_{8.4}^{11.2} \times 10^{-5}$ ph s$^{-1}$ cm$^{-2}$. Taken at the face value, the results imply that the relative overabundance of nickel in the wind of the accretion disc should be at least 1.5 times less than the corresponding excess of nickel observed in the jets of SS 433.Comment: 17 pages, 12 figures, 4 tables, Astronomy Letters, in press, 2018, Volume 44, Issue

Population of persistent high mass X-ray binaries in the Milky Way

We present results of the study of persistent high mass X-ray binaries (HMXBs) in the Milky Way, obtained from the deep INTEGRAL Galactic plane survey. This survey provides us a new insight into the population of high mass X-ray binaries because almost half of the whole sample consists of sources discovered with INTEGRAL. It is demonstrated for the first time that the majority of persistent HMXBs have supergiant companions and their luminosity function steepens somewhere around ~2x10^{36} erg/s. We show that the spatial density distribution of HMXBs correlates well with the star formation rate distribution in the Galaxy. The vertical distribution of HMXBs has a scale-height h~85 pc, that is somewhat larger than the distribution of young stars in the Galaxy. We propose a simple toy model, which adequately describes general properties of HMXBs in which neutron stars accrete a matter from the wind of the its companion (wind-fed NS-HMXBs population). Using the elaborated model we argue that a flaring activity of so-called supergiant fast X-ray transients, the recently recognized sub-sample of HMXBs, is likely related with the magnetic arrest of their accretion.Comment: 17 pages, 12 figures, accepted for publicatiopn in MNRA