High-Mass X-ray Binaries in the Milky Way: A closer look with INTEGRAL

Abstract

High-mass X-ray binaries are fundamental in the study of stellar evolution, nucleosynthesis, structure and evolution of galaxies and accretion processes. Hard X-rays observations by INTEGRAL and Swift have broadened significantly our understanding in particular for the super-giant systems in the Milky Way, which number has increased by almost a factor of three. INTEGRAL played a crucial role in the discovery, study and understanding of heavily obscured systems and of fast X-ray transients. Most super-giant systems can now be classified in three categories: classical/obscured, eccentric and fast transient.The classical systems feature low eccentricity and variability factor of ∼ 10 3 , mostly driven by hydrodynamic phenomena occurring on scales larger than the accretion radius. Among them, systems with short orbital periods and close to Roche-Lobe overflow or with slow winds, appear highly obscured. In eccentric systems, the variability amplitude can reach even higher factors, because of the contrast of the wind density along the orbit. Four super-giant systems, featuring fast outbursts, very short orbital periods and anomalously low accretion rates, are not yet understood.Simulations of the accretion processes on relatively large scales have progressed and reproduce parts of the observations. The combined effects of wind

Is 4U 0114+65 an eclipsing HMXB?

“…Finally we suggest that the variations of the absorption column density (see Figure 6) recorded during the Suzaku observation on time-scales of few thousand seconds might be due to the presence of clumps in the wind of the supergiant companion as observed also in other similar systems (see, e.g., GX 301-2, Vela X-1, Cen X-3 and OAO 1657-415; Mukherjee & Paul 2004;Fürst et al 2010;Naik, Paul & Ali 2011;Pradhan et al 2014;Walter et al 2015 ) 4 ACKNOWLEDGEMENT…”

NuSTARdiscovery of a cyclotron absorption line in the transient X-ray pulsar 2S 1553−542

“…The recent outburst from BeXRP 2S 1553−542 was only the third transient event when the source came into the view of X-ray instruments. Thanks to the NuSTAR wide energy coverage and high sensitivity we were able to discover a cyclotron absorption line with centroid energy Ecyc = 23.5 ± 0.4 keV, corresponding to the neutron star magnetic field strength B ∼ 3 × 10 12 G typical for the known X-ray pulsars (Walter et al 2015). The presence of the cyclotron line in the source spectrum is also supported by the behaviour of the pulse profile and pulsed fraction with the energy.…”

“…The main purpose of the performed NuSTAR observations was searching for the cyclotron resonant scattering feature (CRSF) in the source spectrum, measuring its parameters in the case of the discovery or putting strict limits on its presence. The NuSTAR observatory is perfectly suitable for these purposes, as it covers uniformly the energy range from 3 to 79 keV (without a necessity to combine different instruments with different response matrixes, like it was for the RXTE or INTEGRAL observatories) and has an unprecedented sensitivity in the energy range 10-50 keV, where most of known cyclotron absorption lines were detected (see, e.g., Walter et al 2015, for a recent review of high mass Xray binaries). Moreover, good timing capabilities of NuSTAR allow to perform the same analysis also for pulse phase resolved spectra, as sometimes cyclotron features are detected only for limited pulse phase intervals and not seen in the pulse averaged spectra.…”

Numerical simulations of axisymmetric hydrodynamical Bondi–Hoyle accretion on to a compact object

“…The harvest of X-ray data provided by the last decade satellites not only spotted previously unseen sources but also promoted some accreting systems which were, up to now, merely marginal cases, to the rank of representatives of a well-established observational family. It is, e.g., the case for the super-giant X-ray binaries (sgxb), a kind of wind accreting systems which number has increased by almost a factor of three thanks to integral and Swift monitoring (Walter et al 2015). The last few years have also seen an increasing interest into Hyper-Luminous X-ray sources (hlx) which seem to spectrally behave in a qualitatively similar way as galactic X-ray binaries hosting black hole candidates, exhibiting low/hard and high/soft states (van der Marel 2003;Miller and Colbert 2004;Webb et al 2014).…”