Meta-analysis of Electron Cyclotron Resonance Absorption Features Detected in High-Mass X-ray Binaries

Abstract

Using recent compilations of detailed X-ray observations and spectral models of exceptional quality, we record the electron cyclotron resonance absorption (ECRA) features that have been detected in 45 pulsating high-mass X-ray binaries (HMXBs) and ultraluminous X-ray (ULX) sources harboring neutron stars, although seven of these detections are still questionable and another 21 are single and/or not independently confirmed. From the comprehensive catalogs of Jaisawal \& Naik and Staubert et al. and from several additional recent observations, we produce two lists of HMXB ECRA sources: a list of 17 sources in which multiple ECRA lines or single very low-energy lines are seen, in which we can reasonably assume that the lowest energy reveals the fundamental cyclotron level for each source; and a `contaminated' list of 38 sources including the 21 detections of single ECRA lines that may (not) be higher-level harmonics. Both lists confirm a previous result that we have obtained independently by modeling the propeller lines of Magellanic HMXB pulsars: the surface dipolar magnetic fields $B_{\ast }$ of HMXB neutron stars are segregated around five distinct values with $B_{\ast }=0.28\pm 0.08,0.55\pm 0.11,1.3\pm 0.37,3.0\pm 0.68$, and $7.9\pm 3.1$, in units of TG. An explanation of this phenomenon is currently lacking. We have found no correlation between these $B_{\ast }$ values and the corresponding observed spin periods, spin period derivatives, orbital periods, maximum X-ray luminosities, neutron star masses, or companion star masses.

Submitted to RAA. This version incorporates the referee's comments and matches the published version

References in corpus (3)

• Cyclotron lines in highly magnetized neutron stars
• No magnetars in ULXs
• Evidence of magnetic field decay in massive main-sequence stars

Cited by in corpus (4)

• Ultraluminous X-ray sources
• A NuSTAR observation of the eclipsing binary system OAO 1657-415: The revival of the cyclotron line
• Drop in the hard pulsed fraction and a candidate cyclotron line in IGR J16320-4751 seen by NuSTAR
• Constraints on cyclotron features and accretion regime in the high-mass X-ray binary 4U 1700-37 from NuSTAR