The semicentennial binary system PSR J2032+4127 at periastron: X-ray photometry, optical spectroscopy and SPH modelling.

Abstract

X-ray photometry and optical spectra are presented covering the periastron passage of the highly-eccentric, ∼50 year binary system PSR J2032+4127 in November 2017. This system consists of a 143 ms pulsar in orbit around a massive OB star, MT 91-213. The data show dramatic changes during the encounter as the pulsar wind collided with the stellar wind. The X-ray flux rose on the approach to periastron, then underwent a major dip in the few days around periastron, and then gradually declined over the next few weeks. The optical spectroscopy revealed a steady decline in the Hα line strength on the approach to periastron (from an Equivalent Width of -15Å to -7Å) implying a truncation of the OB star's circumstellar disk by the approaching neutron star. Smooth Particle Hydrodynamic (SPH) modelling is used here to model the system within the context of the observed behaviour and predict the geometrical configuration of the circumstellar disk with respect to the pulsar's orbit.

X-Ray Spectral Evolution of PSR J2032+4127 during the 2017 Periastron Passage

“…Synchrotron radiation is responsible for the emission of X-ray photons in this system (Chen et al 2019). Coe et al (2019) has reported the presence of circumstellar disk and the interaction of the compact object with the circumstellar disk for PSR J2032+4127 during the periastron. Now we can infer that the Inverse Compton Scattering may be the cause of the spectral softening for PSR J2032+4127 after periastron passage.…”

Gamma-ray binaries

“…The time evolution of PSR J2032+4127 was modelled by [Li+18] (radio, X-ray and GeV bands), [Coe+19](optics and X-ray) and [Che+19c] (X-ray to TeV band and spectral modelling). [Li+18] suggested that the strong X-ray dip close to periastron is explained by an increase of the magnetization parameter of the star-pulsar colliding winds shock accompanied by flux suppression due to Doppler boosting effect.…”

X-Ray and Radio Variabilities of PSR J2032+4127 near Periastron

“…We can compare our results with the X-ray light curve from Swift. The latter was converted from the count rates reported by Coe et al (2019), assuming average N H = 1.15 × 10 22 cm −2 and Γ = 1.47 from the XMM-Newton and NuSTAR fits. The results are plotted in Figure 5.…”

“…the third and fourth XMM-Newton/NuSTAR observations. Over a longer timescale, the X-ray flux gradually increased before periastron, then showed a drastic dip at periastron and quick recovery, followed by a long declining trend by more than an order of magnitude in a year (see Li et al 2018;Coe et al 2019).…”

“…There are fewer than ten gamma-ray binaries known and only two of them, PSRs J2032+4127 and B1259−63, have pulsations detected, which firmly established the pulsar nature of the compact objects. The pulsar spin parameters give direct constraints on the energy input from its wind, allowing detailed physical modeling (e.g., Takata et al 2017;Petropoulou et al 2018;Coe et al 2019). PSR J2032+4127 (hereafter J2032) was first identified as a gamma-ray pulsar with the Fermi Gamma-Ray Space Telescope (Abdo et al 2009) and then later detected in radio and X-rays (Camilo et al 2009).…”