Modeling the Multiwavelength Light Curves of PSR B1259-63/Ls 2883. Ii. The Effects of Anisotropic Pulsar Wind and Doppler Boosting

Abstract

PSR B1259-63/LS 2883 is a binary system in which a 48-ms pulsar orbits around a Be star in a high eccentric orbit with a long orbital period of about 3.4 yr. It is special for having asymmetric two-peak profiles in both the X-ray and the TeV light curves. Recently, an unexpected GeV flare was detected by Fermi gamma-ray observatory several weeks after the last periastron passage. In this paper, we show that this observed GeV flare could be produced by the Doppler-boosted synchrotron emission in the bow shock tail. An anisotropic pulsar wind model, which mainly affects the energy flux injection to the termination shock in different orbital phase, is also used in this paper, and we find that the anisotropy in the pulsar wind can play a significant role in producing the asymmetric two-peak profiles in both X-ray and TeV light curves.The X-ray and TeV photons before periastron are mainly produced by the shocked electrons around the shock apex and the light curves after periastron are contributed by the emission from the shock apex and the shock tail together, which result in the asymmetric two-peak light curves.

Multi-wavelength observations of the binary system PSR B1259−63/LS 2883 around the 2014 periastron passage

“…In the model discussed in Kong, Cheng & Huang (2012) the observed X-ray and GeV emission is explained as synchrotron emission from the postshock relativistic electrons Doppler-boosted at the particular orbital phase. This model is able to describe the observed spectra pretty well, but fails to explain the substantial shift of the X-ray and GeV light curve peaks.…”

Pulsar-Wind Nebulae

“…particles escaping from the system. Among other types of binaries which can shed light on the properties of pulsar winds at smaller distances from the pulsar through the interaction with the companion are the famous double pulsar (see e.g., , recently reported very eccentric binary with PSR J2032+4127 (Lyne et al 2015), and black widow pulsar B1957+20 (Huang et al 2012). …”

“…The flare is about 10-times brighter than the predicted emission at periastron, which represents a gamma-ray luminosity comparable to the pulsar spin-down power. A radiative efficiency close to 100% is in principle achievable with inverse Compton scattering, but the density of stellar photons is far too low to explain the flux at these phases, unless there are extra sources of radiation close to the pulsar (see, e.g., Dubus and Cerutti 2013), or significant Doppler boosting of the emission towards the observer (Dubus et al 2010;Kong et al 2012). The flare peaks at 300 MeV and is seen only in the GeV band, which suggests that the particle energy distribution must be very narrow.…”

The Hour-timescale GeV Flares of PSR B1259–63 in 2017

“…In a previous modeling work on the GeV flare, Khangulyan et al (2012) used the IC scattering of the unshocked PW off soft photons from the Be star, while Dubus & Cerutti (2013) brought up an IC model using the X-ray synchrotron radiation from the shock as the IC target photons. Kong et al (2012) used the synchrotron model with relativistic flows beaming toward Earth along the bow shock tails. All of these previous models, which are heavily dependent on the terminal shock geometry, lack an explanation for either the delay of the GeV flaring period or the sporadic hour-timescale flares.…”

“…The unshocked PW particles may also generate γ-rays (Khangulyan et al 2012). The interaction between the stellar disk and the pulsar (Chernyakova et al 2014), as well as Doppler boosting (Dubus et al 2010;Kong et al 2012), was also suggested to play a major role in producing the GeV flares.…”