Post-Periastron Gamma-Ray Flare From PSR B1259–63/Ls 2883 as a Result of Comptonization of the Cold Pulsar Wind

Abstract

We argue that the bright flare of the binary pulsar PSR B1259−63/LS2883 detected by the Fermi Large Area Telescope (LAT), is due to the inverse Compton (IC) scattering of the unshocked electron-positron pulsar wind with a Lorentz factor Γ 0 ≈ 10 4 . The combination of two effects both linked to the circumstellar disk (CD), is a key element in the proposed model. The first effect is related to the impact of the surrounding medium on the termination of the pulsar wind. Inside the disk, the "early" termination of the wind results in suppression of its gamma-ray luminosity. When the pulsar escapes the disk, the conditions for termination of the wind undergo significant changes. This would lead to a dramatic increase of the pulsar wind zone, and thus to the proportional increase of the gamma-ray flux. On the other hand, if the parts of the CD disturbed by the pulsar can supply infrared photons of density high enough for efficient Comptonization of the wind, almost the entire kinetic energy of the pulsar wind

Pulsar-Wind Nebulae

“…Collaboration et al 2013). The very-high energy radiation is often interpreted as inverse Compton scattering of the UV stellar photons on relativistic pairs accelerated near the shock front between the pulsar wind and the stellar wind (e.g., Tavani and Arons 1997;Kirk et al 1999;Khangulyan et al 2007). The model predicts a maximum of GeV gamma-ray emission close to periastron which was indeed observed for the first time by the Fermi-LAT during the 2010 periastron passage (Tam et al 2011;Abdo et al 2011a).…”

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

“…Such a possibility was considered by Khangulyan et al (2012). In this case, the energies of electrons in the unshocked pulsar wind are much lower, in the GeV range.…”

“…Electrons/positrons in the unshocked pulsar wind propagate to larger distances and could give away a larger fraction of their energy to the inverse Compton radiation while remaining in the unshocked wind. With a suitable assumption about the UV luminosity of the circumstellar disk (which turns out to be very high, exceeding the stellar luminosity, possibly as a result of local heating of the Be star disk by the pulsar crossing, see Khangulyan et al (2012)), one could find that nearly 100% of the spin-down luminosity of the pulsar could be converted into γ-ray power in the unshocked wind if its volume becomes sufficiently large during the flare.…”

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

“…This terminal shock model has explained the periodic light curve of the non-thermal X-ray emission very well; see, e.g., Takata et al (2012). 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.…”

“…Electrons accelerated in the shock between the PW and stellar wind can produce synchrotron radiation and/or upscatter stellar or disk photons from LS2883to produce inverse-Compton (IC) radiation (Tavani & Arons 1997;Kirk et al 1999;Dubus 2006;Bogovalov et al 2008;Khangulyan et al 2011;Kong et al 2011;Takata et al 2012;Mochol & Kirk 2013). 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.…”