TeV Flux modulation in PSR B1259-63/LS 2883

TL;DR

This paper investigates the variability of TeV gamma-ray flux in the binary system PSR B1259-63/LS 2883, analyzing how orbital separation and non-radiative cooling influence high-energy emission observed by H.E.S.S.

Contribution

It introduces a model linking TeV flux variability to orbital phase-dependent adiabatic losses and proposes non-radiative cooling profiles to explain observed flux changes.

Findings

TeV flux correlates with binary separation.

Non-radiative cooling dominates near periastron.

Stellar disc location matches radio observations.

Abstract

PSR B1259-63/LS 2883 is a binary system where a 48 ms pulsar orbits a massive Be star with a highly eccentric orbit (e=0.87) with a period of 3.4 years. The system exhibits variable, non-thermal radiation visible from radio to very high energies (VHE) around periastron passage. This radiation is thought to originate from particles accelerated in the shock region between the pulsar wind (PW) and stellar outflows. The consistency of the H.E.S.S. data with the inverse Compton (IC) scenario is studied in the context of dominant orbital phase dependent adiabatic losses. The dependence of the observed TeV flux with the separation distance is analyzed. Model calculations based on IC scattering of shock accelerated PW electrons and UV photons are performed. Different non-radiative cooling profiles are suggested for the primary particle population to account for the variable TeV flux. The TeV fluxes obtained with H.E.S.S. in the years 2004 and 2007 seem to be only dependent on the binary separation. The presented results hint at a peculiar non-radiative cooling profile around periastron dominating the VHE emission in PSR B1259-63. The location of the stellar disc derived from this non-radiative cooling profile is in good agreement with that inferred from radio observations.