High energy $\gamma$-ray emission from PSR B1259$-$63 during 2014 and 2010 periastron passages

TL;DR

This study analyzes the recurrent GeV gamma-ray flares from PSR B1259-63 during its 2014 and 2010 periastron passages, revealing similarities and differences in flare characteristics and raising questions about their underlying mechanisms.

Contribution

It provides a comparative analysis of gamma-ray flares during two periastron passages, highlighting both consistencies and novel differences in flare evolution and structure.

Findings

Flares are recurrent within the orbit.

Similarities in flare duration, flux, and spectra between 2010 and 2014.

Differences in flare light curve structure and decay behavior.

Abstract

PSR B1259$-$63/SS 2883 is a $\gamma$-ray binary system composed of a radio pulsar in a long (1236.7 days) and elliptical ($e\sim0.87$) orbit around a Be star. In its 2010 periastron passage, multiwavelength emission from radio to TeV was observed, and an unexpected GeV flare was detected by the Fermi Large Area Telescope (LAT). Here we present the results of the LAT monitoring of PSR B1259$-$63 during its most recent 2014 periastron passage. We confirm that the GeV flare is recurrent within the orbit. The comparison of the 2014 and 2010 periastron passages shows overall similarities of flare durations, average flux levels, and spectra. In contrast, the detailed time evolutions of the two flares present interesting differences. Indeed, the light curves of the two flares show both a different structure and peak energy flux ($9.6 \pm1.8 \times 10^{-10}$ erg cm$^{-2}$ s$^{-1}$ and $7.1 \pm1.3 \times 10^{-10}$ erg cm$^{-2}$ s$^{-1}$, respectively in 2010 and 2014). While the tail of the 2010 flare the flux decayed exponentially, in 2014 it persisted at a high level. The interpretation of these differences as well as of the flare themselves is subject of debate.