Discovery of GeV gamma-ray emission from PSR B1259-63/LS 2883

TL;DR

This paper reports the discovery of GeV gamma-ray emission from the binary system PSR B1259-63/LS 2883 during its 2010 orbital passage, revealing variable gamma-ray activity and flares that differ from X-ray and TeV patterns.

Contribution

First detection of GeV gamma-ray emission from PSR B1259-63/LS 2883, showing orbital-phase-dependent variability and flares with implications for emission mechanisms.

Findings

Detection of >100 MeV gamma-rays with 13.6 sigma significance.

Observation of two major gamma-ray flares post-periastron.

Gamma-ray emission shows different orbital pattern than X-ray and TeV emissions.

Abstract

The binary system PSR B1259-63/LS 2883 consists of a 47.8 ms radio pulsar that orbits the companion Be star with a period of 3.4 years in a highly eccentric orbit. The system is well sampled in radio, X-rays, and TeV gamma-rays, and shows orbital-phase-dependent variability in all observed frequencies. Here we report on the discovery of >100 MeV gamma-rays from PSR B1259-63/LS 2883 through the 2010 pariastron passage. Using data collected with the Large Area Telescope aboard Fermi from 33 days before pariastron to 75 days after pariastron, PSR B1259-63/LS 2883 is detected at a significance of 13.6 standard deviations. The gamma-ray light curve is highly variable over the above period, with changing photon index that correlates with gamma-ray flux. In particular, two major flares that occur after the pariastron passage were observed. The onset of gamma-ray emission occurs close to, but not at the same orbital phases as, the two disk passages that occur ~1 month before and ~1 month after the pariastron passage. The fact that the GeV orbital light curve is different from that of the X-ray and TeV light curves strongly suggests that GeV gamma-ray emission originates from a different component. We speculate that the observed GeV flares may be resulting from Doppler boosting effects.