Discovery of High-Energy Gamma-Ray Emission from the Binary System PSR B1259-63/LS 2883 Around Periastron with Fermi

TL;DR

This paper reports the discovery of high-energy gamma-ray emission from the binary system PSR B1259-63/LS 2883 around periastron using Fermi, revealing a transient gamma-ray flare not accompanied by radio or X-ray changes.

Contribution

First detection of gamma-ray emission from PSR B1259-63/LS 2883 around periastron with detailed temporal analysis.

Findings

Gamma-ray emission appears near periastron and peaks about 30 days after.

Gamma-ray flux varies significantly on daily timescales.

No corresponding dramatic radio or X-ray flux changes observed.

Abstract

We report on the discovery of \geq 100 MeV {\gamma} rays from the binary system PSR B1259-63/LS 2883 using the Large Area Telescope (LAT) on board Fermi. The system comprises a radio pulsar in orbit around a Be star. We report on LAT observations from near apastron to ~ 60 days after the time of periastron, tp, on 2010 December 15. No {\gamma}-ray emission was detected from this source when it was far from periastron. Faint {\gamma}-ray emission appeared as the pulsar approached periastron. At ~ tp + 30d, the \geq 100 MeV {\gamma}-ray flux increased over a period of a few days to a peak flux 20-30 times that seen during the pre-periastron period, but with a softer spectrum. For the following month, it was seen to be variable on daily time scales, but remained at ~ 1 - 4 \times 10^-6 cm^-2 s^-1 before starting to fade at ~ tp + 57d. The total {\gamma}-ray luminosity observed during this period is comparable to the spin-down power of the pulsar. Simultaneous radio and X-ray observations of the source showed no corresponding dramatic changes in radio and X-ray flux between the pre-periastron and post-periastron flares. We discuss possible explanations for the observed {\gamma}-ray-only flaring of the source.