Very high energy γ-ray observations of the binary PSR B1259-63/SS2883 around the 2007 Periastron

Details Very high energy γ-ray observations of the binary PSR B1259-63/SS2883 around the 2007 Periastron Very high energy γ-ray observations of the binary PSR B1259-63/SS2883 around the 2007 Periastron

Nov 2009

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009a%26a...507..389a&link_type=abstract

Astronomy and Astrophysics, Volume 507, Issue 1, 2009, pp.389-396

Astronomy and Astrophysics

Astrophysics

25

Radiation Mechanisms: Non-Thermal, Methods: Observational, Stars: Binaries: General, Stars: Neutron, Gamma Rays: Observations, Telescopes

Scientific paper

Aims: This article presents very-high-energy (VHE; E > 100 GeV) data from the γ-ray binary PSR B1259-63 as taken during the years 2005, 2006 and before as well as shortly after the 2007 periastron passage. These data extend the knowledge of the lightcurve of this object to all phases of the 3.4 year binary orbit. The lightcurve constrains physical mechanisms present in this TeV source. Methods: Observations of VHE γ-rays with the HESS telescope array using the Imaging Atmospheric Cherenkov Technique were performed. The HESS instrument features an angular resolution of < 0.1° and an energy resolution of < 20%. Gamma-ray events in an energy range of 0.5-70 TeV were recorded. From these data, energy spectra and lightcurve with a monthly time sampling were extracted. Results: VHE γ-ray emission from PSR B1259-63 was detected with an overall significance of 9.5 standard deviations using 55h of exposure, obtained from April to August 2007. The monthly flux of γ-rays during the observation period was measured, yielding VHE lightcurve data for the early pre-periastron phase of the system for the first time. No spectral variability was found on timescales of months. The spectrum is described by a power law with a photon index of Γ = 2.8 ±0.2stat ±0.2sys and flux normalisation Φ0 = (1.1 ±0.1stat ±0.2sys) × 10-12 TeV-1 cm-2 s-1. PSR B1259-63 was also monitored in 2005 and 2006, far from periastron passage, comprising 8.9 h and 7.5 h of exposure, respectively. No significant excess of γ-rays is seen in those observations. Conclusions: PSR B1259-63 has been re-confirmed as a variable TeV γ-ray emitter. The firm detection of VHE photons emitted at a true anomaly θ≈-0.35 of the pulsar orbit, i.e. already ~50 days prior to the periastron passage, disfavors the stellar disc target scenario as a primary emission mechanism, based on current knowledge about the companion star's disc inclination, extension, and density profile.
Supported by CAPES Foundation, Ministry of Education of Brazil.

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