H.E.S.S. observations of PSR B1259-63 during its 2014 periastron passage

TL;DR

This paper reports on extensive H.E.S.S. observations of the gamma-ray binary PSR B1259-63 during its 2014 periastron, providing new insights into its very-high-energy gamma-ray emission down to 200 GeV and its long-term flux behavior.

Contribution

First detailed VHE gamma-ray study of PSR B1259-63 during periastron with H.E.S.S. II, extending energy coverage and enabling long-term flux analysis.

Findings

Detection of VHE gamma-ray emission down to 200 GeV.

Long-term flux characterization across multiple periastron passages.

Correlation with gamma-ray flares observed by Fermi-LAT.

Abstract

An extended observation campaign of the gamma-ray binary system PSR B1259$-$63 has been conducted with the H.E.S.S. (High Energy Stereoscopic System) II 5-telescope array during the system's periastron passage in 2014. We report on the outcome of this campaign, which consists of more than 85 h of data covering both pre- and post-periastron orbital phases. The lower energy threshold of the H.E.S.S. II array allows very-high-energy (VHE; $E \gtrsim 100$ GeV) gamma-ray emission from PSR B1259$-$63 to be studied for the first time down to 200 GeV. The new dataset partly overlaps with and extends in phase previous H.E.S.S. campaigns on this source in 2004, 2007 and 2011, allowing for a detailed long-term characterisation of the flux level at VHEs. In addition, the 2014 campaign reported here includes VHE observations during the exact periastron time, $t_{\rm per}$, as well as data taken simultaneously to the gamma-ray flare detected with the Fermi-LAT. Our results will be discussed in a multiwavelength context, thanks to the dense broad-band monitoring campaign conducted on the system during this last periastron passage.