Observation of the Gamma-Ray Binary HESS J0632+057 with the H.E.S.S., MAGIC, and VERITAS Telescopes

Abstract

The results of gamma-ray observations of the binary system HESS J0632 + 057 collected during 450 hr over 15 yr, between 2004 and 2019, are presented. Data taken with the atmospheric Cherenkov telescopes H.E.S.S., MAGIC, and VERITAS at energies above 350 GeV were used together with observations at X-ray energies obtained with Swift-XRT, Chandra, XMM-Newton, NuSTAR, and Suzaku. Some of these observations were accompanied by measurements of the Hα emission line. A significant detection of the modulation of the very high-energy gamma-ray fluxes with a period of 316.7 ± 4.4 days is reported, consistent with the period of 317.3 ± 0.7 days obtained with a refined analysis of X-ray data. The analysis of data from four orbital cycles with dense observational coverage reveals short-timescale variability, with flux-decay timescales of less than 20 days at very high energies. Flux variations observed over a timescale of several years indicate orbit-to-orbit variability. The analysis confirms the previously reported correlation of X-ray and gamma-ray emission from the system at very high significance, but cannot find any correlation of optical Hα parameters with fluxes at X-ray or gamma-ray energies in simultaneous observations. The key finding is that the emission of HESS J0632 + 057 in the X-ray and gamma-ray energy bands is highly variable on different timescales. The ratio of gamma-ray to X-ray flux shows the equality or even dominance of the gamma-ray energy range. This wealth of new data is interpreted taking into account the insufficient knowledge of the ephemeris of the system, and discussed in the context of results reported on other gamma-ray binary systems.

Investigation of the Broadband Emission of the Gamma-Ray Binary HESS J0632+057 Using an Intrabinary Shock Model

“…The X-ray and the VHE LCs of J0632 exhibit a similar shape characterized by broad bumps at orbital phases f ≈ 0.25 and 0.75 and a sharp spike at f = 0.35 (e.g., Adams et al 2021;Tokayer et al 2021). These features could probe the emission mechanisms and help infer the properties of particle acceleration and flow in the binary system.…”

“…In the VHE band, VERITAS and H.E.S.S. data presented in Adams et al (2021) are used to construct the LCs and SEDs.…”

“…Since the X-ray spectrum of J0632 is variable, we take three representative power-law models (i.e., three orbital phases) in each of the Swift and NuSTAR bands (Figure 10; Aliu et al 2010; TAH21. For the VHE SEDs, we display six representative power-law fits reported by Adams et al (2021). The shapes of the multiband LCs differ slightly depending on the P orb used to fold the data (310-320 days; Casares et al 2012;Moritani et al 2015;Maier et al 2019;Adams et al 2021).…”

“…For the VHE SEDs, we display six representative power-law fits reported by Adams et al (2021). The shapes of the multiband LCs differ slightly depending on the P orb used to fold the data (310-320 days; Casares et al 2012;Moritani et al 2015;Maier et al 2019;Adams et al 2021). We use folded LCs (Figure 11) produced with the most recent orbital period (P orb = 317.3 days; Adams et al 2021).…”

Galactic Observatory Science with the ASTRI Mini-Array at the Observatorio del Teide

“…As shown in Sect. 7.2, the ASTRI Mini-Array on the long-term is able to well track this TeV variability along the orbit; in the case of HESS J0632+057 the orbital period is 316.7 ± 4.4 days with a pronounced peak at phase ∼ 0.3 when the source reaches 6% of the Crab flux (Adams et al, 2021), thus allowing a possible detection and spectral characterisation in the TeV range. The other important -ray binary is LS I 61+303, also high-mass binary hosting a 0.27 sec radio pulsar (Weng et al, 2022).…”