Non-thermal emission from secondary pairs in close TeV binary systems

Abstract

Massive hot stars produce dense ultraviolet (UV) photon fields in their surroundings. If a very high-energy (VHE) gamma-ray emitter is located close to the star, then gamma-rays are absorbed in the stellar photon field, creating secondary (electron-positron) pairs. We study the broadband emission of these secondary pairs in the stellar photon and magnetic fields. Under certain assumptions on the stellar wind and the magnetic field in the surroundings of a massive hot star, we calculate the steady state energy distribution of secondary pairs created in the system and its radiation from radio to gamma-rays. Under the ambient magnetic field, possibly high enough to suppress electromagnetic (EM) cascading, the energy of secondary pairs is radiated via synchrotron and single IC scattering producing radio-to-gamma-ray radiation. The synchrotron spectral energy distribution (SED) is hard, peaks around X-ray energies, and becomes softer. The IC SED is hard as well and peaks around 10 GeV, becoming also softer at higher energies due to synchrotron loss dominance. The radio emission from secondary pairs is moderate and detectable as a point-like and/or extended source. In X-rays, the secondary pair synchrotron component may be dominant. At energies <10 GeV, the secondary pair IC radiation may be the dominant primary gamma-ray emission and possibly detectable by the next generation of instruments.

accepted for publication in Astronomy & Astrophysics, 6 pages, 8 figures

References in corpus (6)

• Accretion vs colliding wind models for the gamma-ray binary LS I +61 303: an assessment
• On the formation of TeV radiation in LS 5039
• Leptonic secondary emission in a hadronic microquasar model
• Exploring the connection between the stellar wind and the non-thermal emission in LS 5039
• Inverse Compton e-p pair cascade model for the gamma-ray production in massive binary LSI +61^o 303
• Gamma-ray absorption in the microquasar SS433

Cited by in corpus (5)

• Understanding the Very High-Energy Emission from Microquasars
• On the interaction of microquasar jets with stellar winds
• The magnetic field and the location of the TeV emitter in Cygnus X-1 and LS 5039
• Spectral signature of a free pulsar wind in the gamma-ray binaries LS 5039 and LSI +61$\degr$303
• Studying the properties of the radio emitter in LS 5039