TeV light curve of PSR B1259-63/SS2883

Abstract

The inverse Compton (IC) scattering of ultrarelativistic electrons accelerated at the pulsar wind termination shock is generally believed to be responsible for TeV gamma‐ray signal recently reported from the binary system PSR B1259−63/SS2883. While this process can explain the energy spectrum of the observed TeV emission, the gamma‐ray fluxes detected by the Array of Imaging Atmospheric Cherenkov Telescopes (HESS) at different epochs do not agree with the published theoretical predictions of the TeV light curve. The main objective of this paper is to show that the HESS results can be explained, under certain reasonable assumptions concerning the cooling of relativistic electrons, by IC scenarios of gamma‐ray production in PSR B1259−63. In this paper we study evolution of the energy spectra of relativistic electrons under different assumptions about the acceleration and energy‐loss rates of electrons, and the impact of these processes on the light curve of IC gamma‐rays. We demonstrate that the observed TeV light curve can be explained (i) by adiabatic losses which dominate over the entire trajectory of the pulsar with a significant increase towards the periastron or (ii) by the ‘early’ (sub‐TeV) cut‐offs in the energy spectra of electrons due to the enhanced rate of Compton losses close to the periastron. The first four data points obtained just after periastron comprise an exception – possibly due to interaction with the Be star disc, which introduces additional physics not included in the presented model. The calculated spectral and temporal characteristics of the TeV radiation provide conclusive tests to distinguish between these two working hypotheses. The Compton deceleration of the electron–positron pulsar wind contributes to the decrease of the non‐thermal power released in the accelerated electrons after the wind termination, and thus to the reduction of the IC and synchrotron components of radiation close to the periastron. Although this effect alone cannot explain the observed TeV and X‐ray light curves, the Comptonization of the cold ultrarelativistic wind leads to the formation of gamma‐radiation with a specific line‐type energy spectrum. While the HESS data already constrain the Lorentz factor of the wind, Γ≤ 106 (for the most likely orbit inclination angle i= 35°, and assuming an isotropic pulsar wind), future observations of this object with GLAST should allow a deep probe of the wind Lorentz factor in the range between 104 and 106.

On the origin of LS 5039 and PSR J1825−1446

“…On the other hand, if the compact object is a young non-accreting pulsar, the particle acceleration would be produced in the shock between the relativistic wind of the pulsar and the stellar wind of the massive companion star. This scenario was described in Maraschi & Treves (1981), Tavani & Arons (1997), Kirk et al (1999), Dubus (2006), Khangulyan et al (2007), and Bogovalov et al (2008Bogovalov et al ( , 2012. Dedicated discussions on the wind-wind collision scenario for LS 5039 can be found in Khangulyan et al (2007), Sierpowska-Bartosik & Torres (2007), Dubus et al (2008), and Khangulyan et al (2008).…”

Simulations of stellar/pulsar-wind interaction along one full orbit

“…Blondin et al 1991;Okazaki et al 2011), which are particularly relevant in Be and/or very close systems; and the impact of the stellar radiation field on the pulsar-wind Lorentz factor through Compton braking (e.g. Ball & Kirk 2000;Khangulyan et al 2007). We note that, even though all these factors may play a major role in particular sources and should be accounted for in more refined treatments of the problem, they can be considered at this stage higher order effects and have therefore been neglected.…”

“…The processes underlying the non-thermal radiation in PSR B1259−63/LS2883 seem to be shocks that take place in the two-wind interaction region and accelerate electrons. These electrons most likely radiate from radio-to-X-rays through synchrotron and at GeV and TeV energies through inverse Compton emission (IC), although some gamma rays may come from IC in the unshocked pulsar wind (e.g., Tavani & Arons 1997;Ball & Kirk 2000;Khangulyan et al 2007Khangulyan et al , 2011Khangulyan et al , 2012. The details of the dynamics of the interacting flows are still poorly known, which affects the interpretation of the observed variability and spectra not only in PSR B1259−63/LS2883 but also in other gamma-ray emitting binaries that may host a non-accreting pulsar (LS 5039 and LS I +61 303, see discussions in, e.g., Chernyakova et al 2006;Dubus 2006;Romero et al 2007;Bosch-Ramon & Khangulyan 2009;Torres 2011;Bednarek 2011;Barkov & Khangulyan 2012; HESS J0632+057, see, e.g., Bongiorno et al 2011; 1FGL J1018.6−5856, see, e.g., Ackermann et al 2012;Abramowski et al 2012).…”

What caused the GeV flare of PSR B1259-63?

“…3 assume that U c stays constant along the orbit. Actually, U c is expected to vary with phase because the changing location A127, page 3 of 6 A&A 557, A127 (2013) and size of the shock region have an impact on the magnetisation at the shock, on the flow timescales, on radiative and adiabatic losses (Tavani et al 1996;Kirk et al 1999;Dubus 2006;Khangulyan et al 2007;Uchiyama et al 2009;Takata & Taam 2009). Modelling these effects is beyond the scope of this work.…”

“…The companion star has a high luminosity so most models have considered Article published by EDP Sciences A127, page 1 of 6 the anisotropic upscattering of stellar photons (Kirk et al 1999;Khangulyan et al 2007;Takata & Taam 2009;Pétri & Dubus 2011). The lightcurve peaks slightly before periastron, when the orbital geometry allows close to head-on scattering.…”