Multi-zone non-thermal radiative model for stellar bowshocks

Abstract

Context. Runaway stars produce bowshocks that are usually observed at infrared (IR) wavelengths. Non-thermal radio emission has been detected so far only from the bowshock of BD+43 • 3654, whereas the detection of non-thermal radiation from these bowshocks at high energies remains elusive. Aims. We aim at characterising in detail the radio, X-ray, and γ-ray emission from stellar bowshocks accounting for the structure of the region of interaction between the stellar wind and its environment. Methods. We develop a broadband-radiative, multi-zone model for stellar bowshocks that takes into account the spatial structure of the emitting region and the observational constraints. The model predicts the evolution and the emission of the relativistic particles accelerated and streaming together with the shocked flow. Results. We present broadband non-thermal spectral energy distributions for different scenarios, synthetic radio-cm synchrotron maps that reproduce the morphology of BD+43 • 3654, and updated predictions in X-ray and γ-ray energy ranges. We also compare the results of the multi-zone model applied in this work with those of a refined one-zone model. Conclusions.A multi-zone model provides better constraints than a one-zone model on the relevant parameters, namely the magnetic field intensity and the amount of energy deposited in non-thermal particles. However, one-zone models can be improved by carefully characterising the intensity of the IR dust photon field and the escape rate of the plasma from the shocked region. Finally, comparing observed radio maps with those obtained from a multi-zone model enables constraints to be obtained on the direction of stellar motion with respect to the observer.

Runaway O-star Bow Shocks as Particle Accelerators? The Case of AE Aur Revisited

“…Our estimate of the IC X-ray emission is consistent with the upper limit reported in Sec. 3.3, but is in dis-agreement with previous and more optimistic estimates reported in the literature (e.g., López-Santiago et al 2012;Pereira et al 2016;del Palacio et al 2018). The main reason for that is the different choice of the parameter η e , which in these previous works was assumed to be equal to η e ≈ 0.1, which implicitly implies that wind termination shocks were assumed to be much more effective than SNR shocks in accelerating electrons.…”

“…so the question arises whether magnetic fields of the order of hundreds of µG could be found at wind termination shocks, and/or whether electrons can be accelerated there beyond 10 TeV. del Palacio et al (2018) noticed that such large values of the magnetic field at the shock are unlikely to be of stellar origin, but require some form of in situ amplification mechanism. One way to estimate the value of the amplified magnetic field is to persist with the analogy with SNR shocks.…”

Cygnus survey with the Giant Metrewave Radio Telescope at 325 and 610 MHz: the catalog

“…Recently, other types of stellar sources have been proposed as possible gamma-ray emitters, and different scenarios were analyzed. In addition to the well-studied microquasars (Romero et al 2003), colliding-wind binaries (Benaglia & Romero 2003), Herbig Haro objects, young stellar objects (YSO), (Bosch-Ramon et al 2010;Araudo et al 2007;Rodríguez-Kamenetzky et al 2019), A&A 642, A136 (2020) and stellar bow shocks (Benaglia et al 2010;del Valle & Pohl 2018;del Palacio et al 2018) are capable of producing gammarays. A signature of high-energy emission is nonthermal radio emission because particles from the same population are likely to be involved in processes at both energy ranges, at the radio through synchrotron process, and at VHE emission through inverse-Compton scattering.…”

Radiación no térmica asociada a estrellas de gran masa

“…El modelo y resultados aquí presentados corresponden al trabajo publicado en [98]. La mayoría de los modelos de emisión NT en BSs estelares previamente presentados en la literatura eran del tipo one-zone (ver Sec.…”

“…Figura 3.3. Esquema (no a escala) del modelo considerado en [98]. A pesar de la representación de los ejes, en nuestros cálculos la posición (0, 0) corresponde a la ubicación de la estrella.…”