Gamma rays from red giant wind bubbles entering the jets of elliptical host blazars

Departament de Física Quàntica i Astrofísica, Institut de Ciències del Cosmos (ICC), Universitat de Barcelona (IEEC-UB), Martí i Franquès 1, 08028 Barcelona, Spain
e-mail: ntorres@fqa.ub.edu

Received: 21 June 2018
Accepted: 29 January 2019

Abstract

Context. Blazars in elliptical hosts have a population of red giants surrounding their jet. These stars can carry large wind-blown bubbles into the jets, leading to gamma-ray emission through bubble-jet interactions.

Aims. We study the interaction dynamics and the gamma-ray emission produced when the bubbles formed by red giant winds penetrate the jet of a blazar in an elliptical galaxy.

Methods. First, we characterized the masses and penetration rates of the red giant wind bubbles that enter the jet. Then, the dynamical evolution of these bubbles under the jet impact was analysed analytically and numerically, and the radiation losses of the particles accelerated in the interaction were characterised. Finally, the synchrotron and the inverse Compton contributions above ∼100 MeV were estimated under different jet magnetic fields, powers, and Lorentz factors.

Results. We find that an analytical dynamical model is a reasonable approximation for the red giant wind bubble-jet interaction. The radiation produced by these wind bubbles interacting with a jet can have a duty cycle of up to ∼1. For realistic magnetic fields, gamma rays could be detectable from sources within the local universe, preferentially from those with high Lorentz factors (∼10), and this could be a relatively common phenomenon for these sources. For magnetic fields in equipartition with the jet power, and high acceleration rates, synchrotron gamma rays may be detectable even for modest Lorentz factors (∼3), but with a much lower duty cycle.

Conclusions. Blazars in elliptical galaxies within the local universe can produce detectable transient or persistent gamma-ray emission from red giant wind bubbles entering their jets.