Gamma rays from Nebulae around Recurrent Novae

Novae were discovered to emit transient gamma rays during the period of several days to a few weeks after initial explosion, indicating presence of acceleration processes of particles in their expanding shells. In the case of recurrent novae, electrons can be in principle accelerated in the nova shells for the whole recurrence period of nova producing delayed $\gamma$ ray emission as considered in Bednarek (2022). Here we extend the ideas presented in this article by considering the fate of electrons which diffuse out of the shells of novae supplying fresh relativistic electrons to the recurrent nova super-remnants during the whole active period of nova ($\ge 10^4$ yrs). We develop a model for the acceleration of electrons and their escape from the nova shells. The electrons within the recurrent nova super-remnants produce $\gamma$ rays in the comptonization process of the radiation from the red giant companion and the Cosmic Microwave Background Radiation. As an example, the case of a symbiotic nova RS Oph (with the recurrence period estimated on $\sim$10-50 yrs) is considered in more detail. Predicted $\gamma$-ray emission from the nova super-remnant around RS Oph is discussed in the context of its observability by satellite experiments (i.e. Fermi-LAT) as well as current and future Cherenkov telescopes.Comment: 17 pages, 9 figures, Journal of High Energy Astrophysics, accepte

Geomagnetic field and altitude effects on the performance of future IACT arrays

The performance of IACT's arrays is sensitive to the altitude and geomagnetic field (GF) of the observatory site. Both effects play important role in the region of the sub-TeV gamma-ray measurements. We investigate the influence of GF on detection rates and the energy thresholds for five possible locations of the future CTA observatory using the Monte Carlo simulations. We conclude that the detection rates of gamma rays and the energy thresholds of the arrays can be fitted with linear functions of the altitude and the component of the GF perpendicular to the shower axis core. These results can be directly extrapolated for any possible localization of the CTA. In this paper we also show the influence of both geophysical effects on the images of shower and gamma/hadron separation.Comment: 4 pages, 6 figures, two-column. Contribution to ICRC 2013 proceeding

Time dependent gamma-ray production in the anisotropic IC e±e^\pm pair cascade initiated by electrons in active galaxies

New high energy emission features have been recently discovered by the Cherenkov telescopes from active galaxies e.g., a few minutes variability time scale of TeV emission from Mrk 501 and PKS 2155-304, sub-TeV $\gamma$-ray emission from GeV peaked blazar 3C 279, and TeV emission from two nearby active galaxies, M87 and Cen A, which jets are inclined at a relatively large angle to the line of sight. These results have put a new light on the high energy processes occurring in central parts of active galaxies stimulating more detailed studies of $\gamma$-ray emission models. Here we report the results of a detailed analysis concerning the most general version of the model for the $\gamma$-ray production by leptons injected in the jet which interact with the thermal radiation from an accretion disk (the so called {\it external inverse Compton model}). We investigate the $\gamma$-ray spectra produced in an anisotropic Inverse Compton (IC) $e^\pm$ pair cascade in the whole volume above the accretion disk. The cascade $\gamma$-ray spectra are obtained for different locations of the observer in respect to the direction of the jet. We also study the time evolution of this $\gamma$-ray emission caused by the propagation of the relativistic leptons along the jet and the delays resulting from different places of the origin of $\gamma$-rays above the accretion disk. We discuss the main features of such a cascade model assuming constant injection rate of electrons along the jet. We are investigating two models for their different maximum energies: constant value independent on the distance along the jet or limited by the synchrotron energy losses considered locally in the jet. The model is discussed in the context of blazars observed at small and large inclination angles taking as an example the parameters of the two famous sources Cen A and 3C 279.Comment: 16 pages, 18 figures, accepted for publication in MNRA