Supernova remnants in clumpy media: particle propagation and gamma-ray emission

Abstract

Observations from the radio to the gamma-ray wavelengths indicate that supernova remnant (SNR) shocks are sites of effective particle acceleration. It has been proposed that the presence of dense clumps in the environment where supernovae explode might have a strong impact in shaping the hadronic gamma-ray spectrum. Here we present a detailed numerical study about the penetration of relativistic protons into clumps which are engulfed by a SNR shock, taking into account the magneto-hydrodynamical properties of the background plasma. We show that the spectrum of protons inside clumps is much harder than that in the diffuse interclump medium and we discuss the implications for the formation of the spectrum of hadronic gamma rays, which does not reflect anymore the acceleration spectrum of protons, resulting substantially modified inside the clumps due to propagation effects. For the Galactic SNR RX J1713.7-3946, we show that a hadronic scenario including dense clumps inside the remnant shell is able to reproduce the broadband gamma-ray spectrum from GeV to TeV energies. Moreover, we argue that small clumps crossed by the shock could provide a natural explanation to the non-thermal X-ray variability observed in some hot spots of RX J1713.7-3946. Finally we discuss the detectability of gamma-ray emission from clumps with the upcoming Cherenkov Telescope Array and the possible detection of the clumps themselves through molecular lines.

G279.0+1.1: a new extended source of high-energy gamma-rays

“…The gamma ray spectra of SNRs are diverse and likely highly depend on the environment in which the expansion takes place (e.g., Yuan et al 2012;Yasuda & Lee 2019;Celli et al 2019a). Some middle-aged SNRs interact with molecular clouds or high-density gas and show bright gamma-ray emission that is consistent with a hadronic scenario.…”

Interstellar anatomy of the TeV gamma-ray peak in the IC443 supernova remnant

“…They inject energy and trigger specific dust and gas-phase chemical processes (e.g., van Dishoeck et al 1993), hence significantly participating in the cycle of matter in galaxies. Cosmic rays accelerated in the earlier stages of the explosion and trapped in the shock fronts now interact with the dense medium, producing observable X-ray to γ-ray photons (Gabici et al 2009;Celli et al 2019; Tang 2019 and references therein). Cosmic rays of Galactic origin can also be reaccelerated in the shock regions (such as in W44, e.g., Cardillo et al 2016).…”

Gamma radiation as a source of information about the characteristics of celestial bodies

“…The possibility of observing the evolution of such a system in the range other than the spectral ranges used so far, gives the possibility of a thorough analysis of one of the most extreme objects found in the Universe. The fact that these objects are created during the explosion of supernova stars, where the matter collapses to a density many times greater than the density of atomic nuclei and we are not able to reproduce this process on Earth, causes that the data collected during the observation of the evolution of such a dual system is very unique [17]. Registered by the Fermi satellite, simultaneous with the collapse, gamma-ray burst, was named GRB 170817A [7].…”

“…Long, lasting from several seconds to even several minutes, called hibernate, accompanied by powerful supernova explosions [14]. Short in turn, they last only a fraction of a second and result from the merging of neutron stars-objects created after supernova explosions [17].…”

“…The technology described is used by projects such as CTA (Cherenkov Telescope Array) or VERITAS (Very Energetic Radiation Imaging Telescope Array System) [17]. Both are equipped with terrestrial telescopes with a mirror of 4 to 24 meters.…”