Ancient Pulsar Wind Nebulae as a natural explanation for unidentified gamma-ray sources

Abstract

A large part of the Galactic sources emitting very high energy (VHE; > 10 11 eV) gamma-rays are currently still unidentified. The evolution of Pulsar Wind Nebulae (PWNe) plays a crucial role in interpreting these sources. The time-dependent modeling of PWNe has been tested on a sample of well-known young and intermediate age PWNe; and it is currently applied to the full-sample of unidentified VHE Galactic sources. The consequences of this interpretation go far beyond the interpretation of "dark sources" (i.e. VHE gamma-ray sources without lower energies, radio or X-ray, counterparts): e.g. there could be strong implication in the origin of cosmic rays and (when considering a leptonic origin of the gamma-ray signal) they can be important for reinterpreting the detection of starburst galaxies in the TeV gamma-ray band. Moreover, the number of Galactic VHE sources is currently increasing with further observation by Imaging Atmospheric Cherenkov Telescopes (IACTs) and by the advent of more sensitive water Cherenkov telescopes such as HAWC (High-Altitude Water Cherenkov Observatory); therefore the physical interpretation of unidentified sources becomes more and more crucial.

Pulsar Wind Nebulae and Unidentified Galactic Very High Energy Sources

“…PWNe are a very natural way to explain unidentified very-high-energy sources. Moreover, ancient PWN models seem to be able to explain most of these sources (e.g., [64][65][66]), as confirmed by the present interpretations of HESS J1616-508 and HESS J1813-126.…”

“…While PWNe models are often built to describe a single source, the purely leptonic model of [64] described above is a very powerful tool which enables the description of any type of PWN and many unidentified gamma ray sources (treated then as "ancient" PWNe). These include both young PWNe systems, such as G21.5-0.9 ( [64] (successfully described by a model developed by O. de Jager [62] which was the starting point of our own models) and HESS J1420-607 [65], and aged/relic PWNe systems, such as HESS J1507-622 and HESS J1427-608 [64], HESS J1837-069, HESS J1702-420, and HESS J1708-410 [66], and IGR J1849-0000 [65].…”

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

“…The observation of gamma radiation allows the discovery of further celestial bodies and the study of already known ones like pulsars, black holes, nuclei of active galaxies or dark matter [12,16,21,3]. In space, there are constantly many processes emitting huge amounts of energy, such as star bursts or asteroid collisions that cause weak gamma-ray bursts [12]. Electromagnetic waves accompanying events occurring in the Universe arise in microscopic processes, strongly interact with the surrounding matter, are absorbed and dispersed.…”

“…They were created as a result of the collapse of the nucleus of a star with a large mass (8-10 solar masses). Such a phenomenon brings about a rapid increase in the magnetic field, hence neutron stars have a magnetic field that is at least one hundred million times more powerful than the Earth's magnetic field [12]. Such a magnetized, fast-rotating star, hereinafter referred to as a pulsar, generates electricity, which is associated with the emission of electromagnetic radiation [13].…”