From young to old: the evolutionary path of Pulsar Wind Nebulae

Abstract

Pulsar wind nebulae are fascinating systems, and archetypal sources for high-energy astrophysics in general. Due to their vicinity, brightness, to the fact that they shine at multi-wavelengths, and especially to their long-living emission at gamma-rays, modelling their properties is particularly important for the correct interpretation of the visible Galaxy. A complication in this respect is the variety of properties and morphologies they show at different ages.Here we discuss the differences among the evolutionary phases of pulsar wind nebulae, how they have been modeled in the past and what progresses have been recently made. We approach the discussion from a phenomenological, theoretical (especially numerical) and observational point of view, with particular attention to the most recent results and open questions about the physics of such intriguing sources.

The LHAASO PeVatron Bright Sky: What We Learned

“…Several theoretical works have been developed after the LHAASO results, analyzing which kinds of source are able to satisfy the requirements needed to explain the CR density in our galaxies, in spite of the acceleration mechanism at the origin (DSA is the main source, but there is the magnetic reconnection that can contribute in microquasar jets or to the wind of the PWNe) [5,[67][68][69][70]. One of the main hypotheses so far is that, since the CR spectrum in the energy range around the "knee" shows various features, maybe we can have different contributions from different kinds of sources at different energies ( [71] and Figure 3).…”

“…With their UHE detection by LHAASO and other EAS experiments, PWNe respect all the observational requirements to be PeVatrons (and possibly hadronic PeVatrons): extended HE γ-ray emission; multiwavelength counterparts, from radio to X-rays; and a nonthermal spectrum, with spectral curvature [26,70]. The main mechanism producing this UHE emission is the IC scattering of UHE accelerated electrons with cosmic microwave background radiation (CMBR).…”

“…PWNe should be the most numerous of the different kinds of galactic source [48] and their γ-ray emission is estimated to last a very long time (∼100 kyrs) [70]. This is likely one of the reasons why more than 30% of the candidate PeVatrons detected by LHAASO seem to be associated with PWNe [26].…”

“…The main problem related to TeV halo detection is the possibility of confusing them with extended SNRs [118]. In order to verify the TeV halo origin of a source, beyond the co-location of the bulk of its emission with a pulsar, this pulsar needs to have a spin-down luminosity sufficient to generate a halo and needs to be enough old to allow electrons to diffuse in the ISM (bow-shock nebula [70]). Furthermore, the extension of the halo has to be larger than the possible PWN X-ray emission, otherwise the emission could be a γ-ray PWN, and its morphology must be explained by slow-diffusion, otherwise this could indicate a hadronic accelerator [119].…”

“…For this reason, instruments such as the ASTRI Mini-Array and CTA will make a difference (see Figure 17, right). In addition, the higher sensitivity of the ASTRI Mini-Array, and in particular of CTA South, will allow enhancing the number of VHE sources detected in the TeV band, up to a factor of several hundred [70] (see Figure 17, left). [207] with the addition of the ASTRI Mini-Array updated curve with optimized cuts from [208] and the LHAASO curve from [77].…”