Supernova Remnants as Galactic cosmic-rays sources revealed by NewAthena

Roberta Giuffrida

Dap-AIM, CEA - Paris Saclay

Supernova remnants (SNRs) are the final product of the explosion of stars as supernovae (SNe), where the shock wave heats the circumstellar medium up to a million-degree temperature, making them strong X-ray sources. SNRs are very interesting laboratories especially because they link to the study of galaxy evolution. They are also thought to be the main Galactic sources for cosmic rays (CRs) up to ∼ 3 PeV and the γ-ray emission provides direct evidence for particle acceleration in the shock fronts.
On average, a SN explosion releases a kinetic energy of 1051 erg, and the rate of SNe in our Galaxy is slightly less than 2 per century. This makes SNRs the only Galactic sources that can provide the power requested to sustain the observed flux of CRs, provided that they transfer to the particles about 10 − 20% of their kinetic energy. The main process which can explain particle acceleration is the Diffusive shock acceleration (DSA), where particles gain energy by crossing the shock front back and forth. This efficient particle acceleration modifies the structure of the forward shock, through the so called shock modification. In this scenario, the shock compression ratio (the ratio between the post shock density and the pre shock density) is expected to deviate from the characteristic value of 4 obtained for adiabatic shocks. Efficient DSA also strongly depends on the angle between the magnetic field and the shock velocity. SN 1006 is an ideal target for these studies because it evolves in a very uniform ambient medium. It shows a bilateral synchrotron emission in its North-East and South-West limbs, where the magnetic field is parallel to the shock velocity. The shock modification should raise near the nonthermal limbs, being smaller in thermal regions, where the shock velocity and magnetic field are almost perpendicular.
These regions typically have angular sizes on the order of few arcseconds, which will be resolvable with NewAthena’s angular resolution of approximately 5″. To date, the detection of shocked interstellar medium at soft X-ray energies (less than 1 keV) has been achieved with Chandra and XMM-Newton, requiring exposures of ~100 ks. In the near future, NewAthena will be uniquely capable of detecting this emission with high fidelity. Thanks to its substantially larger effective area (~25–30 times greater than Chandra), it will enable significantly more precise measurements while reducing the required exposure times. These observations will allow spatially resolved spectral analysis along the limbs, providing key constraints on particle acceleration processes in SNRs.