X-ray Hotspot Flares and Implications for Cosmic Ray Acceleration and Magnetic Field amplification in Supernova Remnants

TL;DR

This paper critically examines recent claims that X-ray hotspot flares in supernova remnants provide direct evidence of cosmic ray acceleration to PeV energies, arguing that current data do not support such conclusions.

Contribution

It challenges the interpretation that X-ray hotspot variability confirms magnetic field amplification and proton acceleration in supernova remnants.

Findings

Existing multiwavelength data do not support claims of PeV cosmic ray acceleration.

X-ray flares are not definitive evidence of nucleonic cosmic ray acceleration.

The interpretation of hotspot variability requires cautious analysis.

Abstract

For more than fifty years, it has been believed that cosmic ray (CR) nuclei are accelerated to high energies in the rapidly expanding shockwaves created by powerful supernova explosions. Yet observational proof of this conjecture is still lacking. Recently, Uchiyama and collaborators reported the detection of small-scale X-ray flares in one such supernova remnant, dubbed 'RX J1713-3946' (a.k.a. G347.3-0.5), which also emits very energetic, TeV (10^12 eV) range, gamma-rays. They contend that the variability of these X-ray 'hotspots' implies that the magnetic field in the remnant is about a hundred times larger than normally assumed; and this, they say, means that the detected TeV range photons were produced in energetic nuclear interactions, providing 'a strong argument for acceleration of protons and nuclei to energies of 1 PeV (10^15 eV) and beyond in young supernova remnants.' We point out here that the existing multiwavelength data on this object certainly do not support such conclusions. Though intriguing, the small-scale X-ray flares are not the long sought-after 'smoking gun' of nucleonic CR acceleration in SNRs.