A PeVatron Candidate: Modelling the Boomerang Nebula in X-ray Band

TL;DR

This study models the Boomerang Nebula's X-ray emission to evaluate its potential as a PeVatron, suggesting it could be a hadronic source of ultra-high-energy gamma rays if future observations confirm PWN contribution.

Contribution

It introduces a detailed X-ray modeling approach for the Boomerang Nebula, highlighting its potential as a hadronic PeVatron, which was not previously considered.

Findings

A magnetic field of 140μG reproduces observed X-ray profiles.

Suppressed inverse Compton scattering implies a need for proton contribution.

Potential identification as a hadronic PeVatron if UHE emission originates from PWN.

Abstract

Pulsar wind nebula (PWN) Boomerang and the associated supernova remnant (SNR) G106.3+2.7 are among candidates for the ultra-high-energy (UHE) gamma-ray counterparts published by LHAASO. Although the centroid of the extended source, LHAASO J2226+6057, deviates from the pulsar's position by about $0.3^\circ$, the source partially covers the PWN. Therefore, we cannot totally exclude the possibility that a part of the UHE emission comes from the PWN. Previous studies mainly focus on whether the SNR is a PeVatron, while neglecting the energetic PWN. Here, we explore the possibility of the Boomerang Nebula being a PeVatron candidate by studying its X-ray radiation. By modelling the diffusion of relativistic electrons injected in the PWN, we fit the radial profiles of the X-ray surface brightness and the photon index. The solution with a magnetic field $B=140\mu$G can well reproduce the observed profiles and implies a severe suppression of IC scattering of electrons. Therefore, a proton component need be introduced to account for the UHE emission, in light of recent LHAASO's measurement on Crab Nebula, if future observations reveal part of the UHE emission originating from the PWN. In this sense, Boomerang Nebula would be a hadronic PeVatron.