Constraining the coherence scale of the interstellar magnetic field using TeV gamma-ray observations of supernova remnants. Issue 2 (12th June 2020)

• Record Type: Journal Article
• Authors: Pais, Matteo; Pfrommer, Christoph; Ehlert, Kristian; Werhahn, Maria; Winner, Georg
• Is Part Of: Monthly notices of the Royal Astronomical Society. Volume 496:Issue 2(2020)
• Page Start: 2448
• Page End: 2461
• Publication Date: 2020-06-12
• Subjects: MHD -- cosmic rays -- ISM: supernova remnants -- gamma-rays; Astronomy -- Periodicals; Periodicals; 520.5
• DOI: 10.1093/mnras/staa1678
• Languages: English
• ISSNs: 0035-8711

Abstract

ABSTRACT: Galactic cosmic rays (CRs) are believed to be accelerated at supernova remnant (SNR) shocks. In the hadronic scenario, the TeV gamma-ray emission from SNRs originates from decaying pions that are produced in collisions of the interstellar gas and CRs. Using CR-magnetohydrodynamic simulations, we show that magnetic obliquity-dependent shock acceleration is able to reproduce the observed TeV gamma-ray morphology of SNRs such as Vela Jr and SN1006 solely by varying the magnetic morphology. This implies that gamma-ray bright regions result from quasi-parallel shocks (i.e. when the shock propagates at a narrow angle to the upstream magnetic field), which are known to efficiently accelerate CR protons, and that gamma-ray dark regions point to quasi-perpendicular shock configurations. Comparison of the simulated gamma-ray morphology to observations allows us to constrain the magnetic coherence scale λ B around Vela Jr and SN1006 to $\lambda _B \simeq 13_{-4.3}^{+13}$ pc and $\lambda _B \gt 200_{-40}^{+50}$ pc, respectively, where the ambient magnetic field of SN1006 is consistent with being largely homogeneous. We find consistent pure hadronic and mixed hadronic-leptonic models that both reproduce the multifrequency spectra from the radio to TeV gamma-rays and match the observed gamma-ray morphology. Finally, to capture the propagation of an SNR shock in a clumpy interstellar medium, we study the interaction of a shock with a dense cloud with numerical simulations and analytics. We construct an analytical gamma-ray model for a core collapse SNR propagating through a structured interstellar medium, and show that the gamma-ray luminosity is only biased by 30 per cent for realistic parameters.