Chandra and H.E.S.S. observations of the Supernova Remnant CTB 37B

TL;DR

This study combines Chandra X-ray and H.E.S.S. gamma-ray observations to analyze the supernova remnant CTB 37B, revealing thermal and non-thermal emissions, estimating its age and density, and suggesting a hadronic origin for its gamma-ray emission.

Contribution

It provides detailed multi-wavelength analysis of CTB 37B, including thermal and non-thermal X-ray data, and proposes a hadronic mechanism for gamma-ray production, advancing understanding of SNRs as cosmic ray sources.

Findings

Thermal emission indicates an age of ~5000 years and density of ~0.5 cm-3.

Detection of a non-thermal X-ray source coincident with the radio shell.

Gamma-ray emission likely originates from pion decay, not inverse Compton scattering.

Abstract

The >100 GeV gamma-ray source, HESS J1713-381, apparently associated with the shell-type supernova remnant (SNR) CTB 37B, was discovered using H.E.S.S. in 2006. X-ray follow-up observations with Chandra were performed in 2007 with the aim of identifying a synchrotron counterpart to the TeV source and/or thermal emission from the SNR shell. These new Chandra data, together with additional TeV data, allow us to investigate the nature of this object in much greater detail than was previously possible. The new X-ray data reveal thermal emission from a ~4' region in close proximity to the radio shell of CTB 37B. The temperature of this emission implies an age for the remnant of ~5000 years and an ambient gas density of ~0.5 cm-3. Both these estimates are considerably uncertain due to the asymmetry of the SNR and possible modifications of the kinematics due to efficient cosmic ray (CR) acceleration. A bright (~7x10-13erg cm-2s-1) and unresolved (<1'') source (CXOU J171405.7-381031) with a soft (\Gamma ~3.3) non-thermal spectrum is also detected in coincidence with the radio shell. Absorption indicates a column density consistent with the thermal emission from the shell suggesting a genuine association rather than a chance alignment. The observed TeV morphology is consistent with an origin in the complete shell of CTB 37B. The lack of diffuse non-thermal X-ray emission suggests an origin of the gamma-ray emission via the decay of neutral pions produced in interactions of protons and nuclei, rather than inverse Compton (IC) emission from relativistic electrons.