X-ray Spectral Variations in the Youngest Galactic Supernova Remnant G1.9+0.3

TL;DR

This study analyzes X-ray spectral variations in the youngest Galactic supernova remnant G1.9+0.3, revealing spatial differences in shock acceleration properties likely influenced by magnetic field orientation, with implications for understanding SNR evolution.

Contribution

It provides the first detailed spectral variation analysis of G1.9+0.3, incorporating dust scattering effects and linking spectral patterns to shock obliquity and magnetic field geometry.

Findings

Spectral hardness varies systematically across the remnant.

Shock acceleration efficiency depends on obliquity angle.

Spectral variations suggest electron acceleration is limited by synchrotron losses.

Abstract

The discovery of the youngest Galactic supernova remnant (SNR) G1.9+0.3 has allowed a look at a stage of SNR evolution never before observed. We analyze the 50 ks Chandra observation with particular regard to spectral variations. The very high column density ($N_H \sim 6 \times 10^{22}$ cm$^{-2}$) implies that dust scattering is important, and we use a simple scattering model in our spectral analysis. The integrated X-ray spectrum of G1.9+0.3 is well described by synchrotron emission from a power-law electron distribution with an exponential cutoff. Using our measured radio flux and including scattering effects, we find a rolloff frequency of $5.4 (3.0, 10.2) \times 10^{17}$ Hz ($h \nu_{\rm roll} = 2.2$ keV). Including scattering in a two-region model gives lower values of \nu_roll by over a factor of 2. Dividing G1.9+0.3 into six regions, we find a systematic pattern in which spectra are hardest (highest \nu_roll) in the bright SE and NW limbs of the shell. They steepen as one moves around the shell or into the interior. The extensions beyond the bright parts of the shell have the hardest spectra of all. We interpret the results in terms of dependence of shock acceleration properties on the obliquity angle $\theta_{\rm Bn}$ between the shock velocity and a fairly uniform upstream magnetic field. This interpretation probably requires a Type Ia event. If electron acceleration is limited by synchrotron losses, the spectral variations require obliquity-dependence of the acceleration rate independent of the magnetic-field strength.