Brightening and Fading in the Youngest Galactic Supernova Remnant G1.9+0.3: 13 years of monitoring with the Chandra X-ray Observatory

Abstract

We report results from 13 years of Chandra monitoring of nonthermal X-ray emission from the youngest Galactic supernova remnant G1.9+0.3, the only remnant known to be increasing in brightness. We confirm the spatially-integrated flux increase rate of $(1.2\pm 0.2)$% yr${}^{-1}$ between 1 and 7 keV, but find large spatial variations, from decreases of $-3$% yr${}^{-1}$ to increases of 7% yr${}^{-1}$, over length scales as small as $10^{\prime \prime }$ or smaller. We observe relatively little change in spectral slope, though one region shows significant hardening (photon index $\Delta \Gamma \sim 0.4$) as it brightens by 1% yr${}^{-1}$. Such rates of change can be accommodated by any of several explanations, including steady evolution of the blast wave, expansion or compression of discrete plasma blobs, strong magnetic turbulence, or variations in magnetic-field aspect angle. Our results do not constrain the mean magnetic-field strength, but a self-consistent picture of the spatially averaged rate of increase can be produced in which the maximum energies of accelerated particles are limited by the remnant age (applying both to electrons and to ions) to about 20 TeV, and the remnant-averaged magnetic field strength is about 30 $\mu$G. The deceleration parameter $m$ (average shock radius varying as $t^m$) is about 0.7, consistent with estimates from overall expansion dynamics, and confirming an explosion date of about 1900 CE. Shock-efficiency factors ${\epsilon }_e$ and ${\epsilon }_B$ (fractions of shock energy in relativistic electrons and magnetic field) are 0.003 and 0.0002 in this picture. However, the large range of rates of brightness change indicates that such a global model is oversimplified. Temporal variations of photon index, expected to be small but measurable with longer time baselines, can discriminate among possible models.

Minor changes made in response to referee's report

References in corpus (17)

• Array Programming with NumPy
• The Astropy Project: Sustaining and Growing a Community-oriented Open-source Project and the Latest Major Release (v5.0) of the Core Package
• Analytical solutions for energy spectra of electrons accelerated by nonrelativistic shock-waves in shell type supernova remnants
• Observational constraints on energetic particle diffusion in young SNRs: amplified magnetic field and maximum energy
• The Youngest Galactic Supernova Remnant: G1.9+0.3
• The radio expansion and brightening of the very young supernova remnant G1.9+0.3
• X-ray Spectral Variations in the Youngest Galactic Supernova Remnant G1.9+0.3
• Asymmetric Expansion of the Youngest Galactic Supernova Remnant G1.9+0.3
• Radio Observations of Supernova Remnant G1.9+0.3
• Nonuniform Expansion of the Youngest Galactic Supernova Remnant G1.9+0.3
• A 20 Year Radio Light Curve for the Young Supernova Remnant G1.9+0.3
• Expansion and Age of the X-ray Synchrotron-Dominated Supernova Remnant G330.2+1.0
• TeV γ-ray observations of the young synchrotron-dominated SNRs G1.9+0.3 and G330.2+1.0 with H.E.S.S
• Non-thermal emission from the reverse shock of the youngest galactic Supernova remnant G1.9+0.3
• Time Variability of Nonthermal X-ray Stripes in Tycho's Supernova Remnant with Chandra
• Type Ia Supernova Models: Asymmetric Remnants and Supernova Remnant G1.9+0.3
• Spatio-temporal characterization of Cassiopeia A