Supernova Ejecta in G1.9+0.3

Astronomy and Astrophysics – Astronomy

Scientific paper

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Scientific paper

Abstract

G1.9+0.3 is the youngest (about 100 yr old) known Galactic supernova remnant. Its X-ray spectrum is dominated by synchrotron emission produced by energetic (100 TeV) electrons accelerated in its fast (14,000 km/s) blast wave. A bilaterally symmetric X-ray morphology and systematic variations of the synchrotron cutoff frequency around the remnant's circumference are best explained by the obliquity-dependent acceleration of electrons in the blast wave expanding into ambient gas with a uniform magnetic field. A recent 240 ks Chandra observation revealed supernova ejecta emitting in Si, S, Ar, Ca, and Fe lines. These X-ray lines are predominantly found in the X-ray faint, but radio bright northern half of the remnant. The inferred element abundances are supersolar, large Doppler shifts (several thousand km/s) are present, and lines are Doppler broadened (FWHM 25,000 km/s). The supernova ejecta are highly clumpy; we map the spatial distribution of heavy-element ejecta with a multiscale image estimation method suitable for our photon-limited Chandra data. Joint spatio-spectral denoising directly applied to Chandra data cubes allows us to spatially localize ejecta clumps down to arcsec scales, notwithstanding low (about 500) total counts in lines. We also map small-scale variations in the synchrotron cutoff frequency along the remnant's circumference. We report on the spatially-varying angular expansion of G1.9+0.3, based on comparison of Chandra observations separated by 2.5 years. The overall expansion is consistent with prior radio- and X-ray based measurements, but there is evidence for slower expansion in the north. Together with the detection of X-ray lines there, this suggests a higher than average ambient medium density in the north. The presence of Fe-rich ejecta favors a Type Ia explosion. Asymmetric distribution of ambient medium around a Type Ia explosion is particularly interesting, as it contains clues about poorly-understood Type Ia progenitors.

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