We present a measurement of the expansion and brightening of G1.9+0.3, the youngest Galactic supernova remnant, comparing Chandra X-ray images obtained in 2007 and 2009. A simple uniform expansion model describes the data well, giving an expansion rate of 0.642 ± 0.049% yr −1 , and a flux increase of 1.7 ± 1.0% yr −1 . Without deceleration, the remnant age would then be 156 ± 11 yr, consistent with earlier results. Since deceleration must have occurred, this age is an upper limit; we estimate an age of about 110 yr, or an explosion date of about 1900. The flux increase is comparable to reported increases at radio wavelengths. G1.9+0.3 is the only Galactic supernova remnant increasing in flux, with implications for the physics of electron acceleration in shock waves.Subject headings: ISM: individual objects (G1.9+0.3) -ISM: supernova remnants -X-rays: ISM

We report the discovery of thermal X-ray emission from the youngest Galactic supernova remnant G1.9+0.3, from a 237-ks Chandra observation. We detect strong Kα lines of Si, S, Ar, Ca, and Fe. In addition, we detect a 4.1 keV line with 99.971% confidence which we attribute to 44 Sc, produced by electron capture from 44 Ti. Combining the data with our earlier Chandra observation allows us to detect the line in two regions independently. For a remnant age of 100 yr, our measured total line strength indicates synthesis of (1 − 7) × 10 −5 M of 44 Ti, in the range predicted for both Type Ia and core-collapse supernovae, but somewhat smaller than the 2 × 10 −4 M reported for Cas A. The line spectrum indicates supersolar abundances. The Fe emission has a width of about 28,000 km s −1 , consistent with an age of ∼ 100 yr and with the inferred mean shock velocity of 14,000 km s −1 deduced assuming a distance of 8.5 kpc. Most thermal emission comes from regions of lower X-ray but higher radio surface brightness. Deeper observations should allow more detailed spatial mapping of 44 Sc, with significant implications for models of nucleosynthesis in Type Ia supernovae.

G1.9+0.3 is the youngest known Galactic supernova remnant (SNR), with an estimated supernova (SN) explosion date of ∼ 1900, and most likely located near the Galactic Center. Only the outermost ejecta layers with free-expansion velocities 18, 000 km s −1 have been shocked so far in this dynamically young, likely Type Ia SNR. A long (980 ks) Chandra observation in 2011 allowed spatially-resolved spectroscopy of heavy-element ejecta. We denoised Chandra data with the spatio-spectral method of Krishnamurthy et al., and used a waveletbased technique to spatially localize thermal emission produced by intermediate-mass elements (IMEs: Si and S) and iron. The spatial distribution of both IMEs and Fe is extremely asymmetric, with the strongest ejecta emission in the northern rim. Fe Kα emission is particularly prominent there, and fits with thermal models indicate strongly oversolar Fe abundances. In a localized, outlying region in the northern rim, IMEs are less abundant than Fe, indicating that undiluted Fe-group elements (including 56 Ni) with velocities > 18, 000 km s −1 were ejected by this SN. But in the inner west rim, we find Si-and S-rich ejecta without any traces of Fe, so high-velocity products of O-burning were also ejected. G1.9+0.3 appears similar to energetic Type Ia SNe such as SN 2010jn where iron-group elements at such high free-expansion velocities have been recently detected. The pronounced asymmetry in the ejecta distribution and abundance inhomogeneities are best explained by a strongly asymmetric SN explosion, similar to those produced in some recent 3D delayed-detonation Type Ia models.

We demonstrate a technique for measuring the range-resolved coherent scatter form factors of different objects from a single snapshot. By illuminating the object with an x-ray pencil beam and placing a coded aperture in front of a linear array of energy-sensitive detector elements, we record the coherently scattered x-rays. This approach yields lateral, range, and momentum transfer resolutions of 1 mm, 5 mm, and 0.2 nm⁻¹, respectively, which is sufficient for the distinguishing a variety of solids and liquids. These results indicate a path toward real-time volumetric molecular imaging for non-destructive examination in a variety of applications, including medical diagnostics, quality inspection, and security detection.

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