Supernova remnants as particle accelerators: results from X-ray studies
Stephen Reynolds (North Carolina State University)

Fast particles, with energies far above thermal, are ubiquitous in astrophysics, playing important roles in star formation, galactic structure, active galaxies, and elsewhere. It is now generally accepted that fast electrons and ions are produced through the diffusive shock acceleration process, with the strong shock waves from supernova remnants (SNRs) a prime candidate for acceleration sites. In particular, electrons make themselves apparent through synchrotron radiation at photon energies from radio through hard X-rays, and through inverse-Compton scattering in gamma rays. Synchrotron radiation dominates the X-ray spectrum of a handful of Galactic SNRs, and contributes substantially to that of several more. These objects allow detailed study of the electron populations and the local environments of their acceleration. I shall summarize the properties of this population of X-ray synchrotron SNRs (XSSNRS), and describe in detail results on several objects. Ongoing monitoring of the youngest Galactic SNR G1.9+0.3 with the sub-arcsecond spatial resolution of the Chandra X-ray Observatory has allowed the characterization of velocities and brightness changes, both increases and decreases, on length scales of a small fraction of the remnant radius. These results and others pose significant problems for theoretical modeling of electron acceleration.

Cosmological Puzzles from JWST's Galaxies
Julian Muñoz - (University of Texas)

TBD