| We perform theoretical and observational studies of supernova remnants (SNRs) and gamma-ray bursts (GRBs), with a view to understanding emission mechanisms and the nature of the ambient medium. In Chapter 1, we provide brief introductions and literature reviews. In Chapter 2, we study the Halpha and Lyalpha emission from SNR 1987A, using the Space Telescope Imaging Spectrograph (STIS) onboard the Hubble Space Telescope. We detect two flavors of emission, surface and interior, which are analogous to the narrow- and broad-line components observed in Balmer-dominated SNRs. In Chapter 3, we present a new formalism for calculating line profiles and ratios in Balmer-dominated SNRs. Charge transfer events between an atomic beam and post-shock ions are capable of generating atoms with velocity distributions intermediate between a beam and a Maxwellian. The length scale on which this happens is on the order of the mean free path of interactions, which defines the width of the shock transition zone. In the zone, hydrodynamical quantities vary from their pre- to post-shock values according to the Rankine-Hugoniot jump conditions; we examine its structure in Chapter 4. We conclude with a study of dust echoes from GRBs in Chapter 5, where we present time-dependent calculations which self-consistently consider dust and echo evolution. For symmetric, bipolar jets, dust echoes display two bumps in their light curve, making them distinguishable from the single rebrightening due to an underlying supernova, thereby presenting a possible way of detecting off-axis GRBs. |
