Emission Measures and Emission-measure-weighted Temperatures of Shocked ISM and Ejecta in Supernova Remnants

A goal of supernova remnant (SNR) evolution models is to relate fundamental parameters of a supernova (SN) explosion and progenitor star to the current state of its SNR. The SNR hot plasma is characterized by its observed X-ray spectrum, which yields electron temperature, emission measure and abundances. Depending on their brightness, the properties of the plasmas heated by the SNR forward shock, reverse shock or both can be measured. The current work utilizes models which are spherically symmetric. One dimensional hydrodynamic simulations are carried out for SNR evolution prior to onset of radiative losses. From these, we derive dimensionless emission measures and emission-measure-weighted temperatures, and we present fitting formulae for these quantities as functions of scaled SNR time. These models allow one to infer SNR explosion energy, circumstellar medium density, age, ejecta mass and ejecta density profile from SNR observations. The new results are incorporated into the SNR modelling code SNRPy. The code is demonstrated with application to three historical SNRs: Kepler, Tycho and SN1006.Comment: 50 pages, 10 figures, 5 table

RADIO STUDY OF SUPERNOVA REMNANTS: UNDERSTANDING THE MISSING SUPERNOVA REMNANT PROBLEM

There is a discrepancy between the observed and predicted numbers of Galactic supernova remnants (SNRs), likely due to observational biases that hinder the detection of old, faint, large remnants, as well as very young, small remnants, caused by poor sensitivity and spatial resolution. The goal of this thesis is to address this issue and explore missing SNRs. As a first step, distances to 29 SNRs and one SNR candidate were estimated using HI absorption and 13CO emission spectra from various surveys, leading to improved distance estimates compared to previous values. Using the THOR survey, two compact young SNRs, G18.760-0.072 and G31.299-0:0493, were identified at distances of 4.7 ± 0.2 kpc and 5.0 ± 0.3 kpc respectively. Additionally, a table of 227 extragalactic sources is presented. The detection of these SNRs is consistent with the THOR sensitivity limit and the distribution of integrated flux densities of SNRs. To determine the radial distribution and estimate the total number of SNRs in the Galaxy, distances to 215 SNRs were compiled using a consistent rotation curve. Two methods were employed: applying correction factors for selection effects and comparing functional forms against the data. I calculated that the total count of SNRs in the Galaxy ranges roughly between 2400 and 5600. Statistical analyses were performed on a sample of 390 SNRs, investigating their diameters, ages, spectral indices, Galactic heights, and spherical symmetries. The accuracy of distance estimation using the Σ-D relation was also examined. The average diameter of Galactic SNRs was determined to be 30.5 pc, with a standard error of 1.7 pc and a standard deviation of 25.4 pc. The geometric mean diameter was found to be 21.9 pc, with a geometric standard deviation factor of 2.4. This suggests that, on average, the sizes of Galactic SNRs are smaller when compared to those observed in other galaxies. Age estimates were obtained for 97 SNRs, revealing a supernova birth rate slightly lower than currently accepted values but within 2σ of those values. The mean spectral index of shell-type SNRs was determined to be -0:51 ± 0:01. No significant correlations were observed between spectral indices and other SNR parameters. The distribution of SNRs with respect to Galactic height was best described by an exponential distribution with a scale height of 48 ± 4 pc. While there is evidence of a large number of unidentified SNRs, their detection remains challenging due to their concentration near the Galactic plane, foreground objects, and the bright Galactic synchrotron background. The current lack of large-scale spiral structure in the SNR distribution may change with the addition of several hundred more SNRs, offering new insights into their distribution

HI Absorption Measurements and Kinematic Distances to 34 Supernova Remnants

Accurate distances to supernova remnants (SNRs) are crucial in determining their size, age, luminosity and evolutionary state. To determine distances, 34 bright SNRs were chosen from the VLA Galactic Plane Survey (VGPS) to extract HI absorption spectra. Analyzing the HI absorption and 13CO emission spectra, HI and 13CO channel maps, distances to the 34 SNRs were calculated. To estimate a distance, an accurate rotation curve is essential in order to obtain orbital velocities V(R). The orbital velocities obtained by the tangent point method were compared with the Universal Rotation Curve as a test of its validity. From the analysis 12 new, 9 changed, 6 revised and 7 confirmed distances are presented. Furthermore, the selection effects of the study sample is discussed. The surface density of SNRs were calculated and found to be proportional to the density of stars. The validity of the Σ-D relation of estimating distances is discussed

Search for and Identification of Young Compact Galactic Supernova Remnants Using THOR

Young Supernova remnants (SNRs) with smaller angular sizes are likely missing from existing radio SNR catalogues, caused by observational constraints and selection effects. In order to find new compact radio SNR candidates, we searched the high angular resolution (25″) THOR radio survey of the first quadrant of the galaxy. We selected sources with non-thermal radio spectra. HI absorption spectra and channel maps were used to identify which sources are galactic and to estimate their distances. Two new compact SNRs were found: G31.299-0.493 and G18.760-0.072, of which the latter was a previously suggested SNR candidate. The distances to these SNRs are 5.0±0.3 kpc and 4.7±0.2 kpc, respectively. Based on the SN rate in the galaxy or on the statistics of known SNRs, we estimate that there are 15–20 not-yet detected compact SNRs in the galaxy and that the THOR survey area should contain three or four. Our detection of two SNRs (half the expected number) is consistent with the THOR sensitivity limit compared with the distribution of integrated flux densities of SNRs

Discovery of 20 UV-emitting SNRs in M31 with UVIT

We present the first catalog of supernova remnants (SNRs) in M31 that exhibit diffuse ultraviolet (UV) emission. UV images of M31 were obtained by the Ultraviolet Imaging Telescope (UVIT) on the AstroSat satellite, and the list of SNRs was obtained from X-ray, optical, and radio catalogs of SNRs in M31. We used the UVIT images to find SNRs with diffuse emission, omitting those too contaminated with stellar emission. A total of 20 SNRs in M31 were detected with diffuse UV emission. Fluxes in the UVIT F148W, F169M, F172M, N219M, and N279N filters are measured for these SNRs. The luminosities are compared to those computed from the spectra of seven known UV-emitting SNRs in the Milky Way, the Large Magellanic Cloud, and the Small Magellanic Cloud. We find similar spectral shapes between the known and the M31 UV-emitting SNRs. The spectral shapes and the diffuse nature of the emission are good evidence that the UV emissions are dominated by line emissions, like known SNRs, and the UV is associated with the SNRs. Models are applied to the six SNRs with X-ray spectra. The main difference is that the two X-ray/UV SNRs are Type Ia and the four X-ray/non-UV SNRs are core-collapse or unknown type. A comparison of M31 SNRs in different wave bands shows that most are detected optically, similar to the case for other nearby galaxies. A total of 19 of the 20 UV-emitting SNRs are detected optically, expected because both UV and optical are from forbidden and recombination lines from shock-ionized gas