Radio Spectral Index Variations of the SNR HB3

We present images of the SNR HB3 at both 408 MHz and 1420 MHz from the Canadian Galactic Plane Survey mainly based on data from the Synthesis Telescope of the Dominion Radio Astrophysical Observatory. We reproduce the 100m-Effelsberg HB3 image at 2695 MHz at large scale, and find that there exists a background emission gradient across the HB3 area. Based on our analysis of background emission and the boundary between W3 and HB3, we give HB3's flux density as 68.6 +/- 11.5 Jy at 408 MHz and 44.8 +/- 12.0 Jy at 1420 MHz, after subtracting flux from compact sources within HB3. The integrated flux-density-based spectral index between 408 MHz and 1420 MHz is 0.34 +/- 0.15. The averaged T-T plot spectral index using all subareas is 0.36. Our measurement values are less than a previously published value of 0.6. The 408-1420 MHz spectral index varies spatially in HB3 in the range 0.1 to 0.7. We investigate the data used by previous authors, and consider more data at 232 MHz, 3650 MHz and 3900 MHz which are not included in previous calculations. There is evidence for two spectral indices for HB3 in the radio band, i.e., 0.63 (38 - 610 MHz) and 0.32 (408 - 3900 MHz). This is consistent with the spatial variations: the low frequency data mainly reflects the steeper indices and the high frequency data mainly reflects the flatter indices.Comment: 8 pages, 4 tables, 3 figures, accepted for publication in A&

Radio observations and spectral index study of SNR G126.2+1.6

We present new images of the low radio surface brightness Supernova Remnant (SNR) G126.2+1.6, based on the 408 MHz and 1420 MHz continuum emission and the HI-line emission data of the Canadian Galactic Plane Survey (CGPS). {\bf We find the SNR's flux densities at 408 MHz (9.7$\pm$3.9 Jy) and 1420 MHz (6.7$\pm$2.1 Jy) which have been} corrected for flux densities from compact sources within the SNR. The integrated flux density based spectral index (S$_{\nu}$$\propto$$\nu$$^{-\alpha}$) is 0.30$\pm$0.41. The respective T-T plot spectral index is 0.30 $\pm$0.08. We also find spatial variations of spectral index within the SNR{\bf:0.2-0.6.} HI observations show structures probably associated with the SNR, i.e, features associated with the SNR's southeastern filaments in the radial velocity range of -33 to -42 km$/$s, and with its northwestern filaments in -47 to -52 km$/$s. This association suggests a distance of 5.6 kpc for SNR G126.2+1.6. The estimated Sedov age for G126.2+1.6 is less than 2.1$\times10^{5}$ yr.Comment: 12 pages, 4 figures, 4 tables, accepted by A&

Investigations of supernovae and supernova remnants in the era of SKA

Two main physical mechanisms are used to explain supernova explosions: thermonuclear explosion of a white dwarf(Type Ia) and core collapse of a massive star (Type II and Type Ib/Ic). Type Ia supernovae serve as distance indicators that led to the discovery of the accelerating expansion of the Universe. The exact nature of their progenitor systems however remain unclear. Radio emission from the interaction between the explosion shock front and its surrounding CSM or ISM provides an important probe into the progenitor star's last evolutionary stage. No radio emission has yet been detected from Type Ia supernovae by current telescopes. The SKA will hopefully detect radio emission from Type Ia supernovae due to its much better sensitivity and resolution. There is a 'supernovae rate problem' for the core collapse supernovae because the optically dim ones are missed due to being intrinsically faint and/or due to dust obscuration. A number of dust-enshrouded optically hidden supernovae should be discovered via SKA1-MID/survey, especially for those located in the innermost regions of their host galaxies. Meanwhile, the detection of intrinsically dim SNe will also benefit from SKA1. The detection rate will provide unique information about the current star formation rate and the initial mass function. A supernova explosion triggers a shock wave which expels and heats the surrounding CSM and ISM, and forms a supernova remnant (SNR). It is expected that more SNRs will be discovered by the SKA. This may decrease the discrepancy between the expected and observed numbers of SNRs. Several SNRs have been confirmed to accelerate protons, the main component of cosmic rays, to very high energy by their shocks. This brings us hope of solving the Galactic cosmic ray origin's puzzle by combining the low frequency (SKA) and very high frequency (Cherenkov Telescope Array: CTA) bands' observations of SNRs.Comment: To be published in: "Advancing Astrophysics with the Square Kilometre Array", Proceedings of Science, PoS(AASKA14

A Study of Radio Knots within Supernova Remnant Cassiopeia A

The study on the dynamic evolution of young supernova remnants (SNRs) is an important way to understand the density structure of the progenitor's circumstellar medium. We have reported the acceleration or deceleration, proper motion and brightness changes of 260 compact radio features in the second youngest known SNR Cas A at 5\,GHz based on the VLA data of five epochs from 1987 to 2004. The radio expansion center locates at $\alpha(1950)=23^{\rm h}21^{\rm m}9^{\rm s}_{\cdot}7 \pm 0^{\rm s}_{\cdot}29, \delta(1950)=+58^{\circ}32^{\prime}25^{\prime\prime}_{\cdot}2 \pm 2^{\prime\prime}_{\cdot}2$. Three-quarters of the compact knots are decelerating, this suggests that there are significant density fluctuations in the stellar winds of the remnant's progenitor. We have verified that the acceleration or deceleration of compact knots are not related with the distribution of brightness. The brightening, fading, disappearing or new appearing of compact radio features in Cas A suggests that the magnetic field in the remnant is changing rapidly.Comment: 20 pages,9 figures, ApJ accepte