Determination of the explosion type of supernova remnants (SNRs) can be challenging, as SNRs are hundreds to thousands of years old and supernovae (SNe) are classified based on spectral properties days after explosion. Previous studies of thermal X-ray emission from Milky Way and Large Magellanic Cloud (LMC) SNRs have shown that Type Ia and core-collapse (CC) SNRs have statistically different symmetries, and thus these sources can be typed based on their X-ray morphologies. In this paper, we extend the same technique, a multipole expansion technique using power ratios, to infrared (IR) images of SNRs to test whether they can be typed using the symmetry of their warm dust emission as well. We analyzed archival Spitzer Space Telescope Multiband Imaging Photometer (MIPS) 24 µm observations of the previously used X-ray sample, and we find that the two classes of SNRs separate according to their IR morphologies. The Type Ia SNRs are statistically more circular and mirror symmetric than the CC SNRs, likely due to the different circumstellar environments and explosion geometries of the progenitors. Broadly, our work indicates that the IR emission retains information of the explosive origins of the SNR and offers a new method to type SNRs based on IR morphology.

We present a search for late-time rebrightening of radio emission from three supernovae (SNe) with associated gamma-ray bursts (GRBs). It has been previously proposed that the unusually energetic SNe associated with GRBs should enter the Sedov-Taylor phase decades after the stellar explosion, and this SN "remnant" emission will outshine the GRB radio afterglow and be detectable at significant distances. We place deep limits on the radio luminosity of GRB 980425/SN 1998bw, GRB 030329/SN 2003dh and GRB 060218/SN 2006aj, 10 − 18 years after explosion, with our deepest limit being L ν < 4 × 10 26 erg s −1 Hz −1 for GRB 980425/SN 1998bw. We put constraints on the density of the surrounding medium for various assumed values of the microphysical parameters related to the magnetic field and synchrotron-emitting electrons. For GRB 060218/SN 2006aj and GRB 980425/SN 1998bw, these density limits have implications for the density profile of the surrounding medium, while the non-detection of GRB 030329/SN 2003dh implies that its afterglow will not be detectable anymore at GHz frequencies.

Although it is well established that some extragalactic radio sources are time-variable, the properties of this radio variability, and its connection with host galaxy properties, remain to be explored—particularly for faint sources. Here we present an analysis of radio variable sources from the CHILES Variable and Explosive Radio Dynamic Evolution Survey (CHILES VERDES)—a partner project of the 1.4 GHz COSMOS H i Large Extragalactic Survey. CHILES VERDES provides an unprecedented combination of survey depth, duration, and cadence, with 960 hr of 1–2 GHz continuum VLA data obtained over 209 epochs between 2013 and 2019 in a 0.44 deg2 section of the well-studied extragalactic deep field, COSMOS. We identified 18 moderate-variability sources (showing 10%–30% flux density variation) and 40 lower-variability sources (2%–10% flux density variation). They are mainly active galactic nuclei (AGNs) with radio luminosities in the range of 1022–1027 W Hz−1, based on cross-matching with COSMOS multiwavelength catalogs. The moderate-variability sources span redshifts z = 0.22–1.56, have mostly flat radio spectra (α > −0.5), and vary on timescales ranging from days to years. The lower-variability sources have similar properties, but generally have higher radio luminosities than the moderate-variability sources, extending to z = 2.8, and have steeper radio spectra (α < −0.5). No star-forming galaxy showed statistically significant variability in our analysis. The observed variability likely originates from scintillation on short (∼week) timescales, and Doppler-boosted intrinsic AGN variability on long (month–year) timescales.

We present results from our optical survey of the position error contours ("error boxes") of unidentified EGRET sources at mid to high Galactic latitude. It is our intention to search for potential blazars that may have been missed in the original identification process of the three EGRET Catalogues and supplementary publications. We have first searched the error contours of unidentified sources at b > |20 • | for flat spectrum radio sources using the NASA Extragalactic Database (NED). For each such radio source found we conducted optical searches for counterparts using the Palomar 60-inch telescope, and University of Wyoming's 2.3 and 0.6 m telescopes. Many of the radio sources have plausible optical counterparts, and spectroscopy will be conducted at a later date to determine which of these sources are quasars or active galaxies. Results show thats several sources are optically variable, and/or have flat or inverted radio to millimeter spectra and are thus potential blazars.

It is clear from previous and ongoing surveys that there are many sources that change in brightness over time. There is a wide range of extragalactic phenomena that create events with time-varying brightness. Variable sources have regular changes in brightness, such as the steady accretion of matter onto a super massive black hole at the center of a galaxy, known as active galactic nuclei (AGN). Despite strongly emitting in radio wavelengths, the radio sky is nearly completely unexplored in terms of these variable events. Most radio surveys on AGN variability have not been deep enough, include a small sample, and only have a few observations to understand how AGN are changing on timescales between weeks and months. Improving our understanding of the fundamental nature these sources requires a deep radio continuum survey with extension data to observe changes happening on timescales longer than days and less than years. The combination of the COSMOS HI Large Extragalactic Survey (CHILES) and 14 hours of extension observations, I will begin to answer: what is the variability of radio AGN and can it be used to predict and classify future events?