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The community agrees that Type Ia supernovae arise from Carbon/Oxygen white dwarfs undergoing thermonuclear runaway. However, the full progenitor system and the process that prompts the white dwarf to explode remain unknown. Most current models suggest that the white dwarf explodes because of interaction with a binary companion which may survive the process and remain within the resulting remnant of the exploded star. Furthermore, both the pre-supernova interaction process and the explosion of the primary are expected to imprint a significant departure from ordinary stellar radii and temperatures onto the secondary, making the star identifiable against the unrelated stellar population. Identification of a surviving companion inside an SN Ia remnant might confirm a specific corresponding SN Ia progenitor channel based on the identity of the companion. We conducted a surviving companion search of the Type Ia remnant SNR 0509-67.5 based in the Large Magellanic Cloud. The well-constrained distance to and foreground extinction of the Large Magellanic Cloud allow for Bayesian inference of stellar parameters with low correlation and uncertainties. We present a deep catalog of fully characterized stars interior to SNR 0509-67.5 with radii, effective temperatures, and metallicities inferred using combined Hubble Space Telescope photometric observations across multiple visits. We then compile a list of surviving companion models appropriate for the age of the remnant (roughly 400 years after the explosion). We compare these predictions with the inferred stellar parameters and conclude that none of the stars are consistent with the predicted signatures of a surviving companion., Comment: 16 pages, 8 figures, 4 tables

Using HST narrow-band H{\alpha} images of supernova remnant 0509-67.5 taken {\sim}10 years apart, we measure the forward shock (FS) proper motions (PMs) at 231 rim locations. The average shock radius and velocity are 3.66 {\pm} 0.036 pc and 6315 {\pm} 310 km s{^{-1}}. Hydrodynamic simulations, recast as similarity solutions, provide models for the remnant's expansion into a uniform ambient medium. These are coupled to a Markov chain Monte Carlo (MCMC) analysis to determine explosion parameters, constrained by the FS measurements. For specific global parameters, the MCMC posterior distributions yield an age of 315.5 {\pm} 1.8 yr, a dynamical explosion center at 5h09m31s.16s -67{^\circ}31{^\prime}17.1{^{\prime\prime}} and ambient medium densities at each azimuth ranging from 3.7-8.0 {\times} 10{^{-25}} g cm{^{-3}}. We can detect stellar PMs corresponding to speeds in the LMC of 770 km s{^{-1}} or more using the H${\alpha}$ images. Five stars in the remnant show measurable PMs but none appear to be moving radially from the center, including a prominent red star 4.6{^{\prime\prime}} from the center. Using coronal [Fe XIV] {\lambda}5303 emission as a proxy for the reverse shock location, we constrain the explosion energy (for a compression factor of 4) to a value of E = (1.30 {\pm} 0.41) {\times} 10{^{51}} erg for the first time from shock kinematics alone. Higher compression factors (7 or more) are strongly disfavored based on multiple criteria, arguing for inefficient particle acceleration in the Balmer shocks of 0509-67.5., Comment: 19 pages, 9 figures, 4 tables

We present an improved weak-lensing (WL) study of the high$-z$ $(z=0.87)$ merging galaxy cluster ACT-CL J0102-4915 (El Gordo) based on new wide-field Hubble Space Telescope (HST) imaging data. The new imaging data cover the 3.5$\times$3.5 Mpc region centered on the cluster and enable us to detect WL signals beyond the virial radius, which was not possible in previous studies. We confirm the binary mass structure consisting of the northwestern (NW) and southeastern (SE) subclusters and the 2$\sigma$ dissociation between the SE mass peak and the X-ray cool core. We obtain the mass estimates of the subclusters by simultaneously fitting two Navarro-Frenk-White (NFW) halos without employing mass-concentration relations. The masses are $M_{200c}^{NW} = 9.9^{+2.1}_{-2.2} \times 10^{14} M_{\sun}$ and $M_{200c}^{SE} = 6.5^{+1.9}_{-1.4} \times 10^{14} M_{\sun}$ for the NW and SE subclusters, respectively. The mass ratio is consistent with our previous WL study but significantly different from the previous strong lensing results. This discrepancy is attributed to the use of extrapolation in strong lensing studies because the SE component possesses a higher concentration. By superposing the two best-fit NFW halos, we determine the total mass of El Gordo to be $M_{200c} = 2.13^{+0.25}_{-0.23} \times 10^{15} M_{\sun}$, which is 23% lower than our previous WL result [$M_{200c} =(2.76\pm0.51) \times 10^{15} M_{\sun}$]. Our updated mass is a more direct measurement since we are not extrapolating to $R_{200c}$ as in all previous studies. The new mass is compatible with the current $\Lambda$CDM cosmology., Comment: 27 pages, 18 figures, 3 tables; matches the version accepted for publication in ApJ