Search

In the framework of the Standard Model Extension (SME), we present improved constraints on anisotropic Lorentz invariance and Charge-Parity-Time (CPT) violation by searching for astrophysical signals of cosmic vacuum birefringence with broadband optical polarimetry of high redshift astronomical sources, including Active Galactic Nuclei and Gamma-Ray Burst afterglows. We generalize the work in Kislat 2018, which studied the SME mass dimension $d = 4$ case, to arbitrary mass dimension for both the CPT-even and CPT-odd cases. We then present constraints on all 10, 16, and 42 anisotropic birefringent SME coefficients for dimension $d = 4$, $d = 5$, and $d = 6$ models, respectively, using 7554 observations for odd d and 7376 observations for even d of 1278 unique sources on the sky, which, to our knowledge, comprises the most complete catalog of optical polarization from extragalactic sources in the literature to date. Compared to the smaller sample of 44 and 45 broadband optical polarimetry observations analyzed in Kislat 2018 and Kislat and Krawczynski 2017, our dimension $d = 4$ and $d = 5$ average constraints are more sensitive by factors of 35 and 10, corresponding to a reduction in allowed SME parameter space volume for these studies of 15 and 16 orders of magnitude, respectively. Constraints from individual lines of sight can be significantly stronger using spectropolarimetry. Nevertheless, due to the increased number of observations and lines of sight in our catalog, our average $d = 4$ and $d = 5$ broadband constraints are within factors of 2 and 12 of previous constraints using spectropolarimetry from Kislat 2018 and Kislat and Krawczynski 2017, respectively, using an independent data set and an improved analysis method. By contrast, our anisotropic constraints on all 42 birefringent SME coefficients for $d = 6$ are the first to be presented in the literature., 29 pages, 14 figures

We report evidence for excess blue light from the Type Ia supernova SN 2012cg at fifteen and sixteen days before maximum B-band brightness. The emission is consistent with predictions for the impact of the supernova on a non-degenerate binary companion. This is the first evidence for emission from a companion to a SN Ia. Sixteen days before maximum light, the B-V color of SN 2012cg is 0.2 mag bluer than for other normal SN~Ia. At later times, this supernova has a typical SN Ia light curve, with extinction-corrected M_B = -19.62 +/- 0.02 mag and Delta m_{15}(B) = 0.86 +/- 0.02. Our data set is extensive, with photometry in 7 filters from 5 independent sources. Early spectra also show the effects of blue light, and high-velocity features are observed at early times. Near maximum, the spectra are normal with a silicon velocity v_{Si} = -10,500$ km s^{-1}. Comparing the early data with models by Kasen (2010) favors a main-sequence companion of about 6 solar masses. It is possible that many other SN Ia have main-sequence companions that have eluded detection because the emission from the impact is fleeting and faint., accepted to ApJ

We present ultraviolet, optical, and near-infrared photometry as well as optical spectra of the peculiar supernova (SN) 2008ha. SN 2008ha had a very low peak luminosity, reaching only M_V = -14.2 mag, and low line velocities of only ~2000 km/s near maximum brightness, indicating a very small kinetic energy per unit mass of ejecta. Spectroscopically, SN 2008ha is a member of the SN 2002cx-like class of SNe, a peculiar subclass of SNe Ia; however, SN 2008ha is the most extreme member, being significantly fainter and having lower line velocities than the typical member, which is already ~2 mag fainter and has line velocities ~5000 km/s smaller (near maximum brightness) than a normal SN Ia. SN 2008ha had a remarkably short rise time of only ~10 days, significantly shorter than either SN 2002cx-like objects (~15 days) or normal SNe Ia (~19.5 days). The bolometric light curve of SN 2008ha indicates that SN 2008ha peaked at L_peak = (9.5 +/- 1.4) x 10^40 ergs/s, making SN 2008ha perhaps the least luminous SN ever observed. From its peak luminosity and rise time, we infer that SN 2008ha generated (3.0 +/- 0.9) x 10^-3 M_sun of 56Ni, had a kinetic energy of ~2 x 10^48 ergs, and ejected 0.15 M_sun of material. We classify three new (and one potential) members of the SN 2002cx-like class, expanding the sample to 14 (and one potential) members. The host-galaxy morphology distribution of the class is consistent with that of SNe Ia, Ib, Ic, and II. Several models for generating low-luminosity SNe can explain the observations of SN 2008ha; however, if a single model is to describe all SN 2002cx-like objects, either electron capture in Ne-Mg white dwarfs causing a core collapse, or deflagration of C-O white dwarfs with SN 2008ha being a partial deflagration and not unbinding the progenitor star, are preferred. Abridged., Comment: 22 pages, 15 figures, submitted to AJ

The use of GRB energetics for cosmography has long been advanced as a means to probe out to high redshifts, to the epoch of deceleration. However, the prompt energy release in GRBs, even when corrected for jetting geometry, is far from being a standard candle. We explore the cosmographic potential of a GRB standard candle based on the newly-discovered relation by Ghirlanda et al. between the apparent geometry-corrected energies (E_gamma) and the peak of the prompt burst spectrum (E_p). We present an explicit, self-consistent formalism for correcting GRB energies with a thorough accounting for observational uncertainties. In contrast to other work, we demonstrate that the current sample of 19 GRBs is not yet cosmographically competitive with results from other studies (e.g., SNe Ia). Although the E_p-E_gamma relation is a significant correlation across a range of cosmologies, the goodness of fit of the data to a power law, depends strongly on input assumptions -- especially the unknown density of the circumburst medium. Independent of assumptions, with very few low-z bursts, the current sample is most sensitive to Omega_M but essentially insensitive to Omega_Lambda. The proper use of the relation clearly brings GRBs an impressive step closer toward a standardizable candle, but until the physical origin of the E_p-E_gamma relation is understood, calibrated with a training set of low redshift bursts, and the major potential systematic uncertainties and selection effects are addressed, we urge caution concerning claims of the utility of GRBs for cosmography (abridged)., Comment: 45 pages, 4 figures, 2 tables. Revised version with updated data from the literature. Cosmographic sensitivity to input assumptions now fully explicated and systematic errors addressed. Main conclusions unchanged from the previous version