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ABSTRACT We present multi-epoch spectropolarimetry and spectra for a sample of 14 Type IIn supernovae (SNe IIn). We find that after correcting for likely interstellar polarization, SNe IIn commonly show intrinsic continuum polarization of 1–3 per cent at the time of peak optical luminosity, although a few show weaker or negligible polarization. While some SNe IIn have even stronger polarization at early times, their polarization tends to drop smoothly over several hundred days after peak. We find a tendency for the intrinsic polarization to be stronger at bluer wavelengths, especially at early times. While polarization from an electron scattering region is expected to be grey, scattering of SN light by dusty circumstellar material (CSM) may induce such a wavelength-dependent polarization. For most SNe IIn, changes in polarization degree and wavelength dependence are not accompanied by changes in the position angle, requiring that asymmetric pre-SN mass loss had a persistent geometry. While 2–3 per cent polarization is typical, about 30 per cent of SNe IIn have very low or undetected polarization. Under the simplifying assumption that all SN IIn progenitors have axisymmetric CSM (i.e. disc/torus/bipolar), then the distribution of polarization values we observe is consistent with similarly asymmetric CSM seen from a distribution of random viewing angles. This asymmetry has very important implications for understanding the origin of pre-SN mass loss in SNe IIn, suggesting that it was shaped by binary interaction. 

Type Ia Supernovae (SNe Ia) arise from carbon oxygen white dwarfs, but the true nature of their progenitor systems and explosion mechanisms remains the subject of considerable debate. The various progenitor models and methods of ignition result in different ejecta morphologies and/or distributions of material. By observing the polarization of SNe spectra we can gather insight into the geometry of these explosions. A key diagnostic that appears to be correlated with other SN Ia properties is the change in polarization observed across the Si II 6355 Å feature near maximum light. To investigate this, we are undertaking a systematic analysis of this feature in a uniformly obtained sample of SNe Ia observed at multiple epochs as part of the Supernova Spectropolarimetry (SNSPOL) Project, which gathered data, from 2010-2018, using the CCD Imaging/Spectropolarimeter (SPOL) on the 61" Kuiper, 6.5 m MMT, and 90" Bok telescopes. Here we present a preliminary analysis of the Si II feature in a particularly well-observed object from our sample, SN 2018gv, and present 10 epochs of data spanning from 10 days before, to 22 days after, peak light. We compare our near-maximum SNSPOL data with complementary data presented by Yang et al. [1]. This work was supported by NSF grants AST-1210311 and AST-2010001, and NASA grant NNX15AU81G. References: [1] Yang, Yi et al. 2020, ApJ, 902. 

Type Ia Supernovae (SNe Ia) arise from carbon oxygen white dwarfs, but the true nature of their progenitor systems and explosion mechanisms remains the subject of considerable debate. The various progenitor models and methods of ignition result in different ejecta morphologies and/or distributions of material. By observing the polarization of SNe spectra we can gather insight into the geometry of these explosions. A key diagnostic that appears to be correlated with other SN Ia properties is the change in polarization observed across the Si II 6355 Å feature near maximum light. To investigate this, we are undertaking a systematic analysis of this feature in a uniformly obtained sample of SNe Ia observed at multiple epochs as part of the Supernova Spectropolarimetry (SNSPOL) Project, which gathered data, from 2010-2018, using the CCD Imaging/Spectropolarimeter (SPOL) on the 61" Kuiper, 6.5 m MMT, and 90" Bok telescopes. Here we present a preliminary analysis of the Si II feature in a particularly well-observed object from our sample, SN 2018gv, and present 10 epochs of data spanning from 10 days before, to 22 days after, peak light. We compare our near-maximum SNSPOL data with complementary data presented by Yang et al. [1]. This work was supported by NSF grants AST-1210311 and AST-2010001, and NASA grant NNX15AU81G. References: [1] Yang, Yi et al. 2020, ApJ, 902. 

Abstract We present multi-epoch optical spectropolarimetric and imaging polarimetric observations of the nearby Type II supernova (SN) 2023ixf discovered in M101 at a distance of 6.85 Mpc. The first imaging polarimetric observations were taken +2.33 days (60085.08 MJD) after the explosion, while the last imaging polarimetric data points (+73.19 and +76.19 days) were acquired after the fall from the light-curve plateau. At +2.33 days there is strong evidence of circumstellar material (CSM) interaction in the spectra and the light curve. A significant level of intrinsic polarizationp_r = 1.02% ± 0.07% is seen during this phase, which indicates that this CSM is aspherical. We find that the polarization evolves with time toward the interstellar polarization level during the photospheric phase, which suggests that the recombination photosphere is spherically symmetric. There is a jump in polarization (p_r = 0.45% ± 0.08% andp_r = 0.62% ± 0.08%) at +73.19 and +76.19 days when the light curve falls from the plateau. This is a phase where polarimetric data are sensitive to nonspherical inner ejecta or a decrease in optical depth into the single-scattering regime. We also present spectropolarimetric data that reveal line (de)polarization during most of the observed epochs. In addition, at +14.50 days we see an “inverse P Cygni” profile in the H and He line polarization, which clearly indicates the presence of asymmetrically distributed material overlying the photosphere. The overall temporal evolution of the polarization is typical for Type II SNe, but the high level of polarization during the rising phase has only been observed in SN 2023ixf. 

ABSTRACT We present multi-epoch spectropolarimetry of Type IIn supernova SN2017hcc, 16–391 d after explosion. Continuum polarization up to 6 per cent is observed during the first epoch, making SN 2017hcc the most intrinsically polarized SN ever reported at visible wavelengths. During the first 29 d, when the polarization is strongest, the continuum polarization exhibits wavelength dependence that rises toward the blue, then becomes wavelength independent by day 45. The polarization drops rapidly during the first month, even as the flux is still climbing to peak brightness. None the less, unusually high polarization is maintained until day 68, at which point the polarization declines to levels comparable to those of previous well-studied SNe IIn. Only minor changes in position angle (PA) are measured throughout the evolution. The blue slope of the polarized continuum and polarized line emission during the first month suggests that an aspherical distribution of dust grains in pre-shock circumstellar material (CSM) is echoing the SN IIn spectrum and strongly influencing the polarization, while the subsequent decline during the wavelength-independent phase appears consistent with electron scattering near the SN/CSM interface. The persistence of the PA between these two phases suggests that the pre-existing CSM responsible for the dust scattering at early times is part of the same geometric structure as the electron-scattering region that dominates the polarization at later times. SN 2017hcc appears to be yet another, but more extreme, case of aspherical yet well-ordered CSM in Type IIn SNe, possibly resulting from pre-SN mass-loss shaped by a binary progenitor system. 

Abstract We present the final data from the Sloan Digital Sky Survey (SDSS) Reverberation Mapping (RM) project, a precursor to the SDSS-V Black Hole Mapper RM program. This data set includes 11 yr photometric and 7 yr spectroscopic light curves for 849 broad-line quasars over a redshift range of 0.1 <z< 4.5 and a luminosity range ofL_bol= 10^44−47.5erg s⁻¹, along with spectral and variability measurements. We report 23, 81, 125, and 110 RM lags (relative to optical continuum variability) for broad Hα, Hβ, Mgii, and Civusing the SDSS-RM sample, spanning much of the luminosity and redshift ranges of the sample. Using 30 low-redshift RM active galactic nuclei with dynamical-modeling black hole masses, we derive a new estimate of the average virial factor of $\left(\log f\right)=0.62\pm 0.07$for the line dispersion measured from the rms spectrum. The intrinsic scatter of individual virial factors is 0.31 ± 0.07 dex, indicating a factor of 2 systematic uncertainty in RM black hole masses. Our lag measurements reveal significantR–Lrelations for Hβand Mgiiat high redshift, consistent with the latest measurements based on heterogeneous samples. While we are unable to robustly constrain the slope of theR–Lrelation for Civgiven the limited dynamic range in luminosity, we found substantially larger scatter in Civlags at fixedL₁₃₅₀. Using the SDSS-RM lag sample, we derive improved single-epoch (SE) mass recipes for Hβ, Mgii, and Civ, which are consistent with their respective RM masses as well as between the SE recipes from two different lines, over the luminosity range probed by our sample. The new Hβand Mgiirecipes are approximately unbiased estimators at given RM masses, but there are systematic biases in the Civrecipe. The intrinsic scatter of SE masses around RM masses is ∼0.45 dex for Hβand Mgii, increasing to ∼0.58 dex for Civ. 

Abstract We report the detection of very high energy gamma-ray emission from the blazar S3 1227+25 (VER J1230+253) with the Very Energetic Radiation Imaging Telescope Array System (VERITAS). VERITAS observations of the source were triggered by the detection of a hard-spectrum GeV flare on 2015 May 15 with the Fermi-Large Area Telescope (LAT). A combined 5 hr VERITAS exposure on May 16 and 18 resulted in a strong 13 σ detection with a differential photon spectral index, Γ = 3.8 ± 0.4, and a flux level at 9% of the Crab Nebula above 120 GeV. This also triggered target-of-opportunity observations with Swift, optical photometry, polarimetry, and radio measurements, also presented in this work, in addition to the VERITAS and Fermi-LAT data. A temporal analysis of the gamma-ray flux during this period finds evidence of a shortest variability timescale of τ obs = 6.2 ± 0.9 hr, indicating emission from compact regions within the jet, and the combined gamma-ray spectrum shows no strong evidence of a spectral cutoff. An investigation into correlations between the multiwavelength observations found evidence of optical and gamma-ray correlations, suggesting a single-zone model of emission. Finally, the multiwavelength spectral energy distribution is well described by a simple one-zone leptonic synchrotron self-Compton radiation model.