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Abstract We conduct an analysis of over 60,000 dwarf galaxies ( $7\lesssim \log M_{*}/M_{\odot }\lesssim 10$ ) in search of photometric variability indicative of active galactic nuclei (AGNs). Using data from the Young Supernova Experiment, a time domain survey on the Pan-STARRS telescopes, we construct light curves for each galaxy in up to four bands (griz) where available. We select objects with AGN-like variability by fitting each light curve with a damped random walk (DRW) model. After quality cuts and removing transient contaminants, we identify 1100 variability-selected AGN candidates (representing 2.4% of the available sample). We analyze their spectra to measure various emission lines and calculate black hole (BH) masses, finding general agreement with previously found mass scaling relations and nine potential intermediate-mass BH candidates. Furthermore, we reanalyze the light curves of our candidates to calculate the dampening timescaleτ_DRWassociated with the DRW and see a similar correlation between this value and the BH mass. Finally, we estimate the active fraction as a function of stellar mass and see evidence that the active fraction increases with host mass. 

Abstract We present near-infrared (NIR) spectroscopy of the hydrogen- and helium-poor (Type Ic supernovae (SNe Ic)) SN 2024aecx, which displays a strong NIR excess emerging 32 days postpeak. SN 2024aecx is a peculiar SN Ic that exhibited luminous shock-cooling emission at early times, suggestive of close-in circumstellar medium (CSM), unexpected for this class of supernovae (SNe). Its early NIR spectra are typical for a SNe Ic but with strong Ciabsorption features. By ∼32 days postpeak, the spectra show a strong NIR excess, while maintaining normal optical colors, unprecedented for SNe Ic. We find that the NIR excess is well fit with a single-temperature, optically thin dust model with declining temperature, increasing mass, and roughly constant luminosity over time. The NIR excess appears too promptly for dust to have formed in the supernova (SN) ejecta, indicating an IR echo from preexisting dust in the CSM. The IR echo is likely powered by the relatively slowly evolving SN peak light, and not the brief shock cooling emission, as the latter requires unrealistically high CSM densities to explain the observed dust mass. We consider different potential CSM geometries and find that a thick face-on disk with an inner edge of around 5 × 10¹⁶cm can best explain the dust mass and temperature evolution. In this scenario, the SN shock should start interacting with this CSM 440 ± 200 days postexplosion. CSM around SNe Ic is rare, and follow-up observations of SN 2024aecx will probe the mass-loss process responsible for removing hydrogen and helium from its progenitor star. 

Abstract We present a detailed analysis of AT 2020nov, a tidal disruption event (TDE) in the center of its host galaxy, located at a redshift ofz= 0.083. AT 2020nov exhibits unique features, including double-peaked Balmer emission lines, a broad UV/optical flare, and a peak log luminosity in the extreme-ultraviolet (EUV) estimated at $\sim 45.66_{-0.33}^{+0.10}\mathrm{erg}{\mathrm{s}}^{-1}$ . A late-time X-ray flare was also observed, reaching an absorbed luminosity of 1.67 × 10⁴³erg s⁻¹approximately 300 days after the UV/optical peak. Multiwavelength coverage, spanning optical, UV, X-ray, and mid-infrared (MIR) bands, reveals a complex spectral energy distribution (SED) that includes MIR flaring indicative of dust echoes, suggesting a dust covering fraction consistent with typical TDEs. Spectral modeling indicates the presence of an extended, quiescent disk around the central supermassive black hole with a radius of $\sim 5.06_{-0.77}^{+0.59}\times 10^4{R}_{\mathrm{g}}$ . The multicomponent SED model, which includes a significant EUV component, suggests that the primary emission from the TDE is reprocessed by this extended disk, producing the observed optical and MIR features. The lack of strong active galactic nuclei signatures in the host galaxy, combined with the quiescent disk structure, highlights AT 2020nov as a rare example of a TDE occurring in a galaxy with a dormant but extended preexisting accretion structure. 

ABSTRACT Type Ia supernovae (SNe Ia) are standardizable candles: their peak magnitudes can be corrected for correlations between light-curve properties and their luminosities to precisely estimate distances. Understanding SN Ia standardization across wavelength improves methods for correcting SN Ia magnitudes. Using 150 SNe Ia from the Foundation Supernova Survey and Young Supernova Experiment, we present the first study focusing on SN Ia standardization properties in the z band. Straddling the optical and near-infrared, SN Ia light in the z band is less sensitive to dust extinction and can be collected alongside the optical on CCDs. Pre-standardization, SNe Ia exhibit less residual scatter in z-band peak magnitudes than in the g and r bands. SNe Ia peak z-band magnitudes still exhibit a significant dependence on light-curve shape. Post-standardization, the z-band Hubble diagram has a total scatter of root mean square $=0.195$ mag. We infer a z-band mass step of $$\gamma _{z} = -0.105 \pm 0.031$$ mag, which is consistent within $$1\sigma$$ of that estimated from $gri$ data, assuming $$R_{V} = 2.61$$. When assuming different $$R_{V}$$ values for high and low mass host galaxies, the z band and optical mass steps remain consistent within $$1\sigma$$. Based on current statistical precision, these results suggest dust reddening cannot fully explain the mass step. SNe Ia in the z band exhibit complementary standardizability properties to the optical that can improve distance estimates. Understanding these properties is important for the upcoming Vera Rubin Observatory and Nancy G. Roman Space Telescope, which will probe the rest-frame z band to redshifts 0.1 and 1.8. 

Abstract We present Young Supernova Experimentgrizyphotometry of SN 2021hpr, the third Type Ia supernova sibling to explode in the Cepheid calibrator galaxy, NGC 3147. Siblings are useful for improving SN-host distance estimates and investigating their contributions toward the SN Ia intrinsic scatter (post-standardization residual scatter in distance estimates). We thus develop a principled Bayesian framework for analyzing SN Ia siblings. At its core is the cosmology-independent relative intrinsic scatter parameter,σ_Rel: the dispersion of siblings distance estimates relative to one another within a galaxy. It quantifies the contribution toward the total intrinsic scatter,σ₀, from within-galaxy variations about the siblings’ common properties. It also affects the combined distance uncertainty. We present analytic formulae for computing aσ_Relposterior from individual siblings distances (estimated using any SN model). Applying a newly trainedBayeSNmodel, we fit the light curves of each sibling in NGC 3147 individually, to yield consistent distance estimates. However, the wideσ_Relposterior meansσ_Rel≈σ₀is not ruled out. We thus combine the distances by marginalizing overσ_Relwith an informative prior:σ_Rel∼U(0,σ₀). Simultaneously fitting the trio’s light curves improves constraints on distanceandeach sibling’s individual dust parameters, compared to individual fits. Higher correlation also tightens dust parameter constraints. Therefore,σ_Relmarginalization yields robust estimates of siblings distances for cosmology, as well as dust parameters for sibling–host correlation studies. Incorporating NGC 3147's Cepheid distance yieldsH₀= 78.4 ± 6.5 km s⁻¹Mpc⁻¹. Our work motivates analyses of homogeneous siblings samples, to constrainσ_Reland its SN-model dependence. 

Abstract We present preexplosion optical and infrared (IR) imaging at the site of the type II supernova (SN II) 2023ixf in Messier 101 at 6.9 Mpc. We astrometrically registered a ground-based image of SN 2023ixf to archival Hubble Space Telescope (HST), Spitzer Space Telescope (Spitzer), and ground-based near-IR images. A single point source is detected at a position consistent with the SN at wavelengths ranging from HSTRband to Spitzer 4.5μm. Fitting with blackbody and red supergiant (RSG) spectral energy distributions (SEDs), we find that the source is anomalously cool with a significant mid-IR excess. We interpret this SED as reprocessed emission in a 8600R_⊙circumstellar shell of dusty material with a mass ∼5 × 10⁻⁵M_⊙surrounding a $\log \left(L/L_{\odot }\right)=4.74\pm 0.07$ and $T_{\mathrm{eff}}={3920}_{-160}^{+200}$ K RSG. This luminosity is consistent with RSG models of initial mass 11M_⊙, depending on assumptions of rotation and overshooting. In addition, the counterpart was significantly variable in preexplosion Spitzer 3.6 and 4.5μm imaging, exhibiting ∼70% variability in both bands correlated across 9 yr and 29 epochs of imaging. The variations appear to have a timescale of 2.8 yr, which is consistent withκ-mechanism pulsations observed in RSGs, albeit with a much larger amplitude than RSGs such asαOrionis (Betelgeuse). 

Abstract The nearby type II supernova, SN 2023ixf in M101 exhibits signatures of early time interaction with circumstellar material in the first week postexplosion. This material may be the consequence of prior mass loss suffered by the progenitor, which possibly manifested in the form of a detectable presupernova outburst. We present an analysis of long-baseline preexplosion photometric data in theg,w,r,i,z, andyfilters from Pan-STARRS as part of the Young Supernova Experiment, spanning ∼5000 days. We find no significant detections in the Pan-STARRS preexplosion light curves. We train a multilayer perceptron neural network to classify presupernova outbursts. We find no evidence of eruptive presupernova activity to a limiting absolute magnitude of −7 mag. The limiting magnitudes from the full set ofgwrizy(average absolute magnitude ≈ −8 mag) data are consistent with previous preexplosion studies. We use deep photometry from the literature to constrain the progenitor of SN 2023ixf, finding that these data are consistent with a dusty red supergiant progenitor with luminosity $\log \left(L/L_{\odot }\right)$ ≈ 5.12 and temperature ≈ 3950 K, corresponding to a mass of 14–20M_⊙. 

Abstract We present panchromatic optical + near-infrared (NIR) + mid-infrared (MIR) observations of the intermediate-luminosity Type Iax supernova (SN Iax) 2024pxl and the extremely low-luminosity SN Iax 2024vjm. JWST observations provide unprecedented MIR spectroscopy of SN Iax, spanning from +11 to +42 day past maximum light. We detect forbidden emission lines in the MIR at these early times while the optical and NIR are dominated by permitted lines with an absorption component. Panchromatic spectra at early times can thus simultaneously show nebular and photospheric lines, probing both inner and outer layers of the ejecta. We identify spectral lines not seen before in SN Iax, including [Mgii] 4.76μm, [Mgii] 9.71μm, [Neii] 12.81μm, and isolated Oi2.76μm that traces unburned material. Forbidden emission lines of all species are centrally peaked with similar kinematic distributions, indicating that the ejecta are well mixed in both SN 2024pxl and SN 2024vjm, a hallmark of pure deflagration explosion models. Radiative transfer modeling of SN 2024pxl shows good agreement with a weak deflagration of a near-Chandrasekhar-mass white dwarf, but additional IR flux is needed to match the observations, potentially attributable to a surviving remnant. Similarly, we find SN 2024vjm is also best explained by a weak deflagration model, despite the large difference in luminosity between the two supernovae. Future modeling should push to even weaker explosions and include the contribution of a bound remnant. Our observations demonstrate the diagnostic power of panchromatic spectroscopy for unveiling explosion physics in thermonuclear supernovae. 

Abstract We present extensive ultraviolet to optical photometric and optical to near-infrared (NIR) spectroscopic follow-up observations of the nearby intermediate-luminosity (M_V= −16.81 ± 0.19 mag) Type Iax supernovae (SNe Iax) 2024pxl in NGC 6384. SN 2024pxl exhibits a faster light curve than the high-luminosity members of this class, and slower than low-luminosity events. The observationally well-constrained rise time of ∼11 days and an estimated synthesized⁵⁶Ni mass of 0.03M_⊙, based on analytical modeling of the integrated spectral energy distribution light curve, are consistent with models of the weak deflagration of a carbon-oxygen white dwarf. Our optical spectral sequence of SN 2024pxl shows weak Siiilines and spectral evolution similar to other high-luminosity SNe Iax, but also a prominent early-time Ciiline, like lower-luminosity SNe Iax. The late-time optical spectrum of SN 2024pxl closely matches that of SN 2014dt, and its NIR spectral evolution aligns with that of other well-studied, high-luminosity SNe Iax. The spectral-line expansion velocities of SN 2024pxl are at the lower end of the SNe Iax velocity distribution, and the velocity distribution of iron-group elements compared to intermediate-mass elements suggests that the ejecta are mixed on large scales, as expected in pure deflagration models. SN 2024pxl exhibits characteristics intermediate between those of high-luminosity and low-luminosity SNe Iax, further establishing a link across this diverse class.