arXiv subjects

D. A. Coulter

Publications and source records attributed to D. A. Coulter.

At least 19 recordsLinked to original sources

arXiv2026

Teglon: A Pixel-Level Pipeline for Galaxy-Informed Gravitational-Wave Follow-up Planning and Efficiency Analysis

We describe Teglon, an open-source database and analysis pipeline engineered to optimize the search for electromagnetic (EM) counterparts to gravitational wave (GW) sources. Teglon constructs a 3D galaxy completeness metric from an input galaxy catalog and convolves it with the 3D localization volume of a GW event, producing an updated posterior map informed by known galaxy distributions. Using Teglon, users can ingest arbitrary instrument footprints --- or download them directly from the Treasure Map --- to generate dynamic observation plans that seamlessly interpolate between targeted galaxy pointing and region tiling. By focusing efforts on high-probability volumes, Teglon significantly reduces the predicted search area to find EM counterparts and increases observational efficiency, especially for small field-of-view (<= 1 deg^2) instruments like the Nancy Grace Roman Space Telescope. Furthermore, Teglon integrates with Redback to calculate pixel-level model detection efficiencies, enabling custom, event-specific observing strategies or retrospective detection efficiencies on an arbitrary grid of EM transient models. Teglon also supports custom science cases, such as prioritizing Active Galactic Nuclei searches for EM counterparts to binary black hole mergers. Having supported Gravity Collective and related programs from the LIGO-Virgo-KAGRA third observing run (O3) through O4, Teglon is being continuously developed to support O5 and beyond. We document the public repository lineage and packaging, and provide Version 2.0 as an open-source tool for the community.

astro-ph.HE↗

arXiv2026

Seeing the Outer Edge of the Infant Type Ia Supernova 2024epr in the Optical and Near Infrared

We present optical-to-near-infrared (NIR) photometry and spectroscopy of the Type Ia supernova (SN Ia) 2024epr, including NIR spectra observed within two days of first light. The early-time optical spectra show strong, high-velocity Ca and Si features near rarely-observed velocities at $\sim$0.1$c$, and the NIR spectra show a C I "knee." Despite early-time, high-velocity features, SN 2024epr evolves into a normal SN Ia, albeit with stronger peak-light Ca absorption than other SNe Ia with the same light curve shape. Although we infer a normal decline rate, $Δm_{15}(B)=1.09\pm0.12$ mag, from the light-curve rise, SN 2024epr is a Branch "cool" object and has red early-time colors ($g-r\approx0.15$ mag at $-10$ days). The high velocities point to a density enhancement in the outer layers of the explosion, predicted by some models, but thick-shell He-detonation models do not match the smoothly rising light curve or apparent lack of He in our early-time NIR spectra. No current models (e.g., delayed detonation or thin He shell double detonation) appear to reproduce all observed properties, particularly the unusual early-time colors. Such constraints are only possible for SN 2024epr from the earliest optical and NIR observations, highlighting their importance for constraining SN Ia models. Finally, we identify several literature SNe Ia with intermediate mass elements at $\sim$30\,000 km s$^{-1}$ within days after the explosion that evolve into otherwise normal SNe Ia at peak light, suggesting the early-time spectra of SNe Ia may hide a broad diversity of observational characteristics.

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arXiv2026

SN 2025ogs: A Spectroscopically-Normal Type Ia Supernova at z = 2 as a Benchmark for Redshift Evolution

The Nancy Grace Roman Space Telescope will provide a revolutionary measurement of the Universe's expansion kinematics, driven by dark matter and dark energy, out to $z \approx 3$. The accuracy of this measurement is predicated on the assumption that standardized Type Ia supernova (SN Ia) luminosities do not evolve with redshift. If present, SN Ia luminosity evolution is expected to be most detectable in the dark matter-dominated era of the Universe ($z \gtrsim 1.5$), with its effects becoming more easily distinguishable from dark energy variation at increasing redshift. We present JWST NIRCam and NIRSpec observations of SN 2025ogs, a normal SN Ia at $z=2.05\pm 0.01$. This SN offers a key point of comparison for interpreting future high-redshift SN Ia samples. The NIRCam light curve indicates a blue color ($B - V = -0.27 \pm 0.06$ mag) and a moderately fast decline ($Δm_{15}(B) = 1.55 \pm 0.15$ mag), both within standard criteria for inclusion in cosmological analyses. Its luminosity distance is in $1.0σ$ agreement with a standard flat $Λ$CDM model, as well as with current cosmological constraints from the Dark Energy Survey (DES 5yr) and Pantheon+. The NIRSpec spectrum displays all of the hallmark absorption features of a normal SN Ia observed at peak brightness. We find that the rest-frame optical color, rest-frame near-ultraviolet properties, and Si II line strengths are all consistent with the moderately fast decline inferred from the light curve. Multiple absorption features (Ca II H&K, O I $\lambda7774$, and the Ca II NIR triplet) all appear at a lower blueshift relative to a sample of low-$z$ SNe Ia. Together, these results suggest that SN Ia standardization remains robust at $z \approx 2$, and also highlight the importance of JWST spectroscopy for uncovering evolutionary effects that could impact Roman's high-precision cosmology.

astro-ph.CO↗

arXiv2026

The New Status Qvo? SN 2021qvo is Another 2003fg-like Type Ia Supernova with a Rising Light-Curve Bump

In recent years, multiple Type Ia supernovae (SNe Ia) have been observed with ''bumps'' in their rising light curves shortly after explosion. Here, we present SN 2021qvo: a SN Ia that exhibits a clear early bump in photometry obtained by the Young Supernova Experiment. Photometric and spectroscopic observations of SN 2021qvo show that it has a broader light curve, higher peak luminosity, shallower Si II $λ$5972 pseudo-equivalent width, and lower ejecta velocities than normal SNe Ia, which are all consistent with the characteristics of the 2003fg-like (often called ''super-Chandrasekhar") SN subtype. Including SN 2021qvo, just four known 2003fg-like SNe Ia have sufficient pre-peak data to reveal a rising light-curve bump, and all four have bump detections. Host-galaxy analysis reveals that SN 2021qvo exploded in a low-mass galaxy ${\rm log}(M_{\ast}/M_{\odot}) = 7.83^{+0.17}_{-0.24}$, also consistent with other members of this class. The current leading early-bump 2003fg-like SN Ia progenitor model involves an interaction between the circumstellar material (CSM) and the SN ejecta. We test the validity of this theory by modeling the early bump and subsequent light-curve evolution of SN 2021qvo with the Modular Open Source Fitter for Transients. We find that the bump can be modeled with a best-fit CSM mass in the range $M_\mathrm{CSM}=3.31-8.51 \times 10^{-3} M_\odot$. SN 2021qvo adds to the small but growing number of 2003fg-like SNe Ia with rising light-curve bumps; as the number of these SNe Ia with CSM estimates continues to grow, population-level inferences about the CSM distribution will be able to constrain the progenitor scenario for these SNe Ia.

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arXiv2025

JWST Observations of SN 2024ggi II: NIRSpec Spectroscopy and CO Modeling at 285 and 385 Days Past the Explosion

We present James Webb Space Telescope (JWST) NIRSpec observations of SN~2024ggi, spanning wavelengths of 1.7--5.5 micron at +285.51 and +385.27 days post-explosion. These nebular spectra are dominated by asymmetric emission lines from atomic species including H, Ca, Ar, C, Mg, Ni, Co, and Fe, indicative of an aspherical explosion. The other strong features are molecular CO vibrational bands from the fundamental and first overtone. We introduce a novel, data-driven approach using non-LTE 3D radiative transfer simulations to model the CO emission with high fidelity. This method enables us to constrain the three-dimensional CO distribution and its radial temperature structure. CO formation is found to occur prior to day +285, with subsequent evolution characterized by progressive evaporation. The CO mass decreases from approximately 8.7 to 1.3*E-3 Mo, while the average temperature drops from about 2900 K to 2500 K. Concurrently, the CO distribution transitions from nearly homogeneous to highly clumped (density contrast increasing from fc=1.2 to 2). The minimum velocity of the CO-emitting region remains nearly constant (v1 = 1200 to 1100 km/s), significantly above the receding photosphere velocity (v(ph) = 500 km/s), suggesting the photosphere resides within Si-rich layers. However, the temperature profile indicates that only a narrow zone reaches the conditions necessary for SiO formation. Due to a lack of observational constraints, SiO clumping is not modeled, and thus, synthetic SiO profiles for mass estimates are not highlighted. We discuss the implications of these findings for dust formation processes in SN~2024ggi.

astro-ph.SR↗

arXiv2025

Normal or transitional? The evolution and properties of two type Ia supernovae in the Virgo cluster

Type Ia supernovae (SNe Ia) are among the most precise cosmological distance indicators used to study the expansion history of the Universe. The vast increase of SN Ia data due to large-scale astrophysical surveys has led to the discovery of a wide variety of SN Ia sub-classes, such as transitional and fast-declining SNe Ia. However, their distinct photometric and spectroscopic properties differentiate them from the population of normal SNe Ia such that their use as cosmological tools remains challenged. Here, we present a high-cadenced photometric and spectroscopic dataset of two SNe Ia, SNe 2020ue and 2020nlb, which were discovered in the nearby Virgo cluster of galaxies. Our study shows that SN 2020nlb is a normal SN Ia whose unusually red color is intrinsic, arising from a lower photospheric temperature rather than interstellar reddening, providing clear evidence that color diversity among normal SNe Ia can have a physical origin. In contrast, SN 2020ue has photometric properties, such as color evolution and light-curve decay rate, similar to those of transitional SNe, spectroscopically it is more aligned with normal SNe Ia. This is evident from spectroscopic indicators such as the pseudo-equivalent width of \ion{Si}{II} lines. Thus, such SNe Ia that are photometrically at the edge of the standard normal SNe Ia range may be missed in cosmological SNe Ia samples. Our results highlight that spectroscopic analysis of SNe Ia around peak brightness is crucial for identifying intrinsic color variations and constructing a more complete and physically homogeneous SN Ia sample for precision cosmology.

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arXiv2025

Characterization of type Ibn SNe

Type Ibn supernovae (SNe) are characterized by narrow helium (He I) lines from photons produced by the unshocked circumstellar material (CSM). About 80 SNe Ibn have been discovered to date, and only a handful have extensive observational records. Thus, many open questions regarding the progenitor system and the origin of the CSM remain. Here we investigate potential correlations between the spectral features of the prominent He I $λ$5876 line and the optical and X-ray light curve properties of SNe Ibn. We compile the largest sample of 61 SNe Ibn to date, of which 24 SNe have photometric and spectroscopic data from the Young Supernova Experiment and 37 SNe have archival data sets. We fit 24 SNe Ibn with sufficient photometric coverage ($B$ to $z$ bands) using semi-analytical models from MOSFiT. We demonstrate that the light curves of SNe Ibn are more diverse than previous analyses suggest, with absolute $r$-band peak magnitudes of $-19.4\pm0.6$~mag and rise (from $-10$ days to peak) and decay-rates (from peak to +10 days) of $-0.08\pm0.06$ and $0.08\pm0.03$ mag/day, respectively. We find that the majority of SNe Ibn in the sub-sample are consistent with a low-energy explosion ($<10^{51}$ erg) of a star with a compact envelope surrounded by $\sim$0.1 M$_{\odot}$ of helium-rich CSM. The inferred ejecta masses are small ($\sim 1$ M$_{\odot}$) and expand with a velocity of $\sim$5000 km/s. Our spectroscopic analysis shows that the mean velocity of the narrow component of the He I lines, associated to the CSM, peaks at $\sim1100$ km/s. The mean CSM and ejecta masses inferred for a sub-sample of SNe Ibn indicate that their progenitors are not massive ($\sim10$ M$_{\odot}$), single stars at the moment of explosion, but are likely binary systems. This agrees with the detection of potential companion stars of SNe Ibn progenitors, and the inferred CSM properties from stellar evolution models.

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arXiv2025

A Panchromatic View of Late-time Shock Power in the Type II Supernova 2023ixf

We present multi-wavelength observations of the type II supernova (SN II) 2023ixf during its first two years of evolution. We combine ground-based optical/NIR spectroscopy with Hubble Space Telescope (HST) far- and near-ultraviolet spectroscopy and James Webb Space Telescope (JWST) near- and mid-infrared photometry and spectroscopy to create spectral energy distributions of SN 2023ixf at +374 and +620 days post-explosion, covering a wavelength range of ~0.1-30 $μ$m. The multi-band light curve of SN 2023ixf follows a standard radioactive decay decline rate after the plateau until ~500 days, at which point shock powered emission from ongoing interaction between the SN ejecta and circumstellar material (CSM) begins to dominate. This evolution is temporally consistent with 0.3-10 keV X-ray detections of SN 2023ixf and broad ''boxy'' spectral line emission from reprocessing of shock luminosity in a cold dense shell located between forward and reverse shocks. Using the expected absorbed radioactive decay power and the detected X-ray luminosity, we quantify the total shock powered emission at the +374 and +620 day epochs and find that it can be explained by nearly complete thermalization of the reverse shock luminosity as SN 2023ixf interacts with a continuous, ''wind-like'' CSM with a progenitor mass-loss rate of $\dot M \approx 10^{-4}$ M$_{\odot}$ yr$^{-1}$ ($v_w = 20 \pm 5$ km/s). Additionally, we construct multi-epoch spectral models from the non-LTE radiative transfer code CMFGEN, which contain radioactive decay and shock powers, as well as dust absorption, scattering, and emission. We find that models with shock powers of $L_{sh} = (0.5-1) \times 10^{40}$ erg s$^{-1}$ and $(0.5 - 1) \times 10^{-3}$ M$_{\odot}$ of silicate dust in the cold dense shell and/or inner SN ejecta can effectively reproduce the global properties of the late-time (>300 days) UV-to-IR spectra of SN 2023ixf.

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arXiv2025

Long-Term Optical Follow Up of S231206cc: Multi-Model Constraints on BBH Merger Emission in AGN Disks

The majority of gravitational wave events detected by the LIGO, Virgo, and KAGRA Collaboration originate from binary black hole (BBH) mergers, for which no confirmed electromagnetic counterparts have been identified to date. However, if such mergers occur within the disk of an active galactic nucleus (AGN), they may generate observable optical flares induced by relativistic jet activity and shock-heated gas. We present results from a long-term optical follow-up of the gravitational wave event S231206cc, conducted with the T80-South telescope as part of the S-PLUS Transient Extension Program (STEP). Our search prioritized AGN-hosted environments by crossmatching the gravitational wave localization with known AGN catalogs. No candidate met the criteria for a viable optical counterpart. We explored three BBH merger scenarios predicting optical emission in AGN disks: (i) ram pressure stripping, (ii) long-term emission from an emerging jet cocoon, and (iii) jet breakout followed by shock cooling. Using our observational cadence and depth, we constrained the BBH parameter space, including the remnant's location within the AGN disk, kick velocity, and supermassive black hole (SMBH) mass. Detectable flares are most likely when mergers occur at 0.01-0.1 parsecs from SMBHs with masses between 10^7 and 10^8 solar masses, where short delay times and long durations best align with our follow-up strategy. These results provide a framework for identifying AGN-hosted BBH counterparts and guiding future multimessenger efforts.

astro-ph.HE↗

arXiv2025

Final Moments III: Explosion Properties and Progenitor Constraints of CSM-Interacting Type II Supernovae

We present analysis of the plateau and late-time phase properties of a sample of 39 Type II supernovae (SNe II) that show narrow, transient, high-ionization emission lines (i.e., "IIn-like") in their early-time spectra from interaction with confined, dense circumstellar material (CSM). Originally presented by Jacobson-Galán et al 2024a, this sample also includes multicolor light curves and spectra extending to late-time phases of 35 SNe with no evidence for IIn-like features at <2 days after first light. We measure photospheric phase light-curve properties for the distance-corrected sample and find that SNe II with IIn-like features have significantly higher luminosities and decline rates at +50 days than the comparison sample, which could be connected to inflated progenitor radii, lower ejecta mass, and/or persistent CSM interaction. However, we find no statistical evidence that the measured plateau durations and $^{56}$Ni masses of SNe II with and without IIn-like features arise from different distributions. We estimate progenitor zero-age main sequence (ZAMS) masses for all SNe with nebular spectroscopy through spectral model comparisons and find that most objects, both with and without IIn-like features, are consistent with progenitor masses <12.5 M$_{\odot}$. Combining progenitor ZAMS masses with CSM densities inferred from early-time spectra suggests multiple channels for enhanced mass loss in the final years before core collapse such as a convection-driven chromosphere or binary interaction. Finally, we find spectroscopic evidence for ongoing ejecta-CSM interaction at radii $>10^{16}$ cm, consistent with substantial progenitor mass-loss rates of $\sim 10^{-4}$--$10^{-5}$ M$_{\odot}$ yr$^{-1}$ ($v_w < 50$ km/s) in the final centuries to millennia before explosion.

astro-ph.HE↗

arXiv2025

Evidence for an Instability-Induced Binary Merger in the Double-Peaked, Helium-Rich Type IIn Supernova 2023zkd

We present ultraviolet to infrared observations of the extraordinary Type IIn supernova 2023zkd (SN 2023zkd). Photometrically, it exhibits persistent and luminous precursor emission spanning $\sim$4 years preceding discovery ($M_r\approx-15$ mag, 1,500~days in the observer frame), followed by a secondary stage of gradual brightening in its final year. Post-discovery, it exhibits two photometric peaks of comparable brightness ($M_r\lesssim-18.7$ mag and $M_r\approx-18.4$ mag, respectively) separated by 240 days. Spectroscopically, SN 2023zkd exhibits highly asymmetric and multi-component Balmer and He I profiles that we attribute to ejecta interaction with fast-moving ($1,\!000-2,\!000\;\mathrm{km}\;\mathrm{s}^{-1}$) He-rich polar material and slow-moving ($\sim$$400\;\mathrm{km}\;\mathrm{s}^{-1}$) equatorially-distributed H-rich material. He II features also appear during the second light curve peak and evolve rapidly. Shock-driven models fit to the multi-band photometry suggest that the event is powered by interaction with $\sim$$5-6\;M_{\odot}$ of CSM, with $2-3\;M_{\odot}$ associated with each light curve peak, expelled during mass-loss episodes $\sim$$3-4$ and $\sim$$1-2$ years prior to explosion. The observed precursor emission, combined with the extreme mass-loss rates required to power each light curve peak, favors either super-Eddington accretion onto a black hole or multiple long-lived eruptions from a massive star to luminosities that have not been previously observed. We consider multiple progenitor scenarios for SN 2023zkd, and find that the brightening optical precursor and inferred explosion properties are most consistent with a massive ($M_{\mathrm{ZAMS}}\geq30\;M_{\odot}$) and partially-stripped He star undergoing an instability-induced merger with a black hole companion.

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arXiv2025

Testing for Intrinsic Type Ia Supernova Luminosity Evolution at z>2 with JWST

The James Webb Space Telescope} (JWST) is opening new frontiers of transient discovery and follow-up at high-redshift. Here we present the discovery of a spectroscopically confirmed Type Ia supernova (SN Ia; SN $2023$aeax) at $z=2.15$ with JWST, including a NIRCam multi-band light curve. SN $2023$aeax lands at the edge of traditional low-$z$ cosmology cuts because of its blue color (peak rest-frame $B-V\sim-0.3$) but with a normal decline rate ($Δm_{15}(B)\sim1.25$), and applying a fiducial standardization with the BayeSN model we find the SN $2023$aeax luminosity distance is in $\sim0.1σ$ agreement with $Λ$CDM. SN $2023$aeax is only the second spectroscopically confirmed SN Ia in the dark matter-dominated Universe at $z>2$ (the other is SN $2023$adsy), giving it rare leverage to constrain any potential evolution in SN Ia standardized luminosities. Similar to SN $2023$adsy ($B-V\sim0.8)$, SN $2023$aeax has a fairly extreme (but opposite) color, which may be due to the small sample size or a secondary factor, such as host galaxy properties. Nevertheless, the SN $2023$aeax spectrum is well-represented by normal low-$z$ SN Ia spectra and we find no definitive evolution in SN Ia standardization with redshift. Still, the first two spectroscopically confirmed $z>2$ SNe Ia have peculiar colors and combine for a $\sim1σ$ distance slope relative to $Λ$CDM, though in agreement with recent SN Ia cosmological measurements.

astro-ph.CO↗

arXiv2025

Discovery of a likely Type II SN at $z$=3.6 with JWST

Transient astronomy in the early, high-redshift (z > 3) Universe is an unexplored regime that offers the possibility of probing the first stars and the Epoch of Reionization. During Cycles 1 and 2 of the James Webb Space Telescope (JWST), the JWST Advanced Deep Extragalactic Survey (JADES) program enabled one of the first searches for transients in deep images (~30 AB mag) over a relatively wide area (25 arcmin^2). One transient, AT 2023adsv, was discovered with an F200W magnitude of 28.04 AB mag, and subsequent JWST observations revealed that the transient is a likely supernova (SN) in a host with z_spec = 3.613 +/- 0.001 and an inferred metallicity at the position of the SN of Z_* = 0.3 +/- 0.1 Z_{\odot}. At this redshift, the first detections in F115W and F150W show that AT 2023adsv had bright rest-frame ultraviolet flux at the time of discovery. The multi-band light curve of AT 2023adsv is best matched by a template of an SN IIP with a peak absolute magnitude of M_B ~ -18.3 AB mag. We find a good match to a 20 M_{\odot} red supergiant progenitor star with an explosion energy of 2.0x10^51 ergs, likely higher than normally observed in the local Universe, but consistent with SNe IIP drawn from local, lower metallicity environments. AT 2023adsv is the most distant photometrically classified SN IIP yet discovered with a spectroscopic redshift measurement, and may represent a global shift in SNe IIP properties as a function of redshift.

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arXiv2024

The Massive and Quiescent Elliptical Host Galaxy of the Repeating Fast Radio Burst FRB20240209A

The discovery and localization of FRB20240209A by the Canadian Hydrogen Intensity Mapping Fast Radio Burst (CHIME/FRB) experiment marks the first repeating FRB localized with the CHIME/FRB Outriggers and adds to the small sample of repeating FRBs with associated host galaxies. Here we present Keck and Gemini observations of the host that reveal a redshift $z=0.1384\pm0.0004$. We perform stellar population modeling to jointly fit the optical through mid-infrared data of the host and infer a median stellar mass log$(M_*/{\rm M_{\odot}})=11.34\pm0.01$ and a mass-weighted stellar population age $\sim11$Gyr, corresponding to the most massive and oldest FRB host discovered to date. Coupled with a star formation rate $<0.36\,{\rm M_{\odot}\ yr^{-1}}$, the specific star formation rate $<10^{-11.8}\rm\ yr^{-1}$ classifies the host as quiescent. Through surface brightness profile modeling, we determine an elliptical galaxy morphology, marking the host as the first confirmed elliptical FRB host. The discovery of a quiescent early-type host galaxy within a transient class predominantly characterized by late-type star-forming hosts is reminiscent of short-duration gamma-ray bursts, Type Ia supernovae, and ultraluminous X-ray sources. Based on these shared host demographics, coupled with a large offset as demonstrated in our companion paper, we conclude that preferred progenitors for FRB20240209A include magnetars formed through merging binary neutron stars/white dwarfs or the accretion-induced collapse of a white dwarf, or a luminous X-ray binary. Together with FRB20200120E localized to a globular cluster in M81, our findings provide strong evidence that some fraction of FRBs may arise from a process distinct from the core collapse of massive stars.

astro-ph.HE↗

arXiv2024

SN 2021foa: The "Flip-Flop" Type IIn / Ibn supernova

We present a comprehensive analysis of the photometric and spectroscopic evolution of SN~2021foa, unique among the class of transitional supernovae for repeatedly changing its spectroscopic appearance from hydrogen-to-helium-to-hydrogen-dominated (IIn-to-Ibn-to-IIn) within 50 days past peak brightness. The spectra exhibit multiple narrow ($\approx$ 300--600~km~s$^{-1}$) absorption lines of hydrogen, helium, calcium and iron together with broad helium emission lines with a full-width-at-half-maximum (FWHM) of $\sim 6000$~km~s$^{-1}$. For a steady, wind-mass loss regime, light curve modeling results in an ejecta mass of $\sim 8$ M$_{\odot}$ and CSM mass below 1 M$_{\odot}$, and an ejecta velocity consistent with the FWHM of the broad helium lines. We obtain a mass-loss rate of $\approx 2$ M$_{\odot} {\rm yr}^{-1}$. This mass-loss rate is three orders of magnitude larger than derived for normal Type II SNe. We estimate that the bulk of the CSM of SN~2021foa must have been expelled within half a year, about 15 years ago. Our analysis suggests that SN~2021foa had a helium rich ejecta which swept up a dense shell of hydrogen rich CSM shortly after explosion. At about 60 days past peak brightness, the photosphere recedes through the dense ejecta-CSM region, occulting much of the red-shifted emission of the hydrogen and helium lines, which results in observed blue-shift ($\sim -3000$~km~s$^{-1}$). Strong mass loss activity prior to explosion, such as those seen in SN~2009ip-like objects and SN~2021foa as precursor emission, are the likely origin of a complex, multiple-shell CSM close to the progenitor star.

astro-ph.HE↗

arXiv2024

Blast: a Web Application for Characterizing the Host Galaxies of Astrophysical Transients

Characterizing the host galaxies of astrophysical transients is important to many areas of astrophysics, including constraining the progenitor systems of core-collapse supernovae, correcting Type Ia supernova distances, and probabilistically classifying transients without photometric or spectroscopic data. Given the increasing transient discovery rate in the coming years, there is substantial utility in providing public, transparent, reproducible, and automatic characterization for large samples of transient host galaxies. Here we present Blast, a web application that ingests live streams of transient alerts, matches transients to their host galaxies, and performs photometry on coincident archival imaging data of the host galaxy. The photometry is then used to infer both global host-galaxy properties and galaxy properties within 2 kpc of the transient location by using the Prospector Bayesian inference framework, with an acceleration in evaluation speed achieved via simulation-based inference. Blast provides host-galaxy properties to users via a web browser or an application program interface. The software can be extended to support alternative photometric or SED-fitting algorithms, and can be scaled via an asynchronous worker queue across multiple compute nodes to handle the processing of large volumes of transient alerts for upcoming transient surveys. Blast has been ingesting newly discovered transients from the Transient Name Server since mid-2024, and has currently measured SED parameters for more than 6000 transients. The service is publicly available at https://blast.scimma.org/.

astro-ph.HE↗

arXiv2024

Discovery of a Relativistic Stripped Envelope Type Ic-BL Supernova at z = 2.83 with JWST

We present JWST NIRCam and NIRSpec observations of a Type Ic supernova (SN Ic) and its host galaxy (JADES-GS+53.13533-27.81457) at $z = 2.83$. This SN (named SN 2023adta) was identified in deep James Webb Space Telescope (JWST)/NIRCam imaging from the JWST Advanced Deep Extragalactic Survey (JADES) Program. Follow-up observations with JWST/NIRSpec provided a spectroscopic redshift of $z = 2.83$ and the classification as a SN Ic-BL. The light curve of SN 2023adta matches well with other stripped envelope supernovae and we find a high peak luminosity, $M_V = -19.0 \pm 0.2$ mag, based on the distribution of best-fit SNe. The broad absorption features in its spectrum are consistent with other SNe Ic-BL 1-3 weeks after peak brightness. We measure a Ca II NIR triplet expansion velocity of $29{,}000 \pm 2{,}000$ km s$^{-1}$. The host galaxy of SN 2023adta is irregular, and modeling of its spectral energy distribution (SED) indicates a metallicity of $Z = 0.35^{+0.16}_{-0.08} Z_{\odot}$. This environment is consistent with the population of low-$z$ SNe Ic-BL which prefer lower metallicities relative to other stripped envelope supernovae, and track long duration $γ$-ray burst (LGRB) environments. We do not identify any GRBs that are coincident with SN 2023adta. Given the rarity of SNe Ic-BL in the local universe, the detection of a SN Ic-BL at $z = 2.83$ could indicate that their rates are enhanced at high redshift.

astro-ph.HE↗

arXiv2024

Double "acct": a distinct double-peaked supernova matching pulsational pair-instability models

We present multi-wavelength data of SN2020acct, a double-peaked stripped-envelope supernova (SN) in NGC2981 at ~150 Mpc. The two peaks are temporally distinct, with maxima separated by 58 rest-frame days, and a factor of 20 reduction in flux between. The first is luminous (M$_{r}$ = -18.00 $\pm$ 0.02 mag), blue (g - r = 0.27 $\pm$ 0.03 mag), and displays spectroscopic signatures of interaction with hydrogen-free circumstellar material. The second peak is fainter (M$_{r}$ = -17.29 $\pm$ 0.03 mag), and spectroscopically similar to an evolved stripped-envelope SNe, with strong blended forbidden [Ca II] and [O II] features. No other known double-peak SN exhibits a light curve similar to that of SN 2020acct. We find the likelihood of two individual SNe occurring in the same star-forming region within that time to be highly improbable, while an implausibly fine-tuned configuration would be required to produce two SNe from a single binary system. We find that the peculiar properties of SN2020acct match models of pulsational pair instability (PPI), in which the initial peak is produced by collisions of shells of ejected material, shortly followed by a terminal explosion. Pulsations from a star with a 72 M$_{\odot}$ helium core provide an excellent match to the double-peaked light curve. The local galactic environment has a metallicity of 0.4 Z$_{\odot}$, a level where massive single stars are not expected retain enough mass to encounter the PPI. However, late binary mergers or a low-metallicity pocket may allow the required core mass. We measure the rate of SN 2020acct-like events to be $<3.3\times10^{-8}$ Mpc$^{-3}$ yr$^{-1}$ at z = 0.07, or <0.1% of the total core-collapse SN rate.

astro-ph.HE↗