arXiv subjects

Wynn Jacobson-Galan

Publications and source records attributed to Wynn Jacobson-Galan.

10 recordsLinked to original sources

arXiv2026

A Multi-Wavelength View of the First Type Ic-BL Supernova with an Einstein Probe X-ray Shock Breakout

In March 2026, the Einstein Probe (EP) discovered its most nearby (z = 0.0343) Fast X-ray Transient (FXT), EP260321a, the first EP FXT to provide a strong match to expectations for X-ray "shock breakout'" (SBO) emission. Here, we present our multi-wavelength follow-up campaign of EP260321a and its broad-line Type Ic (Ic-BL) supernova (SN) counterpart, SN2026gzf. We show that our radio follow-up extending over 5.8 - 54.5 days post-FXT rules out an on-axis jet counterpart of isotropic-equivalent kinetic energy $E_{K} \gtrsim 10^{49}$ erg for circumburst densities $n > 10^{-2}~{\rm cm}^{-3}$ and assuming microphysical parameters $\epsilon_e = \epsilon_B = 0.1$. Our radio data also constrains a median mass-loss rate of $\dot{M} \lesssim 1.2 \times 10^{-5} M_{\odot}~{\rm yr}^{-1}$ for a Wolf-Rayet progenitor. In addition, we derive SN2026gzf's properties, including $^{56}$Ni mass, diffusion timescale, and expansion velocities, from our $\sim$nightly-cadence optical data and compare them with those of optically discovered Type Ic-BL SNe, finding that SN 2026gzf is well within the 90\% confidence interval across all properties. We further fit SN2026gzf's light curve and determine that combined emission from both interaction with CSM and $^{56}$Ni radioactive decay provides the best fit with plausible model parameters. Finally, using the rate of Ic-BL SNe from the ZTF Bright Transient Survey and assuming all Type Ic-BL SNe produce EP260321a-like FXTs, we infer an expected rate of EP-detected SBOs of 4.4 - 16 year$^{-1}$. This is inconsistent at the 90% confidence level with current EP detection rates, potentially indicating that most Type Ic-BL SNe produce less luminous X-ray SBO signals compared to EP260321a.

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arXiv2026

The first radio view of a type Ibn supernova in SN 2023fyq: Understanding the mass-loss history in the last decade before the explosion

Supernovae that interact with hydrogen-poor, helium-rich circumstellar material (CSM), known as Type Ibn supernovae (SNe Ibn), present a unique opportunity to probe mass-loss processes in massive stars. In this work, we report the first radio detection of a SN Ibn, SN 2023fyq, and characterize the mass-loss history of its stellar progenitor using the radio and X-ray observations obtained over 18 months post-explosion. We find that the radio emission from 58--185 days is best modeled by synchrotron radiation attenuated by free-free absorption from a CSM of density $\sim$ $10^{-18}$ g/$\rm{cm^{3}}$ ($\sim 10^{6} \mathrm{ρ_{ISM}}$) at a radius of $10^{16}$ cm, corresponding to a mass-loss rate of $\sim$ $4 \times 10^{-3} \ \mathrm{M_{\odot} \ yr^{-1}}$ (for a wind velocity of 1700 km/s from optical spectroscopy) from 0.7 to 3 years before the explosion. This timescale is consistent with the time frame over which pre-explosion optical outbursts were observed. However, our late-time observations at 525 days post-explosion yield non-detections, and the 3$σ$ upper limits (along with an X-ray non-detection) allow us to infer lower-density CSM at $2\times 10^{16}$ cm with $\rm{\dot{M}}$ $< 2.5\times 10^{-3} \ \mathrm{M_{\odot} \ yr^{-1}}$. These results suggest a shell-like CSM from at most $4 \times 10^{15}$ to $2 \times 10^{16}$ cm ($\sim 10^{5} R_{\rm{\odot}}$) with an elevated CSM density (0.004 $\mathrm{M_{\odot} \ yr^{-1}}$) that is roughly consistent with predictions from a merger model for this object. Future radio observations of a larger sample of SNe Ibn will provide key details on the extent and density of their helium-rich CSM.

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arXiv2026

SN 2024iss: A Multi-Wavelength Exposé of a Type IIb Supernova with an Early-Time Ultraviolet Spectrum and Shock Breakout Constraints

We present multi-wavelength observations and a comprehensive analysis of the nearby (D$\sim$14 Mpc) Type IIb supernova (SN IIb) 2024iss. Observations of SN2024iss include an early ZTF detection at $\sim$40 minutes after first light and the earliest Hubble Space Telescope UV spectrum for a SN IIb to date at 7 days after first light. With the bolometric light curve and He-star models, we estimate an ejecta mass range of $\sim 1.1-3.3~M_{\odot}$ and a $^{56}\textrm{Ni}$ mass of $0.11 \pm 0.01~M_{\odot}$. We fit shock-cooling emission models to the first peak in the light curve and estimate a progenitor radius of $100-320~R_{\odot}$ and a H-rich envelope mass of $0.07-0.46~M_{\odot}$. We also compared optical/UV spectra to binary progenitor model spectra, which indicate a stripped H-rich envelope mass of $0.19-0.28~M_{\odot}$. We use early-time X-ray detections to calculate CSM densities that are consistent with a progenitor mass-loss rate of $5\times10^{-4}~M_{\odot}$ ($v_w = 100~$km/s), corresponding to a period of significant mass ejection in the final ~2-5 years before core collapse. In the UV spectrum, we observe strong Mg II emission extending to $\sim15,000 ~$km/s as well as weak P-Cygni profiles of iron-group elements (e.g., Fe, Ti, Al, Ni) present in the outer SN ejecta during the end of shock cooling phase. We find that the overall spectroscopic evolution of SN2024iss is comparable to other SNe IIb, but that the increased brightness following the initial light curve peak is likely influenced by SN ejecta-CSM interaction. Finally, optical/NIR nebular spectroscopy of SN2024iss at $\sim 260-412~$ days reveals multi-peaked forbidden line profiles of O I and Mg I] indicative of inner ejecta asymmetry and/or clumping. We demonstrate the utility of a rich, multi-wavelength dataset for constraining the progenitor systems and explosion dynamics of SNe IIb.

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arXiv2025

An optical to infrared study of type II SN2024ggi at nebular times

We present 0.3-21mic observations at ~275d and ~400d for Type II supernova (SN) 2024ggi, combining ground-based optical and near-infrared data from the Keck I/II telescopes and space-based infrared data from the James Webb Space Telescope. Although the optical regions dominate the observed flux, SN2024ggi is bright at infrared wavelengths (65%/35% falls each side of 1mic). SN2024ggi exhibits a plethora of emission lines from H, He, intermediate-mass elements (O, Na, Mg, S, Ar, Ca), and iron-group elements (IGEs; Fe, Co, and Ni) -- all lines have essentially the same width, suggesting efficient macroscopic chemical mixing of the inner ejecta at <~2000km/s and little mixing of 56Ni at larger velocities. Molecular emission in the infrared range is dominated by the CO fundamental, which radiates about 5% of the total SN luminosity. A molecule-free radiative-transfer model based on a standard red-supergiant star explosion (i.e., ~1e51erg, 0.06Msun of 56Ni from a 15.2Msun progenitor) yields a satisfactory match throughout the optical and infrared at both epochs. The SN2024ggi CO luminosity is comparable to the fractional decay-power absorbed in the model C/O-rich shell -- accounting for CO cooling would likely resolve the model overestimate of the [OI]0.632mic flux. The relative weakness of the molecular emission in SN2024ggi and the good overall match obtained with our molecule-free model suggests negligible microscopic mixing -- about 95% of the SN luminosity is radiated by atoms and ions. Lines from IGEs, which form from explosion ashes at such late times, are ideal diagnostics of the magnitude of 56Ni mixing in core-collapse SN ejecta. Stable Ni, clearly identified in SN2024ggi (e.g., [NiII]6.634mic), is probably a common product of massive-star explosions.

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arXiv2025

The Most Luminous Known Fast Blue Optical Transient AT 2024wpp: Unprecedented Evolution and Properties in the Ultraviolet to the Near-Infrared

We present an extensive photometric and spectroscopic ultraviolet-optical-infrared campaign on the luminous fast blue optical transient (LFBOT) AT 2024wpp over the first ~100 d. AT 2024wpp is the most luminous LFBOT discovered to date, with $L_{\rm{pk}}\approx(2-4)\times10^{45}$ erg s$^{-1}$ (5-10 times that of the prototypical AT 2018cow). This extreme luminosity enabled the acquisition of the most detailed LFBOT UV light curve thus far. In the first ~45 d, AT 2024wpp radiated $>10^{51}$ erg, surpassing AT 2018cow by an order of magnitude and requiring a power source beyond the radioactive $^{56}$Ni decay of traditional supernovae. Like AT 2018cow, the UV-optical spectrum of AT 2024wpp is dominated by a persistently blue thermal continuum throughout our monitoring, with blackbody parameters at peak of T>30,000 K and $R_{\rm{BB}}/t\approx0.2-0.3c$. A temperature of $\gtrsim$20,000 K is maintained thereafter without evidence for cooling. We interpret the featureless spectra as a consequence of continuous energy injection from a central source of high-energy emission which maintains high ejecta ionization. After 35 d, faint (equivalent width <10 Å) H and He spectral features with kinematically separate velocity components centered at 0 km s$^{-1}$ and -6400 km s$^{-1}$ emerge, implying spherical symmetry deviations. A near-infrared excess of emission above the optical blackbody emerges between 20-30 d with a power-law spectrum $F_{\rmν,NIR}\proptoν^{-0.3}$ at 30 d. We interpret this distinct emission component as either reprocessing of early UV emission in a dust echo or free-free emission in an extended medium above the optical photosphere. LFBOT asphericity and multiple outflow components (including mildly relativistic ejecta) together with the large radiated energy are naturally realized by super-Eddington accretion disks around neutron stars or black holes and their outflows.

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arXiv2025

Near-Infrared Spectroscopy and Detection of Carbon Monoxide in the Type II Supernova SN 2023ixf

Core-collapse supernovae (CCSNe) may contribute a significant amount of dust in the early universe. Freshly formed coolant molecules (e.g., CO) and warm dust can be found in CCSNe as early as ~100 d after the explosion, allowing the study of their evolution with time series observations. In the Type II SN 2023ixf, we aim to investigate the temporal evolution of the temperature, velocity, and mass of CO and compare them with other CCSNe, exploring their implications for the dust formation in CCSNe. From observations of velocity profiles of lines of other species (e.g., H and He), we also aim to characterize and understand the interaction of the SN ejecta with preexisting circumstellar material (CSM). We present a time series of 16 near-infrared spectra of SN 2023ixf from 9 to 307 d, taken with multiple instruments: Gemini/GNIRS, Keck/NIRES, IRTF/SpeX, and MMT/MMIRS. The early (t<70 d) spectra indicate interaction between the expanding ejecta and nearby CSM. At t<20 d, intermediate-width line profiles corresponding to the ejecta-wind interaction are superposed on evolving broad P Cygni profiles. We find intermediate-width and narrow lines in the spectra until t<70 d, which suggest continued CSM interaction. We also observe and discuss high-velocity absorption features in H $α$ and H $β$ line profiles formed by CSM interaction. The spectra contain CO first overtone emission between 199 and 307 d after the explosion. We model the CO emission and find the CO to have a higher velocity (3000-3500 km/s) than that in Type II-pec SN 1987A (1800-2000 km/s) during similar phases (t=199-307 d) and a comparable CO temperature to SN 1987A. A flattened continuum at wavelengths greater than 1.5 $μ$m accompanies the CO emission, suggesting that the warm dust is likely formed in the ejecta. The warm dust masses are estimated to be on the order of ~10$^{-5} M_{\odot}$.}

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arXiv2025

Evidence for Extended Hydrogen-Poor CSM in the Three-Peaked Light Curve of Stripped Envelope Ib Supernova

We present multi-band ATLAS photometry for SN 2019tsf, a stripped-envelope Type Ib supernova (SESN). The SN shows a triple-peaked light curve and a late (re-)brightening, making it unique among stripped-envelope systems. The re-brightening observations represent the latest photometric measurements of a multi-peaked Type Ib SN to date. As late-time photometry and spectroscopy suggest no hydrogen, the potential circumstellar material (CSM) must be H-poor. Moreover, late (>150 days) spectra show no signs of narrow emission lines, further disfavouring CSM interaction. On the contrary, an extended CSM structure is seen through a follow-up radio campaign with Karl G. Jansky Very Large Array (VLA), indicating a source of bright optically thick radio emission at late times, which is highly unusual among H-poor SESNe. We attribute this phenomenology to an interaction of the supernova ejecta with spherically-asymmetric CSM, potentially disk-like, and we present several models that can potentially explain the origin of this rare Type Ib supernova. The warped disc model paints a novel picture, where the tertiary companion perturbs the progenitors CSM, that can explain the multi-peaked light curves of SNe, and here we apply it to SN 2019tsf. This SN 2019tsf is likely a member of a new sub-class of Type Ib SNe and among the recently discovered class of SNe that undergo mass transfer at the moment of explosion

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arXiv2024

shock_cooling_curve: A Python-Based Package for Extensive and Efficient Modeling of Shock Cooling Emission in Supernovae

The light-curve evolution of a supernova contains information of the exploding star. Early-time photometry of a variety of explosive transients, including Calcium-rich transients and type IIb/Ibc and IIP supernovae shows evidence for an early light curve peak as a result of the explosion's shock wave passing through extended material (i.e., shock cooling emission (SCE)). Analytic modeling of the shock cooling emission allows us to estimate progenitor properties such as the radius and mass of extended material (e.g., the stellar envelope) as well as the shock velocity. In this work, we present a Python-based modular package that implements four analytic models originally developed in Piro 2015, Piro 2020 and Sapir & Waxman (2017) applied to photometric data to obtain progenitor parameter properties via different modeling techniques (including non-linear optimization, MCMC sampling). Our software is easily extendable to other analytic models for SCE and different methods of parameter estimation.

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arXiv2021

Constraints on the Sub-pc Environment of the Nearby Type Iax SN 2014dt from Deep X-ray and Radio Observations

We present X-ray and radio observations of what may be the closest type Iax supernova (SN) to date, SN 2014dt (d=12.3-19.3 Mpc) and provide tight constraints on the radio and X-ray emission. We infer a specific radio luminosity of < (1.0-2.4)E25 erg/s/Hz at a frequency of 7.5 GHz and a X-ray luminosity < 1.4E38 erg/s (0.3-10 keV) at ~38-48 days post-explosion. We interpret these limits in the context of Inverse Compton (IC) emission and synchrotron emission from a population of electrons accelerated at the forward shock of the explosion in a power-law distribution $N_e(γ_e)\propto γ_e^{-p}$ with p=3. Our analysis constrains the progenitor system mass-loss rate to be smaller than 5E-6 solar masses per year at distances where r <= 1E16 cm for an assumed wind velocity v=100 km/s, and a fraction of post-shock energy into magnetic fields and relativistic electrons of epsilon_B=0.01 and epsilon_e=0.1, respectively. This result rules out some of the parameter space of symbiotic giant star companions, and it is consistent with the low mass-loss rates expected from He-star companions. Our calculations also show that the improved sensitivity of the next generation Very Large Array (ngVLA) is needed to probe the very low-density media characteristic of He stars that are the leading model for binary stellar companions of white dwarfs giving origin to type Iax SNe.

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arXiv2019

Detection of Circumstellar Helium in Type Iax Progenitor Systems

We present direct spectroscopic modeling of 44 Type Iax supernovae (SNe Iax) using spectral synthesis code SYNAPPS. We confirm detections of helium emission in the early-time spectra of two SNe Iax: SNe 2004cs and 2007J. These He I features are better fit by a pure-emission Gaussian than by a P-Cygni profile, indicating that the helium emission originates from the circumstellar environment rather than the SN ejecta. Based on the modeling of the remaining 42 SNe Iax, we find no obvious helium features in other SN Iax spectra. However, $\approx 76\%$ of our sample lack sufficiently deep luminosity limits to detect helium emission with a luminosity of that seen in SNe 2004cs and 2007J. Using the objects with constraining luminosity limits, we calculate that 33% of SNe Iax have detectable helium in their spectra. We examine 11 SNe Iax with late-time spectra and find no hydrogen or helium emission from swept up material. For late-time spectra, we calculate typical upper limits of stripped hydrogen and helium to be $2 \times 10^{-3}$ M$_{\odot}$ and $10^{-2}$ M$_{\odot}$, respectively. While detections of helium in SNe Iax support a white dwarf-He star binary progenitor system (i.e., a single-degenerate [SD] channel), non-detections may be explained by variations in the explosion and ejecta material. The lack of helium in the majority of our sample demonstrates the complexity of SN Iax progenitor systems and the need for further modeling. With strong independent evidence indicating that SNe Iax arise from a SD channel, we caution the common interpretation that the lack of helium or hydrogen emission at late-time in SN Ia spectra rules out SD progenitor scenarios for this class.

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