arXiv subjects

J. Sollerman

Publications and source records attributed to J. Sollerman.

At least 37 records · Page 2Linked to original sources

arXiv2026

SN 2021lwz: Another Exotic Luminous and Fast Evolving Optical Stripped Envelope Supernova ?

Current large-scale, high-cadence surveys, such as the ZTF, provide detections of new and rare types of transients and supernovae whose physical origins are not well understood. We investigate the nature of SN 2021lwz at a redshift $z=0.065$, an overluminous supernova (SN) of absolute magnitude, $M_{g} \sim -20.1$ AB, falling in the lower range of superluminous supernovae (SLSNe) luminosities, and discovered in a faint dwarf galaxy with an absolute magnitude of $M_{g} \simeq -14.5$ AB. SN 2021lwz is studied using optical spectroscopy, photometry and imaging linear polarimetry obtained during several follow-up campaigns. All the data are used to analyse and model the evolution of the explosion. Comparisons with other SNe of well known or rarer types are investigated. SN 2021lwz belongs to the rare class of rapidly evolving transients. The bolometric light curve rises in about $7$ days to a peak luminosity of about $5 \times 10^{43}$ erg/s, at a rate of 0.2 mag day$^{-1}$ close to the peak. Spectroscopy modelling reveals more similarities with a normal Type Ic-like SN than with a SLSN before peak, showing slightly broadened lines after peak. Light curve modelling shows that the Arnett model of the bolometric light curve using a radioactive source ($^{56}$ Ni) is not able to reasonably explain the light curve evolution. A magnetar model seems more appropriate, suggesting that the explosion of low ejecta mass ($M_{\rm ej} \sim 0.24 ~M_\odot$) took place in a low mass ($M \sim 10^{6.66}~M_\odot$) dwarf galaxy of specific star-formation rate about ten times larger than typical star-forming galaxies. In conclusion SN 2021lwz is an uncommon transient showing many similarities with several classes of transients, and with rare transients. It may be an interesting example pointing on how differences in ejecta mass and engine parameters could produce a wide range of engine-driven SESNe.

astro-ph.HE↗

arXiv2026

Late-Time HST UV Detections Reveal Eruptive Mass Loss and Circumstellar Interaction in a Quarter of Stripped-Envelope Supernovae

We present HST WFC3/UVIS F275W near-UV imaging of 91stripped-envelope supernovae (SE SNe; Types IIb, Ib, Ic) from Snapshot program SNAP-16657, observed at phases of 270-1845 days (median 952 days) after first optical detection. We detect UV counterparts in 13 SE~SNe, of which 6 are classified as secure and 7 as ambiguous after comparison to nearby H\textsc{ii} regions, interpreting the secure sources as signatures of interaction with circumstellar material (CSM). Independent WISE W1/W2 light curves show $>300$ day mid-IR excesses in two of the secure UV sources, corroborating the interaction interpretation, and reveal two additional IR-only candidates without UV counterparts, indicating dust-obscured interaction episodes missed by the UV survey. A forward-modeling MCMC analysis using a physics-based CSM interaction model with three free parameters, the interaction fraction $f_\mathrm{CSM}$, shell mass $M_\mathrm{CSM}$, and thickness fraction $f_\mathrm{thick}$, yields $f_\mathrm{CSM} = 0.23^{+0.17}_{-0.09}$, $M_\mathrm{CSM} \approx 0.013~M_\odot$, and $f_\mathrm{thick} \approx 0.07$. The inferred thin-shell geometry implies an ejection duration of $\sim$6 yr for an outflow velocity of $300$ km s$^{-1}$, two to three orders of magnitude shorter than the thermal timescale of stable Roche-lobe overflow. This result disfavors steady binary mass transfer as the origin of the detected CSM and instead points to eruptive pre-supernova mass ejection in the final years before core collapse, either from wave-driven outbursts or from mass transfer triggered by late-stage progenitor re-expansion.

astro-ph.HE↗

arXiv2026

Nebular Phase Evolution of SN 2023ixf (I): From Circumstellar Infrared Echo to the onset of in-situ Dust Formation in a Type II Supernova

We present optical and near-infrared (NIR) photometric and spectroscopic observations of the Type II supernova SN 2023ixf spanning 150 to 750 days, combined with published early-time optical and infrared photometry, and JWST NIRSpec and MIRI spectroscopy, to disentangle circumstellar echo emission from newly formed internal dust. The combined dataset reveals an early infrared excess by 1.8 days, a broad secondary NIR rebrightening over about 89 to 175 days, progressive attenuation of the red wing of H-alpha from about 132 days, and CO emission detected by about 217 days. We identify the onset of H-alpha asymmetry as the first direct signature for internal dust formation, and modeling of the H-alpha profile over 140 to 418 days yields an internal silicate-equivalent dust mass of about 1.5e-6 to 6e-5 solar masses. By contrast, the early infrared evolution is best interpreted as echo-dominated: the 1.8 to 33.6 day excess is consistent with a radiative-flash infrared echo from pre-existing circumstellar dust, while the 89 to 175 day rebrightening is more naturally explained by a more extended echo arising from structured wind material. JWST spectral energy distribution modeling further reveals a multi-component infrared continuum in which a cold graphite component traces lingering echo emission, while a colder silicate-bearing component grows to about 2e-3 solar masses, providing the strongest late-time spectral energy distribution evidence that internal CDS/ejecta dust becomes substantial. SN 2023ixf therefore provides one of the clearest time-resolved case studies of dust signatures in a Type II supernova, linking early circumstellar reprocessing with increasingly important in situ dust formation.

astro-ph.SR↗

arXiv2026

Massive stars exploding in a He-rich circumstellar medium XII. SN 2024acyl: A fast, linearly declining Type Ibn supernova with early flash-ionisation features

We present a photometric and spectroscopic analysis of the Type Ibn supernova (SN) 2024acyl. It rises to an absolute magnitude peak of about -17.58 mag in 10.6 days, and displays a rapid linear post-peak light-curve decline in all bands, similar to most SNe Ibn. The optical pseudobolometric light curve peaks at $(3.5\pm0.8) \times 10^{42}$ erg s$^{-1}$, with a total radiated energy of $(5.0\pm0.4) \times 10^{48}$ erg. The spectra are dominated by a blue continuum at early stages, with narrow P Cygni He I lines and flash-ionisation emission lines of C III, N III, and He II. The P Cygni He I features gradually evolve and become emission-dominated in late-time spectra. Our multi-band light-curve modelling yields estimates of the ejecta mass of $M_{\rm ej} = 0.49^{+0.11}_{-0.09}$ M$_\odot$ with a kinetic energy of $E_{\rm k} = 0.06^{+0.01}_{-0.01} \times 10^{51}$ erg, and a $^{56}$Ni mass of $M_{\rm Ni} = 0.018$ M$_\odot$. The inferred CSM properties are characterised by a mass of $M_{\rm CSM} = 0.51^{+0.05}_{-0.04}$ M$_\odot$, an inner radius of $R_0 = 17.8^{+3.6}_{-3.0}$ AU, and a density of $ρ_{\rm CSM} =(8.3_{-1.2}^{+2.7})\times10^{-12}$ g cm$^{-3}$. The multi-epoch spectra are well reproduced by the CMFGEN/he4p0 model, corresponding to a He-ZAMS mass of 4 M$_\odot$ (H-ZAMS mass 18.11 M$_\odot$, pre-SN mass 3.16 M$_\odot$). These findings are consistent with a scenario of an SN powered by ejecta-CSM interaction, originating from a low-mass helium star that evolved within an interacting binary system where the CSM with some residual hydrogen may originate from the mass-transfer process. In addition, a channel of core-collapse explosion of a late-type Wolf-Rayet star with H, or an Ofpe/WN9 star with fallback accretion, cannot be entirely ruled out.

astro-ph.SR↗

arXiv2026

Photometric classification of supernovae detected by the Zwicky Transient Facility using noise augmentation

Modern time-domain surveys, such as the Zwicky Transient Facility (ZTF), detect far more extragalactic transients than can be spectroscopically classified. Photometric classification offers a scalable alternative, enabling the identification of larger, fainter, and higher-redshift supernova samples suitable for applications such as Type Ia supernova (SN Ia) cosmology. We present a feature-based photometric classifier for SNe detected by ZTF, with the primary goal of constructing a photometric SN Ia sample for cosmological analyses. Our approach utilises the autoencoder architecture of ParSNIP (Boone 2021) to capture the intrinsic diversity of SN light curves. We trained the model on a spectroscopically classified ZTF SN sample, incorporating a realistic noise augmentation procedure that simulates the flux uncertainties of fainter sources. Light curve features were used to train a gradient-boosted decision tree classifier, implemented in both binary (SN Ia vs. non-Ia) and multi-class configurations. We validated our classifier on independent, fainter ZTF data with and without noise augmentation. To evaluate real-time performance, we also applied our classifier to live ZTF alerts and conducted a spectroscopic classification survey within the ePESSTO+ collaboration. We found that noise augmentation significantly improves classification performance, particularly for fainter sources. Our binary classifier achieves an SN Ia recall of (98.1 $\pm$ 0.4)%, averaged across five train-test splits. SN Ia recall exceeds 98% for events with a peak apparent magnitude up to 20 and more than 10 detections, and remains above 96% up to magnitude 20.5. Overall, 95% of sources were correctly classified in both binary and multi-class modes. Our classifier performs efficiently on real ZTF data and enables construction of a large photometric SN Ia sample for cosmology.

astro-ph.IM↗

arXiv2026

Light-Curve and Spectral Properties of Type II Supernovae from the ATLAS survey

Type II supernovae (SNe II) are the most common terminal stellar explosions in the Universe. With SNe now being detected within days after explosion, there is growing evidence that the majority of Type II SNe show signs of interaction with a confined, dense cirumstellar material (CSM) in the first few days post explosion. In this work we aim to bridge the gap between single SN studies showing early-time interaction in their spectra, and the statistical studies of early-time SN light curves, which imply the existence of CSM. We present a sample of 68 Type II SNe with both early photometric data, obtained with the ATLAS survey, and spectroscopic data, obtained with the ePESSTO+ collaboration. A subset of the sample is classified based on the presence or absence of narrow spectral features with electron-scattered broadened wings in the early spectra, indicative of interaction with CSM. We characterise the photometric and spectroscopic properties of the sample by measuring rise times to maximum light, peak magnitudes, decline rates and line velocities. Additionally, we measure the ratio of absorption to emission (a/e) of the H alpha P-Cygni profile. Our analysis reveals that SNe II showing early spectroscopic signs of interaction with CSM decline faster and are brighter than those without. However no difference is found in rise times between the two groups. A clear separation is observed in the a/e ratio: SNe with signs of interaction exhibit lower a/e ratios at all epochs compared to those without. Our results highlight that understanding SN II ejecta-CSM interaction requires large, uniform samples of photometric and spectroscopic data, such as the one presented in this work.

astro-ph.SR↗

arXiv2026

Study of the anisotropy of cosmic expansion on ZTF type Iasupernovae simulations

The cosmological principle assumes the isotropy of the Universe at large scales. It is a foundational assumption in the $Λ$CDM model, which is the current standard model of cosmology. Recent tensions give legitimacy to investigating the possibility of anisotropies in the Universe. The large sky coverage achieved by the Zwicky Transient Facility survey (ZTF) allows us to test the veracity of the cosmological principle using observations of Type Ia supernovae (SNe Ia). In this article, we develop a methodology to measure potential anisotropies in the Hubble constant $H_0$. We test our method on realistic simulations of the second data release (DR2) of ZTF SNe Ia in which we introduce a dipole. We develop an unbiased method both to introduce a dipole in the simulations and to recover it. We test a potential $H_0$ dependency of our method while varying the dipole amplitude. We analyse the impact of introducing large-scale structures in the simulations and the efficiency of using a volume-limited sample, which is an unbiased subsample of the ZTF SNe Ia sample. Finally, we build an error model applied to the recovered dipole amplitude ($ΔH_0$) and its direction ($α_0$, $δ_0$). Our analysis allows us to recover a dipole with an error on the amplitude of $0.33\,\mathrm{km\,s^{-1}\,Mpc^{-1}}$, and uncertainties of $3.4^\circ$ and $6.1^\circ$ on the right ascension and declination, respectively, for an initial dipole amplitude of $ΔH_0 = 3\,\mathrm{km\,s^{-1}\,Mpc^{-1}}$. The resulting dipole is independent of the chosen $H_0$ value and sky coverage. This paper paves the way for a future precise ZTF dipole investigation.

astro-ph.CO↗

arXiv2026

GRB 180728A and SN 2018fip: the nearest high-energy cosmological gamma-ray burst with an associated supernova

The long GRB 180728A, at a redshift of $z = 0.1171$, stands out due to its high isotropic energy of $E_{γ,iso} \sim 2.5 \times 10^{51}$ erg, in contrast with most events at redshift $z<0.2$. We analyze the properties of GRB 180728A's prompt emission, afterglow, and associated supernova SN 2018fip, comparing them with other GRB-SN events. This study employs a dense photometric and spectroscopic follow-up of the afterglow and the SN up to 80 days after the burst, supported by image subtraction to remove the presence of a nearby bright star, and modelling of both the afterglow and the supernova. GRB 180728A lies on the $E_{p,i}-E_{γ,iso}$ plane occupied by classical collapsar events, and the prompt emission is one of the most energetic at $z < 0.2$ after GRB 030329 and GRB 221009A. The afterglow of GRB 180728A is less luminous than that of most long GRBs, showing a shallow early phase that steepens around 5 hours (0.2 days). The GRB exploded in an irregular, low-mass, blue, star-forming galaxy, typical of low-z collapsar events. Because of the relatively faint afterglow, the light curve bump of SN 2018fip dominates the optical emission already after $\sim$3 days and is one of the best sampled to date. The strong suppression below $\sim$ 4000 angstrom and a largely featureless continuum in the early 6--9 days spectra favor aspherical two-component ejecta with a high-velocity collimated component ($> 20,000 km s^{-1}$), dominant early-on, and a more massive, low-velocity component, which dominates at much later epochs. Our findings indicate that asymmetries need to be considered in order to better understand GRB-SNe. In any case, SN 2018fip shares many characteristics with typical GRB-SNe. Its kinetic energy is below the common range of $10^{52}-10^{53}$ erg and does not correlate with the high energy of the GRB, highlighting the diversity of the GRB-SN energy budget partition.

astro-ph.HE↗

arXiv2025

The ambiguous AT2022rze: Changing-look AGN mimicking a supernova in a merging galaxy system

AT2022rze is a luminous, ambiguous transient located South-East of the geometric center of its host galaxy at redshift z = 0.08. The host appears to be formed by a merging galaxy system. The observed characteristics of AT2022rze are reminiscent of active galactic nuclei (AGN), tidal disruption events (TDEs), and superluminous supernovae (SLSNe). The transient reached a peak absolute magnitude of -20.2 +- 0.2 mag, showing a sharp rise (trise,1/e = 27.5 +- 0.6 days) followed by a slow decline (tdec,1/e = 382.9 +- 0.6). Its bumpy light curve and narrow Balmer lines indicate the presence of gas (and dust). Its light curve shows rather red colors, indicating that the transient could be affected by significant host extinction. The spectra reveal coronal lines, indicative of high-energy (X-ray/UV) emission. Archival data reveal no prior activity at this location, disfavoring a steady-state AGN, although an optical spectrum obtained prior to the transient is consistent with an AGN classification of the host. Based on this, we conclude that the transient most likely represents a Changing-look AGN at the center of the smallest component of the merging system.

astro-ph.HE↗

arXiv2025

A thermonuclear supernova interacting with hydrogen- and helium-deficient circumstellar material. SN 2020aeuh as a SN Ia-CSM-C/O?

Identifying the progenitors of thermonuclear supernovae (Type Ia supernovae; SNe Ia) remains a key objective in contemporary astronomy. The rare subclass of SNe Ia that interacts with circumstellar material (Type Ia-CSM) allows for studies of the progenitor's environment before explosion, and generally favours single-degenerate progenitor channels. The case of SN Ia-CSM PTF11kx clearly connected thermonuclear explosions with hydrogen-rich CSM-interacting events, and the more recent SN 2020eyj connected SNe Ia with helum-rich companion progenitors. Here we present a study of SN 2020aeuh, a Type Ia-CSM with delayed interaction. We analyse photometric and spectroscopic data that monitor the evolution of SN 2020aeuh and compare its properties with those of peculiar SNe Ia and core-collapse SNe. At early times, the evolution of SN 2020aeuh resembles a slightly overluminous SN Ia. Later, the interaction-dominated spectra develop the same pseudocontinuum seen in Type Ia-CSM PTF11kx and SN 2020eyj. However, the later-time spectra of SN 2020aeuh lack hydrogen and helium narrow lines. Instead, a few narrow lines could be attributed to carbon and oxygen. We fit the pseudobolometric light curve with a CSM-interaction mode, yielding a CSM mass of 1-2 M$_{\odot}$. We propose that SN 2020aeuh was a Type Ia supernova that eventually interacted with a dense medium which was deficient in both hydrogen and helium. Whereas previous SNe Ia-CSM constitute our best evidence for nondegenerate companion progenitors, the CSM around SN 2020aeuh is more difficult to understand. We include a hydrodynamical simulation for a double-degenerate system to showcase how the dynamical evolution of such a progenitor scenario could produce the CSM observed around SN 2020aeuh. It is clear that SN 2020aeuh challenges current models for stellar evolution leading up to a SN Ia explosion.

astro-ph.HE↗

arXiv2025

The hydrogen-free circumstellar interaction in the Type Ib supernova 2021efd: A clue to the mechanism of the helium-layer stripping

Stripped-envelope supernovae (SESNe), including Type IIb, Ib, and Ic supernovae (SNe), originate from the explosions of massive stars whose outer envelopes have been largely removed during their lifetimes. The main stripping mechanism for the hydrogen (H) envelope in the progenitors of SESNe is often considered to be interaction with a binary companion, while that for the helium (He) layer is unclear. We conducted photometric and spectroscopic observations of the Type Ib SN 2021efd, which shows signs of interaction with H-free circumstellar material (CSM). Around 30 days after the r-band light curve (LC) peak, until at least ~ 770 days, its LCs display excessive luminosity compared to regular SESNe and at least three distinct peaks. The light curve evolution is similar to that of SN 2019tsf, whose previously unpublished spectrum at 400 days is also presented here. The nebular spectrum of SN 2021efd shows narrow emission lines (~ 1000 km/s) in various species. Our observations suggest that SN 2021efd is a Type Ib SN interacting with CSM with the following parameters: The estimated CSM mass, composition, and distribution are at least a few times 0.1 M_sun, H-free, and clumpy, respectively. Based on the estimated ejecta properties, we conclude that this event is a transitional SN whose progenitor was experiencing He-layer stripping at the epoch of the explosion, and was on the way to becoming a carbon-oxygen star from a He star. The estimated CSM properties suggest that the progenitor had some episodic mass ejections with a rate of ~ 0.001-0.01 M_sun/yr for the last decade and slightly smaller before this final phase at least from ~ 200 years before the explosion, for the assumed CSM velocity of 100 km/s. For the case of ~ 1000 km/s, the necessary mass-loss rate would be increased by a factor of ten, and the timescales decreased by a factor of ten.

astro-ph.SR↗

arXiv2025

ZTF-SEDm Type Ia supernova sample for Twins Embedding spectrophotometric standardisation

This paper has two aims: the first one is to build a large homogeneous spectrophotometric Type Ia supernova (SN Ia) sample, using 3069 spectra from the second Zwicky Transient Facility data release (ZTF DR2). Using this sample we reproduce, as the second objective of the paper, the Twins Embedding (TE) spectrophotometric standardisation method, which led to an exceptionally low value of 0.073 mag for the intrinsic scatter. We improve the flux-calibration accuracy of the SEDm SN Ia spectral sample using the ZTF photometric data, which are calibrated at the percent level. We then apply the three steps of the TE parameterisation to a subset of 783 ZTF SN spectra near maximum light, and analyse the resulting standardisation methods. The precision of the phase correction model, which is the first step of the TE, is estimated at 0.01 mag in g band, using ZTF data. Despite the challenge posed by the ZTF spectrum extraction pipeline, we apply a first standardisation in color based on the second step of the TE, the Read Between The Lines (RBTL). When considering the scatter due to the redshift error and the flux calibration error, we estimate a 0.129 mag Hubble residual scatter for this ZTF sample as an upper limit. As expected from the low spectral quality, the final TE standardisation based on three non-linear parameters did not improve the overall dispersion. We release 1897 flux calibrated spectra of 1607 SNe Ia with an estimated photometric accuracy of 0.07 mag. We further demonstrate the ability to apply a spectrophotometric standardisation with limited quality spectra. The RBTL standardisation is more efficient than that of SALT with one less parameter, and the resulting host steps are consistent with zero, making it less prone to astrophysical bias. For future spectroscopic surveys, a better spectral quality would enable the full TE standardisation to be computed. (Abridged)

astro-ph.CO↗

arXiv2025

ZTF SNe Ia DR2: Towards cosmology-grade ZTF supernova light curves using scene modeling photometry

The Zwicky Transient Facility (ZTF) is conducting a wide-field survey of the northern sky in three optical bands and the collaboration cosmology working group has released 3628 spectroscopically confirmed Type Ia supernovae (SNe Ia) discovered during its first 2.5 years of operation. This "ZTF SN Ia DR2" sample is the largest SN Ia dataset to date. Fully exploiting this dataset to improve understanding of the properties of dark energy requires a photometric accuracy of O(0.1%). This can be achieved using Scene Modeling Photometry (SMP), which is optimal to extract a transient signal (SN) from a complex background (its host), while ensuring a common flux estimator with nearby stars used as calibration reference. In this paper, we present the status of the SMP development and use it to assess the precision and accuracy of the ZTF SN Ia DR2 force photometry light curves. We reach a repeatability of the star observations better than 1%. However, we have identified a new sensor effect, dubbed "pocket-effect", which distorts the Point Spread Function (PSF) in a flux-dependent manner leading to non-linearities in the photometry of a few percent. Correcting for this effect requires time- and sensor-dependent corrections to be applied at the pixel level, which is currently under development. This effects affects all light curve releases to date -- both from forced photometry and scene modelling preventing ZTF SN Ia DR2 to be used for accurate cosmological inference. Comparing the SMP and forced photometry measurements, we find that stretch and color estimated from both processings are consistent, aside from a 10 mmag shift in color. This assess the robustness of results presented as part of the the ZTF SN Ia DR2 release. The absolute calibration however shifts by 90 mmag. A reprocessing of the full ZTF SN Ia DR2 dataset using the SMP method is currently in progress.

astro-ph.CO↗

arXiv2025

ZTF SN Ia DR2 follow-up: Exploring the origin of the Type Ia supernova host galaxy step through Si II velocities

The relationship between Type Ia supernovae (SNe Ia) and their host galaxy stellar masses is well documented. In particular, Hubble residuals display a luminosity shift based on host mass, known as the mass step, which is often used as an extra correction in the standardisation of SN Ia luminosities. Here we investigate Hubble residuals and the mass step in the context of Si II $λ6355$ velocities, using 277 near-peak SNe Ia from ZTF DR2. We divide the sample into high-velocity (HV) and normal-velocity (NV) SNe Ia, separated at 12,000 km/s, resulting in 70 HV and 207 NV objects. We then examine links between Si II $λ$6355 velocities, light-curve stretch $x_{1}$, colour $c$, and host properties to explore potential environmental and/or progenitor-related effects. Although we only find a marginal difference between the Hubble residuals of HV and NV SNe Ia, the NV mass step is $0.149 \pm 0.024$ mag ($6.3σ$), while HV SNe Ia show $0.046 \pm 0.041$ mag ($1.1σ$), consistent with zero. The NV-HV mass-step difference is $\sim 2.2σ$. The clearest subtype difference is seen in central regions ($d_{DLR} < 1$), where NV SNe Ia show a strong mass step but HV SNe Ia none, yielding a $3.1-3.6σ$ difference. A host-colour step appears for both: NV $0.142 \pm 0.024$ mag ($5.9σ$) and HV $0.158 \pm 0.042$ mag ($3.8σ$). Overall, NV and HV colour steps are consistent. HV SNe Ia show modest ($\sim 2.5$-$3σ$) steps in outer regions ($d_{DLR} > 1$), while NV SNe show stronger environmental trends. Thus, NV SNe Ia appear more environmentally sensitive, especially in central, likely metal-rich and older regions, while HV SNe Ia show weaker, subset-dependent trends, and applying a universal mass-step correction could introduce biases. Refined classifications or environment-dependent factors may improve future cosmological analyses beyond standard $x_{1}$ and $c$ cuts.

astro-ph.GA↗

arXiv2025

MUSE Observations Reveal Optical Coronal Iron Lines from Shock Emission in Supernova Remnant 0540-69.3

We investigate the optical shock emission from the Large Magellanic Cloud supernova remnant 0540-69.3 (SNR 0540) using MUSE integral-field-unit data from the VLT. The observations cover the spectral range 4650-9300 $Å$ and provide a $1\times1$ arcmin$^{2}$ field of view, encompassing nearly the entire remnant. We analyse the spatial and spectral properties of shock-related emission lines, and identify clumpy optical shock emission e.g. from [S II] $λλ$6716,6731 doublet and the coronal [Fe XIV] $λ$5303 line (typically at radial velocities $\lesssim|100|$ km s$^{-1}$ and $\lesssim|170|$ km s$^{-1}$, respectively). These features trace the blast-wave shell seen in previous X-ray studies. Post-shock electron density estimates, based on the [S II]-line ratio, reveal spatial variation, with the highest densities ($\sim10^4$ cm$^{-3}$) in the bright knots in the west, and lower densities ($\sim3\times10^3$ cm$^{-3}$) in the east. The density in the north (southwest) appears significantly lower (higher) but remains unconstrained due to limited signal. We also estimate blast-wave shock velocities using the [Fe XIV] $λ$5303/[Fe XI] $λ$7892 ratio, finding low velocities ($\sim400$ km s$^{-1}$), consistent with previous studies. All these results support the scenario that the blast wave is interacting with the surrounding interstellar medium, particularly in the western regions. Additionally, we detect four unidentified emission lines, $\sim$2000-3000 km s$^{-1}$ south from the pulsar in transverse velocity, but their origin remains unclear. Possible explanations, including Fe lines from a high-velocity ejecta clump, all present challenges. Our findings highlight the complex nature of the circum- and interstellar medium surrounding SNR 0540.

astro-ph.HE↗

arXiv2025

Luminous, rapidly declining supernovae as stripped transitional objects in low metallicity environments: the case of SN 2022lxg

We present an analysis of the optical and near-infrared properties of SN 2022lxg, a bright ($\rm M_{g\, \mathrm{peak}}=-19.41$ mag) and rapidly evolving SN. It was discovered within a day of explosion, and rose to peak brightness in 10 d. Two distinct phases of circumstellar interaction are evident in the data. The first is marked by a steep blue continuum (T $>15,000$ K) with flash-ionisation features due to hydrogen and He II. The second, weaker phase is marked by a change in the colour evolution accompanied by changes in the shapes and velocities of the spectral line profiles. Narrow P-Cygni profiles (~ $150$ km s$^{-1}$) of He I further indicate the presence of slow-moving unshocked material and suggesting partial stripping of the progenitor. The fast decline of the light curve from peak (3.48$\pm$ 0.26 mag $\rm (50\,d)^{-1}$ in $g$-band) implies that the ejecta mass must be low. Spectroscopically, until $+35$ d there are similarities to some Type IIb SNe but then there is a transition to spectra that are more reminiscent of an interacting SN II. However, metal lines are largely absent in the spectra, even at epochs of 80 d. Its remote location from the presumed host galaxy, a dwarf with $\rm M_B$ ~ $-14.4$ mag, is consistent with our metallicity estimate - close to the SMC value - obtained from scaling relations. Furthermore, several lines of evidence (including intrinsic polarisation of $p$ ~ (0.5-1.0) %) point to deviations from spherical symmetry. We suggest that a plausible way of uniting the observational clues is to consider a binary system that underwent case C mass transfer. This failed to remove the entire H-envelope of the progenitor before it underwent core-collapse. In this scenario, the progenitor itself would be more compact and perhaps straddle the boundary between blue and yellow supergiants, tying in with the early spectroscopic similarity to Type IIb SNe.

astro-ph.HE↗

arXiv2025

SN 2024abfo: a partially stripped SN II from a yellow supergiant

We present photometric and spectroscopic data of the type IIb supernova (SN) 2024abfo in NGC 1493 (at 11 Mpc). The ATLAS survey discovered the object just a few hours after the explosion, and observed a fast rise on the first day. Signs of the sharp shock break-out peak and the subsequent cooling phase are observed in the ultraviolet and the bluest optical bands in the first couple of days, while no peak is visible in the reddest filters. Subsequently, in analogy with normal SNe IIb, the light curve of SN 2024abfo rises again in all bands to the broad peak, with the maximum light reached around one month after the explosion. Its absolute magnitude at peak is $M_r=-16.5\pm0.1$ mag, making it a faint SN IIb. The early spectra are dominated by Balmer lines with broad P-Cygni profiles indicating ejecta velocity of 22,500 km/s. One month after the explosion, the spectra display a transition towards being He-dominated, though the H lines do not completely disappear, supporting the classification of SN 2024abfo as a relatively H-rich SN IIb. We identify the progenitor of SN 2024abfo in archival images of the Hubble Space Telescope, the Dark Energy Survey, and the XMM-Newton space telescope, in multiple optical filters. From its spectral energy distribution, the progenitor is consistent with being a yellow supergiant, having an initial mass of 15 $M_{\odot}$. This detection supports an emerging trend of SN IIb progenitors being more luminous and hotter than SN II ones, and being primaries of massive binaries. Within the SN IIb class, fainter events such as SN 2024abfo tend to have cooler and more expanded progenitors than luminous SNe IIb.

astro-ph.HE↗

arXiv2025

Observational diversity of bright long-lived Type II supernovae

In various types of supernovae (SNe), strong interaction between the SN ejecta and circumstellar material (CSM) has been reported. This raises questions on their progenitors and mass-loss processes shortly before the explosion. Recently, the bright long-lived Type~II SN 2021irp was proposed to be a standard Type II SN interacting with disk-like CSM. The observational properties suggest that the progenitor was a massive star in a binary system and underwent a mass-ejection process due to the binary interaction just before the explosion. Here, we study the diversity of the observational properties of bright long-lived Type II (21irp-like) SNe. We analyse the diversity of their CSM properties, in order to understand their progenitors and mass-loss mechanisms and their relations with the other types of interacting SNe. We performed photometry, spectroscopy, and/or polarimetry for four 21irp-like SNe. Based on these observations as well as published data of SN~2021irp itself and well-observed bright and long-lived type II SNe including SNe~2010jl, 2015da and 2017hcc, we discuss their CSM characteristics. This sample of SNe shows luminous and long-lived photometric evolution, with some variations in the photometric evolution (from $\sim-17$ to $\sim-20$ absolute mag in the $r$/$o$ band even at $\sim 200$ days after the explosion). They show photospheric spectra characterized mainly by Balmer lines for several hundreds of days, with some variations in the shapes of the lines. They show high polarization with slight variations in the polarization degrees with rapid declines with time (from $\sim3-6$ \% before the peak to $\sim1$ \% at $\sim200$ days after the peak). The observational properties are consistent with the disk-CSM-interaction scenario, i.e., typical Type~II SNe interacting with disk-like CSM.

astro-ph.HE↗