Priscila J. Pessi

Context . Time-domain photometric monitoring is essential for characterizing cometary evolution, particularly for rare interstellar objects with limited observing opportunities. Aims . We aimed to characterize the pre-perihelion photometric behavior and dust activity of the interstellar comet 3I/ATLAS and to test the capability of the Black Hole Target and Observation Manager (BHTOM) platform and telescope network for coordinated high-cadence non-sidereal observations. Methods . We obtained 70 days of time-series photometry of 3I/ATLAS from 2025 July 4 to September 11 using 16 telescopes and 1554 images. The data were processed and calibrated with the BHTOM pipeline. High-cadence multiband imaging was used to measure the rotation period and color evolution, while the dust activity was quantified via Afρ measurements. Results . We present a pre-perihelion light curve of 3I/ATLAS from R _h = 3.18–2.19 au, which exhibited a steady brightening by ∼3 magnitudes with no evidence of anomalous behavior. We measured a rotation period of P _rot = 15.98 ± 0.08 h. The colors were statistically non-changing, with only a weak, non-significant tendency for 3I/ATLAS to become bluer at 3.5 > R _h > 2.2 au. The relative dust production increased from A (0°) fρ ∼600 to 1100 cm, and the upper limit on the dust mass-loss rate increased from ≤217 kg s ⁻¹ to ≤328 kg s ⁻¹ . We measured an activity index of n = −1.24 ± 0.02, which is consistent with a well-developed dust coma.

We investigate the thermal emission and the extinction from dust associated with the nearby ( z = 0.0267) superluminous supernova (SLSN) 2018bsz. Our dataset combines daily cadence, simultaneous optical and near-infrared (NIR) coverage up to ∼100 days with late-time (+ 1.7 yr) mid-infrared (MIR) observations. At 230 days after the light-curve peak, the supernova (SN) is not detected in the optical, but shows a surprisingly strong NIR excess, with r − J > 3 mag and r − K _s > 5 mag. The temporal evolution of the infrared (IR) light curve allows us to assess whether the MIR emission originates from newly formed dust, either in the SN ejecta or in a postshock circumstellar shell, or instead from an IR echo produced by preexisting circumstellar or interstellar dust heated by the SN radiation. Our radiative-transfer modeling shows that the circumstellar and interstellar echo scenarios cannot simultaneously reproduce the observed IR luminosity and its temporal evolution, and we therefore disfavor these interpretations. In contrast, a scenario in which new dust forms in the SN ejecta at epochs ≳200 days provides a self-consistent explanation for the evolution of the SN flux. We can fit the spectral energy distribution well at +230 days with 5 × 10 ⁻⁴ M _⊙ of carbon dust, increasing over the following several hundred days to 10 ⁻² M _⊙ by +535 days. SN 2018bsz is the first SLSN showing evidence for dust formation within the SN ejecta, and appears to form 10 times more dust than normal core-collapse supernovae (SNe) at similar epochs. Together with their preference for low-mass, low-metallicity host galaxies, we suggest that superluminous SNe may be a significant contributor to dust formation in the early Universe.

We present multiwavelength observations and analysis of SN 2024iss, a Type IIb supernova (SN IIb) located at ∼14 Mpc. The first Zwicky Transient Facility detection of SN 2024iss is ∼40 minutes after first light (one of the earliest detections of a SN IIb to date) and a Hubble Space Telescope (HST) UV spectrum was obtained at 7 days (the earliest HST UV SN IIb spectrum to date). We estimate an ejecta mass range of 1.1–3.3 M _⊙ and a ⁵⁶ Ni mass of 0.11 ± 0.01 M _⊙ from bolometric light-curve modeling and He-star model comparisons. We fit shock-cooling emission models to estimate a progenitor radius of 100–320 R _⊙ and an envelope mass of 0.07–0.46 M _⊙ . We compare optical/UV spectra to binary progenitor models, which indicate a stripped H-rich envelope mass of 0.19–0.28 M _⊙ . We use early-time X-ray detections to calculate circumstellar material (CSM) densities that are consistent with a progenitor mass-loss rate of 5 × 10 ⁻⁴ M _⊙ yr ⁻¹ ( v _w = 100 km s ⁻¹ ), corresponding to 2–5 yr preexplosion. In the UV, we observe strong Mg ii emission extending to 15,000 km s ⁻¹ as well as weak P Cygni profiles of iron-group elements (e.g., Fe, Ti, Al, Ni) present in outer SN ejecta. The overall spectroscopic evolution of SN 2024iss is comparable to that of SNe IIb, but its increased brightness at peak is influenced by SN ejecta–CSM interaction. Nebular spectroscopy of SN 2024iss at ∼260–412 days reveals multipeaked forbidden-line profiles of O i and Mg i ] indicative of inner ejecta asymmetry and/or clumping. We demonstrate the utility of a rich, multiwavelength data set for constraining the progenitor systems and explosion dynamics of SNe IIb.

Superluminous supernovae (SLSNe) are one of the most luminous stellar explosions known, yet they remain poorly understood. Because they are intrinsically rare, efficiently identifying them in the large alert streams produced by modern time-domain surveys is essential for building larger observational samples and enabling spectroscopic follow-up. We present NOMAI, a machine-learning classifier designed to identify SLSN candidates directly from photometric alerts in the ZTF stream, using light curves accumulated over at least 30 days. It does not require any spectroscopic redshift and is running in real time within the Fink broker. ZTF light curves were transformed into a set of physically motivated features derived primarily from model-fitting procedures using SALT2 and Rainbow, a blackbody-based multiband fitting framework. These features were used to train an XGBoost classifier on a curated dataset of labeled ZTF sources constructed using literature samples of SLSNe, along with TNS and internal ZTF labeled sources. The final dataset contains 5280 unique sources, including 225 spectroscopically classified SLSNe. Averaged over 100 bootstrap realizations, the classifier reaches 66% completeness and 58% purity. Deployed within the Fink broker, NOMAI has been running continuously since 18 December 2025 on the ZTF alert stream and publicly reports SLSN candidates every night by automatically posting them to dedicated communication channels. Based on this, we also report the first two-month evaluation period, where the classifier successfully recovered 22 of the 24 active SLSNe reported on the Transient Name Server, providing an upper limit on its real-time completeness. The achieved performances, particularly the high completeness in real-time operations, demonstrate that the classifier provides a valuable tool for experts to efficiently scan the alert stream and identify promising candidates. In the near future, NOMAI is intended to be adapted to operate on the Legacy Survey of Space and Time conducted by the Vera C. Rubin Observatory, which is expected to uncover an unprecedented number of transients, making machine-learning based photometric classification essential.

Context. Type II supernovae (SNe) are the most common terminal stellar explosions in the Universe. With SNe now being detected within days after first light, there is growing evidence that most Type II SNe (SNe II) show signs of interaction with a dense, confined circumstellar material (CSM) in the first few days after first light. Aims. We aim to bridge the gap between single SN studies showing early-time interaction in their spectra and statistical studies of early-time SN light curves, which imply the existence of CSM. Methods. We present a sample of 68 Type II SNe with both early photometric data obtained by the ATLAS survey and spectroscopic data obtained by 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 the CSM. We characterised the photometric and spectroscopic properties of the sample by measuring rise times to maximum light, peak magnitudes, decline rates, and line velocities. Additionally, we measured the ratio of absorption to emission (a/e) of the H α P-Cygni profile. Results. Our analysis reveals that SNe II showing early spectroscopic signs of interaction with the CSM decline faster and are brighter than those without. However no difference was found in rise times between the two groups. A clear separation can be observed in the a/e ratio, namely, 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.

Understanding dust attenuation toward extragalactic transients is critical for recovering their intrinsic properties and probing the local environments of distant galaxies. A popular diagnostic is the Na i D absorption equivalent width, widely applied to extragalactic transients. In this paper, we present early-time optical and near-infrared observations of the Type Ib supernova (SN Ib) SN 2024vjc, followed for ∼130 days postexplosion. SN 2024vjc exhibits only weak Na I D absorption, indicating only a modest host attenuation with E ( B − V ) _host ∼ 0.18 mag; if this argument were applied, SN 2024vjc would be a peculiar, faint, and red SN Ib while showing the light-curve shape and spectral evolution broadly consistent with those of canonical Type Ib supernovae. We show that this is not the case; SN-based diagnostics (intrinsic color templates, color-curve evolution, and spectral dereddening) together with the Balmer decrement indicate substantial attenuation, E ( B − V ) ∼ 0.45−0.8 mag. The weak Na i D absorption may result from photoionization of neutral sodium by the intense radiation field of a young H ii region at the explosion site; this scenario is directly supported by the detection of narrow H α , [N ii ], and H β emission lines and a blue continuum excess in late-time spectroscopy. SN 2024vjc represents a clear counterexample to the common assumption that weak or absent Na I D absorption implies negligible host-galaxy attenuation, and highlights the importance of employing multiple, independent attenuation diagnostics.

Mapping how the explosion properties of Type II supernovae (SNe II) relate to the properties of their progenitors can provide strong constraints for understanding the final evolutionary stages of massive stars. Type IIP SNe, linked to the explosions of single red supergiant (RSG) stars, have recently been found to require some form of interaction with circumstellar material (CSM) to reproduce the rapid rise to the plateau often seen in their light curves. In this work, we present observations and analysis of the Type IIP SN 2020bij, characterized by a slow rise to its plateau as well as high expansion velocities. We identify four other SNe IIP from the literature (ASASSN-14 kg, SN 2018fif, SN 2021yja, and SN 2023axu) with similarly slowly rising light curves and find that they also show high expansion velocities. Using both analytical and numerical models, all five events can be explained with weak to no CSM interaction. We therefore propose that these events constitute a new subclass of Type IIP SNe that could be associated with relatively confined CSM. Early and dense photometric coverage of future SNe IIP together with early spectroscopic observations will further map this subclass and its physical properties. Understanding such rare events could be key to constraining the diversity of late-stage mass loss in RSGs.

Context. Current large-scale, high-cadence surveys, such as the Zwicky Transient Facility (ZTF), provide detections of new and rare types of transients and supernovae (SNe) whose physical origins are not well understood. Aims. We aim to investigate the nature of SN 2021lwz at a redshift z = 0.065, an over-luminous SN with an absolute magnitude of M _g ∼ −20.1 AB that falls in the lower range of superluminous supernovae (SLSNe) luminosities and was discovered in a faint dwarf galaxy with an absolute magnitude of M _g ≃ −14.5 AB. Methods. We studied SN 2021lwz using optical spectroscopy and photometry and by imaging linear polarimetry obtained during several follow-up campaigns. All the data were used to analyse and model the evolution of the explosion. Comparisons with other SNe of well-known or rarer types were investigated. Results. SN 2021lwz belongs to the rare class of rapidly evolving transients. The bolometric light curve rises in about seven days to a peak luminosity of about 5 × 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 an 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 _ej ∼ 0.24 M _⊙ ) took place in a low-mass ( M ∼ 10 ^6.66 M _⊙ ) dwarf galaxy of specific star formation rate about ten times larger than typical star-forming galaxies. Conclusions. SN 2021lwz is an uncommon transient showing many similarities with several classes of transients, including rare transients. It may be an interesting example of how differences in ejecta mass and engine parameters could produce a wide range of engine-driven stripped-envelope SNe.

Aims. We present and interpret the data of the nearby hydrogen-deficient but helium-rich superluminous supernova SN 2021bnw, which reached a magnitude of –20.7 at maximum luminosity in g band. Methods. We discuss the light curves and spectra of SN 2021bnw based on its spectro-photometric follow-up, exploiting different observational facilities. We reproduced the near-IR spectrum of SN 2021bnw with TARDIS to inspect the chemical composition at late photospheric phases and identify helium features. We also used a STELLA model coupling hydrodynamics and radiation transport to constrain the physical parameters of the explosion assuming a ⁵⁶ Ni+CSM scenario. Results. We suggest that SN 2021bnw was mainly powered by the interaction of the ejecta with a previously lost He-rich circumstellar material, coupled with a central power source. Conclusions. This work expands the data sample of He-rich superluminous supernovae (SLSNe Ib), and for a single-progenitor scenario, it can constrain the masses and physics of their progenitors.

We report the results of a photometric and spectroscopic follow-up campaign of the unusual interacting supernova (SN) 2022pda. Precursor variability lasting ∼100 days is observed before the explosion. The SN light curve has a double-peak shape. It reached a first maximum of M _r = −19.6 ± 0.2 mag, followed by an initial 2 month decline and a second, broad peak lasting about 6 months. The early spectra show a blue continuum with dominant H and He emission lines. A high-resolution pre-maximum spectrum shows that the profile of the He i λ 5876 line consists of a moderately narrow (∼1900 km s ⁻¹ ) P Cygni absorption superposed on a broader (∼3300 km s ⁻¹ ) component. In the blue region, several spectral features are identified, including C iii /N iii /O ii blends. Two broad bumps at 4600–5200 Å and 6400–6800 Å regions reveal a complex profile, which are likely due to blends of H, He, and other emission lines. Late-time spectra are still dominated by prominent and broad H and He lines in emission. Shock-driven model fits to the bolometric light curve suggest that the SN is powered by interaction with a massive CSM with enhanced mass-loss rates ∼5 M _⊙ yr ⁻¹ , expelled during two events that occurred ∼1 and ∼0.2 yr before the explosion. The overall SN evolution indicates that SN 2022pda is a transitional event between an H-rich SN IIn (SN 2009ip-like) and an He-rich SN Ibn. Our findings suggest that the progenitor was likely a luminous blue variable transitioning towards a Wolf–Rayet stage.