arXiv subjects

Chiara Ventura

Publications and source records attributed to Chiara Ventura.

5 recordsLinked to original sources

arXiv2026

Deciphering the Physical Origin of GRB 240825A: A Long GRB Lacking a Bright Supernova

We present a comprehensive multiwavelength analysis of GRB 240825A, a bright gamma-ray burst (GRB) detected by Fermi and Swift, with a prompt duration ($T_{\rm 90}$ $\sim$ 4 sec in 50-300 keV in GBM) near the boundary separating short and long GRBs, prompting a detailed investigation into its classification and progenitor. We use classical prompt metrics (duration, minimum variability timescale (MVT), lag, and spectral hardness) and modern classification techniques (machine-learning (ML) based t-SNE, support vector machine, energy-hardness-duration, and $\varepsilon \equiv E_{γ,\mathrm{iso},52} / E_{p,z,2}^{5/3}$) and find most properties (prompt energetics, placement on the Amati relation, and spectral lag) of GRB 240825A consistent with a collapsar origin. However, extensive late-time optical and NIR follow-up with the 10.4m GTC and 8.4m binocular LBT telescopes reveals no bright supernova (like SN 1998bw) is detected down to stringent limits (e.g., $m_r > 25.0$ mag at 17.59 days), despite a redshift of $z = 0.659$ measured from GTC spectroscopy. Host galaxy SED modeling with Prospector indicates a massive, and star-forming galaxy-typical of collapsar GRB hosts, though with a large offset. We compare these findings with hybrid events like GRB 211211A, GRB 230307A, GRB 200826A, including SNe-GRBs, and conclude that GRB 240825A most likely originated from a massive star collapse, possibly with the associated SN heavily obscured or intrinsically faint. This study emphasizes the need for multiwavelength follow-up and a multi-layered classification to determine GRB progenitors.

astro-ph.HE↗

arXiv2026

Follow-up of SN 2025wny VI: The Rate and Detectable Population of Strongly Lensed SLSNe-I in ZTF

The Type I superluminous supernova (SLSN-I) SN 2025wny, multiply imaged by two foreground galaxies at $z_l = 0.375$, is the first confirmed strongly lensed SLSN and the highest-redshift ($z_s = 2.015$) multiply imaged supernova in a galaxy-scale configuration. We ask whether one discovery in seven years of Zwicky Transient Facility (ZTF) operations is consistent with expectations, and whether SN 2025wny is typical of the detectable population. We develop a forward simulation of strongly lensed SLSNe-I in ZTF, combining an empirically calibrated volumetric rate and luminosity function with a galaxy-scale deflector population, unresolved lensed light curves, and the actual ZTF observing history. We predict $0.037^{+0.022}_{-0.020}\,{\rm yr}^{-1}$, consistent with the rate of $0.14^{+0.31}_{-0.11}\,{\rm yr}^{-1}$ inferred from a single discovery in seven years of ZTF operations. Conditioning the simulation on discovery by ZTF corrects the magnifications and intrinsic luminosity of SN 2025wny for Malmquist- and magnification biases: the debiased peak bolometric luminosity, $\log_{10}(L_{\rm bol,int}/{\rm erg\,s^{-1}}) = 44.60^{+0.05}_{-0.10}$, places it at the $\sim$97th percentile of the assumed SLSNe-I luminosity function. SN 2025wny is typical of the detectable population in redshift, luminosity, and magnification, but its $4.9''$ image separation exceeds single-galaxy deflector expectations, implying our rates are conservative for wide-separation systems.

astro-ph.CO↗

arXiv2026

Follow-up of SN 2025wny II: Superluminous Supernova Physics at Cosmic Noon

SN 2025wny is a gravitationally lensed, hydrogen-poor superluminous supernova (SLSN-I) at z = 2.015. To date, it is the most extensively observed high-redshift core-collapse SN and has the most detailed rest-frame UV observations of any SLSN. We present densely sampled rest-frame UV-to-optical photometry and spectroscopy out to +80 d post-peak (rest frame) from several facilities, including JWST, Keck, VLT, Gemini, the Palomar 200-inch, the Fraunhofer Telescope at Wendelstein, and the Liverpool Telescope. Correcting for lensing magnification, SN 2025wny reaches a peak pseudo-bolometric luminosity of $L_{\rm peak}\gtrsim4\times10^{44}$ erg s$^{-1}$ over rest-frame 1500-4230 Å, placing it within the luminosity range of typical SLSNe-I. SN 2025wny exhibits several unusual features, including a continuum excess and sharp spectral features in the FUV from +20-60 d that coincide with an FUV light-curve plateau and higher inferred blackbody temperatures. SN 2025wny's spectra also show little to no UV line blanketing, no obvious O II absorption despite high temperatures, and evidence for C II, H$α$, and possible He I. Light-curve modeling suggests that SN 2025wny may require a hybrid or non-standard power source. This work provides some of the first detailed constraints on high-redshift SLSNe and establishes SN 2025wny as an essential spectral and photometric reference for identifying and interpreting high-redshift SLSNe discovered by Rubin and Roman.

astro-ph.CO↗

arXiv2026

Follow-up of SN 2025wny IV: Photometric Time-delay Measurements of a Strongly Lensed Superluminous Supernova

We present photometric time-delay measurements of SN 2025wny, the first strongly lensed Type I superluminous supernova (SLSN-I), discovered at $z = 2.015$. Time-delay measurements from strongly lensed supernovae provide an independent probe of cosmology and the Hubble constant, $H_0$, without reliance on the local distance ladder. Using multi-facility imaging data, we performed scene-modelling photometry to deblend four of the lensed images (A-D) and construct $grizJ$-band light curves. We modelled the resolved light curves with Gaussian process regression using GausSN (Hayes et al. 2024) to infer relative time delays and magnifications between the lensed images. We found that a constant magnification model provides a suboptimal description of the data, motivating a time-dependent sigmoid magnification model to account for evolving relative magnification of image A. We measured time delays of $Δt_{AB} = -10.6^{+2.2}_{-2.5}$ days and $Δt_{AC} = 1.2^{+2.7}_{-2.6}$ days (68% credible intervals), consistent with independent spectroscopic measurements from Johansson et al. (2026). Combining the photometric time delays with the lens model of Mörtsell et al. (2026) gives $H_{0,\:\rm photo} = 80.5^{+26.4}_{-16.7}\;\rm km\,s^{-1}\,Mpc^{-1}$, while including the spectroscopic time delays as well yields $H_{0,\:\rm comb} = 70.8^{+8.2}_{-6.1}\;{\rm km\,s^{-1}\,Mpc^{-1}}$. Our results further demonstrate the potential of strongly lensed supernovae as independent probes of $H_0$.

astro-ph.CO↗

arXiv2026

The applicability of the JAGB method for measuring the distance of galaxies subject to different metal enrichment rates

The JAGB method has been proposed in recent years as a possible distance indicator for galaxies in the Local Group and beyond. However, the nature of the stars populating the J region, and the conditions required for the direct application of this method, still need to be clarified. We investigate the robustness of the JAGB method through a detailed theoretical analysis of the stars populating the J region of the (J-Ks, J) diagram. The main goal is to identify the properties of the corresponding J luminosity function (JLF) that are minimally affected by the previous evolutionary history of the host galaxy, particularly its metal enrichment history. We use a population synthesis approach based on AGB stellar evolution models coupled consistently with dust formation in the stellar wind. Synthetic stellar distributions in the (J-Ks, J) diagram and the related JLFs are calculated for different assumptions on the metallicity evolution of the interstellar medium, in order to study how the JLF depends on the efficiency of metal enrichment. We find that the JAGB population is dominated by stars formed between about 1 and 6 Gyr ago, while stars formed outside this interval contribute only marginally to the JAGB region. The shape of the JLF strongly depends on the metal enrichment history, and the position of the J-band peak varies by more than 0.3 mag among the different cases explored. Conversely, the mean J-band magnitude, MavJ, is much less sensitive to the previous history of the galaxy and therefore represents a more reliable distance indicator. For all the cases investigated we find MavJ = -6.2 +/- 0.05 mag. We also discuss the uncertainties related to the still poorly constrained mass-loss process experienced by low-mass stars during the red giant branch phase.

astro-ph.GA↗