arXiv subjects

Andrea Simongini

Publications and source records attributed to Andrea Simongini.

5 recordsLinked to original sources

arXiv2026

Statistical treatment of searches for counterparts of positionally-uncertain astrophysical sources: from flux upper limits to detection

Rapid growth of the multimessenger and multiwavelength astrophysics had led to an increasing number of observations of the same events with instruments with different point spread functions. In particular pointing instruments with good angular resolution are used to pin-point the source of poorly-localized alert. In case no clear detection of the source counterpart is reached, the interpretation of the results requires statistical analysis. We investigate two approaches using the probability density function of the alert: frequentist and Bayesian, as well as agnostic approach not using this information. We discuss the advantages and problems of all the methods, and compare their reliability and performance. We consider both a simple one-dimensional toy simulations and a realistic use case of full simulations of the follow-up of a gravitational wave event with gamma-ray telescopes. The performance of both frequentist and Bayesian approaches for weak signals is comparable and superior to the agnostic one.

astro-ph.IM↗

arXiv2026

Early emission characterization of TDE 2025aarm

In this Letter, we present early emission data analysis of the tidal disruption event TDE 2025aarm, including optical, UV and X-ray data. At a redshift of z = 0.01368, TDE 2025aarm is the second closest TDE ever discovered, offering an unprecedented opportunity to study such phenomena in great details. We observed TDE 2025aarm in optical with the Liverpool Telescope for a total of three epochs, and complemented our dataset with ancillary spectroscopic and photometric data. The early optical spectra are characterized by a blue-continuum and helium, hydrogen and possibly Bowen lines typical of H+He events. The optical light curves peak at M_g ~ -18.68 mag and are well described by fallback of a M_star ~ 0.16 M_sun star onto a M_BH ~ 2x10^{7}M_sun black hole. We report Swift-XRT detection in the 0.3-10 keV range, with a total flux of F_X ~ 1.42x10^{-14} erg cm^{-2} s^{-1}, fitted by a black-body with k_BT ~ 0.39 keV. This makes TDE~2025aarm a new event among optical/UV bright TDEs detected in soft X-rays. Our analysis suggests that the early emission from TDE 2025aarm is powered by circularization shocks, and that the delayed accretion scenario best describes the observed features.

astro-ph.HE↗

arXiv2025

Core-collapse supernova parameter estimation with the upcoming Vera C. Rubin Observatory

The Vera Rubin Observatory's Legacy Survey of Space and Time (LSST) is expected to revolutionize time-domain optical astronomy as we know it. With its unprecedented depth, the LSST will survey the southern hemisphere sky, generating nearly 32 trillion observations over its nominal 10-year operation. Among these, approximately 10 million will be supernovae (SNe). These observations will uniquely characterize the SN population, enabling studies of known and rare SN types, detailed parameterization of their light curves, deep searches for new SN progenitor populations, the discovery of strongly lensed SNe, and the compilation of a large, well-characterized sample of superluminous SNe. We analyzed a sample of 22663 simulations of LSST light curves for core collapse SNe (CCSNe), modeled using the radiative transfer code STELLA. We analyzed this dataset with the software CASTOR, which enables the reconstruction of synthetic light curves and spectra via a machine learning technique that allows one to retrieve the complete parameter map of a SN. For each parameter we compared the observed and the true values, determining how LSST light curves alone will contribute to characterize the progenitor and the explosion. Our results indicate that LSST alone will not suffice for a comprehensive and precise characterization of progenitor properties and explosion parameters. The limited spectral coverage of LSST light curves (in most cases) does not allow for the accurate estimation of bolometric luminosity, and consequently, of the explosion energy and nickel yield. Additionally, the redshift-absorption degeneracy is difficult to resolve without supplementary information. These findings suggest that for the most interesting SNe, complementary follow-up observations using spectrographs and optical facilities (particularly in the infrared bands) will be essential for accurate parameter determination.

astro-ph.HE↗

arXiv2025

On the Binary Nature of the Progenitor of SN2015ap: Insights from Its Light Curve and Spectral Evolution

Stripped-envelope supernovae (SESNe) display a wide range of photometric and spectroscopic behaviours, often reflecting complex progenitor evolution. SN~2015ap is a type Ib event located in the nearby galaxy IC~1776, previously modelled as powered by radioactive decay and possibly a magnetar engine. In this work, we revisit its multi-band photometry and spectroscopy, {gathering all publicly available observational data for this source}, to investigate the nature of its progenitor and power source. {We use an innovative time analysis method based on Gaussian Process, leveraging its ability to model both noise and periodic components in unevenly sampled data without requiring regular sampling.} We detect significant periodic modulations in the post-peak light curve, with a characteristic timescale of $\sim$8.4 days. These modulations are also seen in the $H_{\alpha}$ line velocity, suggesting a structured circumstellar medium (CSM) shaped by binary interaction. We model the light curve with semi-analytical prescriptions (MOSFiT), including CSM and central engine components, and derive an ejecta mass of $\sim$2.2--2.4~$M_\odot$, explosion energy of $\sim$3.4$\times$10$^{51}$~erg, and a $^{56}$Ni mass of $\sim$0.11~$M_\odot$. The colour evolution indicates an additional energy injection, consistent with either prolonged breakout or delayed central powering. While the data are compatible with a weak magnetar contribution, the overall evidence favours a binary progenitor system, with non-conservative mass transfer shaping the observed CSM. SN~2015ap thus adds to the growing sample of SESNe where binarity plays a central role in driving both the explosion and its observables.

astro-ph.HE↗

arXiv2024

Building spectral templates and reconstructing parameters for core collapse supernovae with CASTOR

The future of time-domain optical astronomy relies on the development of techniques and software capable of handling a rising amount of data and gradually complementing, or replacing if necessary, real observations. Next generation surveys, like the Large Synoptic Survey Telescope (LSST), will open the door to the new era of optical astrophysics, creating, at the same time, a deficiency in spectroscopic data necessary to confirm the nature of each event and to fully recover the parametric space. In this framework, we developed Core collApse Supernovae parameTers estimatOR (CASTOR), a novel software for data analysis. CASTOR combines Gaussian Process and other Machine Learning techniques to build time-series templates of synthetic spectra and to estimate parameters of core collapse supernovae for which only multi-band photometry is available. Techniques to build templates are fully data driven and non-parametric through empirical and robust models, and rely on the direct comparison with a training set of 111 core collapse supernovae from the literature. Furthermore, CASTOR employees the real photometric data and the reconstructed synthetic spectra of an event to estimate parameters that belong to the supernova ejecta, to the stellar progenitor and to the event itself, in a rapid and user-friendly framework. In this work we provide a demonstration of how CASTOR works, studying available data from SN2015ap and comparing our results with those available in literature.

astro-ph.HE↗