arXiv subjects

Dafne Guetta

Publications and source records attributed to Dafne Guetta.

At least 19 recordsLinked to original sources

arXiv2026

Search for Long-Transient Gravitational Waves from Supernova SN2023ixf using GFH-v2 Pipeline

We present a directed search for long-transient gravitational waves from the possible newborn magnetar remnant of SN2023ixf, a nearby Type II core-collapse supernova in the M101 galaxy. The analysis uses LIGO Hanford and Livingston data from Engineering Run 15, using coincident data lying within the on-source window associated with the supernova. We target signals from a rapidly rotating, non-axisymmetric neutron star whose spin-down is dominated by gravitational-wave emission, producing a power-law decrease in frequency and a corresponding decrease in strain amplitude. The search is performed with the GFH-v2 pipeline, based on the Generalized Frequency Hough transform. No candidate survives the coincidence and follow-up analysis. We therefore set upper limits on the maximum detectable distance as a function of initial frequency and ellipticity. For the highest ellipticity interval, the 90% upper limits reach distances of about 1-2.5~Mpc across most of the analysed band. Although these limits are below the distance to M101, the search provides the first application of GFH-v2 to a nearby core-collapse supernova and characterizes its performance on real detector data.

astro-ph.IM↗

arXiv2026

A Deep Precursor-Dip-Main Superoutburst Sequence in VW Hydri Observed with TESS: High-Cadence Constraints on the Thermal-Tidal Instability Model

We present 120s cadence TESS observations of three superoutbursts of the SU UMa-type dwarf nova VW Hydri. Two events (SO2 in Sectors 87+88 and SO3 in Sector 93) exhibit a pronounced, temporally pronounced precursor-dip followed by a rapid rise into the main superoutburst plateau. This morphology, previously seen in Kepler light curves of V1504 Cyg and V344 Lyr, is a key prediction of the thermal-tidal instability (TTI) model when a normal (precursor) outburst expands the disk only marginally beyond the 3:1 resonance radius, allowing the tidal instability to grow slowly and produce a deep dip approaching quiescence before rapid amplification drives the main superoutburst. A sliding-window time-frequency analysis reveals superhump power already during the decline and near minimum light, with a smooth period evolution across the dip and stabilization after the system returns to the hot state, consistent with the growth and saturation of disk eccentricity at the 3:1 resonance. From the stabilized Stage A superhump periods, we infer a representative mass ratio $q = 0.131 \pm 0.002$. Combined with either a typical SU UMa white-dwarf mass prior or the semi-empirical donor sequence at an orbital period of 107~min, the implied component masses are $M_1 \simeq 0.6$--$1.0\,M_\odot$ and $M_2 \simeq 0.08$--$0.14\,M_\odot$, ruling out a brown-dwarf donor and establishing VW~Hyi as a benchmark system for testing tidal-instability models in low-$q$ dwarf novae.

astro-ph.SR↗

arXiv2025

GFH-v2 Pipeline for Searches of Long-Transient Gravitational Waves from Newborn Magnetars

This paper presents an enhanced methodology for searching long transient gravitational waves associated with a newborn magnetar, with particular focus on the regime in which the early spin-down is dominated by gravitational-wave emission. The analysis is performed using a strongly improved version of the generalized Frequency Hough Transform algorithm, called GFH-v2. We describe the main developments introduced relative to the original implementation and outline the optimized parameter-space selection used in the search. We then compute the theoretical sensitivity of the method and compare it with an empirical sensitivity estimate obtained by injecting simulated signals into LIGO-Virgo-KAGRA O4a data. The updated framework achieves improved sensitivity and computational performance. These results provide a robust basis for future directed searches for long-transient gravitational-wave signals from core-collapse supernovae and other transient events in current and upcoming observing runs.

astro-ph.IM↗

arXiv2025

The TEQUILA catalog of variables in TESS full-frame images: Differential photometry light curves from the first two years of observations

Stellar variability and transient events provide critical insights into astrophysics, accelerated by missions like CoRoT, Kepler, and K2. NASA's Transiting Exoplanet Survey Satellite (TESS) adds a unique combination of long baseline and all-sky coverage, though extracting light curves from full-frame images (FFIs) is challenging due to scattered light and blending. We processed TESS FFIs to produce TEQUILA (TESS quick-look and light curve analysis), a comprehensive catalog of variable point sources from the prime mission, enabling diverse studies without requiring raw data processing. We used difference image analysis, constructing reference images from quality-filtered FFIs for each CCD across sectors 1-26. Iterative subtraction mitigated systematics, and light curves were created using aperture photometry for sources varying in residual images. The pipeline yields over six million light curves, including stellar variables, transients, systematics, and moving objects. Approximately $6 \times 10^5$ span multiple sectors, with roughly $10^3$ from continuous viewing zones. We achieve median differential variability noise of $10^{-3}$ to $10^0$ for sources between 5.0 and 16.0 Tmag, while typical photometric RMS variability ranges from $10^{-2}$ to $10^1$. A convolutional neural network identifies light curves caused by instrumental noise, assigning a confidence score to each classification. To avoid confusion with astrophysical variables, we also flag light curves prompted by known Solar System objects (SSOs). All light curves are accessible via MAST as a High-Level Science Product. This catalog serves as a discovery tool for new variables; future work will refine methods and extend coverage to the TESS extended mission.

astro-ph.SR↗

arXiv2025

An optical--mid-infrared color evolution tool for nova identification using WISE data

We present a novel approach for characterizing nova candidates by exploiting the infrared capabilities of the Wide-field Infrared Survey Explorer (WISE) catalog. We developed a pipeline to identify novae based on well-defined infrared criteria, and leveraging this pipeline, we successfully identified 41 optically confirmed novae in the WISE catalog. In particular, we focus on the color difference between the optical V band and the WISE 3.4 microns W1 band as a diagnostic. We compared their infrared light curves with their optical counterparts. We identified a strong correlation from which we proposed a color difference model that can be used for further identification and characterization of novae. Our analysis validates the mass-loss timescale theory, which predicts that systems with lower accretion rates accumulate larger envelopes and produce more massive ejecta. We also confirm models' prediction that the early color evolution of novae is governed by ejecta expansion and cooling. From our sample statistics, we infer a Galactic nova rate of approximately 40 to 50 novae per year, consistent with modern and infrared-corrected estimates. The resultant model from this work paves the way for future large-scale investigations of nova candidates.

astro-ph.SR↗

arXiv2025

Ultraviolet radiation and neutrinos: two messengers from CCSNe in the CSM scenario

Massive stars (>8 $M_{\odot}$) often undergo intense mass loss through winds or eruptive events in the final stages of their evolution, leading to the formation of a dense circumstellar medium (CSM). This material, expelled months to years before core collapse, shapes the pre-explosion environment and influences the early supernova (SN) emission. In particular, the interaction of the SN ejecta with the dense CSM can power an extended emission into the UV/optical bands, as seen in a growing fraction of type II SN. Recent events such as SN 2023ixf and SN 2024ggi confirm the relevance of dense environments and highlight the value of UV observations. Moreover, Fast Blue Optical Transients (FBOTs) may represent extreme cases of this interaction, possibly linked to more compact/massive CSM. In this work, we model the SN-CSM shock interaction in order to (i) estimate the maximum detection horizons and expected rates for future UV missions like ULTRASAT, and (ii) to estimate the intensity and expected rate of potential neutrino signals detectable by IceCube and KM3NeT. We then discuss the prospects for multi-messenger observations of such events in the near future.

astro-ph.HE↗

arXiv2025

Prospects for Time-Domain and Multi-Messenger Science with eXTP

In this new era of time-domain and multi-messenger astronomy, various new transients and new phenomena are constantly being discovered thanks to the rapid advances in observations, which provide the excellent opportunity to study the physics in the extreme environments. The enhanced X-ray Timing and Polarimetry mission (eXTP), planned to be launched in 2030, has several key advantages, including advanced polarimetry, high sensitivity & large effective area, and wide energy range coverage, which make it a groundbreaking project in high-energy astrophysics. In this article, we briefly introduce the potential time-domain and multi-messenger targets for eXTP, including gravitational-wave (GW) counterparts, gamma-ray bursts (GRBs), magnetars and fast radio bursts (FRBs), tidal disruption events (TDEs), supernovae, high energy neutrinos and TeV active galactic nucleus (AGNs), and so on. We discuss the advantages of future eXTP observations for detecting these sources, their detection capabilities, the abilities to distinguish theoretical models, and their applications in gravity and cosmology.

astro-ph.HE↗

arXiv2025

Hunting for newborn magnetars: a multi-messenger approach

We carry out a numerical calculation of magnetar-powered shock break-outs (SBOs) and supernova (SN) light-curves. In particular, we investigate the impact of gravitational wave (GW) emission by the magnetar central engine on its electromagnetic (EM) counterparts in the ULTRASAT band. Our results show that GW emission by the magnetar has only a minor effect on the SBO light-curve. However, we find that SN light-curves can carry a direct signature of GW emission, which becomes more evident at late times (> 20-30 days).~Our results demonstrate that future ULTRASAT observations will provide crucial insights into the magnetar formation process, and unique information for direct searches of long-transient signals with current and future generation GW detectors. In particular, we estimate a rate of multi-messenger (UV+GW) detections of newly formed magnetars $>$ 1 every two years with ULTRASAT and the Einstein Telescope.

astro-ph.HE↗

arXiv2025

On the light-curves of disk and bulge novae

We examine the light curves of a sample of novae, classifying them into single-peaked and multiple-peaked morphologies. Using accurate distances from Gaia, we determine the spatial distribution of these novae by computing their heights, $Z$, above the Galactic plane. We show that novae exhibiting a single peak in their light curves tend to concentrate near the Galactic plane, while those displaying multiple peaks are more homogeneously distributed, reaching heights up to 1000 pc above the plane. A KS test rejects the null hypothesis that the two distributions originate from the same population at a significance level corresponding to $4.2\sigma$.

astro-ph.GA↗

arXiv2025

Redshift leverage for the search of GRB neutrinos affected by quantum properties of spacetime

Some previous studies based on IceCube neutrinos had found intriguing preliminary evidence that some of them might be GRB neutrinos with travel times affected by quantum properties of spacetime delaying them proportionally to their energy, an effect often labeled as "quantum-spacetime-induced in-vacuo dispersion". Those previous studies looked for candidate GRB neutrinos in a fixed (neutrino-energy-independent) time window after the GRB onset and relied rather crucially on crude estimates of the redshift of GRBs whose redshift has not been measured. We here introduce a complementary approach to the search of quantum-spacetime-affected GRB neutrinos which restricts the analysis to GRBs of sharply known redshift, and, in a way that we argue is synergistic with having sharp information on redshift, adopts a neutrino-energy-dependent time window. We find that knowing the redshift of the GRBs strengthens the analysis enough to compensate for the fact that of course the restriction to GRBs of known redshift reduces the number of candidate GRB neutrinos. And rather remarkably our estimate of the magnitude of the in-vacuo-dispersion effects is fully consistent with what had been found using the previous approach. Our findings are still inconclusive, since their significance is quantified by a $p$-value of little less than $0.01$, but provide motivation for monitoring the accrual of neutrino observations by IceCube and KM3NeT as well as for further refinements of the strategy of analysis here proposed.

gr-qc↗

arXiv2024

Neutrino fluxes from different classes of galactic sources

We estimate the neutrino flux from different kinds of galactic sources and compare it with the recently diffuse neutrino flux detected by IceCube. We find that the flux from these sources may contribute to ~ 20% of the IceCube neutrino flux. Most of the sources selected in this work populate the southern hemisphere, therefore a detector like KM3NeT could help in resolving the sources out of the observed diffused galactic neutrino flux.

astro-ph.HE↗

arXiv2023

Low and High Energy Neutrinos from SN 2023ixf in M101

Supernova (SN) 2023ixf in M101 is the closest SN explosion observed in the last decade. Therefore it is a suitable test bed to study the role of jets in powering the SN ejecta. With this aim, we explored the idea that high-energy neutrinos could be produced during the interaction between the jets and the intense radiation field produced in the SN explosion and eventually be observed by the IceCube neutrino telescope. The lack of detection of such neutrinos has significantly constrained both the fraction of stellar collapses that produce jets and/or the theoretical models for neutrino production. Finally, we investigated the possibility of detecting low-energy neutrinos from SN 2023ixf with the Super- and Hyper-Kamiokande experiments, obtaining in both cases sub-threshold estimates.

astro-ph.HE↗

arXiv2023

UV signatures of magnetar formation and their crucial role for Gravitational Wave detection

The emission from shock breakouts (SBOs) represents the earliest electromagnetic (EM) signal emitted by cataclysmic events involving the formation or the merger of neutron stars (NSs). As such, SBOs carry unique information on the structure of their progenitors and on the explosion energy. The characteristic~SBO emission is expected in the UV range, and its detection is one of the key targets of~the ULTRASAT satellite. Among SBO sources, we focus on a specific class involving the formation of fast spinning magnetars in the core-collapse (CC) of massive stars. Fast spinning magnetars are expected to produce a specific signature in the early UV supernova light curve, powered by the extra spin energy quickly released by the NS. Moreover, they are considered as optimal candidates for the emission of long-transient gravitational wave (GW) signals, the detection of which requires early EM triggers to boost the sensitivity of dedicated GW search pipelines. We calculate early supernova UV light curves in the presence of a magnetar central engine, as a function of the explosion energy, ejecta mass and magnetar parameters. We then estimate the ULTRASAT detection horizon (z < 0.15) as a function of the same physical parameters, and the overall expected detection rate finding that magnetar-powered SBOs may represent up to 1/5 of the total events detected by ULTRASAT. Moreover, at the expected sensitivity of the LIGO/Virgo/Kagra O5 science run, one such event occurring within 5 Mpc will providean ideal trigger for a GW long transient search. Future GW detectors like the Einstein Telescope will push the horizon for joint EM-GW detections to 35-40 Mpc.

astro-ph.HE↗

arXiv2022

Nova Neutrinos in the Multi-Messenger Era

The recently discovered high energy emission from the recurrent nova RS Ophiuchi by Fermi-LAT ($>$ 100 MeV), H.E.S.S. and MAGIC ($>$ 100 GeV), hints towards a possible hadronic origin of this radiation component. From the observed high energy photon flux we derive the expected number of neutrino events that could be detected by present and future neutrino telescopes in the different energy ranges. We find that both hadronic and leptonic processes remain valid interpretations for this $ \ gamma $ emission. Preliminary estimates indicate that with the "next-generation" instrument IceCube-Gen2, the expected number of neutrino detections from Galactic novae is of the order of $\sim $ once per decade. Given the current uncertainties in the frequency of the occurrence of nova outbursts, the detection rate may possibly increase to up to once every $\sim $ three years.

astro-ph.HE↗

arXiv2022

GeV Signatures of Short Gamma-Ray Bursts in Active Galactic Nuclei

The joint detection of gravitational waves and the gamma-ray counterpart of a binary neutron star merger event, GW170817, unambiguously validates the connection between short gamma-ray bursts and compact binary object (CBO) mergers. We focus on a special scenario where short gamma-ray bursts produced by CBO mergers are embedded in disks of active galactic nuclei (AGN), and we investigate the $γ$-ray emission produced in the internal dissipation region via synchrotron, synchrotron self-Compton and external inverse-Compton (EIC) processes. In this scenario, isotropic thermal photons from the AGN disks contribute to the EIC component. We show that a low-density cavity can be formed in the migration traps, leading to the embedded mergers producing successful GRB jets. We find that the EIC component would dominate the GeV emission for typical CBO mergers with an isotropic-equivalent luminosity of $L_{j,\rm iso}=10^{48.5}~\rm erg~s^{-1}$ which are located close to the central supermassive black hole. Considering a long-lasting jet of duration $T_{\rm dur}\sim10^2-10^3$ s, we find that the future CTA will be able to detect its $25-100$ GeV emission out to a redshift $z=1.0$. {In the optimistic case, it is possible to detect the on-axis extended emission simultaneously with GWs within one decade using MAGIC, H.E.S.S., VERITAS, CTA, and LHAASO-WCDA. Early diagnosis of prompt emissions with Fermi-GBM and HAWC can provide valuable directional information for the follow-up observations.

astro-ph.HE↗

arXiv2022

Luminosity Selection for Gamma Ray Burst

There exists an inevitable scatter in intrinsic luminosity of Gamma Ray Bursts(GRBs). If there is relativistic beaming in the source, viewing angle variation necessarily introduces variation in the intrinsic luminosity function (ILF). Scatter in the ILF can cause a selection bias where distant sources that are detected have a larger median luminosity than those detected close by. Median luminosity divides any given population into equal halves. When the functional form of a distribution is unknown, it can be a more robust diagnostic than any that use trial functional forms. In this work we employ a statistical test based on median luminosity and apply it to test a class of models for GRBs. We assume that the GRB jet has a finite opening angle and that the orientation of the GRB jet is random relative to the observer.We calculate $L_{median}$ as a function of redshift by simulating GRBs empirically, theoretically and use the luminosity vs redshift {\it Swift} data in order to compare the theoretical results with the observed ones. The method accounts for the fact that at some redshifts there may be some GRBs that go undetected. We find that $L_{median}$ is extremely insensitive to the on-axis (i.e. maximal) luminosity of the jet.

astro-ph.HE↗

arXiv2022

Luminosity Selection for Gamma Ray Bursts

There exists an inevitable scatter in intrinsic luminosity of Gamma Ray Bursts(GRBs). If there is relativistic beaming in the source, viewing angle variation necessarily introduces variation in the intrinsic luminosity function(ILF). Scatter in the ILF can cause a selection bias where distant sources that are detected have a larger median luminosity than those detected close by. Median luminosity, as we know, divides any given population into equal halves. When the functional form of a distribution is unknown, it can be a more robust diagnostic than any that use trial functional forms. In this work we employ a statistical test based on median luminosity and apply it to test a class of models for GRBs. We assume that the GRB jet has a finite opening angle and that the orientation of the GRB jet is random relative to the observer. We parameterize the jet with constant Lorentz factor $Γ$ and opening angle $θ_0$. We calculate $L_{median}$ as a function of redshift with an average of 17 grbs in each redshift bin($dz=0.01$) empirically, theoretically and use Fermi GBM data, noting that SWIFT data is problematic as it is biased, specially at high redshifts. We find that $L_{median}$ is close to $L_{max}$ for sufficiently extended GRB jet and does not fit the data. We find an acceptable fit with the data when $Γ$ is between $100$ and $200$, $θ_0\leq 0.1$, provided that the jet material along the line of sight to the on axis observer is optically thick, such that the shielded maximum luminosity is well below the bare $L_{max}$. If we associate an on-axis observer with a classically projected monotonically decreasing afterglow, we find that their ILF is similar to those of off-jet observer which we associate with flat phase afterglows.

astro-ph.HE↗

arXiv2021

Estimating the Neutrino Flux from Choked Gamma-Ray Bursts

The strong constraints from the Fermi-LAT data on the isotropic gamma-ray background suggest that the neutrinos observed by IceCube might possibly come from sources that are hidden to gamma-ray observations. A possibility recently discussed in the literature is that neutrinos may come from jets of collapsing massive stars which fail to break out of the stellar envelope, and for this reason they are known as choked jets, or choked Gamma-Ray Bursts (GRBs). In this paper, we estimate the neutrino flux and spectrum expected from these sources, focusing on Type II SNe. We perform detailed calculations of pg interactions, accounting for all the neutrino production channels and scattering angles. We provide predictions of expected event rates for operating neutrino telescopes, such as ANTARES and IceCube, as well as for the future generation telescope KM3NeT. We find that for GRB energies channeled into protons spanning between 10^51 - 10^53 erg, choked GRBs may substantially contribute to the observed astrophysical neutrino flux, if their local rate is 80 - 1 Gpc^-3 yr^-1 respectively.

astro-ph.HE↗