arXiv subjects

G. Gianfagna

Publications and source records attributed to G. Gianfagna.

9 recordsLinked to original sources

arXiv2026

Comparative properties of X-Ray Flashes and Gamma-Ray Bursts from BeppoSAX observations of Fast X-ray Transients

We present the homogeneous and complete sample of 96 bona-fide Gamma Ray Bursts (GRBs) detected by the Wide Field Cameras and Gamma Ray Burst Monitor of BeppoSAX. We derive the spectral and temporal properties of the prompt emission, and assess the properties of the soft population of GRB, namely X-ray flashes (XRFs) in comparison with normal GRBs. We find that 36 events are XRFs, 40 X-ray rich events (XRR), and 20 normal GRBs. We analyze the distribution of the spectral parameters of the Band function, finding that the spectral indexes of the three classes are broadly similar. On the contrary the peak energy is the parameter driving the spectra shape, from 8.5 keV for XRF keV to 83 keV for GRBs. For the 67 events that are detected in both instruments we find that 9 events exhibit a soft X-ray precursor taking place from 14 to 105 s before the onset of the gamma-ray burst. About 90\% of the events that were identified in real time exhibit an X-ray afterglow, with a similar fraction for the three classes. In the optical and radio the the corresponding fractions are 35% and 33%. All the similarities in the spectrum, duration and afterglow properties suggest common progenitors for the three classes, where the differences are likely a combination of the effect of different baryon loading, energy, structure and orientation of the jet with respect to the observer. A comparison with Einstein Probe shows that the latter, thanks to its sensitivity, reaches out to a population of fainter and more numerous events, whose presence was firstly hinted at by the unique very low luminosity BeppoSAX GRB980425.

astro-ph.HE↗

arXiv2026

BeppoSAX-WFC catalog of fast X-ray transients

We performed a search for fast X-ray transients (FXTs), with durations longer than one second and less than one day, through data of the Wide Field Camera (WFC) instrument onboard the BeppoSAX X-ray observatory collected between June 1996 and April 2002. (..) We focused our search on gamma-ray bursts (GRBs), X-ray flashes (XRFs), X-ray flares from high-mass X-ray binaries and stellar flares, while Type-I and II X-ray bursts from Galactic neutron stars were excluded. 149 such fast transient events were detected. 63 of these are new to the literature. 38 flares are identified with 22 nearby stars. Three stars have never been seen flaring before in X-rays or optical (NLTT 51688, GR Dra and UCAC4 255-003783). We find that the MeV transient GRO J1753+57 is most likely the same object as GR Dra rather than an AGN as previously thought. Eleven flares were detected from known high-mass X-ray binaries with irregular wind accretion (four of which are of the subclass of supergiant fast X-ray transients). 100 GRBs were identified of which 24 have not been published before. We classify 37% of the X-ray detected GRBs as XRFs with relatively large X-ray to gamma-ray flux ratio, gamma-rays being measured with the BeppoSAX Gamma Ray Burst Monitor. The duration/spectral hardness distribution of all FXTs is bimodal, separating the group roughly in transients shorter and longer than 1 ksec and with relatively hard and soft spectra, respectively. We identify the 'short' FXTs as GRBs and XRFs and the `long' FXTs as flares from nearby late-type stars and X-ray binaries. The BeppoSAX-WFC FXT sample is found to be consistent with the one observed by Einstein Probe, when the sensitivity of the two instruments is taken into account.

astro-ph.HE↗

arXiv2026

ENGRAVE follow-up of a type IIb supernova spatially coincident with the sub-threshold gravitational wave trigger S250818k

The candidate gravitational wave (GW) event S250818k was one of only three non-retracted LIGO-Virgo-KAGRA public alerts issued during the fourth observing run of the network (O4) with a binary neutron star (BNS) merger classification probability exceeding one percent. This triggered a prompt search for a potential electromagnetic (EM) counterpart in the large localisation error region (949 deg$^2$ projected in the sky at 90% credible level). The transient SN2025ulz, discovered by the Zwicky Transient Facility (ZTF) during the search, attracted a great deal of attention due to a potential spatial and temporal coincidence, and due to its initial fast decay and featureless spectrum. Here, we report on the follow up of this transient by the Electromagnetic counterparts of gravitational wave sources at the Very Large Telescope (ENGRAVE) Collaboration. We conducted an extensive multi-wavelength observational campaign, which led to the spectral classification of the transient as a type IIb supernova (SN), indicating that it is unrelated to the candidate GW event. In this article, we describe our observing strategies, data reduction, and interpretation. All of our results confirm and strengthen our classification of the source, and also show that shock cooling tails associated with type IIb SNe are one of the most prominent contaminants in kilonova searches.

astro-ph.HE↗

arXiv2025

SVOM GRB 250314A at z $\simeq$ 7.3: an exploding star in the era of reionization

Most long Gamma-ray bursts originate from a rare type of massive stellar explosion. Their afterglows, while rapidly fading, can be initially extremely luminous at optical/near-infrared wavelengths, making them detectable at large cosmological distances. Here we report the detection and observations of GRB 250314A by the SVOM satellite and the subsequent follow-up campaign with the near-infrared afterglow discovery and the spectroscopic measurements of its redshift z $\simeq$ 7.3 . This burst happened when the Universe was only $\sim$ 5% of its current age. We discuss the signature of these rare events within the context of the SVOM operating model, and the ways to optimize their identification with adapted ground follow-up observation strategies.

astro-ph.HE↗

arXiv2025

The impact of baryons on the sparsity of simulated galaxy clusters from The Three Hundred Project

Measurements of the sparsity of galaxy clusters can be used to probe the cosmological information encoded in the host dark matter halo profile, and infer constraints on the cosmological model parameters. Key to the success of these analyses is the control of potential sources of systematic uncertainty. As an example, the presence of baryons can alter the cluster sparsity with respect to predictions from N-body simulations. Similarly, a radial dependent mass bias, as in the case of masses inferred under the hydrostatic equilibrium (HE) hypothesis, can affect sparsity estimates. We examine the imprint of baryonic processes on the sparsity statistics. Then, we investigate the relation between cluster sparsities and gas mass fraction. Finally, we perform a study of the impact of HE mass bias on sparsity measurements and the implication on cosmological parameter inference analyses. We use catalogues of simulated galaxy clusters from The Three Hundred project and run a comparative analysis of the sparsity of clusters from N-body/hydro simulations implementing different feedback model scenarios. Sparsities which probe the mass profile across a large radial range are affected by the presence of baryons in a way that is particularly sensitive to astrophysical feedback, whereas those probing exclusively external cluster regions are less affected. In the former case, we find the sparsities to be moderately correlated with measurements of the gas fraction in the inner cluster regions. We infer constraints on $S_8$ using synthetic average sparsity measurements generated to evaluate the impact of baryons, selection effects and HE bias. In the case of multiple sparsities these lead to highly bias results. Hence, we calibrate linear bias models that enable us to correct for these effects and recover unbiased constraints that are significantly tighter than those inferred from single sparsity analyses.

astro-ph.CO↗

arXiv2024

Soft X-ray prompt emission from a high-redshift gamma-ray burst EP240315a

Long gamma-ray bursts (GRBs) are believed to originate from core collapse of massive stars. High-redshift GRBs can probe the star formation and reionization history of the early universe, but their detection remains rare. Here we report the detection of a GRB triggered in the 0.5--4 keV band by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission, designated as EP240315a, whose bright peak was also detected by the Swift Burst Alert Telescope and Konus-Wind through off-line analyses. At a redshift of $z=4.859$, EP240315a showed a much longer and more complicated light curve in the soft X-ray band than in gamma-rays. Benefiting from a large field-of-view ($\sim$3600 deg$^2$) and a high sensitivity, EP-WXT captured the earlier engine activation and extended late engine activity through a continuous detection. With a peak X-ray flux at the faint end of previously known high-$z$ GRBs, the detection of EP240315a demonstrates the great potential for EP to study the early universe via GRBs.

astro-ph.HE↗

arXiv2023

The Three Hundred project: A Machine Learning method to infer clusters of galaxies mass radial profiles from mock Sunyaev-Zel'dovich maps

We develop a machine learning algorithm to infer the 3D cumulative radial profiles of total and gas mass in galaxy clusters from thermal Sunyaev-Zel'dovich effect maps. We generate around 73,000 mock images along various lines of sight using 2,522 simulated clusters from the \thethreehundred{} project at redshift $z< 0.12$ and train a model that combines an autoencoder and a random forest. Without making any prior assumptions about the hydrostatic equilibrium of the clusters, the model is capable of reconstructing the total mass profile as well as the gas mass profile, which is responsible for the SZ effect. We show that the recovered profiles are unbiased with a scatter of about $10\%$, slightly increasing towards the core and the outskirts of the cluster. We selected clusters in the mass range of $10^{13.5} \leq M_{200} /(\hMsun) \leq 10^{15.5}$, spanning different dynamical states, from relaxed to disturbed halos. We verify that both the accuracy and precision of this method show a slight dependence on the dynamical state, but not on the cluster mass. To further verify the consistency of our model, we fit the inferred total mass profiles with an NFW model and contrast the concentration values with those of the true profiles. We note that the inferred profiles are unbiased for higher concentration values, reproducing a trustworthy mass-concentration relation. The comparison with a widely used mass estimation technique, such as hydrostatic equilibrium, demonstrates that our method recovers the total mass that is not biased by non-thermal motions of the gas.

astro-ph.CO↗

arXiv2021

The Three Hundred-NIKA2 Sunyaev-Zeldovich Large Program twin samples: Synthetic clusters to support real observations

The simulation database of THE THREE HUNDRED Project has been used to pick synthetic clusters of galaxies with properties close to the observational targets of the NIKA2 camera Sunyaev-Zeldovich (SZ) Large Program. Cross-matching of cluster parameters such as mass and redshift of the cluster in the two databases has been implemented to generate the so-called twin samples for the Large Program. This SZ Large Program is observing a selection of galaxy clusters at intermediate and high redshift $\left( 0.5 < z < 0.9 \right)$, covering one order of magnitude in mass. These are SZ-selected clusters from the Planck and Atacama Cosmology Telescope catalogs, wherein the selection is based on their integrated Compton parameter values, $Y_{500}$: the value of the parameter within the characteristics radius $R_{500}$. THE THREE HUNDRED hydrodynamical simulations provide us with hundreds of clusters satisfying these redshift, mass, and $Y_{500}$ requirements. In addition to the standard post-processing analysis of the simulation, mock observational maps are available mimicking X-ray, optical, gravitational lensing, radio, and SZ observations of galaxy clusters. The primary goal of employing the twin samples is to compare different cluster mass proxies from synthetic X-ray, SZ effect and optical maps (via the velocity dispersion of member galaxies and lensing $κ$-maps) of the clusters. Eventually, scaling laws between different mass proxies and the cluster mass will be cross-correlated to reduce the scatter on the inferred mass and the mass bias will be related to various physical parameters.

astro-ph.CO↗

arXiv2019

Confirmation of NIKA2 investigation of the Sunyaev-Zel'dovich effect by using synthetic clusters of galaxies

The NIKA2 Sunyaev-Zel'dovich Large Program (SZLP) is focused on mapping the thermal SZ signal of a representative sample of selected Planck and ACT clusters spanning the redshift range 0.5<$z$<0.9. Hydrodynamical N-body simulations prove to be a powerful tool to endorse NIKA2 capabilities for estimating the impact of IntraCluster Medium (ICM) disturbances when recovering the pressure radial profiles. For this goal we employ a subsample of objects, carefully extracted from the catalog "Marenostrum MUltidark SImulations of galaxy Clusters" (MUSIC), spanning equivalent redshift and mass ranges as the LPSZ. The joint analysis of real observations of the tSZ with NIKA2 and Planck enables to validate the NIKA2 pipeline and to estimate the ICM pressure profiles. Moreover, the possibility to identify "a priori" the dynamical state of the selected synthetic clusters allows us to verify the impact on the recovered ICM profile shapes and their scatters. Morphological analysis of maps of the Compton parameter seems to be a way to observationally segregate the sample based on the dynamical state in relaxed and disturbed synthetic clusters.

astro-ph.CO↗