arXiv subjects

Alberto Colombo

Publications and source records attributed to Alberto Colombo.

8 recordsLinked to original sources

arXiv2026

Gamma-ray Bursts and Kilonovae from Gravitational Wave Events

The detection of gravitational waves (GWs) from binary black holes in 2015 and the joint GW-electromagnetic (EM) observation of the binary neutron star merger GW170817 set a milestone in the multimessenger era in astrophysics. After four observing runs by the LIGO, Virgo, and KAGRA interferometers, a new cycle is planned for 2028, paving the way for next-generation detectors in the 2030s -- such as the Einstein Telescope, Cosmic Explorer, and LISA. The prospects for joint GW-EM studies, including kilonova searches in wide optical surveys, are vast but demanding. In the radio domain, connected interferometers and VLBI arrays have already proven essential in constraining the ejecta properties of GW170817. Radio emission from gamma-ray burst (GRB) afterglows, whether on- or off-axis, remains detectable for very long time, making radio observations the most effective method for identifying and tracking GW merger counterparts. These observations enable precise characterization of system evolution, detailed probing of GRB jet structures, and possible detection of misaligned jets once their velocity becomes non-relativistic. Even in its initial configuration (AA*), the SKAO will provide the sensitivity and field of view needed to complement GW counterpart searches during O5 and beyond, offering unmatched capabilities for long-term monitoring. Furthermore, independent of the GW detections, SKAO will enable population studies of the properties of both long (produced by the collapse of massive stars) and short (produced by the merger of neutron stars) GRBs, of their jets and of their environment. We present an overview of this evolving observational landscape and of the key scientific questions SKAO will address.

astro-ph.HE↗

arXiv2026

Cosmology from Synergies Between SKAO Surveys and Gravitational Wave Observations

Both radio surveys and gravitational wave observations have the potential to probe unprecedented volumes in the Universe with systematics independent of existing cosmological probes. This gives them the potential, especially in combination, to solve some of the outstanding issues in cosmology. Here we show how the use of radio observations as electromagnetic signals tracing large scale structures can be used to provide information on gravitational wave \textit{standard sirens}. By providing a way to link luminosity distance to redshift, this combination can constrain the expansion history of the Universe, and provide information on the Hubble constant ($H_0$). We describe the utility of SKA-Mid neutral hydrogen (\hi) intensity maps, \hi\ galaxy redshift surveys, and continuum galaxy surveys compared to and in conjunction with large contemporaneous optical surveys. Such radio tracers provide a unique, large volume and high redshift information for gravitational wave source, capable of probing effectively the expansion history of the Universe $H(z)$.

astro-ph.CO↗

arXiv2025

Non-Parametric Reconstruction of the Hubble Parameter from the Fourth Gravitational Wave Transient Catalog and DESI Baryonic Acoustic Oscillations

The release of the fourth Gravitational Wave Transient Catalog (GWTC-4.0) by the LIGO-Virgo-KAGRA collaboration includes more than 200 compact binary coalescence (CBC) candidates that can be used to probe the cosmic expansion. The population of merging binary black holes has been used so far to provide a constraint on the Hubble constant and dark matter fraction under the hypothesis of a flat-$\Lambda$-Cold-Dark-Matter Universe. In this work, we provide the first non-parametric constrain on the Hubble parameter from 137 dark sirens reported in GWTC-4.0. We employ the relation between detector and source frame masses for detected GW signals, to obtain a statistical redshift evaluation for the population of binary black holes (BBHs). We model the Hubble parameter as a non-parametric autoregressive process in terms of the scale factor, using splines. In addition, we introduce two novel features: the use of \textit{anchor} points for $H(z)$ derived from an external probe - here, Baryon Acoustic Oscillations (BAOs) - and a constraining power coefficient that quantifies where the inference is most data-driven by GW detections. We highlight three key findings: (i) using GWs alone, the Hubble parameter determination is the most GW-data-driven around redshift $z = 0.44$, yielding to $H(0.44) = 92.3_{-36.6}^{+29.9}\rm\, km s^{-1} Mpc^{-1}$. Its value at $z = 0$, the Hubble constant, is therefore less constrained by the GW data. (ii) The Hubble parameter inferred from analyses assuming a flat-$\Lambda$CDM cosmological model is strongly affected by the cosmological model assumption. (iii) Introducing an anchor point for $H(z)$ enhances the inferred constraints and provides a clear visualization of the redshift range where GWs contribute most to the constraining power.

astro-ph.CO↗

arXiv2025

The Science of the Einstein Telescope

Einstein Telescope (ET) is the European project for a gravitational-wave (GW) observatory of third-generation. In this paper we present a comprehensive discussion of its science objectives, providing state-of-the-art predictions for the capabilities of ET in both geometries currently under consideration, a single-site triangular configuration or two L-shaped detectors. We discuss the impact that ET will have on domains as broad and diverse as fundamental physics, cosmology, early Universe, astrophysics of compact objects, physics of matter in extreme conditions, and dynamics of stellar collapse. We discuss how the study of extreme astrophysical events will be enhanced by multi-messenger observations. We highlight the ET synergies with ground-based and space-borne GW observatories, including multi-band investigations of the same sources, improved parameter estimation, and complementary information on astrophysical or cosmological mechanisms obtained combining observations from different frequency bands. We present advancements in waveform modeling dedicated to third-generation observatories, along with open tools developed within the ET Collaboration for assessing the scientific potentials of different detector configurations. We finally discuss the data analysis challenges posed by third-generation observatories, which will enable access to large populations of sources and provide unprecedented precision.

gr-qc↗

arXiv2025

Multi-messenger observations in the Einstein Telescope era: binary neutron star and black hole - neutron star mergers

The Einstein Telescope (ET), a proposed next-generation gravitational wave (GW) observatory, will expand the reach of GW astronomy of stellar-mass compact object binaries to unprecedented distances, enhancing opportunities for multi-messenger observations. Here we investigate multi-messenger emission properties of binary neutron star (NSNS) and black hole-neutron star (BHNS) mergers detectable by ET, providing projections to optimize observational strategies and maximize scientific insights from these sources. Using a synthetic population of compact binary mergers, we model each source's GW signal-to-noise ratio, sky localization uncertainty, kilonova (KN) light curves in optical and near-infrared bands, fluence of the relativistic jet gamma-ray burst (GRB) prompt emission and afterglow light curves across radio, optical, X-ray and very high energy wavelengths. We analyze multi-messenger detectability prospects for ET as a standalone observatory with two different configurations and within a network of next-generation GW detectors. ET will detect over $10^4$ NSNS mergers annually, enabling potential observation of tens to hundreds of electromagnetic (EM) counterparts. BHNS mergers have more limited multi-messenger prospects, but joint GW-EM rates will increase by an order of magnitude compared to current-generation instruments. We quantify uncertainties due to the NS equation of state (EoS) and mass distribution of NSNSs, as well as the NS EoS and BH spin for BHNSs. While a single ET will achieve an impressive GW detection rate, the fraction of well-localized events is orders of magnitude lower than in a network with additional detectors. This significantly limits efficient EM follow-up and science cases requiring well-characterized counterparts or early observations. The challenge is even greater for BHNS mergers due to their low EM rate.

astro-ph.HE↗

arXiv2024

Kilonova parameters estimation with LSST at Vera C. Rubin Observatory

The up-coming Vera Rubin Observatory's Legacy Survey of Space and Time (LSST) opens a new opportunity to rapidly survey the southern Sky at optical wavelenghts (\ie ugrizy bands). In this study, we aim to test the possibility of using LSST observations to constrain the mass and velocity of different KN ejecta components from the observation of a combined set of light curves from GRB afterglows and KN\ae. We used a sample of simulated light curves from the aforementioned events as they would have been seen during the LSST survey to study how observing strategies' choice impacts the parameters' estimation. We found that the observing strategy design to be the best compromise between light curves coverage, observed filters and fit reliability involves a high number of visits with long gap pairs of about 4 hours every 2 nights in the same or different filters. The features of the observing strategy will allow us to recognize the different stages of the light curve evolution and gather observations in at least 3 filters.

astro-ph.HE↗

arXiv2023

Multi-messenger prospects for black hole - neutron star mergers in the O4 and O5 runs

The existence of merging black hole-neutron star (BHNS) binaries has been ascertained through the observation of their gravitational wave (GW) signals. However, to date, no definitive electromagnetic (EM) emission has been confidently associated with these mergers. Such an association could help unravel crucial information on these systems, for example, their BH spin distribution, the equation of state (EoS) of NS and the rate of heavy element production. We model the multi-messenger (MM) emission from BHNS mergers detectable during the fourth (O4) and fifth (O5) observing runs of the LIGO-Virgo-KAGRA GW detector network, in order to provide detailed predictions that can help enhance the effectiveness of observational efforts and extract the highest possible scientific information from such remarkable events. Our methodology is based on a population synthesis-approach, which includes the modelling of the signal-to-noise ratio of the GW signal in the detectors, the GW-inferred sky localization of the source, the kilonova (KN) optical and near-infrared light curves, the relativistic jet gamma-ray burst (GRB) prompt emission peak photon flux, and the GRB afterglow light curves in the radio, optical and X-ray bands. The resulting prospects for BHNS MM detections during O4 are not promising, with a GW detection rate of $15.0^{+15.4}_{-8.8}$ yr$^{-1}$, but joint MM rates of $\sim 10^{-1}$ yr$^{-1}$ for the KN and $\sim 10^{-2}$ yr$^{-1}$ for the jet-related emission. In O5 we find an overall increase in expected detection rates by around an order of magnitude, owing to both the enhanced sensitivity of the GW detector network, and the coming online of future EM facilities. Finally, we discuss direct searches for the GRB radio afterglow with large-field-of-view instruments as a new possible follow-up strategy in the context of ever-dimming prospects for KN detection.

astro-ph.HE↗

arXiv2019

Filling the Mass Gap: How Kilonova Observations can Unveil the Nature of the Compact Object Merging with the Neutron Star

In this letter we focus on the peculiar case of a coalescing compact-object binary whose chirp mass is compatible both with a neutron star-neutron star and black hole-neutron star system, with the black hole in the $\sim 3-5M_\odot$ range defined as the "mass gap". Some models of core-collapse supernovae predict the formation of such low-mass black holes and a recent observation seems to confirm their existence. Here we show that the nature of the companion to the neutron star can be inferred from the properties of the kilonova emission once we know the chirp mass, which is the best constrained parameter inferred from the gravitational signal in low-latency searches. In particular, we find that the kilonova in the black hole-neutron star case is far more luminous than in the neutron star-neutron star case, even when the black hole is non spinning. The difference in the kilonovae brightness arises primarily from the mass ejected during the merger. Indeed, in the considered interval of chirp masses, the mass ejection in double neutron star mergers is at its worst as the system promptly forms a black hole. Instead mass ejection for black hole-neutron star case is at its best as the neutron stars have low mass/large deformability. The kilonovae from black hole-neutron star systems can differ by two to three magnitudes. The outcome is only marginally dependent on the equation of state. The difference is above the systematics in the modeling.

astro-ph.HE↗