arXiv subjects

G. Lombardi

Publications and source records attributed to G. Lombardi.

At least 19 recordsLinked to original sources

arXiv2025

Discovery and Analysis of Afterglows from Poorly Localised GRBs with the Gravitational-wave Optical Transient Observer (GOTO) All-sky Survey

Gamma-ray bursts (GRBs), particularly those detected by wide-field instruments such as the Fermi/GBM, pose a challenge for optical follow-up due to their large initial localisation regions, leaving many GRBs without identified afterglows. The Gravitational-wave Optical Transient Observer (GOTO), with its wide field of view, dual-site coverage, and robotic rapid-response capability, bridges this gap by rapidly identifying and localising afterglows from alerts issued by space-based facilities, including Fermi, SVOM, Swift, and EP, providing early optical positions for coordinated multiwavelength follow-up. In this paper, we present optical afterglow localisation and multiband follow-up of five Fermi/GBM (240619A, 240910A, 240916A, 241002B, and 241228B) and two MAXI/GSC (240122A and 240225B) triggered long GRBs (LGRBs) discovered by GOTO in 2024. Spectroscopy for six GRBs (no spectroscopic data for GRB 241002B) with VLT/X-shooter and GTC/OSIRIS yields precise redshifts spanning $z\approx0.40-$3.16 and absorption-line diagnostics of host and intervening systems. Radio detections for four events confirm the presence of long-lived synchrotron emission. Prompt-emission analysis with Fermi and MAXI data reveals a spectrally hard population, with two bursts lying $>3σ$ above the Amati relation. Although their optical afterglows resemble those of typical LGRBs, the prompt spectra are consistently harder than the LGRBs' average. Consistent modelling of six GOTO-discovered GRB afterglows yields jet half-opening angles of a few degrees and beaming-corrected kinetic energies ($E_{jet}\sim10^{51-52}$)erg, consistent with the canonical LGRB population. These findings suggest that optical discovery of poorly localised GRBs may be subject to observational biases favouring luminous events with high spectral peak energy, while also providing insight into jet microphysics and central engine diversity.

astro-ph.HE↗

arXiv2025

Effective and anatomical connectivity of the dorso-central insula during the processing of action forms

In both human and monkeys the observation and execution of actions produced the activation of a network consisting of parietal and frontal areas. Although this network is involved in the encoding of the action goal, it does not consider the affective component of the action: vitality form (VF). Several studies showed that the observation and execution of actions conveying VFs selectively activated the dorso-central insula (DCI). In the present study, we aimed to clarify, by using Dynamic Causal Modeling (DCM), the direction of the information flow across DCI, parieto-frontal areas (PMv, IPL) and posterior superior temporal sulcus (pSTS) during both observation and execution of actions conveying VFs. Results indicate that, during observation, DCI receives the visual input from pSTS, and, in turn, sends it to the fronto-parietal network. Moreover, DCI significantly modulates PMv. Conversely, during execution, the motor input starts from PMv, reaches DCI and IPL, with a significant modulation from PMv to DCI. The reciprocal exchange of information between PMv and DCI suggests that these areas work closely together in the VFs action processing. An additional tractography analysis corroborates our DCM models, showing a correspondence between functional connections and anatomical tracts.

q-bio.NC↗

arXiv2025

Assessing interstellar comet 3I/ATLAS with the 10.4 m Gran Telescopio Canarias and the Two-meter Twin Telescope

Context. Theories of the formation and evolution of small bodies in planetary systems predict that they may escape into interstellar space at any time. After having characterized just two such interlopers -1I/2017 U1 (Oumuamua) and 2I/Borisov more questions were raised than answered. Assessing the recently discovered interstellar comet 3I/ATLAS will only broaden our understanding of this complex topic. Aims. Here, we investigate the spectral, cometary, and rotational properties of 3I/ATLAS as well as its dynamical context. Methods. We identified the spectral type of 3I/ATLAS from the visible reflectance spectrum and used photometric observations to derive its level of activity and rotational properties. Observational data were obtained with the OSIRIS camera spectrograph at the 10.4 m Gran Telescopio Canarias and the Two-meter Twin Telescope. We used N-body simulations and statistical analyses of Gaia DR3 data to investigate the origin of 3I/ATLAS and its Galactic background. Results. Interstellar comet 3I/ATLAS has a visible spectrum slightly redder than those of D-type asteroids, 1I/'Oumuamua and 2I/Borisov, with a spectral slope of 18.3%/1000 A in the 4000-9000 A range, which is similar to those of TNOs and Centaurs. It has a conspicuous coma and its rotation period is 16.79 h. The heliocentric components of its Galactic velocity were (U, V, W) = (-51.233, -19.456, 18.930) km/s with a radiant in Sagittarius. The analysis of a sample of kinematic analogs of 3I/ATLAS extracted from Gaia DR3 suggests that its parent system is part of the Galactic thin disk and includes a solar-like star with slightly sub-solar metallicity.

astro-ph.EP↗

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

Assessment of the AlUla Manara astronomical site in Saudi Arabia using ECMWF ERA5 Reanalysis data

As part of Saudi Arabia Vision 2030 and under the guidance of the Royal Commission for AlUla (RCU), efforts are underway to establish AlUla Manara as the Kingdom first major astronomical observatory. This study presents a preliminary assessment of the site based on ECMWF ERA5 reanalysis data to evaluate its suitability for hosting a 4m-class optical-IR telescope. AlUla Manara is located on a remote plateau 74 km north of the historical town of AlUla and was recently designated as an International Dark Sky Park. The analysis focuses on key astro-meteorological parameters such as seeing, temperature regimes, wind patterns, cloud cover and precipitable water vapor (PWV). Results show a median nighttime seeing of 1.5 arcsec, a median cold season PWV of 3.2 mm, and over 79% of nighttime hours with clear sky conditions. Wind regimes are generally mild, posing no constraints on infrastructure. The analysis includes three further sites in the Kingdom, namely Volcanic Top, Ward Mountain, and Dubba Mountain. These sites exhibit better turbulence conditions, but are located outside RCU jurisdiction. Nevertheless, AlUla Manara remains a competitive candidate thanks to its alignment with broader regional development goals. To validate these preliminary results, a dedicated Astronomical Site Monitor has been deployed on site to support the design and operational planning of the observatory.

astro-ph.IM↗

arXiv2024

The ground calibration of the HERMES-Pathfinder payload flight models

HERMES-Pathfinder is a space-borne mission based on a constellation of six nano-satellites flying in a low-Earth orbit. The 3U CubeSats, to be launched in early 2025, host miniaturized instruments with a hybrid Silicon Drift Detector/scintillator photodetector system, sensitive to both X-rays and gamma-rays. A seventh payload unit is installed onboard SpIRIT, an Australian-Italian nano-satellite developed by a consortium led by the University of Melbourne and launched in December 2023. The project aims at demonstrating the feasibility of Gamma-Ray Burst detection and localization using miniaturized instruments onboard nano-satellites. The HERMES flight model payloads were exposed to multiple well-known radioactive sources for spectroscopic calibration under controlled laboratory conditions. The analysis of the calibration data allows both to determine the detector parameters, necessary to map instrumental units to accurate energy measurements, and to assess the performance of the instruments. We report on these efforts and quantify features such as spectroscopic resolution and energy thresholds, at different temperatures and for all payloads of the constellation. Finally we review the performance of the HERMES payload as a photon counter, and discuss the strengths and the limitations of the architecture.

astro-ph.IM↗

arXiv2024

Characterization of avalanche photodiodes (APDs) for the CUbesat Solar Polarimeter (CUSP) mission

The CUbesat Solar Polarimeter (CUSP) project is a CubeSat mission orbiting the Earth aimed to measure the linear polarization of solar flares in the hard X-ray band by means of a Compton scattering polarimeter. CUSP will allow the study of the magnetic reconnection and particle acceleration in the flaring magnetic structures of our star. CUSP is a project in the framework of the Alcor Program of the Italian Space Agency aimed at developing new CubeSat missions. It is approved for a Phase B study. In this work, we report on the characterization of the Avalanche Photodiodes (APDs) that will be used as readout sensors of the absorption stage of the Compton polarimeter. We assessed the APDs gain and energy resolution as a function of temperature by irradiating the sensor with a \textsuperscript{55}Fe radioactive source. Moreover, the APDs were also characterized as being coupled to a GAGG scintillator.

astro-ph.IM↗

arXiv2022

Laser Guide Star uplink beam: scattering and Raman emission measurements with the 10.4m Gran Telescopio CANARIAS

Laser Guide Star Adaptive Optics (LGS-AO) is becoming routine in several astronomical observatories. The use of powerful lasers generates sensible Raman emissions on the uplink laser beam path, plus secondary Rayleigh scattering from atmospheric molecules and Mie scattering from aerosols. This paper reports the results of a campaign done with the 10.4m Gran Telescopio CANARIAS (GTC); this campaign was undertaken to assess the spectral and photometric contamination coming from a 589 nm laser uplink beam scattering and Raman emission induced on the GTC spectro-imager OSIRIS by laser launched about 1 km off-axis. The photometric contamination is due to primary and secondary scattering of the uplink photons, as well by the Raman inelastic scattering. We have propagated the laser beam creating a mesospheric LGS, then pointed and focused the GTC telescope toward the uplink laser beam, at different heights and up to the LGS, taking into account the observing geometry. In our observations, the Raman emissions for O2 and N2 vibrational lines are visible at 20 km, weakening with altitude and becoming undetectable above 30 km. The scattering of the focused uplink beam is detectable at less than +/-0.2 arcmin from the center of the beam, while for the focused LGS the scattering is narrower, being detectable at less than +/-0.1 arcmin around the plume. Recommendations for Laser Traffic Control Systems (LTCS) are given accordingly.

astro-ph.IM↗

arXiv2020

Picosecond two-photon absorption laser induced fluorescence (ps-TALIF) in krypton: the role of photoionization on the density depletion of the fluorescing state Kr 5p'[3/2]$_2$

The present study focuses on the application of a picosecond (ps) TALIF technique in krypton (Kr) at variable pressure (0.1-10 mbar). The laser intensity (I, units W.cm$^{-2}$) is tuned between 1 and 480 MW.cm$^{-2}$, and the depletion of the density of the Kr 5p'[3/2]$_2$ fluorescing state through photoionization (PIN) and amplified stimulated emission (ASE) is investigated. This is done by combining TALIF experiments with a simple 0D numerical model. We demonstrate that for a gas pressure of 3 mbar and 15 < $\le$ 480 MW.cm$^{-2}$, a saturated fluorescence signal is obtained, which is largely attributed to PIN, ASE being negligible. Also, a broadening of the two-photon absorption line (i.e. 4p$^6$ $^1$S0$\to$5p'[3/2]$_2$) is recorded due to the production of charged species through PIN, inducing a Stark effect. For I$\le$15 MW.cm$^{-2}$, though, PIN is significantly limited, the absorption line is noticeably narrowed, and the quadratic dependence of the TALIF signal intensity versus the laser energy is obtained. Thus, in this case, the investigated Kr TALIF scheme, using the 5p'[3/2]$_2\to$5s[3/2]$_1$ fluorescence channel, can be used for calibration purposes in ps-TALIF experiments. These results are of interest for fundamental research since most ps-TALIF studies performed in Kr do not investigate in detail the role of PIN and ASE on the depletion of the Kr 5p'[3/2]$_2$ state density. Moreover, this work contributes to the development of ps-TALIF for determining absolute densities and quenching coefficients of H and N atoms in plasmas. This is useful in numerous plasma-based applications (e.g. thin film synthesis, biomedical treatments, plasma-assisted combustion, ...), for which the knowledge of the density/kinetics of reactive atoms is essential.

physics.atom-ph↗

arXiv2020

A simplified procedure to capture N(4S) kinetics during the transients of a strongly emissive pulsed ECR plasma using TALIF

A simplified and straightforward methodology that may be used to measure N(4 S) density by TALIF technique in strongly emissive plasmas is presented. The method makes use of the absorption peak intensities instead of the fully integrated absorption line intensity. The use of this method, along with a physics-based fitting/filtering procedure enables strongly reducing the experimental uncertainty and performing measurement even in strongly emitting discharges. After validation, the method was employed to investigate the transients of a strongly emissive pulsed microwave discharge. We especially showed the existence of unexpected increase of N(4 S) density at the early stage of the transition from high-to lowpower phase. The use of a self-consistent quasi-homogenous plasma model taking into account a detailed state-to-state kinetics, enables to attribute this enhancement to surface deexcitation of N(2 D) and N(2 P).

physics.plasm-ph↗

arXiv2017

On-sky demonstration of matched filters for wavefront measurements using ELT-scale elongated laser guide stars

The performance of adaptive optics systems is partially dependant on the algorithms used within the real-time control system to compute wavefront slope measurements. We demonstrate use of a matched filter algorithm for the processing of elongated laser guide star (LGS) Shack-Hartmann images, using the CANARY adaptive optics instrument on the 4.2m William Herschel Telescope and the European Southern Observatory Wendelstein LGS Unit placed 40m away. This algorithm has been selected for use with the forthcoming Thirty Meter Telescope, but until now had not been demonstrated on-sky. From the results of a first observing run, we show that the use of matched filtering improves our adaptive optics system performance, with increases in on-sky H-band Strehl measured up to about a factor of 1.1 with respect to a conventional centre of gravity approach. We describe the algorithm used, and the methods that we implemented to enable on-sky demonstration.

astro-ph.IM↗

arXiv2015

Soliton core filling in superfluid Fermi gases with spin-imbalance

In this paper the properties of dark solitons in superfluid Fermi gases with spin-imbalance are studied by means of a recently developed effective field theory [S. N. Klimin, J. Tempere, G. Lombardi, J. T. Devreese, Eur. Phys. J. B 88, 122 (2015)] suitable to describe the BEC-BCS crossover in ultracold gases in an extended range of temperatures as compared to the usual Ginzburg-Landau treatments. The spatial profiles for the total density and for the density of the excess-spin component, and the changes of their properties across the BEC-BCS crossover are examined in different conditions of temperature and imbalance. The presence of population imbalance is shown to strongly affect the structure of the soliton excitation by filling its core with unpaired atoms. This in turn influences the dynamical properties of the soliton since the additional particles in the core have to be dragged along thus altering the effective mass.

cond-mat.quant-gas↗

arXiv2015

Finite temperature effective field theory and two-band superfluidity in Fermi gases

We develop a description of fermionic superfluids in terms of an effective field theory for the pairing order parameter. Our effective field theory improves on the existing Ginzburg - Landau theory for superfluid Fermi gases in that it is not restricted to temperatures close to the critical temperature. This is achieved by taking into account long-range fluctuations to all orders. The results of the present effective field theory compare well with the results obtained in the framework of the Bogoliubov - de Gennes method. The advantage of an effective field theory over Bogoliubov - de Gennes calculations is that much less computation time is required. In the second part of the paper, we extend the effective field theory to the case of a two-band superfluid. The present theory allows us to reveal the presence of two healing lengths in the two-band superfluids, to analyze the finite-temperature vortex structure in the BEC-BCS crossover, and to obtain the ground state parameters and spectra of collective excitations. For the Leggett mode our treatment provides an interpretation of the observation of this mode in two-band superconductors.

cond-mat.quant-gas↗

arXiv2013

On the comparison between MASS and G-SCIDAR techniques

The Multi Aperture Scintillation Sensor (MASS) and the Generalized-Scintillation Detection and Ranging (Generalized SCIDAR) are two instruments conceived to measure the optical turbulence (OT) vertical distribution on the whole troposphere and low stratosphere (~ 20 km) widely used in the astronomical context. In this paper we perform a detailed analysis/comparison of measurements provided by the two instruments and taken during the extended site testing campaign carried out on 2007 at Cerro Paranal and promoted by the European Southern Observatory (ESO). The main and final goal of the study is to provide a detailed estimation of the measurements reliability i.e dispersion of turbulence measurements done by the two instruments at different heights above the ground. This information is directly related to our ability in estimating the absolute value of the turbulence stratification. To better analyse the uncertainties between the MASS and the GS we took advantage of the availability of measurements taken during the same campaign by a third independent instrument (DIMM - Differential Imaging Motion Monitor) measuring the integrated turbulence extended on the whole 20 km. Such a cross-check comparison permitted us to define the reliability of the instruments and their measurements, their limits and the contexts in which their use can present some risk.

astro-ph.IM↗

arXiv2012

Re-calibrated Generalized-Scidar measurements at Cerro Paranal (VLT's site)

Generalized Scidar (GS) measurements taken at the Paranal Observatory in November/December 2007 in the context of a site qualification for the future European Extremely Large Telescope E-ELT are re-calibrated to overcome the bias induced on the CN2 profiles by a not correct normalization of the autocorrelation of the scintillation maps that has been recently identified in the GS technique. A complete analysis of the GS corrected measurements as well as of the corrected errors is performed statistically as well as on individual nights and for each time during all nights. The relative errors of the CN2 profiles can reach up to 60% in some narrow temporal windows and some vertical slabs, the total seeing up to 12% and the total integrated turbulence J up to 21%. However, the statistic analysis tells us that the absolute errors of the median values of the total seeing is 0.06 arcsec (relative error 5.6%), for the boundary seeing 0.05 arcsec (relative error 5.6%) and for the seeing in the free atmosphere 0.04 arcsec (relative error 9%). We find that, in spite of the fact that the relative error increases with the height, the boundary and the free atmosphere seeing contribute in an equivalent way to the error on the total seeing in absolute terms. Besides, we find that there are no correlations between the relative errors and the value of the correspondent seeing. The absolute error of the median value of the isoplanatic angle is 0.13 arcsec (relative error 6.9%).

astro-ph.IM↗

arXiv2011

Near-infrared thermal emissivity from ground based atmospheric dust measurements at ORM

We present an analysis of the atmospheric content of aerosols measured at Observatorio del Roque de los Muchachos (ORM; Canary Islands). Using a laser diode particle counter located at the Telescopio Nazionale Galileo (TNG) we have detected particles of 0.3, 0.5, 1.0, 3.0, 5.0 and 10.0 um size. The seasonal behavior of the dust content in the atmosphere is calculated. The Spring has been found to be dustier than the Summer, but dusty conditions may also occur in Winter. A method to estimate the contribution of the aerosols emissivity to the sky brightness in the near-infrared (NIR) is presented. The contribution of dust emission to the sky background in the NIR has been found to be negligible comparable to the airglow, with a maximum contribution of about 8-10% in the Ks band in the dusty days.

astro-ph.IM↗

arXiv2011

A study of NIR atmospheric properties at Paranal Observatory

In order to maximize the scientific return of the telescopes located at the Paranal Observatory, we analyse the properties of the atmosphere above Paranal in the near-infrared (NIR). We estimate atmospheric extinction in the spectral range 1.10-2.30 um (J, Js, H, and Ks) using standard stars that were observed during photometric and clear nights with ISAAC on the Very Large Telescope UT1 between 2000 and 2004. We have built a database consisting of hundreds of observations, which allows us to examine how extinction varies with airmass and the column density of water vapour. In addition, we use theoretical models of the atmosphere to estimate Rayleigh scattering and molecular absorption in order to quantify their fractional contribution to the total extinction in each filter. Finally, we have observed 8 bright red standard stars to evaluate filter color terms. We find that extinction coefficients are < 0.1 mag/airmass in all the considered bands. The extinction coefficient in the J-band strongly depends on the column density of water vapour. Molecular absorption dominates the extinction in J, H and Ks, while Rayleigh scattering contributes most to the extinction in Js. We have found negligible color terms for J, H and Ks and a non-negligible color term for Js.

astro-ph.IM↗

arXiv2008

El Roque de Los Muchachos Site Characteristics. III. Analysis of Atmospheric Dust and Aerosol Extinction

Canary Islands are normally interested by dominant North-East winds that, in some meteorological conditions, can transport sand at high altitude from the Sahara desert. The dust may affect the efficiency of the telescopes and decreases the transparency of the sky. In order to maximize the scientific return of the telescopes located at the ORM, we present an analysis of the atmospheric dust content and its effects on astronomical observations. B, V and I dust aerosol astronomical extinction are derived. Using a 5 years series database of data taken from the four channel TNG dust monitor, we compute a mean hourly and daily values of the dust content. We have detected particles having size 0.3, 0.5, 1.0 and 5.0 um. Using a power law we have derived the content of 10.0 um particles. We found a typical local dust concentration ranging from 3x10^6 particles per cubic meter at 0.3 um, to 10^3 at 5.0 um and 10 at 10.0 um, increasing up to 3 order of magnitudes during the dust storms, with a relative higher increase of 1.0, 5.0 and 10.0 um particles. The number of local dust storm events is the same in winter- and summertime, but, the average background and storm-related increases in the dust concentration in summer are significantly higher than in winter. In a uniform approximation, during the dust storms, an average height of the dust layer of 2.5 km above the telescope is inferred. During the sand storms La Palma Island is affected by an almost uniform layer extending up to 5 km above the sea level, down, at least the height of the telescope. The visible extinction is dominated by particles at 1.0, 5.0 and 10.0 um. In agreement with the results from Carlsberg Automatic Meridian Circle (CAMC) we find a typical extinction during dust storms of about 0.2 mag/airmass.

astro-ph↗