arXiv subjects

C. Pinto

Publications and source records attributed to C. Pinto.

At least 37 records · Page 2Linked to original sources

arXiv2025

Line detections in photospheric radius expansion bursts from 4U 1820-303

Context: NICER (Neutron star Interior Composition ExploreR) is the instrument of choice for the spectral analysis of type I X-ray bursts, as it provides high throughput at X-ray CCD resolution, down to 0.3 keV. Aims: This study investigates whether the energies of absorption lines detected in photospheric radius expansion (PRE) bursts correlate with the inferred blackbody radius. Previous reports suggested such a correlation, attributed to a combination of weaker gravitational redshift and higher blueshifts in bursts with larger radii. Methods: The analysis reexamines four previously studied PRE bursts and examines eight additional bursts from 4U 1820-303, evidencing PRE. Spectral evolution is tracked on the shortest possible timescales (tenth of a second) adopting two parallel continuum descriptions to characterise the photospheric expansion and line evolution. Applying the accretion-enhanced model, maximum blackbody radii of up to $\sim$ 900 km are inferred, with peak bolometric luminosities exceeding the Eddington limit of an Helium accretor. Absorption lines are assessed for significance using Monte Carlo simulations, and spectral lines are characterised using the state-of-art plasma codes available within {\sc{spex}} with a phenomenological continuum. A thorough parameter search explores Doppler shifts to avoid local minima. Results: Several significant (> 99.9%) absorption lines, including the previously reported 2.97 keV line, are detected. While no consistent correlation between line energies and blackbody radii is confirmed, bursts with larger radii exhibit up to four lines and the line strength is higher. The modelling suggests that the observed lines mostly originate from slightly redshifted (almost rest-frame) photo-/collisionally ionised gas in emission. For the burst with the largest PRE, a combination of photo-ionised plasma in both emission and absorption is preferred.

astro-ph.HE↗

arXiv2024

Detection of a Highly Ionized Outflow in the Quasi-periodically Erupting Source GSN 069

Quasi-periodic eruptions (QPEs) are high-amplitude, soft X-ray bursts recurring every few hours, associated with supermassive black holes. Many interpretations for QPEs were proposed since their recent discovery in 2019, including extreme mass ratio inspirals and accretion disk instabilities. But, as of today, their nature still remains debated. We perform the first high-resolution X-ray spectral study of a QPE source using the RGS gratings onboard XMM-Newton, leveraging nearly 2 Ms of exposure on GSN 069, the first discovered source of this class. We resolve several absorption and emission lines including a strong line pair near the N VII rest-frame energy, resembling the P-Cygni profile. We apply photoionization spectral models and identify the absorption lines as an outflow blueshifted by $1700-2900$ km/s, with a column density of about $10^{22}$ cm$^{-2}$ and an ionization parameter $\log (ξ$/erg cm s$^{-1})$ of $3.9-4.6$. The emission lines are instead redshifted by up to 2900 km/s, and likely originate from the same outflow that imprints the absorption features, and covers the full $4π$ sky from the point of view of GSN 069. The column density and ionization are comparable to the outflows detected in some tidal disruption events, but this outflow is significantly faster and has a strong emission component. The outflow is more highly ionized when the system is in the phase during which QPEs are present, and from the limits we derive on its location, we conclude that the outflow is connected to the recent complex, transient activity of GSN 069 which began around 2010.

astro-ph.HE↗

arXiv2024

Hidden Cooling Flows in Elliptical Galaxies

The radiative cooling time of hot gas in the cool cores of many galaxy clusters and massive elliptical galaxies drops in the centre to below 100 million years. The mass cooling rates inferred from simple modelling of X-ray observations of these objects are very low, indicating that either AGN feedback is tightly balanced or that soft X-rays from cooling gas are somehow hidden from view. An intrinsic absorption model developed for application to galaxy clusters is used here to search for hidden cooling flows (HCFs) in seven nearby elliptical galaxies. Mass cooling rates of 0.5-8 solar masses per year are found in each galaxy. The absorbed cooling flow luminosity is in agreement with the observed Far Infrared (FIR) luminosity in each case, indicating absorbed emission is energetically capable of emerging in the FIR band. An observed lack of agreement between HCF rates and normal star formation rates suggests the cooled material must have an alternative fate, with low-mass star formation considered as the primary outcome.

astro-ph.GA↗

arXiv2024

Hidden Cooling Flows IV: More Details on Centaurus and the Efficiency of AGN Feedback in Clusters

Cooling flows are common in galaxy clusters which have cool cores. The soft X-ray emission below 1 keV from the flows is mostly absorbed by cold dusty gas within the central cooling sites. Further evidence for this process is presented here through a more detailed analysis of the nearby Centaurus cluster and some additional clusters. Predictions of JWST near and mid-infrared spectra from cooling gas are presented. [NeVI] emission at 7.65 micron should be an important diagnostic of gas cooling between 6 and 1.5 times 10^5 K. The emerging overall picture of hidden cooling flows is explored. The efficiency of AGN feedback in reducing the total cooling rate in cool cores is shown to be above 50 percent for many clusters but is rarely above 90 per cent. The reduction is mostly in outer gas. Cooling dominates in elliptical galaxies and galaxy groups which have mass flow rates below about 15M/yr and in some massive clusters where rates can exceed 1000M/yr.

astro-ph.GA↗

arXiv2024

First results on new helium based eco-gas mixtures for the Extreme Energy Events Project

The Extreme Energy Events (EEE) Project, a joint project of the Centro Fermi (Museo Storico della Fisica e Centro Studi e Ricerche "E.Fermi") and INFN, has a dual purpose: a scientific research program on cosmic rays at ground level and an intense outreach and educational program. The project consists in a network of about 60 tracking detectors, called telescopes, mostly hosted in Italian High Schools. Each telescope is made by three Multigap Resistive Plate Chambers, operated so far with a gas mixture composed by 98% C$_2$H$_2$F$_4$ and 2% SF$_6$. Due to its high Global Warming Potential, a few years ago the EEE collaboration has started an extensive R&D on alternative mixtures environmentally sustainable and compatible with the current experimental setup and operational environment. Among other gas mixtures, the one with helium and hydrofluoroolefin R1234ze gave the best result during the preliminary tests performed with two of the network telescopes. The detector has proved to reach performance levels comparable to those obtained with previous mixtures, without any modification of the hardware. We will discuss the first results obtained with the new mixture, tested with different percentages of the two components.

hep-ex↗

arXiv2024

Measuring the ICM velocity structure within the A3266 galaxy cluster

We present a detailed analysis of the velocity structure of the hot intracluster medium (ICM) within the A3266 galaxy cluster, including new observations taken between June and November 2023. Firstly, morphological structures within the galaxy cluster were examined using a Gaussian Gradient Magnitude (GGM) and adaptively smoothed GGM filter applied to the EPIC-pn X-ray image. Then, we applied a novel {\it XMM-Newton} EPIC-pn energy scale calibration, which uses instrumental Cu K$α$ as reference for the line emission, to measure line-of-sight velocities of the hot gas within the system. This approach enabled us to create two-dimensional projected maps for velocity, temperature, and metallicity, showing that the hot gas displays a redshifted systemic velocity relative to the cluster redshift across all fields of view. Further analysis of the velocity distribution through non-overlapping circular regions demonstrated consistent redshifted velocities extending up to 1125 kpc from the cluster core. Additionally, the velocity distribution was assessed along regions following surface brightness discontinuities, where we observed redshifted velocities in all regions, with the largest velocities reaching $768 \pm 284$ km/s. Moreover, we computed the velocity Probability Density Function (PDF) from the velocity map. We applied a normality test, finding that the PDF adheres to an unimodal normal distribution consistent with theoretical predictions. Lastly, we computed a velocity structure function (VSF) for this system using the measured line-of-sight velocities. These insights advance our understanding of the dynamic processes within the A3266 galaxy cluster and contribute to our broader knowledge of ICM behavior in merging galaxy clusters.

astro-ph.HE↗

arXiv2024

Constraining the Number Density of the Accretion Disk Wind in Hercules X-1 Using its Ionization Response to X-ray Pulsations

X-ray binaries are known to launch powerful accretion disk winds that can have significant impact on the binary systems and their surroundings. To quantify the impact and determine the launching mechanisms of these outflows, we need to measure the wind plasma number density, an important ingredient in the theoretical disk wind models. While X-ray spectroscopy is a crucial tool to understanding the wind properties, such as their velocity and ionization, in nearly all cases, we lack the signal-to-noise to constrain the plasma number density, weakening the constraints on outflow location and mass outflow rate. We present a new approach to determine this number density in the X-ray binary Hercules X-1 by measuring the speed of the wind ionization response to time-variable illuminating continuum. Hercules X-1 is powered by a highly magnetized neutron star, pulsating with a period of 1.24 s. We show that the wind number density in Hercules X-1 is sufficiently high to respond to these pulsations by modeling the ionization response with the time-dependent photoionization model TPHO. We then perform a pulse-resolved analysis of the best-quality XMM-Newton observation of Hercules X-1 and directly detect the wind response, confirming that the wind density is at least $10^{12}$ cm$^{-3}$. Finally, we simulate XRISM observations of Hercules X-1 and show that they will allow us to accurately measure the number density at different locations within the outflow. With XRISM we will rule out $\sim3$ orders of magnitude in density parameter space, constraining the wind mass outflow rate, energetics, and its launching mechanism.

astro-ph.HE↗

arXiv2024

Study of silicon photomultipliers for the readout of a lead/scintillating-fiber calorimeter

The KLOE electromagnetic calorimeter is expected to be reused in the Near Detector complex of the DUNE experiment at Fermilab. The possible substitution of traditional Photomultiplier Tubes (PMTs) with Silicon Photomultipliers (SiPMs) in the refurbished calorimeter is the object of this investigation. A block of the KLOE lead-scintillating fiber calorimeter has been equipped with light guides and external trigger scintillators. The signals induced by cosmic rays and environmental radioactivity have been collected by SiPM arrays on one side of the calorimeter, and by conventional PMTs on the opposite side. Efficiency, stability, and timing resolution of SiPMs have been studied and compared with KLOE-PMTs performance. Conclusions about the convenience of substituting PMTs with SiPMs are drawn.

physics.ins-det↗

arXiv2024

Consequences of a low-mass, high-pressure, star formation mode in early galaxies

High resolution X-ray spectra reveal hidden cooling flows depositing cold gas at the centres of massive nearby early-type galaxies with little sign of normal star formation. Optical observations are revealing that a bottom-heavy Initial Mass Function is common within the inner kpc of similar galaxies. We revive the possibility that a low-mass star formation mode is operating due to the high thermal pressure in the cooling flow, thus explaining the accumulation of low-mass stars. We further explore whether such a mode operated in early, high-redshift galaxies and has sporadically continued to the present day. The idea links observed distant galaxies with black holes which are ultramassive for their stellar mass, nearby red nuggets and massive early-type galaxies. Nearby elliptical galaxies may be red but they are not dead.

astro-ph.GA↗

arXiv2023

On the nature of the ultraluminous X-ray source Holmberg II X-1

We present a comprehensive spectral analysis of the ultraluminous X-ray source Holmberg II X-1 using broadband and high-resolution X-ray spectra taken with the XMM-Newton satellite over a period of 19 years benefiting from a recent campaign. We tested several models for the broadband spectra among which a double thermal component provided a reasonable description for the continuum between 0.3-10 keV and enabled us to constrain the properties of the accretion disc. The Luminosity-Temperature trends of the inner and outer disc components broadly agree with the expectations for a thin disc, although the exact values of the slopes are slightly sensitive to the adopted model. However, all tested models show L-T trends which deviate from a power law above a bolometric luminosity of about 5 $\times \ 10^{39} $erg/s, particularly for the hot thermal component associated to the inner accretion flow. Assuming that such deviations are due to the accretion rate exceeding its Eddington limit or, most likely, the super-critical rate, a compact object with a mass 16-36 Msun, i.e. a stellar-mass black hole, is inferred. The time-averaged (2021) high resolution spectra present narrow emission lines at 1 keV primarily from Ne IX-X and a very strong at 0.5 keV from N VII, which indicate Ne-N-rich gas with non-Solar abundances. This favours a nitrogen-rich donor star, such as a blue/red supergiant, which has escaped from its native stellar cluster characterised by a low-metallicity environment.

astro-ph.HE↗

arXiv2023

A soft and transient ultraluminous X-ray source with 6-h modulation in the NGC 300 galaxy

We investigate the nature of CXOU J005440.5-374320 (J0054), a peculiar bright ($\sim$$4\times10^{39}$ erg/s) and soft X-ray transient in the spiral galaxy NGC 300 with a 6-hour periodic flux modulation that was detected in a 2014 Chandra observation. Subsequent observations with Chandra and XMM-Newton, as well as a large observational campaign of NGC 300 and its sources performed with the Swift Neil Gehrels Observatory, showed that this source exhibits recurrent flaring activity: four other outbursts were detected across $\sim$8 years of monitoring. Using data from the Swift/UVOT archive and from the XMM-Newton/OM and Gaia catalogues, we noted the source is likely associated with a bright blue optical/ultraviolet counterpart. This prompted us to perform follow-up observations with the Southern African Large Telescope in December 2019. With the multi-wavelength information at hand, we discuss several possibilities for the nature of J0054. Although none is able to account for the full range of the observed peculiar features, we found that the two most promising scenarios are a stellar-mass compact object in a binary system with a Wolf$-$Rayet star companion, or the recurrent tidal stripping of a stellar object trapped in a system with an intermediate-mass ($\sim1000$ $M_\odot$) black hole.

astro-ph.HE↗

arXiv2023

Ecological transition for the gas mixtures of the MRPC cosmic ray telescopes of the EEE Project

The Extreme Energy Events (EEE) Collaboration is fully involved in an ecological transition. The use of the standard gas mixture, \ce{C_{2}H_{2}F_{4}}+ \ce{SF_{6}}, has stopped in favor of an alternative green mixture based on \ce{C_{3}H_{2}F_{4}} with the addition of He or \ce{CO_{2}}. The choise of these new mixtures is motivated by the significant lower Global Warming Potential (GWP) to reduce the emission of gases potentially contributing to the greenhouse effect. The EEE experiment consists of 61 muon telescopes based on Multigap Resistive Plate Chambers (MRPCs), each telescope composed of 3 chambers filled with gas. Several EEE detectors are today completely fluxed with the new ecological mixture. This contribution will report recent results about the telescope performance obtained from studies with the eco-friendly alternative mixture carried out in the last years.

hep-ex↗

arXiv2023

Accretion disk wind of Hercules X-1 during the Short High state

Hercules X-1 is a nearly edge-on X-ray binary with a warped, precessing accretion disk, which manifests through a 35-day cycle of alternating High and Low flux states. This disk precession introduces a changing line of sight towards the X-ray source, through an ionized accretion disk wind. The sightline variation allows us to uniquely determine how the wind properties vary with height above the disk. All the previous wind measurements were made in the brighter Main High state of Her X-1. Here, we analyze the only Chandra observation during the fainter `Short' High state, and significantly detect blueshifted ionized absorption. We find a column density of $2.0_{-0.6}^{+1.1}\times10^{22}$ cm$^{-2}$, an ionization parameter $\log (ξ$/erg cm s$^{-1})=3.41_{-0.12}^{+0.15}$ and an outflow velocity of $380 \pm 40$ km/s. The properties of the outflow measured during the Short High state are in good agreement with those measured at equivalent precession phases during Main High. We conclude that we are sampling the same wind structure, seen during both Main and Short High, which is precessing alongside with the warped accretion disk every 35 days. Finally, the high spectral resolution of Chandra gratings above 1 keV in this observation enabled us to measure the abundances of certain elements in the outflow. We find Mg/O$=1.5_{-0.4}^{+0.5}$, Si/O$=1.5 \pm 0.4$ and S/O$=3.0_{-1.1}^{+1.2}$, whereas in our previous study of Her X-1 with XMM-Newton, we found an over-abundance of N, Ne and Fe compared with O. These peculiar abundance ratios were likely introduced by pollution of the donor by the supernova which created Her X-1.

astro-ph.HE↗

arXiv2023

Chemical enrichment of ICM within the Ophiuchus cluster I: radial profiles

The analysis of the elemental abundances in galaxy clusters offers valuable insights into the formation and evolution of galaxies. In this study, we explore the chemical enrichment of the intergalactic medium (ICM) in the Ophiuchus cluster by utilizing {\it XMM-Newton} EPIC-pn observations. We explore the radial profiles of Si, S, Ar, Ca, and Fe. Due to the high absorption of the system, we have obtained only upper limits for O, Ne, Mg, and Ni. We model the X/Fe ratio profiles with a linear combination of core-collapse supernovae (SNcc) and type~Ia supernovae (SNIa) models. We found a flat radial distribution of SNIa ratio over the total cluster enrichment $10-30\%$ for all radii. However, the absence of light $α$-elements abundances may lead to over-estimation of the SNcc contribution.

astro-ph.HE↗

arXiv2023

Chemical enrichment of ICM within the Centaurus cluster I: radial profiles

We examine deep {\it XMM-Newton} EPIC-pn observations of the Centaurus cluster to study the hot intracluster medium (ICM) and radial metal distributions within such an environment. We found that the best-fit spectral model corresponds to a log-normal temperature distribution, with discontinuities around $\sim10$~kpc, $\sim50$~kpc, and $\sim100$~kpc, also observed in the abundances distributions. We measured the radial profiles of O, Si, S, Ar, Ca, and Fe. These profiles reveal prominent negative gradients for distances $<90$~kpc, which then transition to flatter profiles. We modeled X/Fe ratio profiles with a linear combination of SNIcc and SNIa models. The best-fit model suggests a uniform SNIa percentage contribution to the total cluster enrichment, thus supporting an early enrichment of the ICM, with most of the metals present being produced before clustering.

astro-ph.HE↗

arXiv2023

The accretion/ejection link in the neutron star X-ray binary 4U 1820-30 I: A boundary layer-jet coupling?

The accretion flow / jet correlation in neutron star (NS) low-mass X-ray binaries (LMXBs) is far less understood when compared to black hole (BH) LMXBs. In this paper we will present the results of a dense multi-wavelength observational campaign on the NS LMXB 4U 1820-30, including X-ray (Nicer, NuSTAR and AstroSAT) and quasi-simultaneous radio (ATCA) observations in 2022. 4U 1820-30 shows a peculiar 170 day super-orbital accretion modulation, during which the system evolves between "modes" of high and low X-ray flux. During our monitoring, the source did not show any transition to a full hard state. X-ray spectra were well described using a disc blackbody, a Comptonisation spectrum along with a Fe K emission line at 6.6 keV. Our results show that the observed X-ray flux modulation is almost entirely produced by changes in the size of the region providing seed photons for the Comptonisation spectrum. This region is large (about 15 km) in the high mode and likely coincides with the whole boundary layer, while it shrinks significantly (<10 km) in low mode. The electron temperature of the corona and the observed RMS variability in the hard X-rays also exhibit a slight increase in low mode. As the source moves from high to low mode, the radio emission due to the jet becomes about 5 fainter. These radio changes appear not to be strongly connected to the hard-to-soft transitions as in BH systems, while they seem to be connected mostly to variations observed in the boundary layer.

astro-ph.HE↗

arXiv2023

Measuring the hot ICM velocity structure function using XMM-Newton observations

It has been shown that the gas velocities within the intracluster medium (ICM) can be measured by applying novel XMM-Newton EPIC-pn energy scale calibration, which uses instrumental Cu Ka as reference for the line emission. Using this technique, we have measured the velocity distribution of the ICM for clusters involving AGN feedback and sloshing of the plasma within the gravitational well (Virgo and Centaurus) and a relaxed one (Ophiuchus). We present a detailed study of the kinematics of the hot ICM for these systems. First, we compute the velocity probability distribution functions (PDFs) from the velocity maps. We find that for all sources the PDF follows a normal distribution, with a hint for a multimodal distribution in the case of Ophiuchus. Then, we compute the velocity structure function (VSF) for all sources in order to study the variation with scale as well as the nature of turbulence in the ICM. We measure a turbulence driving scale of 10-20 kpc for the Virgo cluster, while the Ophiuchus cluster VSF reflects the absence of strong interaction between the ICM and a powerful Active Galactic Nucleus (AGN) at such spatial scales. For the former, we compute a dissipation time larger than the jet activity cycle, thus indicating that a more efficient heating process than turbulence is required to reach equilibrium. This is the first time that the VSF of the hot ICM has been computed using direct velocity measurements from X-ray astronomical observations.

astro-ph.HE↗

arXiv2023

Hidden Cooling Flows in Clusters of Galaxies III: Accretion onto the Central Black Hole

Recently, we have uncovered Hidden Cooling Flows (HCF) in the X-ray spectra of the central Brightest Galaxies of 11 clusters, 1 group and 2 elliptical galaxies. Here we report such flows in a further 15 objects, consisting of 8 clusters, 3 groups, 3 ellipticals and 1 Red Nugget. The mass cooling rates are about 1 Msun/yr in the ellipticals, 2 to 20 Msun/yr in the groups and 20 to 100 Msun/yr in regular clusters. The Red Nugget, MRK1216, has an HCF of 10 Msun/yr. We review the fate of the cooled gas and investigate how some of it might accrete onto the central black hole. The gas is likely to be very cold and to have fragmented into low mass stars and smaller objects before being swallowed whole, with little luminous output. If such a scenario is correct and operates at a few Msun/yr then such objects may host the fastest growing black holes in the low redshift Universe. We briefly discuss the relevance of HCF to the growth of early galaxies and black holes.

astro-ph.GA↗