arXiv subjects

Elisabete M. de Gouveia Dal Pino

Publications and source records attributed to Elisabete M. de Gouveia Dal Pino.

At least 37 records · Page 2Linked to original sources

arXiv2025

Retrograde Precession of Relativistic Orbits and the Quest for Charged Black Holes

The S-stars around the center of the milky way galaxy provide us with detailed information about the nature of the supermassive compact object Sagittarius A* (Sgr A*). In this work, we derive the fully relativistic orbit equations for the case of the Reissner-Nordström (RN) and Kerr-Newman spacetimes. We solve these orbit equations numerically to analyze the periastron shift of relativistic orbits. We show that retrograde precession (or negative precession) of timelike bound orbits is possible in the case of naked singularity arising from these spacetimes. We have then compared our results with the non-charged Schwarzschild and Kerr spacetimes. This theoretical analysis of relativistic orbits would be helpful in either confirming or ruling out such charged black holes and naked singularities through the future trajectories of S-stars and will also help us constrain the geometry of Sgr A*.

gr-qc↗

arXiv2023

Neutrinos and gamma-rays from Galaxy Clusters constrained by the upper limits of IceCube

Clusters of galaxies possess the capability to accelerate cosmic rays (CRs) to very high energy up to $\sim10^{18}$~eV due to their large size and magnetic field strength which favor CR confinement for cosmological times. During their confinement, they can produce neutrinos and $γ-$rays out of interactions with the background gas and photon fields. In recent work, \cite{hussain2021high, hussain2023diffuse} have conducted three-dimensional cosmological magnetohydrodynamical (MHD) simulations of the turbulent intracluster medium (ICM) combined with multi-dimensional Monte Carlo simulations of CR propagation for redshifts ranging from $z \sim 5$ to $z = 0$ to study the multi-messenger emission from these sources. They found that when CRs with a spectral index in the range $1.5 - 2.5$ and cutoff energy $E_\mathrm{max} = 10^{16} - 10^{17}$~eV are injected into the system, they make significant contributions to the diffuse background emission of both neutrinos and gamma-rays. In this work, we have revisited this model and undertaken further constraints on the parametric space. This was achieved by incorporating the recently established upper limits on neutrino emission from galaxy clusters, as obtained by the IceCube experiment. We find that for CRs injected with spectral indices in the range $2.0 - 2.5$, cutoff energy $E_\mathrm{max} = 10^{16} - 10^{17}$~eV, and power corresponding to $(0.1-1)\%$ of the cluster luminosity, our neutrino flux aligns with the upper limits estimated by IceCube. Additionally, the resulting contribution from clusters to the diffuse $γ$-ray background (DGRB) remains significant with values of the order of $ \sim 10^{-5}\, \mathrm{MeV} \, \mathrm{cm}^{-2} \,\mathrm{s}^{-1} \, \mathrm{sr}^{-1}$ at energies above $500$ GeV.

astro-ph.HE↗

arXiv2023

High-Energy Neutrino and Gamma Ray Production in Clusters of Galaxies

We compute the contribution from clusters of galaxies to the diffuse neutrino and $γ-$ray background. Due to their unique magnetic-field configuration, cosmic rays (CRs) with energy $\leq10^{17}$ eV can be confined within these structures over cosmological time scales, and generate secondary particles, including neutrinos and $γ-$rays, through interactions with the background gas and photons. We employ three-dimensional (3D) cosmological magnetohydrodynamical (MHD) simulations of structure formation to model the turbulent intergalactic and intracluster media. We propagate CRs in these environments using multi-dimensional Monte Carlo simulations across different redshifts (from $z \sim 5$ to $z = 0$), considering all relevant photohadronic, photonuclear, and hadronuclear interactions. We also include the cosmological evolution of the CR sources. We find that for CRs injected with a spectral index $1.5 - 2.7$ and cutoff energy $E_\text{max} = 10^{16} - 10^{17}$~eV, clusters contribute to a substantial fraction to the diffuse fluxes observed by the IceCube and Fermi-LAT, and most of the contribution comes from clusters with $M > 10^{14} \, M_{\odot}$ and redshift $z < 0.3$. We also estimated the multimessenger contributions from the local galaxy cluster.

astro-ph.HE↗

arXiv2023

AGN and Star Formation feedback in the evolution of galaxy outflows

We conducted 3D-MHD simulations to investigate the feedback processes in the central 1kpc scale of galaxies hosting both active star formation (SF) and an AGN wind. Our simulations naturally generated a turbulent and clumpy interstellar medium driven by SF evolution. We found that the AGN wind duty cycle plays a crucial role in shaping the evolution of the outflows. This cycle consists of an active, a remnant and an inactive phase, lasting up to 1.5 Myr. The duration of the cycle increases with larger star formation rate (SFR) and smaller AGN wind power (tested for luminosities log L = 42-44 ergs per second and SFR=1-1000 solar masses per year. The feedback on SF, whether positive or negative, depends on various factors, including the AGN outflow opening angle, power, and phase of activity, as well as the initial SFR. The passage of the AGN wind enhances SF in a ring around it, resembling the structures observed in ULIRGs, and is stronger for larger AGN power or SFR. Also, a higher SFR enhances the mixing of interstellar matter with the AGN wind, resulting in a greater number of colder, denser structures with volume filling factors ~ 0.02 to 0.12 and velocities comparable to those observed in Seyferts and LINERs, but smaller than those observed in ULIRGs. The efficiency of the AGN wind in transporting mass to kiloparsec distances diminishes with increasing SFR. The mass loss rates range from 50 to 250 solar masses per year within the initial 2 Myr of evolution, which aligns with observed rates in nearby Seyferts and ULIRGs.

astro-ph.GA↗

arXiv2023

Particle acceleration by magnetic reconnection in relativistic jets: the transition from small to large scales

Several MHD works and, in particular, the recent one by Medina-Torrejon et al. (2021) based on three-dimensional MHD simulations of relativistic jets, have evidenced that particle acceleration by magnetic reconnection driven by the turbulence in the flow occurs from the resistive up to the large injection scale of the turbulence. Particles experience Fermi-type acceleration up to ultra-high-energies, predominantly of the parallel velocity component to the local magnetic field, in the reconnection layers in all scales due to the ideal electric fields of the background fluctuations ($V\times B$, where $V$ and $B$ are the velocity and magnetic field of the fluctuations, respectively). In this work, we show MHD-particle-in-cell (MHD-PIC) simulations following the early stages of the particle acceleration in the relativistic jet which confirm these previous results, demonstrating the strong potential of magnetic reconnection driven by turbulence to accelerate relativistic particles to extreme energies in magnetically dominated flows. Our results also show that the dynamical time variations of the background magnetic fields do not influence the acceleration of the particles in this process.

astro-ph.HE↗

arXiv2023

The Diffuse Gamma-Ray Flux from Clusters of Galaxies

The origin of the diffuse gamma-ray background (DGRB), the one that remains after subtracting all individual sources from observed gamma-ray sky, is unknown. The DGRB possibly encompasses contributions from different source populations such as star-forming galaxies, starburst galaxies, active galactic nuclei, gamma-ray bursts, or galaxy clusters. Here, we combine cosmological magnetohydrodynamical simulations of clusters of galaxies with the propagation of cosmic rays (CRs) using Monte Carlo simulations, in the redshift range $z\leq 5.0$, and show that the integrated gamma-ray flux from clusters can contribute up to $100\%$ of the DGRB flux observed by Fermi-LAT above $100$ GeV, for CRs spectral indices $α= 1.5 - 2.5$ and energy cutoffs $E_{\text{max}} = 10^{16} - 10^{17}$ eV. The flux is dominated by clusters with masses $10^{13} \lesssim M/M_{\odot} \lesssim 10^{15}$ and redshift $ z \lesssim 0.3$. Our results also predict the potential observation of high-energy gamma rays from clusters by experiments like the High Altitude Water Cherenkov (HAWC), the Large High Altitude Air Shower Observatory (LHAASO), and potentially the upcoming Cherenkov Telescope Array (CTA).

astro-ph.HE↗

arXiv2021

Fast magnetic reconnection structures in Poynting-flux dominated jets

The ubiquitous relativistic jet phenomena associated with black holes play a major role in high and very-high-energy (VHE) astrophysics. In particular, observations have demonstrated that blazars show VHE emission with time-variability from days (in the GeV band) to minutes (in the TeV band), implying very compact emission regions. The real mechanism able to explain the particle acceleration process responsible for this emission is still debated, but magnetic reconnection has been lately discussed as a strong potential candidate and, in some circumstances, as the only possible one. In this work, we present the results of three-dimensional special relativistic magnetohydrodynamic simulations of the development of reconnection events driven by turbulence induced by current-driven kink instability along a relativistic jet. We have performed a systematic identification of all reconnection regions in the system, characterizing their local magnetic field topology and quantifying the reconnection rates. We obtained average rates of $0.051\pm0.026$ (in units of the Alfvén speed) which are comparable to the predictions of the theory of turbulence-induced fast reconnection. Detailed statistical analysis also demonstrated that the fast reconnection events follow a log-normal distribution, which is a signature of its turbulent origin. To probe the robustness of our method, we have applied our results to the blazar Mrk 421. Building a synthetic light curve from the integrated power of the magnetic reconnection events, we evaluated the time-variability from a power spectral density analysis, obtaining a good agreement with the observations in the GeV band. This suggests that turbulent fast magnetic reconnection driven by kink instability can be a possible process behind the high energy emission variability phenomena observed in blazars.

astro-ph.HE↗

arXiv2021

Magnetic Field Orientation in Self-Gravitating Turbulent Molecular Clouds

Stars form inside molecular cloud filaments from the competition of gravitational forces with turbulence and magnetic fields. The exact orientation of these filaments with the magnetic fields depends on the strength of these fields, the gravitational potential, and the line-of-sight (LOS) relative to the mean field. To disentangle these effects we employ three-dimensional magnetohydrodynamical numerical simulations that explore a wide range of initial turbulent and magnetic states, i.e., sub-Alfvénic to super-Alfvénic turbulence, with and without gravity. We use histogram of relative orientation (HRO) and the associated projected Rayleigh statistics (PRS) to study the orientation of density and, in order to compare with observations, the integrated density relative to the magnetic field. We find that in sub-Alfvénic systems the initial coherence of the magnetic is maintained inside the cloud and filaments form perpendicular to the field. This trend is not observed in super-Alfvénic models, where the lines are dragged by gravity and turbulence and filaments are mainly aligned to the field. The PRS analysis of integrated maps shows that LOS effects are important only for sub-Alfvénic clouds. When the LOS is perpendicular to the initial field orientation most of the filaments are perpendicular to the projected magnetic field. The inclusion of gravity increases the number of dense structures perpendicular to the magnetic field, reflected as lower values of the PRS for denser regions, regardless of whether the model is sub- or super-Alfvénic. The comparison of our results with observed molecular clouds reveal that most are compatible with sub-Alfvénic models.

astro-ph.GA↗

arXiv2021

High-Energy Neutrino Production in Clusters of Galaxies

Clusters of galaxies can potentially produce cosmic rays (CRs) up to very-high energies via large-scale shocks and turbulent acceleration. Due to their unique magnetic-field configuration, CRs with energy $\leq 10^{17}$ eV can be trapped within these structures over cosmological time scales, and generate secondary particles, including neutrinos and gamma rays, through interactions with the background gas and photons. In this work, we compute the contribution from clusters of galaxies to the diffuse neutrino background. We employ three-dimensional cosmological magnetohydrodynamical simulations of structure formation to model the turbulent intergalactic medium. We use the distribution of clusters within this cosmological volume to extract the properties of this population, including mass, magnetic field, temperature, and density. We propagate CRs in this environment using multi-dimensional Monte Carlo simulations across different redshifts (from $z \sim 5$ to $z =0$), considering all relevant photohadronic, photonuclear, and hadronuclear interaction processes. We find that, for CRs injected with a spectral index $α= 1.5 - 2.7$ and cutoff energy $E_\text{max} = 10^{16} - 5\times10^{17} \; \text{eV}$, clusters contribute to a sizeable fraction to the diffuse flux observed by the IceCube Neutrino Observatory, but most of the contribution comes from clusters with $M \gtrsim 10^{14} \; M_{\odot}$ and redshift $ z \lesssim 0.3$. If we include the cosmological evolution of the CR sources, this flux can be even higher.

astro-ph.HE↗

arXiv2020

Particle acceleration by relativistic magnetic reconnection driven by kink instability turbulence in Poynting flux dominated jets

Particle acceleration in magnetized relativistic jets still puzzles theorists, specially when one tries to explain the highly variable emission observed in blazar jets or gamma-ray bursts putting severe constraints on current models. In this work we investigate the acceleration of particles injected in a three-dimensional relativistic magnetohydrodynamical jet subject to current driven kink instability (CDKI), which drives turbulence and fast magnetic reconnection. Test protons injected in the nearly stationary snapshots of the jet, experience an exponential acceleration up to a maximum energy. For a background magnetic field of $B \sim 0.1$ G, this saturation energy is $\sim 10^{16}$ eV, while for $B \sim 10$ G it is $\sim 10^{18}$ eV. The simulations also reveal a clear association of the accelerated particles with the regions of fast reconnection. In the early stages of the development of the non-linear growth of CDKI in the jet, when there are still no sites of fast reconnection, injected particles are also efficiently accelerated, but by magnetic curvature drift in the wiggling jet spine. However, they have to be injected with an initial energy much larger than that required for particles to accelerate in reconnection sites. Finally, we have also obtained from the simulations an acceleration time due to reconnection with a weak dependence on the particles energy $E$, $t_A \propto E^{0.1}$. The energy spectrum of the accelerated particles develops a high energy tail with a power law index $p \sim$ -1.2 in the beginning of the acceleration, in agreement with earlier works. Our results provide an appropriate multi-dimensional framework for exploring this process in real systems and explain their complex emission patterns, specially in the very high energy bands and the associated neutrino emission recently detected in some blazars.

astro-ph.HE↗

arXiv2019

The Impact of Plasma Instabilities on the Spectra of TeV Blazars

Relativistic jets from blazars are known to be sources of very-high-energy gamma rays (VHEGRs). During their propagation in the intergalactic space, VHEGRs interact with pervasive cosmological photon fields such as the extragalactic background light (EBL) and the cosmic microwave background (CMB), producing electron-positron pairs. These pairs can upscatter CMB/EBL photons to high energies via inverse Compton scattering, thereby continuing the cascade process. This is often used to set limits on intergalactic magnetic fields (IGMFs). However, the picture may change if plasma instabilities, arising due to the interaction of the pairs with the intergalactic medium (IGM), cool down the electrons/positrons faster than inverse Compton scattering. As a consequence, the kinetic energy lost by the pairs to the IGM could cause a hardening in the observed gamma-ray spectrum at energies below $\sim$100 GeV. Here we study several types and models of instabilities and assess their impact for interpreting observations of distant blazars. Our results suggest that plasma instabilities can describe the spectra of some blazars and mimic the effects of IGMFs, depending on parameters such as intrinsic spectrum of the object, the density and temperature of the IGM, and the luminosity of the beam. On the other hand, we find that for our fiducial set of parameters plasma instabilities do not have a major impact on the spectra of some of the blazars studied. Therefore, they may be used for constraining IGMFs.

astro-ph.HE↗

arXiv2019

The Cherenkov Telescope Array view of the Galactic Center region

Among all the high-energy environments of our Galaxy, the Galactic Center (GC) region is definitely the richest. It harbors a large amount of non-thermal emitters, including the closest supermassive black hole, dense molecular clouds, regions with strong star forming activity, multiple supernova remnants and pulsar wind nebulae, arc-like radio structures, as well as the base of what may be large-scale Galactic outflows, possibly related to the Fermi Bubbles. It also contains a strong diffuse TeV gamma-ray emission along the Galactic ridge, with a disputed origin, including the presence of a possible Pevatron, unresolved sources, and an increased relevance of the diffuse sea of cosmic rays. This very rich region will be one of the key targets for the next generation ground-based observatory for gamma-ray astronomy, the Cherenkov Telescope Array (CTA). Here we review the CTA science case for the study of the GC region, and present the planned survey strategy. These observations are simulated and we assess CTA's potential to better characterize the origin and nature of a selection of gamma-ray sources in the region.

astro-ph.HE↗

arXiv2019

Intermediate-Mass Black Hole Growth and Feedback in Dwarf Galaxies at High Redshifts

Intermediate-mass black holes (IMBHs: masses between $100 - 10^{6} M_{\odot}$) historically comprise of an elusive population compared to stellar-mass and supermassive BHs. Recently IMBHs have started to be observed at the centers of low-mass galaxies. We perform cosmological hydrodynamical simulations of $(2 h^{-1} ~ {\rm Mpc})^3$ comoving boxes and investigate the growth and feedback of central IMBHs in dwarf galaxies (DGs). The earliest BHs appear at $z \sim 18 - 25$, and grow thereafter by accreting gas and by merger with other BHs. We find that, starting from $10^{2} M_{\odot}$, it is possible to build up IMBHs of a few$\times 10^{5} - 10^{6} M_{\odot}$ by $z = 5$, when the BHs are seeded in halos less massive than $4 \times 10^{7} M_{\odot}$. The BH accretion rates increase with time, and reaches $\dot{M}_{\rm BH} = (0.2 - 0.8) \dot{M}_{\rm Edd}$ for the massive IMBHs by $z = 4$. The star formation rate density (SFRD) evolution of the DGs (stellar mass $10^{5} - 10^{8} M_{\odot}$) has a peak plateau between $z = 4 - 6$. Star formation is quenched between $z = 9 - 4$. The SFRD is reduced by factors up to $3$, when the BHs have grown to a few times $10^5 M_{\odot}$. Even in the presence of stronger SN-driven mass ejection, the BHs continue to grow up to $z \sim 6$, sustained by gas inflows driven by galaxy mergers and interactions in a cosmological environment. Our conclusions, based on numerical simulation results, support the scenario that early feedback from IMBHs in gas-rich DGs at $z = 5 - 8$ can potentially solve several anomalies in the DG mass range within the concordance $Λ$CDM cosmological scenario (Silk 2017). Our results suggest that IMBHs at DG centers grow faster than their host galaxies in the early Universe, and the resulting BH feedback turns the DGs and the BHs dormant.

astro-ph.GA↗

arXiv2019

VHE Emission from Magnetic Reconnection in the RIAF of SgrA*

The cosmic-ray (CR) accelerator at the galactic centre (GC) is not yet established by current observations. Here we investigate the radiative-inefficient accretion flow (RIAF) of Sagittarius A* (SgrA*) as a CR accelerator assuming acceleration by turbulent magnetic reconnection, and derive possible emission fluxes of CRs interacting within the RIAF (the central $\sim10^{13}$cm). The target environment of the RIAF is modelled with numerical, general relativistic magneto-hydrodynamics (GRMHD) together with leptonic radiative transfer simulations. The acceleration of the CRs is not computed here. Instead, we inject CRs constrained by the magnetic reconnection power of the accretion flow and compute the emission/absorption of $γ$-rays due to these CRs interacting with the RIAF, through Monte Carlo simulations employing the {\tt CRPropa 3} code. The resulting very-high-energy (VHE) fluxes are not expected to reproduce the point source HESS J1745-290 as the emission of this source is most likely produced at pc scales. The emission profiles derived here intend to trace the VHE signatures of the RIAF as a CR accelerator and provide predictions for observations of the GC with improved angular resolution and differential flux sensitivity as those of the forthcoming Cherenkov Telescope Array (CTA). Within the scenario presented here, we find that for mass accretion rates $\gtrsim 10^{-7}$M$_\odot$yr$^{-1}$, the RIAF of SgrA* produces VHE fluxes which are consistent with the H.E.S.S. upper limits for the GC and potentially observable by the future CTA. The associated neutrino fluxes are negligible compared with the diffuse neutrino emission measured by the IceCube.

astro-ph.HE↗

arXiv2019

A statistical study of fast magnetic reconnection in turbulent accretion disks and jets

Fast magnetic reconnection events can play an important role in accretion disk systems. A potential model to explain the non-thermal very-high-energy (VHE) emission (from GeV to TeV) observed in black-hole binaries (BHBs) and Active Galatic Nuclei (AGNs) can be attributed to fast magnetic reconnection induced in the turbulent corona of accretion disks and/or jets. In this work, we will discuss the results of global general relativistic MHD (GRMHD) simulations of accretion disks around black holes, whose turbulence is naturally driven by MHD instabilities, such as the magnetorotational instability (MRI). We will also present studies of magnetic reconnection driven by kink instabilities inside jets employing special relativistic MHD (SRMHD) simulations. As we expect, our simulations reveal the development of a nearly steady-state turbulence driven by these instabilities. We have performed a detailed statistical analysis to identify the presence of current sheets in the turbulent regions of both the accretion flow and jet. We then determined the magnetic reconnection rates in these locations obtaining average reconnection velocities in Alfvén speed units of the order of $0.01-0.7$, which are consistent with the predictions of the theory of turbulence-induced fast reconnection.

astro-ph.HE↗

arXiv2019

Magnetic Reconnection, Cosmic Ray Acceleration, and Gamma-Ray emission around Black Holes and Relativistic Jets

Particle acceleration by magnetic reconnection is now recognized as an important process in magnetically dominated regions of galactic and extragalactic black hole sources. This process helps to solve current puzzles specially related to the origin of the very high energy flare emission in these sources. In this review, we discuss this acceleration mechanism and show recent analytical studies and multidimensional numerical SRMHD and GRMHD (special and general relativistic magnetohydrodynamical) simulations with the injection of test particles, which help us to understand this process both in relativistic jets and coronal regions of these sources. The very high energy and neutrino emission resulting from the accelerated particles by reconnection is also discussed.

astro-ph.HE↗

arXiv2019

Supermassive and Intermediate-Mass Black Hole Growth at Galaxy Centers and Resulting Feedback using Cosmological Simulations

Accretion of matter onto central Black Holes (BHs) in galaxies liberates enormous amounts of feedback energy, which influence the formation and evolution of structures, affecting the environment from pc to Mpc scales. These BHs are usually Supermassive BHs (SMBHs: mass $\geq 10^6 M_{\odot}$) existing at the centers of active galactic nuclei (AGN), which are widely observed through their multi-wavelength emission at all cosmic epochs. The SMBH energy output is often observed as powerful AGN outflows in a wide variety of forms. Relatively recently, Intermediate-Mass BHs (IMBHs: mass = $100 - 10^6 M_{\odot}$) have started to be observed hosted in Dwarf Galaxy (DG) centers. Some of the central IMBHs in DGs show signatures of activity in the form of low-luminosity AGN. We have performed Cosmological Hydrodynamical Simulations to probe SMBHs in high-z quasars (Barai et al. 2018), and IMBHs in DGs (Barai & de Gouveia Dal Pino 2019). Our simulations employ the 3D TreePM SPH code GADGET-3, and include metal cooling, star formation, chemical enrichment, stellar evolution, supernova feedback, AGN accretion and feedback. Analyzing the simulation output in post-processing, we investigate the growth of the first IMBHs, and the growth of the first SMBHs, their impact on star-formation, as well as their co-evolution with the respective host galaxies. We quantify the impact of SMBHs and IMBHs on their host galaxies, especially the effects on quenching star-formation. We also study the corresponding BH outflow properties.

astro-ph.GA↗

arXiv2019

A Possible Model for the Long-Term Flares of Sgr A*

We examine the effects of magnetic field on low angular momentum flows with standing shock around black holes in two dimensions. The magnetic field brings change in behavior and location of the shock which results in regularly or chaotically oscillating phenomena of the flow. Adopting fiducial parameters like specific angular momentum, specific energy and magnetic field strength for the flow around Sgr A*, we find that the shock moves back and forth in the range 60--170R_g, irregularly recurring with a time-scale of ~5 days with an accompanying more rapid small modulation with a period of 25 hrs without fading, where R_g is the Schwarzschild radius. The time variability associated with two different periods is attributed to the oscillating outer strong shock, together with another rapidly oscillating inner weak shock. As a consequence of the variable shock location, the luminosities vary roughly by more than a factor of 3. The time-dependent behaviors of the flow are well compatible with luminous flares with a frequency of ~one per day and bright flares occurring every ~5 -- 10 days in the latest observations by Chandra, Swift and XMM-Newton monitoring of Sgr A*.

astro-ph.HE↗