arXiv subjects

Viviana Gammaldi

Publications and source records attributed to Viviana Gammaldi.

18 recordsLinked to original sources

arXiv2026

Sgr A* as a Galactic PeVatron: Multimessenger Signatures of the Magnetic Penrose Process

The magnetic Penrose process (MPP) is one of the most efficient mechanisms for extracting rotational energy from a magnetized Kerr black hole (BH), enabling charged particles to reach very-high energies. We investigate this process in Sagittarius A* (Sgr A*), the supermassive BH at the Galactic center (GC), focusing on its ultra-high-efficiency regime, in which neutrons undergo beta decay inside the BH ergosphere. As a key novelty, we compute the neutron production spectrum in the accretion flow directly from the nuclear reaction kinematics and follow neutron trajectories in the Kerr spacetime to determine the population that reaches the ergosphere and undergoes the MPP. From this population, we derive the spectrum of accelerated protons and show that Sgr A* can accelerate them up to PeV energies, strengthening its interpretation as a candidate Galactic PeVatron. We further compute the gamma-ray and neutrino emission produced through hadronic interactions of the escaping protons in the Central Molecular Zone. The predicted gamma-ray fluxes exhibit distinctive spectral features that could provide an observational signature of the MPP and may constitute a non-negligible contribution to the very-high-energy emission detected by H.E.S.S. and HAWC. The associated neutrino fluxes remain below the diffuse Galactic component inferred by IceCube, but may still contribute to the high-energy emission from the GC. Remarkably, the predicted signals lie within the projected sensitivity of SWGO for all scenarios considered here and, for some models, only a factor of a few below the nominal CTAO sensitivity, while KM3NeT/ARCA and IceCube-Gen2 will provide complementary tests. Our results establish the MPP as an observable mechanism for extracting BH rotational energy, providing a direct connection between horizon-scale physics and multimessenger observations that can be extended to other magnetized BHs.

astro-ph.HE↗

arXiv2026

Search for dark matter subhalos among unassociated Fermi-LAT sources in presence of dataset shift

We present a search for dark matter (DM) annihilating subhalos of the Milky Way halo among the {\Fermi} Large Area Telescope (LAT) unassociated sources. For this purpose, we construct the first statistical model of the unassociated sources at latitudes above 10 degrees, combining potential DM subhalos with Galactic and extragalactic astrophysical components. The distributions of astrophysical sources are constructed based on associated sources, while the DM subhalo distribution is derived from Monte Carlo simulations. We account for differences between associated and unassociated source distributions using a model with covariate and prior probability shifts, which are particular cases of more general dataset shifts. This approach is based on quantification learning, advancing beyond previous classify-and-count strategies by providing a well-defined statistical interpretation of the potential contribution from a DM subhalo population. For the $b\bar{b}$ annihilation channel and DM masses from 10 GeV to 1 TeV, we find no significant contribution from DM subhalos, and therefore derive 95% confidence upper limits on the annihilation cross section. Our analysis yields limits consistent with previous classify-and-count approaches, while the underlying generative model provides a more robust statistical framework, opening new avenues for population studies of Fermi-LAT sources and, more generally, for searches of anomalies, such as a new class of sources in addition to the known classes of sources, in presence of statistical and systematic uncertainties.

astro-ph.HE↗

arXiv2026

The potential of diffuse Galactic Ridge neutrino measurements to constrain dark matter

We use the latest ANTARES Galactic Ridge neutrino measurements to investigate their implications for indirect dark matter (DM) searches. We consider both annihilating and decaying DM scenarios, spanning a wide range of masses and final states, and systematically compare the resulting neutrino fluxes with the expected astrophysical Galactic diffuse emission. Furthermore, we compare the results for different DM density profiles allowed by the observations, from spike and cuspy to cored profiles. We do so for the WIMP model-independent scenario and explore two more specific models: branons and very heavy sterile neutrinos, where a cold DM candidate arises naturally from the theory. We show the potential neutrino measurements in the Galactic Ridge for DM and make predictions for future neutrino observatories.

astro-ph.HE↗

arXiv2026

Sensitivity of the Cherenkov Telescope Array Observatory to Gamma-Ray Signals in Dwarf Irregular Galaxies

Dwarf irregular galaxies (dIrrs) are rotationally supported galaxies with a low star formation rate. Thus, their gamma-ray astrophysical emission is expected to be low, making them interesting targets for WIMP dark matter (DM) indirect searches. In this work, we build upon previous work on these objects in this DM context, and identify the best four dIrrs to be observed by the forthcoming Cherenkov Telescope Array Observatory (CTAO). Since dIrrs have not been detected in gamma rays yet, we first explore the prospects for detecting their astrophysical emission with the CTAO. Secondly, we compute the CTAO sensitivity prospects to a DM annihilating signal from these objects, accounting for the presence of DM substructures in them. We do so for both cuspy and cored DM density profiles, as the cusp-core debate remains particularly open for dIrrs. Our best combined limits show the potential to exclude DM annihilation cross-section values around $2\times 10^{-24} \ \mathrm{cm^{3}}\mathrm{s^{-1}}$ for 100 GeV WIMP masses annihilating in the $τ^+τ^-$ channel. These prospective results are competitive with and complementary to benchmark targets such as galaxy clusters. We also analyze the case of the velocity-dependent annihilation cross-section (Sommerfeld enhancement), obtaining projected DM constraints that exceed those expected for dwarf spheroidal galaxies, thanks to the contribution of subhalos to the signal. We conclude that dIrrs are compelling targets for the CTAO, not only for DM indirect searches but also as possible astrophysical sources.

astro-ph.HE↗

arXiv2023

Multi-TeV dark matter density in the inner Milky Way halo: spectral and dynamical constraints

We develop a comprehensive study of the gamma-ray flux observed by H.E.S.S. in 5 regions of the Galactic Center (GC). Motivated by previous works on a possible Dark Matter (DM) explanation for the TeV cut-off observed in the innermost $\sim 16$ pc of the Galaxy, we aim to constrain the DM density profile up to a radius $\sim 450$ pc from the GC. In this region, cosmological simulations and Galactic dynamics studies fail to produce a strong prediction of the DM profile. With our proof-of-concept analysis, we set upper limits on the density distribution of thermal multi-TeV WIMPs, compatible with the observed gamma-ray flux. The results agree with the hypothesis of a DM density enhancement in the GC with respect to the benchmark NFW profile ($γ=1$) and allow us to exclude profiles with a slope $γ\gtrsim 1.3$. We also investigate the possibility that such an enhancement could be related to the existence of a DM spike associated with the supermassive black hole Sgr A*. We find out that the existence of an adiabatic DM spike smoothed by the scattering off of WIMPs by the bulge stars may be consistent with the observed gamma-ray flux if the spike forms on an underlying generalized NFW profile with $γ\lesssim 0.8$, corresponding to a spike slope $γ_{sp-star}= 1.5$ and radius $R_\text{sp-stars} \sim 25$-$30$ pc. Instead, in the extreme case of the instantaneous growth of the black hole, the profile could have up to $γ\sim 1.2$, a corresponding $γ_{sp-inst}=1.4$ and $R_\text{sp-inst}\sim 15$-$25$ pc. Moreover, the results of our analysis of the total DM mass enclosed within the S2 orbit are less stringent than the spectral analysis. Our work aims to guide future studies of the GC region, with both current and next-generation telescopes, like the next Cherenkov Telescope Array, that will be able to scan the GC with improved flux sensitivity and angular resolution.

astro-ph.HE↗

arXiv2023

The Third Fermi Large Area Telescope Catalog of Gamma-ray Pulsars

We present 294 pulsars found in GeV data from the Large Area Telescope (LAT) on the Fermi Gamma-ray Space Telescope. Another 33 millisecond pulsars (MSPs) discovered in deep radio searches of LAT sources will likely reveal pulsations once phase-connected rotation ephemerides are achieved. A further dozen optical and/or X-ray binary systems co-located with LAT sources also likely harbor gamma-ray MSPs. This catalog thus reports roughly 340 gamma-ray pulsars and candidates, 10% of all known pulsars, compared to $\leq 11$ known before Fermi. Half of the gamma-ray pulsars are young. Of these, the half that are undetected in radio have a broader Galactic latitude distribution than the young radio-loud pulsars. The others are MSPs, with 6 undetected in radio. Overall, >235 are bright enough above 50 MeV to fit the pulse profile, the energy spectrum, or both. For the common two-peaked profiles, the gamma-ray peak closest to the magnetic pole crossing generally has a softer spectrum. The spectral energy distributions tend to narrow as the spindown power $\dot E$ decreases to its observed minimum near $10^{33}$ erg s$^{-1}$, approaching the shape for synchrotron radiation from monoenergetic electrons. We calculate gamma-ray luminosities when distances are available. Our all-sky gamma-ray sensitivity map is useful for population syntheses. The electronic catalog version provides gamma-ray pulsar ephemerides, properties and fit results to guide and be compared with modeling results.

astro-ph.HE↗

arXiv2022

The Fourth Catalog of Active Galactic Nuclei Detected by the Fermi Large Area Telescope -- Data Release 3

An incremental version of the fourth catalog of active galactic nuclei (AGNs) detected by the Fermi-Large Area Telescope is presented. This version (4LAC-DR3) derives from the third data release of the 4FGL catalog based on 12 years of E>50 MeV gamma-ray data, where the spectral parameters, spectral energy distributions (SEDs), yearly light curves, and associations have been updated for all sources. The new reported AGNs include 587 blazar candidates and four radio galaxies. We describe the properties of the new sample and outline changes affecting the previously published one. We also introduce two new parameters in this release, namely the peak energy of the SED high-energy component and the corresponding flux. These parameters allow an assessment of the Compton dominance, the ratio of the Inverse-Compton to the synchrotron peak luminosities, without relying on X-ray data.

astro-ph.HE↗

arXiv2022

Constraining branon dark matter from observations of the dwarf spheroidal galaxies with the MAGIC telescopes

We present the first branon dark matter (DM) search in the very high-energy gamma-ray band with observations of the dwarf spheroidal galaxy Segue~1 carried out by the Major Atmospheric Gamma Imaging Cherenkov (MAGIC) telescope system. Branons are new degrees of freedom that appear in flexible brane-world models corresponding to brane fluctuations. They behave as weakly interacting massive particles, which are natural DM candidates. In the absence of a gamma-ray signal in the Segue~1 data, we place constraints on the branon DM parameter space by using a binned likelihood analysis. Our most constraining limit to the thermally-averaged annihilation cross-section (at $95\%$ confidence level) corresponds to $ \langle σv \rangle \simeq 1.4 \times 10^{-23}~\text{cm}^{3}\text{s}^{-1} $ at a branon DM mass of $ \sim 0.7~\text{TeV}$.

astro-ph.HE↗

arXiv2022

Incremental Fermi Large Area Telescope Fourth Source Catalog

We present an incremental version (4FGL-DR3, for Data Release 3) of the fourth Fermi-LAT catalog of gamma-ray sources. Based on the first twelve years of science data in the energy range from 50 MeV to 1 TeV, it contains 6658 sources. The analysis improves on that used for the 4FGL catalog over eight years of data: more sources are fit with curved spectra, we introduce a more robust spectral parameterization for pulsars, and we extend the spectral points to 1 TeV. The spectral parameters, spectral energy distributions, and associations are updated for all sources. Light curves are rebuilt for all sources with 1 yr intervals (not 2 month intervals). Among the 5064 original 4FGL sources, 16 were deleted, 112 are formally below the detection threshold over 12 yr (but are kept in the list), while 74 are newly associated, 10 have an improved association, and seven associations were withdrawn. Pulsars are split explicitly between young and millisecond pulsars. Pulsars and binaries newly detected in LAT sources, as well as more than 100 newly classified blazars, are reported. We add three extended sources and 1607 new point sources, mostly just above the detection threshold, among which eight are considered identified, and 699 have a plausible counterpart at other wavelengths. We discuss degree-scale residuals to the global sky model and clusters of soft unassociated point sources close to the Galactic plane, which are possibly related to limitations of the interstellar emission model and missing extended sources.

astro-ph.HE↗

arXiv2022

Constraining branon dark matter from observations of the Segue 1 dwarf spheroidal galaxy with the MAGIC telescopes

We present the first search for signatures of brane-world extra-dimensional dark matter (DM) in the very-high-energy gamma-ray band by scrutinizing observations of the dwarf spheroidal galaxy Segue 1 with the Major Atmospheric Gamma Imaging Cherenkov (MAGIC) telescope system. Branons are new degrees of freedom that appear within flexible brane-world models: they are weakly interacting massive particles and natural DM candidates. The ground-based gamma-ray telescopes MAGIC could indirectly detect branon DM in the multi-TeV mass range by observing secondary products of DM annihilation into Standard Model particles. In the absence of a signal, we place constraints on the branon DM parameter space by using a binned likelihood analysis of almost 160-hours deep exposure on the Segue 1 dwarf spheroidal galaxy by the MAGIC telescopes. Our most stringent limit to the thermally-averaged annihilation cross-section (at $95\%$ confidence level) corresponds to $ \langle σv \rangle \simeq 1.4 \times 10^{-23}~\text{cm}^{3}\text{s}^{-1} $ at a branon mass of $ \sim 0.7~\text{TeV}$.

astro-ph.HE↗

arXiv2020

Einstein, Planck and Vera Rubin: relevant encounters between the Cosmological and the Quantum Worlds

In Cosmology and in Fundamental Physics there is a crucial question like: where the elusive substance that we call Dark Matter is hidden in the Universe and what is it made of?, that, even after 40 years from the Vera Rubin seminal discovery does not have a proper answer. Actually, the more we have investigated, the more this issue has become strongly entangled with aspects that go beyond the established Quantum Physics, the Standard Model of Elementary particles and the General Relativity and related to processes like the Inflation, the accelerated expansion of the Universe and High Energy Phenomena around compact objects. Even Quantum Gravity and very exotic DM particle candidates may play a role in framing the Dark Matter mystery that seems to be accomplice of new unknown Physics. Observations and experiments have clearly indicated that the above phenomenon cannot be considered as already theoretically framed, as hoped for decades. The Special Topic to which this review belongs wants to penetrate this newly realized mystery from different angles, including that of a contamination of different fields of Physics apparently unrelated. We show with the works of this ST that this contamination is able to guide us into the required new Physics. This review wants to provide a good number of these "paths or contamination" beyond/among the three worlds above; in most of the cases, the results presented here open a direct link with the multi-scale dark matter phenomenon, enlightening some of its important aspects. Also in the remaining cases, possible interesting contacts emerges.

gr-qc↗

arXiv2020

Cherenkov Telescope Array sensitivity to branon dark matter models

In the absence of a clear hint of dark matter (DM) signals in the GeV regime so far, heavy, $\mathcal{O}$(TeV) DM candidates are gradually earning more and more attention within the community. Among others, extra-dimensional \textit{brane-world} models may produce thermal DM candidates with masses up to 100 TeV. These heavy DM candidates could be detected with the next generation of very-high-energy gamma-ray observatories such as the Cherenkov Telescope Array (CTA). In this work, we study the sensitivity of CTA to branon DM via the observation of representative astrophysical DM targets, namely dwarf spheroidal galaxies. In particular, we focus on Draco and Sculptor, two well-known dwarfs visible from the Northern and Southern Hemisphere, respectively. For each of these targets, we simulated 300\,h of CTA observations and studied the sensitivity of both CTA-North and CTA-South to branon annihilations using the latest publicly available instrument response functions and most recent analysis tools. We computed annihilation cross section values needed to reach a $5σ$ detection as a function of the branon mass. Additionally, in the absence of a predicted DM signal, we obtained $2σ$ upper limits on the annihilation cross section. These limits lie $1.5-2$ orders of magnitude above the thermal relic cross section value, depending on the considered branon mass. Yet, CTA will allow to exclude a significant portion of the brane tension-mass parameter space in the $0.1-60$ TeV branon mass range, and up to tensions of $\sim 10$ TeV. More importantly, CTA will significantly enlarge the region already excluded by AMS and CMS, and will provide valuable complementary information to future SKA radio observations. We conclude that CTA will possess potential to constrain brane-world models and, more in general, TeV DM candidates.

astro-ph.HE↗

arXiv2019

Constraints on cross-section and lifetime of dark matter with HAWC Observations of dwarf Irregular galaxies

It has been shown that the dynamics of dwarf Irregular (dIrr) galaxies are dominated by dark matter. It is also observed that these galaxies have low star formation rates and metallicities, and no gamma-ray emission at ultra very high energies is expected. Because of their distance, dark matter content and vast number, dIrr galaxies are good targets to perform indirect dark matter searches by ground-based and wide field of view gamma-ray experiments, like HAWC. We analyzed data at the position of 31 dIrr galaxies within the HAWC field-of-view and no significant excess was found. Here, we present the individual and combined limits on the annihilation cross-section and decay lifetime of weakly interacting massive particles with a mass between 1 and 100 TeV.

astro-ph.HE↗

arXiv2019

Multimessenger TeV Dark Matter: a mini review

We briefly review the general insight into the indirect searches of dark matter. We discuss the primary equation in a three-level multimessenger approach (gamma rays, neutrinos and antiprotons), and we introduce the reader to the main topics and related uncertainties (e.g. dark matter density distribution, cosmic rays, particle physics). As an application of the general concept, we focus on the multi-TeV dark matter candidate among other weak interactive massive particles. We present the state-of-the-art on this sub-field, and we discuss open questions and experimental limitations.

astro-ph.HE↗

arXiv2017

Searching for TeV DM evidence from Dwarf Irregular Galaxies with the HAWC Observatory

The dynamics of dwarf irregular (dIrr) galaxies are observed to be dominated by dark matter (DM). Recently, the DM density distribution has been studied for 31 dIrrs. Their extended DM halo (Burket type profile) makes these objects good candidates for DM searches. Located in Puebla (Mexico), the High Altitude Water Cherenkov (HAWC) Observatory is an optimal in- strument to perform such DM searches, because of its large sky coverage (8.4 sr per day). We analyzed a set of two years of HAWC data and we found no significant DM signal from dIrr galaxies. We present the upper limits for DM annihilation cross-section with dIrr galaxies.

astro-ph.HE↗

arXiv2014

Highlights on gamma rays, neutrinos and antiprotons from TeV Dark Matter

It has been shown that the gamma-ray flux observed by HESS from the J1745-290 Galactic Center source is well fitted as the secondary gamma-rays photons generated from Dark Matter annihilating into Standard Model particles in combination with a simple power law background. The neutrino flux expected from such Dark Matter source has been also analyzed. The main results of such analyses for 50 TeV Dark Matter annihilating into W+W- gauge boson and preliminary results for antiprotons are presented.

astro-ph.HE↗

arXiv2013

Cosmic Rays from Heavy Dark Matter from the Galactic Center

The gamma-ray fluxes observed by the High Energy Stereoscopic System (HESS) from the J1745-290 Galactic Center source is well fitted by the secondary photons coming from Dark Matter (DM) annihilation in particle-antiparticle standard model pairs over a diffuse power-law background. The spectral features of the signal are consistent with different channels: light quarks, electro-weak gauge bosons and top-antitop production. The amount of photons and morphology of the signal localized within a region of few parsecs, require compressed DM profiles as those resulting from baryonic contraction, which offer large enhancements in the signal over DM alone simulations. The fits return a heavy WIMP, with a mass above 10 TeV, but well below the unitarity limit for thermal relic annihilation. The fitted background spectral index is compatible with the Fermi-Large Area Telescope (LAT) data from the same region. This possibility can be potentially tested with the observations of other high energy cosmic rays.

astro-ph.HE↗

arXiv2011

Dark matter with photons

If the present dark matter in the Universe annihilates into Standard Model particles, it must contribute to the gamma ray fluxes detected on the Earth. The magnitude of such contribution depends on the particular dark matter candidate, but certain features of the produced spectra may be analyzed in a rather model-independent fashion. In this communication we briefly revise the complete photon spectra coming from WIMP annihilation into Standard Model particle-antiparticle pairs obtained by extensive Monte Carlo simulations and consequent fitting functions presented by Dombriz et al. in a wide range of WIMP masses. In order to illustrate the usefulness of these fitting functions, we mention how these results may be applied to the so-called brane-world theories whose fluctuations, the branons, behave as WIMPs and therefore may spontaneously annihilate in SM particles. The subsequent $γ$-rays signal in the framework of dark matter indirect searches from Milky Way dSphs and Galactic Center may provide first evidences for this scenario.

hep-ph↗