arXiv subjects

Rita C. dos Anjos

Publications and source records attributed to Rita C. dos Anjos.

8 recordsLinked to original sources

arXiv2026

Probing Low-Luminosity Gamma-Ray Emission from SNR G296.5+10.0 and CCO 1E 1207.4-5209 with CTAO

The acceleration mechanisms of cosmic rays (CR) in supernova remnants (SNRs) and their associated compact central objects (CCOs) remain an open question in high-energy astrophysics. In this study, we perform a modeling of CR transport and gamma-ray emission from SNR G296.5+10.0 and its CCO 1E 1207.4-5209, using the latest public release of the GALPROP code (v57) and focusing, in particular, on the contribution from the CCO. Our simulations predict the contribution of CR from this source to the Galactic flux, accounting for energy losses and particle interaction processes. We find that, under time-evolving scenarios, the environment around SNR G296.5+10.0 and 1E 1207.4-5209 is suitable for CR acceleration and gamma-ray production. The analysis distinguishes between gamma rays produced by hadronic interactions in SNR G296.5+10.0 and by leptonic processes in CCO 1E 1207.4-5209, revealing that each mechanism dominates in different energy bands. We show that the Cherenkov Telescope Array Observatory (CTAO) can detect this emission with a significance of 5σ after 50 h of exposure, providing the first constraints on particle acceleration in this unique CCO-SNR system. These findings suggest that CCOs may be efficient electron accelerators, even in the absence of pulsar wind nebulae, and emphasize the critical role of next-generation observatories such as CTAO in unraveling CR acceleration processes in low-luminosity SNR-CCO systems.

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arXiv2025

Blazars Jets and prospects for TeV-PeV neutrinos & gamma-rays through cosmic-ray interactions

This study explores the origins of cosmic rays and their secondary messengers, focusing on the potential role of four BL Lacs W Comae, 1ES 1959+650, PKS 2005-489, and PKS 2155-304 as potential sources of astrophysical neutrinos and gamma rays. We analyzed a single-zone model to understand the interactions between high-energy protons and ambient photons within blazar jets, leading to neutrino production observables and gamma-ray emission. This modeling contextualizes the emissions within multiwavelength observations and evaluates the capabilities of the next-generation Cherenkov Telescope Array Observatory (CTAO) in detecting these emissions. Our estimations suggest that these sources could be effective emitters of CRs, highlighting the need for future multimessenger observations to further investigate and constrain this class of sources.

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arXiv2024

Multi-messenger particles as a probe for UHECR luminosity

Very-high energy (GeV-TeV) gamma rays in the universe suggest the presence of an accelerator in the source. Neutrinos and gamma rays are intriguing astrophysical messengers. Multi-messenger particle emission produced by interactions of cosmic rays with radiation fields and interstellar matter is a probe of luminosity of sources of cosmic rays with EeV energies, known as Ultra-High Energy Cosmic Rays (UHECRs). This work estimates the neutrino flux and suggests that gamma-ray emission is primarily caused by cosmic-ray interactions during propagation. As energy loss processes occur, secondary fluxes are generated, primarily by pion decay. We provide UHECR luminosity of galaxies from multi-messenger particles. These findings not only highlight the potential of certain galaxies as sources of UHECR, but also underscore the intricate interplay of various astrophysical processes within them. By understanding the luminosity patterns and multi-messenger particle emissions, we can gain valuable insights into the environmental conditions, acceleration mechanisms, and other intrinsic properties that position these galaxies as candidates for UHECR production.

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arXiv2024

Binary coalescences as sources of Ultra-High Energy Cosmic Rays

Binary coalescences are known sources of gravitational waves (GWs) and they encompass combinations of black holes (BHs) and neutron stars (NSs). Here we show that when BHs are embedded in magnetic fields ($B$s) larger than approximately $10^{10}$ G, charged particles colliding around their event horizons can easily have center-of-mass energies in the range of ultra-high energies ($\gtrsim 10^{18}$ eV) and escape. Such B-embedding and high-energy particles can take place in BH-NS binaries, or even in BH-BH binaries with one of the BHs being charged (with charge-to-mass ratios as small as $10^{-5}$, which do not change GW waveforms) and having a residual accretion disk. Ultra-high center-of-mass energies for particle collisions arise for basically any rotation parameter of the BH when $B \gtrsim 10^{10}$ G, meaning that it should be a common aspect in binaries, especially in BH-NS ones given the natural presence of a $B$ onto the BH and charged particles due to the NS's magnetosphere. We estimate that up to millions of ultra-high center-of-mass collisions may happen before the merger of BH-BH and BH-NS binaries. Thus, binary coalescences can also be efficient sources of ultra-high energy cosmic rays (UHECRs) and constraints to NS/BH parameters would be possible if UHECRs are detected along with GWs.

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arXiv2022

An updated view and perspectives on high-energy gamma-ray emission from SGR J1935+2154 and its environment

SGR J1935+2154 was discovered in 2016 and is currently one of the most burst-active Soft Gamma-ray Repeaters (SGR), having emitted several X-ray bursts in recent years. In one of our previous articles, we investigated the contribution to high-energy and very high-energy gamma-ray emission (VHE, $E > 100$ GeV) due to cosmic-ray acceleration of SNR G57.2+0.8 hosting SGR J1935+2154 using the GALPROP propagation code. However, follow-up observations of SGR 1935+2154 were made for 2 hours on April 28, 2020, using the High Energy Stereoscopic System (H.E.S.S.). The observations coincide with X-ray bursts detected by INTEGRAL and Fermi/Gamma-ray Burst Monitor (GBM). These are the first high-energy gamma-ray observations of an SGR in a flaring state, and upper limits on sustained and transient emission have been derived. Now that new H.E.S.S. observations have been made, it is interesting to update our model with respect to these new upper limits. We extend our previous results to a more general situation using the new version of GALPROP. We obtain a hadronic model that confirms the results discussed by H.E.S.S.. This leads to an optimistic prospect that cosmic ray gamma rays from SGR J1935+2154 can contribute to the overall gamma energy density distribution and in particular to the diffusion gamma rays from the Galactic center.

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arXiv2021

High-energy gamma-ray emission from SNR G57.2+0.8 hosting SGR J1935+2154

In recent years some efforts have been made to identify active sources capable of accelerating particles up to $10^{15}$ eV, known as PeVatrons. Measurements of TeV ($10^{12}$ eV) gamma-rays from supernova remnants (SNRs) have shown that efficient particle acceleration can occur in SNR diffusive shocks. In this paper, we obtain the contribution to the high energy and very-high-energy gamma-ray (VHE, $E > 100$ GeV) emission due to cosmic-ray acceleration from SNR G57.2+0.8 hosting the Soft Gamma Repeater (SGR) J1935+2154 with the use of the GALPROP code. To do so, we take into account the SNR + SGR association as a single source close to the Galactic center. We propose that the above setting can provide a more comprehensive scenario for the generation of GeV-TeV gamma-rays. We also discuss the contribution from the SNR G57.2+0.8 and SGR J1935+2154 region to the diffusive TeV energy gamma-ray emission from the Galactic center.

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arXiv2018

Ultrahigh-Energy Cosmic Ray Composition from the Distribution of Arrival Directions

The sources of ultrahigh-energy cosmic rays (UHECRs) have been difficult to catch. It was recently pointed out that while sources of UHECR protons exhibit anisotropy patterns that become denser and compressed with rising energy, nucleus-emitting-sources give rise to a cepa stratis (onion-like) structure with layers that become more distant from the source position with rising energy. The peculiar shape of the hot spots from nucleus-accelerators is steered by the competition between energy loss during propagation and deflection on the Galactic magnetic field (GMF). Here, we run a full-blown simulation study to accurately characterize the deflections of UHECR nuclei in the GMF. We show that while the cepa stratis structure provides a global description of anisotropy patterns produced by UHECR nuclei en route to Earth, the hot spots are elongated depending on their location in the sky due to the regular structure of the GMF. We demonstrate that with a high-statistics sample at the high-energy-end of the spectrum, like the one to be collected by NASA's POEMMA mission, the energy dependence of the hot-spot contours could become a useful observable to identify the nuclear composition of UHECRs. This new method to determine the nature of the particle species is complementary to those using observables of extensive air showers, and therefore is unaffected by the large systematic uncertainties of hadronic interaction models.

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arXiv2017

The influence of the observatory latitude on the study of ultra high energy cosmic rays

Recent precision measurements of the Ultra High Energy Cosmic Rays (UHECR) arrival directions, spectrum and parameters related to the mass of the primary particle have been done by the HiRes, Pierre Auger and Telescope Array (TA) Observatories. In this paper, distributions of arrival directions of events in the nearby Universe are assumed to correlate with sources in the 2MASS Redshift Survey (2MRS), IRAS 1.2 Jy Survey, Palermo Swift-BAT and Swift-BAT catalogs, and the effect of the latitude of the observatory on the measurement of the energy spectrum and on the capability of measuring anisotropy is studied. The differences between given latitudes on the northern and southern hemispheres are quantified. It is shown that the latitude of the observatory: a) has an influence on the total flux measured and b) imposes an important limitation on the capability of measuring an anisotropic sky.

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