arXiv subjects

J. A. Morales-Soto

Publications and source records attributed to J. A. Morales-Soto.

At least 19 recordsLinked to original sources

arXiv2026

TeV Gamma-Ray Emission in the DA 495 Region from HAWC Observations of J1952+2924, J1954+2837, and J1958+2848

Previous observations of the DA 495 region, which contains the pulsar wind nebula (PWN) DA 495 and other very-high-energy (VHE; $>100~\textrm{GeV}$) gamma-ray emitters, showed inconsistent results across different VHE experiments, including differences in the measured flux of DA 495 and in the number of reported sources. Our new dedicated analysis using 3071 days of HAWC data resolves these discrepancies. We identify three extended sources, HAWC J1952+2924 (DA 495), HAWC J1954+2837, and HAWC J1958+2848, all with curved spectra, and find a hint of a fourth source. For DA 495, a multi-wavelength analysis, including our results, radio, X-ray, and other gamma-ray data, reveals that its extended emission is best described by leptonic interactions with an inferred magnetic field of $B\sim10~μ\textrm{G}$ and that hadronic components are not required. On the other hand, we interpret the other two sources, which have no confirmed counterparts, as TeV halos associated with nearby pulsars, PSR J1954+2836 and PSR J1958+2846, respectively. These results reinforce the interpretation of DA 495 as a leptonic-dominated PWN and add two candidates to the growing population of TeV halos.

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arXiv2026

Improved Heavy Dark Matter Annihilation Search from Dwarf Galaxies with HAWC

Understanding dark matter's elusive nature is crucial for the framework of particle physics and expanding the Standard Model. This analysis utilizes the High Altitude Water Cherenkov (HAWC) gamma ray Observatory to indirectly search for dark matter (DM) by studying gamma ray emission from dwarf spheroidal galaxies (dSphs). Selected for their high ratio of dark matter to baryonic matter, dSphs are useful for this type of search owing to the low background emission. In comparison to previous HAWC studies, we significantly improve our sensitivity to DM from dSphs due to improvements to our event reconstruction and reduced hadronic contamination. We expanded the number of dSphs studied, DM annihilation channels into the Standard Model (SM), and the amount of data collected on each previously studied dSph. We searched for DM signals in each dSph using the latest version of the algorithms used to reconstruct data from the primary detector of the HAWC instrument. We report that we do not detect evidence of DM from dSphs, so we place upper limits for the velocity-weighted DM annihilation cross-section ($\langleσv \rangle$) on the order of $10^{-23}~\text{cm}^3\text{s}^{-1}$ for a DM mass range of $1-10^4$ TeV.

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arXiv2026

HAWC Study on the Ultra-High-Energy Gamma-Ray Emissions from the Pulsar Wind Nebula G32.64+0.53

Multi-TeV gamma-ray emission around eHWC J1850+001 (a source from the first HAWC catalog of gamma-ray sources emitting above 56 TeV) is spatially coincident with the pulsar wind nebula (PWN) G32.64+0.53, powered by PSR J1849-0001. The absence of counterparts in radio, optical, and GeV energy ranges, contrasted with clear detections in X-rays and very-high-energy (VHE) gamma-rays, is indicative of a non-thermal leptonic origin for the nebula. We apply a systematic analysis pipeline, including a sophisticated model for the Galactic diffuse emission, to 2860 days of data from the HAWC Observatory. Our detailed analysis confirms that the ultra-high-energy (UHE) emission originates from G32.64+0.53, and we measure its spectrum up to 270 TeV with significant emission well beyond 100 TeV. We fit the multi-wavelength observations with a time-dependent leptonic model powered by the pulsar's rotational energy, and the results establish the nebula as a leptonic PeV accelerator, capable of accelerating electrons to a maximum energy of $E_{\mathrm{cut}}\geq2.9~\mathrm{PeV}$ (95\% one-sided lower bound). The model also constrains the nebular magnetic field to $4.28 ~\mathrm{μG}$, supporting a leptonic PWN origin for the observed UHE emission.

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arXiv2026

Constraints on axion-like particles from ultra-high-energy observations of M87 with the HAWC observatory

In this work, we perform an indirect search for axion-like particles (ALPs) through their hypothesized mixing with photons in the presence of magnetic fields. ALPs are a well-motivated dark-matter candidate class, and the photon-ALP conversion mechanism provides a unique channel to constrain their mass and coupling constant using very-high-energy gamma-ray observations. The photon-ALP mixing could alter the observed gamma-ray spectrum from extragalactic sources by effectively reducing the apparent attenuation due to extragalactic-background-light absorption. We analyze 7.5 years of data from the High Altitude Water Cherenkov (HAWC) Observatory, targeting the nearby radio galaxy M87. This source is located within the Virgo cluster and is an ideal environment for photon-ALP conversion due to its low redshift and the large-scale, strongly magnetized medium of the cluster. We find no evidence for a photon-ALP conversion signal and, consequently, set constraints on the ALP mass and photon-ALP coupling constant with emission from M87 which are consistent with previous results. Our analysis places competitive constraints on the ALP parameter space, defining an exclusion region in the mass range of approximately $10^{-8}$ to $10^{-6}$ eV for coupling constants above $5\times10^{-12}$ GeV$^{-1}$, complementing previous constraints from other gamma-ray observatories.

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arXiv2026

Search for TeV emission from spider millisecond pulsars with HAWC

Millisecond pulsars (MSPs) are observed to emit multi-wavelength radiation, from radio to GeV. Spider MSPs, which interact with their low-mass companion in close orbit (orbital periods $< 1$ day), may lead to strong intrabinary shocks that can further accelerate electron and positron pairs produced in the magnetosphere, possibly emitting very-high-energy (0.1--100 TeV; VHE) photons through inverse Compton scattering. Using 2565 days of HAWC Pass 5 data, we search for VHE emission from spider MSPs and present upper limits on individual sources. We also perform a stacking analysis to examine whether the two sets of spider systems, classified as redbacks and black widows depending on the companion mass, exhibit different spectral properties. Our study places constraints on TeV emission from MSPs and suggests that they are unlikely to contribute significantly to the Galactic diffuse emission at TeV and higher energies.

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arXiv2026

A Multi-messenger Search for Ultra-high-energy Gamma Rays in Coincidence with Neutrinos

The last five years have shown us that ultra-high-energy (UHE; $>$100 TeV) gamma-ray sources are ubiquitous, but the nature of these sources remain highly uncertain. UHE gamma rays can be produced via either leptonic (Inverse compton) or hadronic (pion decay) emission mechanisms. To decisively determine the emission mechanisms, multimessenger searches are essential. Neutrinos are of particular interest as they are only created via hadronic channels. In this work, we describe a metric to select high-quality UHE events from the High Altitude Water Cherenkov (HAWC) Observatory. We use this metric to search for correlations between HAWC archival data and IceCube public neutrino alerts. 24 spatial coincidences are found, which is higher than the number of events expected by random chance. Therefore, we conclude that there are likely associations between HAWC gamma rays and IceCube neutrinos, but the angular resolutions of the two instruments prevent us from conclusively making any definitive associations between the coincidences and specific astrophysical sources. More sensitive detectors are needed.

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arXiv2026

Search for Signatures of Dark Matter Annihilation in the Galactic Center with HAWC

We conduct an indirect dark matter (DM) search in the Galactic Center, focusing on a square region within $\pm 9^{\circ}$ in Galactic longitude and latutide, using 2,865 days of data ($\sim$8 years) from the High-Altitude Water Cherenkov (HAWC) Observatory. We explore DM particles within the Weakly Interacting Massive Particles framework with masses from 1 TeV to 10 PeV. Analyzing three annihilation channels ($b\bar{b}$, $τ^{+}τ^{-}$, $W^{+}W^{-}$) and three density profiles (Navarro-Frenk-White, Einasto, Burkert), we find no significant excess and set 95\% confidence-level upper limits on the velocity-weighted annihilation cross section. Our results provide the first constraints on DM particles well above 100 TeV using gamma-ray data from the Galactic Center, with the strongest limits $\mathcal{O}(10^{-24})$~cm$^{3}$/s, from the $τ^{+}τ^{-}$ channel and the Einasto profile.

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arXiv2026

Constraints on Axion-Like Particles from Ultra-High-Energy Observations of 3HWC J1908+063 with HAWC

Axion-like particles (ALPs) are hypothetical particles and compelling candidates for cold dark matter. Their existence could be probed through their conversions into photons in the presence of magnetic fields. In this work, we explore the effect of these photon-ALP conversions by searching for an attenuation in the observed gamma ray spectra of galactic sources that emit at energies of hundreds of TeV. We analyze data from the High-Altitude Water Cherenkov (HAWC) Observatory for the source 3HWC J1908+063. No evidence of photon-ALP conversions was found, and we set constraints on the ALP parameter space. Specifically, we derive exclusion limits for ALPs with masses in the range $10^{-8}~\mathrm{eV} \leq m_a \leq 10^{-6}~\mathrm{eV}$ and photon-ALP couplings in the range $10^{-12}~\mathrm{GeV}^{-1} \leq g_{aγ} \leq 10^{-10}~\mathrm{GeV}^{-1}$, based on HAWC observations.

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arXiv2025

Study of the IC 443 region with the HAWC observatory

Supernova remnants are one potential source class considered a PeVatron (i.e. capable of accelerating cosmic rays above PeV energies). The shock fronts produced after the explosion of the supernova are ideal regions for particle acceleration. IC 443 is a supernova remnant that has been studied extensively at different wavelengths. Using 2966 days of gamma-ray data from the HAWC observatory, we study the emission of IC 443 with the objective of finding signatures of cosmic-ray acceleration at the PeV scale. Using a maximum likelihood method, we find a point source located at ($α$=94.42$^{\circ}$, $δ$=22.35$^{\circ}$) that we associate with IC 443. The measured spectrum is a simple power law with an index of $-3.14\pm$0.18, which is consistent with previous TeV observations. Although we cannot confirm that IC 443 is a hadronic PeVatron, we do not find any sign that the spectrum has a cut off at tens of TeV energies, with the spectrum extending to $\sim$30 TeV. Furthermore, we also find a new extended component in the region whose emission is described by a simple power law with an index of $-2.49\pm$0.08 and which we call HAWC J0615+2213. While we show evidence that this new source might be a new TeV halo, we defer a detailed analysis of this new source to another publication.

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arXiv2025

HAWC Performance Enhanced by Machine Learning in Gamma-Hadron Separation

Improving gamma-hadron separation is one of the most effective ways to enhance the performance of ground-based gamma-ray observatories. With over a decade of continuous operation, the High-Altitude Water Cherenkov (HAWC) Observatory has contributed significantly to high-energy astrophysics. To further leverage its rich dataset, we introduce a machine learning approach for gamma-hadron separation. A Multilayer Perceptron shows the best performance, surpassing traditional and other Machine Learning based methods. This approach shows a notable improvement in the detector's sensitivity, supported by results from both simulated and real HAWC data. In particular, it achieves a 19\% increase in significance for the Crab Nebula, commonly used as a benchmark. These improvements highlight the potential of machine learning to significantly enhance the performance of HAWC and provide a valuable reference for ground-based observatories, such as Large High Altitude Air Shower Observatory (LHAASO) and the upcoming Southern Wide-field Gamma-ray Observatory (SWGO).

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arXiv2025

Longtime Monitoring of TeV Radio Galaxies with HAWC

We present the monitoring of the TeV-emitting radio galaxies M87, NGC~1275, 3C~264, and IC~310 with the High Altitude Water Cherenkov Observatory (HAWC) over a period of approximately $7.5$ years. The analysis includes light curves at daily, weekly and monthly time scales for the four sources. We report the detection of gamma-ray emission from M87 with a significance exceeding 5$σ$. Due to its significant detection, this work reports the integrated TeV spectrum of M87 from the longest temporal coverage up to date. The source is well described as a point-like source modeled by a power law spectrum with spectral index $α= 2.53\pm0.29$ and a flux of $(7.09\pm 1.24)\times10^{-13}$ $\rm{cm}^{-2}\,{s}^{-1}\,{TeV}^{-1}$ at $1\,\rm{TeV}$. The maximum energy of the detected emission in M87, at 1$σ$ confidence level (C.L.), reaches 26.5 TeV. HAWC's observation of M87 reveals a low flux spectrum for the longest observation to date of this radio galaxy. 3C~264 is marginally detected with a significance slightly below 4$σ$, while NGC~1275 and IC~310 are not detected. The weekly light curves show an increased number of fluxes above $2σ$ for M87 starting in 2019, and for 3C~264 starting in 2018, which can be interpreted as the moment for which these sources start to exhibit an enhanced steady TeV emission. Overall, in the four radio galaxies, the cumulative significance over time indicates a behavior that resembles that of a gamma-ray variable active galaxy, such as the blazar Markarian 421. This supports the importance of monitoring radio galaxies to identify periods of higher activity and flares, enabling further multi-messenger studies.

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arXiv2025

Absence of TeV halos around millisecond pulsars

TeV halos are extended very-high-energy (VHE; 0.1-100 TeV) gamma-ray emission around middle-aged pulsars. So far they have only been found around isolated pulsars, but it has been suggested that they may also be powered by millisecond pulsars (MSPs). We searched for VHE gamma-ray emission from MSPs reported by radio and GeV gamma-ray observatories in 2565 days of data from the High Altitude Water Cherenkov (HAWC) Observatory. We found no significant emission from individual pulsars. By combining the likelihood profiles of all MSPs accessible to HAWC, our analysis suggests that the excess emission around the MSP population is consistent with a background. Our result suggests that MSPs are not as efficient as isolated pulsars in producing TeV halos. This finding has strong implications on the physics interpretation of the Galactic Center GeV excess and high-latitude Galactic diffuse emission.

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arXiv2025

Extended TeV Halos May Commonly Exist around Middle-Aged Pulsars

Extended gamma-ray emission around isolated pulsars at TeV energies, also known as TeV halos, have been found around a handful of middle-aged pulsars. The halos are significantly more extended than their pulsar wind nebulae but much smaller than the particle diffusion length in the interstellar medium. The origin of TeV halos is unknown. Interpretations invoke either local effects related to the environment of a pulsar or generic particle transport behaviors. The latter scenario predicts that TeV halos would be a universal phenomena for all pulsars. We searched for extended gamma-ray emission around 36 isolated middle-aged pulsars identified by radio and gamma-ray facilities using 2321 days of data from the High-Altitude Water Cherenkov (HAWC) Observatory. Through a stacking analysis comparing TeV flux models against a background-only hypothesis, we identified TeV halo-like emission at a significance level of $5.10\,σ$. Our results imply that extended TeV gamma-ray halos may commonly exist around middle-aged pulsars. This reveals a previously unknown feature about pulsars and opens a new window to identify the pulsar population that is invisible to radio, x-ray, and GeV gamma-ray observations due to magnetospheric configurations.

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arXiv2025

Orbital Modulation of Gamma-Rays Beyond 100 TeV from LS 5039

Gamma-ray binaries are systems composed of a compact object orbiting a massive companion star. The interaction between these two objects can drive relativistic outflows, either jets or winds, in which particles can be accelerated to energies reaching hundreds of tera-electronvolts (TeV). It is however still debated where and under which physical conditions particles are accelerated in these objects and ultimately whether protons can be accelerated up to PeV energies. Among the well-known gamma-ray binaries, LS 5039 is a high-mass X-ray binary (HMXB) with an orbital period of 3.9 days that has been observed up to TeV energies by the High Energy Stereoscopic System (H.E.S.S.). In this work, we present new observations of LS 5039 obtained with the High Altitude Water Cherenkov (HAWC) observatory. Our data reveal that the gamma-ray spectrum of LS 5039 extends up to 200 TeV with no apparent spectral cut-off. Furthermore, we confirm, with a confidence level of 4.7σ, that the emission between 2 TeV and 118 TeV is modulated by the orbital motion of the system, which indicates that these photons are likely produced within or near the binary orbit where they can undergo absorption by the stellar photons. In a leptonic scenario, the highest energy photons detected by HAWC can be emitted by ~200 TeV electrons inverse Compton scattering stellar photons, which would require an extremely efficient acceleration mechanism operating within LS 5039. Alternatively, a hadronic scenario could explain the data through proton-proton or proton-γ collisions of protons accelerated to peta-electronvolt (PeV) energies.

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arXiv2024

Ultra-High-Energy Gamma-Ray Bubble around Microquasar V4641 Sgr

Microquasars are laboratories for the study of jets of relativistic particles produced by accretion onto a spinning black hole. Microquasars are near enough to allow detailed imaging of spatial features across the multiwavelength spectrum. The recent extension of the spatial morphology of a microquasar, SS 433, to TeV gamma rays \cite{abeysekara2018very} localizes the acceleration of electrons at shocks in the jet far from the black hole \cite{hess2024ss433}. Here we report TeV gamma-ray emission from another microquasar, V4641~Sgr, which reveals particle acceleration at similar distances from the black hole as SS~433. Additionally, the gamma-ray spectrum of V4641 is among the hardest TeV spectra observed from any known gamma-ray source and is detected up to 200 TeV. Gamma rays are produced by particles, either electrons or hadrons, of higher energies. Because electrons lose energy more quickly the higher their energy, such a spectrum either very strongly constrains the electron production mechanism or points to the acceleration of high-energy hadrons. This observation suggests that large-scale jets from microquasars could be more common than previously expected and that microquasars could be a significant source of Galactic cosmic rays. high energy gamma-rays also provide unique constraints on the acceleration mechanisms of extra-Galactic cosmic rays postulated to be produced by the supermassive black holes and relativistic jets of quasars. The distance to quasars limits imaging studies due to insufficient angular resolution of gamma-rays and due to attenuation of the highest energy gamma-rays by the extragalactic background light.

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arXiv2024

Observation of the Galactic Center PeVatron Beyond 100 TeV with HAWC

We report an observation of ultra-high energy (UHE) gamma rays from the Galactic Center region, using seven years of data collected by the High-Altitude Water Cherenkov (HAWC) Observatory. The HAWC data are best described as a point-like source (HAWC J1746-2856) with a power-law spectrum ($\mathrm{d}N/\mathrm{d}E=ϕ(E/26 \,\text{TeV})^γ$), where $γ=-2.88 \pm 0.15_{\text{stat}} - 0.1_{\text{sys}} $ and $ϕ=1.5 \times 10^{-15}$ (TeV cm$^{2}$s)$^{-1}$ $\pm\, 0.3_{\text{stat}}\,^{+0.08_{\text{sys}}}_{-0.13_{\text{sys}}}$ extending from 6 to 114 TeV. We find no evidence of a spectral cutoff up to $100$ TeV using HAWC data. Two known point-like gamma-ray sources are spatially coincident with the HAWC gamma-ray excess: Sgr A$^{*}$ (HESS J1745-290) and the Arc (HESS J1746-285). We subtract the known flux contribution of these point sources from the measured flux of HAWC J1746-2856 to exclude their contamination and show that the excess observed by HAWC remains significant ($>$5$σ$) with the spectrum extending to $>$100 TeV. Our result supports that these detected UHE gamma rays can originate via hadronic interaction of PeV cosmic-ray protons with the dense ambient gas and confirms the presence of a proton PeVatron at the Galactic Center.

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arXiv2024

TeV Analysis of a Source Rich Region with HAWC Observatory: Is HESS J1809-193 a Potential Hadronic PeVatron?

HESS J1809-193 is an unidentified TeV source, first detected by the High Energy Stereoscopic System (H.E.S.S.) Collaboration. The emission originates in a source-rich region that includes several Supernova Remnants (SNR) and Pulsars (PSR) including SNR G11.1+0.1, SNR G11.0-0.0, and the young radio pulsar J1809-1917. Originally classified as a pulsar wind nebula (PWN) candidate, recent studies show the peak of the TeV region overlapping with a system of molecular clouds. This resulted in the revision of the original leptonic scenario to look for alternate hadronic scenarios. Marked as a potential PeVatron candidate, this region has been studied extensively by H.E.S.S. due to its emission extending up-to several tens of TeV. In this work, we use 2398 days of data from the High Altitude Water Cherenkov (HAWC) observatory to carry out a systematic source search for the HESS J1809-193 region. We were able to resolve emission detected as an extended component (modelled as a Symmetric Gaussian with a 1 $σ$ radius of 0.21 $^\circ$) with no clear cutoff at high energies and emitting photons up-to 210 TeV. We model the multi-wavelength observations for the region HESS J1809-193 using a time-dependent leptonic model and a lepto-hadronic model. Our model indicates that both scenarios could explain the observed data within the region of HESS J1809-193.

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arXiv2024

Search for Decaying Dark Matter in the Virgo Cluster of Galaxies with HAWC

The decay or annihilation of dark matter particles may produce a steady flux of very-high-energy gamma rays detectable above the diffuse background. Nearby clusters of galaxies provide excellent targets to search for the signatures of particle dark matter interactions. In particular, the Virgo cluster spans several degrees across the sky and can be efficiently probed with a wide field-of-view instrument. The High Altitude Water Cherenkov (HAWC) observatory, due to its wide field of view and sensitivity to gamma rays at an energy scale of 300 GeV--100 TeV is well-suited for this search. Using 2141 days of data, we search for gamma-ray emission from the Virgo cluster, assuming well-motivated dark matter sub-structure models. Our results provide some of the strongest constraints on the decay lifetime of dark matter for masses above 10 TeV.

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