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Abstract 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 yr. The analysis includes light curves at daily, weekly, and monthly timescales for the four sources. We report the detection of gamma-ray emission from M87 with a significance exceeding 5σ, providing the integrated TeV spectrum from the longest temporal coverage to date. The source is well described as a point-like source modeled by a power-law spectrum with spectral index Γ = 2.53 ± 0.29 and a flux of (7.09 ± 1.24) × 10⁻¹³cm⁻²s⁻¹TeV⁻¹at 1 TeV. The maximum energy of the detected emission in M87, at 1σconfidence level, 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 4σ, while NGC 1275 and IC 310 are not detected. The weekly light curves show an increased number of fluxes above 2σfor M87 starting in 2019 and for 3C 264 starting in 2018, which can be interpreted as the moments at which these sources start to exhibit an enhanced steady TeV emission. Cumulative significance analysis reveals quantitative evidence for long-term variability. M87 shows enhanced emission from 2019, while 3C 264 exhibits increased activity from 2018, resembling variable sources like Markarian 421 rather than steady sources like the Crab. This supports the importance of monitoring radio galaxies to identify periods of higher activity and flares, enabling further multimessenger studies. 

Abstract Gamma-ray binaries are luminous in gamma rays, 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 teraelectronvolts (TeV). However, it is 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 with an orbital period of 3.9 days that has been observed up to TeV energies by the High Energy Stereoscopic System. 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 cutoff. Furthermore, we confirm, with a confidence level of 4.7σ, that the emission between 2 and 118 TeV is modulated by the orbital motion of the system, and find a 2.2σhint of variability above 100 TeV. This 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–gamma collisions of protons accelerated to petaelectronvolt energies. 

The High-Altitude Water Cherenkov (HAWC) Observatory, located on the slopes of the Sierra Negra volcano in Mexico, began operations in March 2015. Over the past decade, HAWC has enabled the exploration of a broad range of topics in high-energy astrophysics and particle physics, resulting in more than 90 peer-reviewed publications. These studies have significantly advanced our understanding of several previously unexplored and poorly understood phenomena in the TeV energy regime. The present work provides an overview of the key scientific contributions of HAWC during its first ten years of operation. 

Abstract 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 High Altitude Water Cherenkov (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 $\stackrel{\text{°}}{.}$42,δ= 22 $\stackrel{\text{°}}{.}$35) that we associate with IC 443. The measured spectrum is a simple power law with an index of −3.14 ± 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 cutoff at tens of TeV energies, with the spectrum extending to ∼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 ± 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. 

Abstract Very-high-energy (0.1–100 TeV) gamma-ray emissions were observed in High-Altitude Water Cherenkov (HAWC) data from the lobes of the microquasar SS 433, making them the first set of astrophysical jets that were resolved at TeV energies. In this work, we update the analysis of SS 433 using 2565 days of data from the HAWC observatory. Our analysis reports the detection of a point-like source in the east lobe at a significance of 6.6σand in the west lobe at a significance of 8.2σ. For each jet lobe, we localize the gamma-ray emission and identify a best-fit position. The locations are close to the X-ray emission sites “e1” and “w1” for the east and west lobes, respectively. We analyze the spectral energy distributions and find that the energy spectra of the lobes are consistent with a simple power lawdN/dE∝E^αwith $\alpha =-{2.44}_{-0.12-0.04}^{+0.13+0.04}$and $\alpha =-{2.35}_{-0.11-0.03}^{+0.12+0.03}$for the east and west lobes, respectively. The maximum energy of photons from the east and west lobes reaches 56 TeV and 123 TeV, respectively. We compare our observations to various models and conclude that the very-high-energy gamma-ray emission can be produced by a population of electrons that were efficiently accelerated. 

Abstract The first TeVγ-ray source with no lower energy counterparts, TeV J2032+4130, was discovered by HEGRA. It appears in the third HAWC catalog as 3HWC J2031+415 and it is a bright TeVγ-ray source whose emission has previously been resolved as two sources: HAWC J2031+415 and HAWC J2030+409. While HAWC J2030+409 has since been associated with the Fermi Large Area Telescope Cygnus Cocoon, no such association for HAWC J2031+415 has yet been found. In this work, we investigate the spectrum and energy-dependent morphology of HAWC J2031+415. We associate HAWC J2031+415 with aγ-ray binary system containing the pulsar PSR J2032+4127 and its companion MT91 213. We study HAWC data to observe their periastron in 2017. Additionally, we perform a combined multiwavelength analysis using radio, X-ray, andγ-ray emission. We conclude that HAWC J2031+415 and, by extension, TeV J2032+4130 are most probably a pulsar wind nebula powered by PSR J2032+4127.