Explore the vast range of titles available.

The Southern Wide-Field Gamma-Ray Observatory (SWGO) observatory will use water Cherenkov detector (WCD) technology to construct a large-area, high-altitude observatory to measure gamma and cosmic rays’ energy and arrival direction. The proposed observatory will have a sensitive area of approximately 0.3 km2 with possible extensions to 1 km2 and be located at a high altitude (>4400m) between 14 degrees and 24 degrees south latitude. The high altitude of the observatory facilitates the detection and measurement of gamma and cosmic rays by placing the detector well into their extensive air shower (EAS) for energies down to several hundred GeV. The large detector area provides significant sensitivity to energies into the PeV range. The location in the southern hemisphere offers a view of sources in the southern sky, including the Galactic Center. WCDs can be operated during daylight, continuously monitoring the overhead sky, enabling coverage of a large fraction of the sky. The detector design also seeks to optimize gamma-hadron discrimination to distinguish the gamma-ray-induced EAS from those induced by the far more numerous cosmic rays. The reference design utilizes double-chamber WCD detector units. The larger volume of the WCD’s upper compartment provides calorimetry and timing information for the electromagnetic component of the EAS. The lower compartment will be used for muon tagging to aid in the rejection of muon-rich hadronic showers. The array layout of the individual WCDs is optimized to provide the best performance at the lowest cost. Excellent sensitivity and gamma-hadron separation over a wide range of energies with good angular resolution will be achieved by varying detector unit spacing, with a dense inner core and an outer region populated at a lower density. This proceeding will describe the research and development program for mechanical design, photosensors, readout electronics, and data-acquisition systems to produce the optimal detector for SWGO.

The High-Altitude Water Cherenkov (HAWC) Observatory is designed to observe astrophysical sources of cosmic and gamma rays with energies from several hundred GeV up to several hundred TeV. HAWC is a survey instrument that maps a significant fraction of the gamma-ray sky due to its wide field of view. HAWC has extensively studied galactic sources of gamma rays, measuring their energy spectra and morphology. HAWC observes and measures variable and transient sources due to its continuous operation. HAWC has also measured the energy spectrum and anisotropy of the arrival directions of cosmic rays. HAWC participates in multimessenger studies with other observatories, including the IceCube neutrino and LIGO/Virgo gravitational wave observatories. HAWC has also performed indirect dark matter searches and studies of beyond-standard model particle physics measurements.

The unexpectedly high flux of cosmic-ray positrons detected at Earth may originate from nearby astrophysical sources, dark matter, or unknown processes of cosmic-ray secondary production. We report the detection, using the High-Altitude Water Cherenkov Observatory (HAWC), of extended tera–electron volt gamma-ray emission coincident with the locations of two nearby middle-aged pulsars (Geminga and PSR B0656+14). The HAWC observations demonstrate that these pulsars are indeed local sources of accelerated leptons, but the measured tera–electron volt emission profile constrains the diffusion of particles away from these sources to be much slower than previously assumed. We demonstrate that the leptons emitted by these objects are therefore unlikely to be the origin of the excess positrons, which may have a more exotic origin.

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 measurement of the spatial morphology of a microquasar, SS 433, to TeV gamma rays 1 localizes the acceleration of electrons at shocks in the jet far from the black hole 2 . V4641 Sagittarii (V4641 Sgr) is a similar binary system with a black hole and B-type main-sequence companion star and has an orbit period of 2.8 days (refs.  3 , 4 ). It stands out for its super-Eddington accretion 5 and for its radio jet, which is one of the fastest superluminal jets in the Milky Way. Previous observations of V4641 Sgr did not report gamma-ray emission 6 . Here we report TeV gamma-ray emission from V4641 Sgr that reveals particle acceleration at similar distances from the black hole as SS 433. Furthermore, the gamma-ray spectrum of V4641 Sgr is among the hardest TeV spectra observed from any known gamma-ray source and is detected above 200 TeV. Gamma rays are produced by particles, either electrons or protons, of higher energies. Because energetic 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 protons. This suggests that large-scale jets from microquasars could be more common than previously expected and that they could be a notable source of galactic cosmic rays 7 – 9 . Ultra-high-energy gamma-ray emission from the microquasar V4641 Sagittarii is reported, suggesting that large-scale jets from microquasars could be more common than previously thought and also could be a notable source of galactic cosmic rays.

SS 433 is a binary system containing a supergiant star that is overflowing its Roche lobe with matter accreting onto a compact object (either a black hole or neutron star) 1 – 3 . Two jets of ionized matter with a bulk velocity of approximately 0.26 c (where c is the speed of light in vacuum) extend from the binary, perpendicular to the line of sight, and terminate inside W50, a supernova remnant that is being distorted by the jets 2 , 4 – 8 . SS 433 differs from other microquasars (small-scale versions of quasars that are present within our own Galaxy) in that the accretion is believed to be super-Eddington 9 – 11 , and the luminosity of the system is about 10 40 ergs per second 2 , 9 , 12 , 13 . The lobes of W50 in which the jets terminate, about 40 parsecs from the central source, are expected to accelerate charged particles, and indeed radio and X-ray emission consistent with electron synchrotron emission in a magnetic field have been observed 14 – 16 . At higher energies (greater than 100 gigaelectronvolts), the particle fluxes of γ -rays from X-ray hotspots around SS 433 have been reported as flux upper limits 6 , 17 – 20 . In this energy regime, it has been unclear whether the emission is dominated by electrons that are interacting with photons from the cosmic microwave background through inverse-Compton scattering or by protons that are interacting with the ambient gas. Here we report teraelectronvolt γ-ray observations of the SS 433/W50 system that spatially resolve the lobes. The teraelectronvolt emission is localized to structures in the lobes, far from the centre of the system where the jets are formed. We have measured photon energies of at least 25 teraelectronvolts, and these are certainly not Doppler-boosted, because of the viewing geometry. We conclude that the emission—from radio to teraelectronvolt energies—is consistent with a single population of electrons with energies extending to at least hundreds of teraelectronvolts in a magnetic field of about 16 microgauss. Observations of teraelectronvolt γ-rays accelerated by the jets of the miniature quasar SS 433 are reported.

Cosmic rays with energies up to a few PeV are known to be accelerated within the Milky Way 1 , 2 . Traditionally, it has been presumed that supernova remnants were the main source of these very-high-energy cosmic rays 3 , 4 , but theoretically it is difficult to accelerate protons to PeV energies 5 , 6 and observationally there simply is no evidence of the remnants being sources of hadrons with energies above a few tens of TeV 7 , 8 . One possible source of protons with those energies is the Galactic Centre region 9 . Here, we report observations of 1–100 TeV γ rays coming from the ‘Cygnus Cocoon’ 10 , which is a superbubble that surrounds a region of massive star formation. These γ rays are likely produced by 10–1,000 TeV freshly accelerated cosmic rays that originate from the enclosed star-forming region Cyg OB2. Until now it was not known that such regions could accelerate particles to these energies. The measured flux likely originates from hadronic interactions. The spectral shape and the emission profile of the Cocoon changes from GeV to TeV energies, which reveals the transport of cosmic particles and historical activity in the superbubble. Following HAWC observations of the Cygnus Cocoon, massive star-forming regions can now be considered to be sources of very-high-energy (TeV to PeV) Galactic cosmic rays.

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\\,\\). 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.

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.

Very-high-energy (0.1-100 TeV) gamma-ray emission was observed in 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 2,565 days of data from the High Altitude Water Cherenkov (HAWC) observatory. Our analysis reports the detection of a point-like source in the east lobe at a significance of \\(6.6\\,\\sigma\\) and in the west lobe at a significance of \\(8.2\\,\\sigma\\). 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-law \\(\\text{d}N/\\text{d}E\\propto E^{\\alpha}\\) with \\(\\alpha = -2.44^{+0.13+0.04}_{-0.12-0.04}\\) and \\(\\alpha = -2.35^{+0.12+0.03}_{-0.11-0.03}\\) 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.

The first TeV gamma-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 TeV gamma-ray source whose emission has previously been resolved as 2 sources: HAWC J2031+415 and HAWC J2030+409. While HAWC J2030+409 has since been associated with the Fermi-LAT 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 the pulsar PSR J2032+4127 and perform a combined multi-wavelength analysis using radio, X-ray, and \\(\\)-ray emission. We conclude that HAWC J2031+415 and, by extension, TeV J2032+4130 are most probably a pulsar wind nebula (PWN) powered by PSR J2032+4127.