We present the sensitivity of HAWC to Gamma Ray Bursts (GRBs). HAWC is a very high-energy gamma-ray observatory currently under construction in Mexico at an altitude of 4100 m. It will observe ...atmospheric air showers via the water Cherenkov method. HAWC will consist of 300 large water tanks instrumented with 4 photomultipliers each. HAWC has two data acquisition (DAQ) systems. The main DAQ system reads out coincident signals in the tanks and reconstructs the direction and energy of individual atmospheric showers. The scaler DAQ counts the hits in each photomultiplier tube (PMT) in the detector and searches for a statistical excess over the noise of all PMTs. We show that HAWC has a realistic opportunity to observe the high-energy power law components of GRBs that extend at least up to 30 GeV, as it has been observed by Fermi LAT. The two DAQ systems have an energy threshold that is low enough to observe events similar to GRB 090510 and GRB 090902b with the characteristics observed by Fermi LAT. HAWC will provide information about the high-energy spectra of GRBs which in turn could help to understanding about e-pair attenuation in GRB jets, extragalactic background light absorption, as well as establishing the highest energy to which GRBs accelerate particles.
A measurement with high statistics of the differential energy spectrum of light elements in cosmic rays, in particular, of primary H plus He nuclei, is reported. The spectrum is presented in the ...energy range from \(6\) to \(158\) TeV per nucleus. Data was collected with the High Altitude Water Cherenkov (HAWC) Observatory between June 2015 and June 2019. The analysis was based on a Bayesian unfolding procedure, which was applied on a subsample of vertical HAWC data that was enriched to \(82\%\) of events induced by light nuclei. To achieve the mass separation, a cut on the lateral age of air shower data was set guided by predictions of CORSIKA/QGSJET-II-04 simulations. The measured spectrum is consistent with a broken power-law spectrum and shows a kneelike feature at around \(E = 24.0^{+3.6}_{-3.1} \) TeV, with a spectral index \(\gamma = -2.51 \pm 0.02\) before the break and with \(\gamma = -2.83 \pm 0.02\) above it. The feature has a statistical significance of \(4.1 \, \sigma\). Within systematic uncertainties, the significance of the spectral break is \(0.8 \, \sigma\).
The High Altitude Water Cherenkov (HAWC) Gamma-Ray Observatory surveys the very high energy sky in the 300 GeV to \(>100\) TeV energy range. HAWC has detected two blazars above \(11\sigma\), ...Markarian 421 (Mrk 421) and Markarian 501 (Mrk 501). The observations are comprised of data taken in the period between June 2015 and July 2018, resulting in a \(\sim 1038\) days of exposure. In this work we report the time-averaged spectral analysis for both sources above 0.5 TeV. Taking into account the flux attenuation due to the extragalactic background light (EBL), the intrinsic spectrum of Mrk 421 is described by a power law with an exponential energy cut-off with index \(\alpha=2.26\pm(0.12)_{stat}(_{-0.2}^{+0.17})_{sys}\) and energy cut-off \(E_c=5.1\pm(1.6)_{stat}(_{-2.5}^{+1.4})_{sys}\) TeV, while the intrinsic spectrum of Mrk 501 is better described by a simple power law with index \(\alpha=2.61\pm(0.11)_{stat}(_{-0.07}^{+0.01})_{sys}\). The maximum energies at which the Mrk 421 and Mrk 501 signals are detected are 9 and 12 TeV, respectively. This makes these some of the highest energy detections to date for spectra averaged over years-long timescales. Since the observation of gamma radiation from blazars provides information about the physical processes that take place in their relativistic jets, it is important to study the broad-band spectral energy distribution (SED) of these objects. To this purpose, contemporaneous data in the gamma-ray band to X-ray range, and literature data in the radio to UV range, were used to build time-averaged SEDs that were modeled within a synchrotron self-Compton leptonic scenario.
The close location of the HAWC observatory to the largest volcano in Mexico allows to perform a search for neutrino-induced horizontal muon and tau charged leptons. The section of the volcano located ...at the horizon reaches values of slant depth larger than 8 km of rock, making it an excellent shield for the cosmic ray horizontal background. We report the search method and background suppression technique developed for the detection of Earth-skimming neutrinos with HAWC, as well as a model that describes the remaining background produced by scattered muons. We show that by increasing the detection energy threshold we could use HAWC to search for neutrino-induced charged leptons.
Astroph. J. 940(2) (2022) 141 This paper reports on the $\gamma$-ray properties of the 2018 Galactic nova
V392 Per, spanning photon energies $\sim$0.1 GeV to 100 TeV by combining
observations from ...the Fermi Gamma-ray Space Telescope and the HAWC Observatory.
In one of the most rapidly evolving $\gamma$-ray signals yet observed for a
nova, GeV $\gamma$ rays with a power law spectrum with index $\Gamma = 2.0 \pm
0.1$ were detected over eight days following V392 Per's optical maximum. HAWC
observations constrain the TeV $\gamma$-ray signal during this time and also
before and after. We observe no statistically significant evidence of TeV
$\gamma$-ray emission from V392 Per, but present flux limits. Tests of the
extension of the Fermi/LAT spectrum to energies above 5 TeV are disfavored by 2
standard deviations (95\%) or more. We fit V392 Per's GeV $\gamma$ rays with
hadronic acceleration models, incorporating optical observations, and compare
the calculations with HAWC limits.
The radio galaxy M87 is the central dominant galaxy of the Virgo Cluster. Very High Energy (VHE,\(\gtrsim 0.1\) TeV) emission, from M87 has been detected by Imaging Air Cherenkov Telescopes (IACTs ). ...Recently, marginal evidence for VHE long-term emission has also been observed by the High Altitude Water Cherenkov (HAWC) Observatory, a gamma ray and cosmic-ray detector array located in Puebla, Mexico. The mechanism that produces VHE emission in M87 remains unclear. This emission is originated in its prominent jet, which has been spatially resolved from radio to X-rays. In this paper, we constructed a spectral energy distribution from radio to gamma rays that is representative of the non-flaring activity of the source, and in order to explain the observed emission, we fit it with a lepto-hadronic emission model. We found that this model is able to explain non-flaring VHE emission of M87 as well as an orphan flare reported in 2005.
We report the ground-level detection of a Galactic Cosmic-Ray (GCR) flux enhancement lasting \(\sim\) 17 hr and associated with the passage of a magnetic flux rope (MFR) over the Earth. The MFR was ...associated with a slow Coronal Mass Ejection (CME) caused by the eruption of a filament on 2016 October 9. Due to the quiet conditions during the eruption and the lack of interactions during the interplanetary CME transport to the Earth, the associated MFR preserved its configuration and reached the Earth with a strong magnetic field, low density, and a very low turbulence level compared to the local background, thus generating the ideal conditions to redirect and guide GCRs (in the \(\sim\) 8 to 60 GV rigidity range) along the magnetic field of the MFR. An important negative \(B_Z\) component inside the MFR caused large disturbances in the geomagnetic field and a relatively strong geomagnetic storm. However, these disturbances are not the main factors behind the GCR enhancement. Instead, we found that the major factor was the alignment between the MFR axis and the asymptotic direction of the observer.
The MGRO J2019+37 region is one of the brightest sources in the sky at TeV energies. It was detected in the 2 year HAWC catalog as 2HWC J2019+367 and here we present a detailed study of this region ...using data from HAWC. This analysis resolves the region into two sources: HAWC J2019+368 and HAWC J2016+371. We associate HAWC J2016+371 with the evolved supernova remnant CTB 87, although its low significance in this analysis prevents a detailed study at this time. An investigation of the morphology (including possible energy dependent morphology) and spectrum for HAWC J2019+368 is the focus of this work. We associate HAWC J2019+368 with PSR J2021+3651 and its X-ray pulsar wind nebula, the Dragonfly nebula. Modeling the spectrum measured by HAWC and Suzaku reveals a \(\sim\)7 kyr pulsar and nebula system producing the observed emission at X-ray and \({\gamma}\)-ray energies.
The Earth is bombarded by ultra-relativistic particles, known as cosmic rays (CRs). CRs with energies up to a few PeV (=10\(^{15}\) eV), the knee in the particle spectrum, are believed to have a ...Galactic origin. One or more factories of PeV CRs, or PeVatrons, must thus be active within our Galaxy. The direct detection of PeV protons from their sources is not possible since they are deflected in the Galactic magnetic fields. Hundred TeV \(\gamma\)-rays from decaying \(\pi^0\), produced when PeV CRs collide with the ambient gas, can provide the decisive evidence of proton acceleration up to the knee. Here we report the discovery by the High Altitude Water Cherenkov (HAWC) observatory of the \(\gamma\)-ray source, HAWC~J1825-134, whose energy spectrum extends well beyond 200 TeV without a break or cutoff. The source is found to be coincident with a giant molecular cloud. The ambient gas density is as high as 700 protons/cm\(^3\). While the nature of this extreme accelerator remains unclear, CRs accelerated to energies of several PeV colliding with the ambient gas likely produce the observed radiation.
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