- Galactic Cosmic Rays
- Extreme Galactic Accelerators
- Extended TeV Sources
- Diffuse Galactic Emission
- Extragalactic Cosmic Rays
- Active Galactic Nuclei
- Gamma Ray Bursts
- Discovery Potential of HAWC
- Multi-Messenger Astronomy
HAWC Obervations up to 100 TeV Probe Galactic Cosmic Rays
Cosmic rays up to at least 103 TeV, and perhaps as high as 106 TeV, are of Galactic origin. Observations of gamma rays near 100 TeV may be the key to identifying where and how these cosmic rays are accelerated.
Discovering and Understanding Extreme Galactic Accelerators
Because the flux of gamma rays from all sources drops rapidly as a function of energy, observations of sources require a large effective area and long integration times, especially if the goal is to observe gamma rays above 10 TeV.
Extended TeV Sources
Observations of TeV gamma rays with the HESS imaging air Cherenkov telescope (IACT) have shown that most Galactic sources in the TeV range are extended, i.e., larger than the point response of the telescope. Unfortunately, while facilities like HESS are quite sensitive, it is difficult for such narrow-field instruments to observe the full extent of large sources.
Diffuse Emission from the Galactic Plane
Observations of the GeV and TeV sky have shown that the Galactic plane is the brightest feature in both wavelength bands. While some of the emission is likely due to unresolved point sources, a large fraction of the gamma rays likely originate when the cosmic rays interact with gas and dust in the Galaxy.
HAWC Observations of Transient Sources probe Extragalactic Cosmic Rays
The origin of extragalactic cosmic rays is still largely unknown. The most likely candidate sources fall into two classes: active galactic nuclei (AGNs) and gamma-ray bursts (GRBs). While AGNs (but not GRBs) have been observed in the TeV band, many questions surround the nature of TeV emission.
Active Galactic Nuclei
Active galactic nuclei (AGNs) are supermassive black holes (about 108 times the mass of the Sun) with luminosities that far outshine the rest of the galaxy in which they are located.
Gamma Ray Bursts
Emitting over 1052 ergs in gamma rays, gamma-ray bursts (GRBs) are the most energetic phenomena known in the universe.
HAWC Survey Observations have Discovery Potential
When new wavelength bands are explored in astronomy, previously unknown sources and unknown types of sources are discovered. The discovery of new classes of objects unobserved at other wavelengths is a major strength of all-sky monitors. These serendipitous discoveries, while not possible to predict a priori, are frequently the most important scientifically.
Multi-messenger impact of HAWC
Multi-wavelength and multi-messenger observations are essential to understanding the gamma-ray sky. HAWC will search the TeV sky in real time for flaring sources and notify the community of short-duration flares within seconds. This early-warning system will enable observations at other wavelengths or with more sensitive IACT observations. For steady sources, HAWC will provide a TeV flux or upper limit for all sources within >2π sr.