2HWC Survey
The 2HWC survey is the first high-sensitivity survey reported from HAWC data in the instrument's near-complete configuration. The survey is based on the first 507 days of operation of the HAWC instrument. It is the deepest survey of multi-TeV photons ever conducted, resulting in 39 detected sources. Of these 39 sources, 19 are new detections, more than 0.5o from previously-known emission.
The main publication record of the survey consists of two papers:
- The 2HWC HAWC Observatory Gamma-Ray Catalog contains the catalog list of identified 2HWC sources and discussion of the confirmed and new multi-TeV sources in the survey.
- Observation of the Crab Nebula with the HAWC Gamma-Ray Observatory contains a comprehensive discussion of the analysis used in the 2HWC catalog using the Crab Nebula (the brightest TeV source in the Northern hemisphere) for confirmation.
Upper Limits/Confidence Intervals
In addition to the sources reported in the catalog, the HAWC data carries information on the maximum steady TeV flux across more than 8 sr of the sky. In Coordinate View you can find the flux and √TS maps used to generate the catalog. All locations in the sky visible to HAWC are available, whether or not they are part of the catalog.
You'll find four different maps which corresponds to the hypotheses and resolutions described in Section 3.3 of the 2HWC paper. The values for each pixel are the result of assuming a source located at its center and convoluting the physical model with the declination dependent response of the experiment, as predicted by simulation. We then float the flux normalization of the model and use the counts from within 1o+extension to estimate it using a maximum likelihood technique.
We provide significance, best flux estimate and a flux confidence interval. The significance corresponds to √TS, multiplied by a minus sign if it is the result of an underfluctuation (TS would be maximized by a flux value less than 0). The flux estimate is quoted at 7TeV, and is restricted to physical values (equal or greater than 0).
The flux estimate is followed by a Feldman-Cousins confidence interval for which we report its lower and upper bounds (2 sigma confidence level, or about 95%). For locations with a large TS, as the sources in the catalog, they are equivalent to central confidence intervals; for lower TS location the bounds become assymmetric around the flux best estimate and the flux upper bound can be regarded as an upper limit.