3HWC Survey

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Downloadable 3HWC Maps

You can download the skymaps with significance/flux information (healpix format in FITS files) used in the creation of the 3HWC catalog here:

If you use these files, please reference the following publication:

Map-making

We provide here the results of a putative point and extended source searches, described in more detail in the 3HWC catalog paper. For each pixel in HEALPix binning (NSIDE=1024) in celestial coordinates (RA/Dec, J2000), we perform an independent fit to HAWC event counts, using events recorded within (1o + source exension) of the pixel center. For the point (extended) source searches, the source model consists of a point source (extended, disk-like source) with a power-law energy spectrum with a spectral index of -2.5, convolved with HAWC's instrument response function. The only fit parameter is the flux normalization. The best-fit source+background model is compared to a background-only model to calculate the test statistic, TS = 2 log( Ls+b / Lb ).

Additionally, for each pixel, we calculate the value of the flux norm that maximixes the likelihood function, under the constraint that the flux norm must be greater or equal to 0 (as sources with negative flux would be considered unphysical), and the 2 sigma confidence level Feldman-Cousins confidence interval. For locations with a large TS, as the sources in the catalog, these intervals are equivalent to central confidence intervals; for lower TS location the bounds become asymmetric around the flux best estimate and the flux upper bound can be regarded as an upper limit.

Content of the FITS files

The FITS files contain the following columns:

  • Column 0: significance = +-sqrt(TS), as defined above. The negative sign is used when the unconstrained best-fit flux norm is negative.
  • Column 1: Best-fit flux norm at the pivot energy of 7 TeV in TeV-1cm-2s-1.
  • Column 2: 2 sigma lower limit on the flux norm (same units).
  • Column 3: 2 sigma upper limit on the flux norm (same units).

Pixels with invalid values (failed fit, outside the field of view) are set to -1.6375e30, the default value of healpy.UNSEEN.

Accessing the FITS files

The following code snippet provides an example for how to obtain the signifiance and best-fit flux at a given position on the sky: 

import numpy as np
import healpy as hp

file="aerie-apps_bin1-9__allsky_1024_i2.5_r0.0_p1.0_fc2Flux_negSigMap.fits.gz"
sigmap, fluxmap, fluxmap_lower, fluxmap_upper = hp.read_map(file, (0, 1, 2, 3))
NSIDE = hp.get_nside(sigmap)

lon, lat = 83.63, 22.02 # Crab coordinates in degrees, J2000 RA/Dec
th, ph = np.deg2rad([90.0-lat, lon])
pixel = hp.ang2pix(NSIDE, th, ph)

sig = sigmap[pixel]
flux_best = fluxmap[pixel]
flux_lower = fluxmap_lower[pixel]
flux_upper = fluxmap_upper[pixel]

print (sig, flux_best, flux_lower, flux_upper)

Check out the healpy documentation for more information about how to use and display healpix-format maps within python.