Swift BAT 70 Month All-Sky Survey: 14\-20 keV: flux

Users can get flux maps corresponding to a given SNR image from the results pages. The batch interfaces may directly query any of the surveys since the user chooses the names explicitly rather than from a selection box. <p> The values displayed in the significance maps are the local signal to noise ratio in each pixel. The noise in these coded-mask images follows a Gaussian distribution with center at zero and a characteristic width (sigma) of 1.0.

The noise is calculated locally for each pixel by measuring the RMS value of all pixel values in an annulus around each pixel and hence includs both statistical and systematic components. Known sources are excluded from the annuli. <p> The signal in each pixel is taken from the flux maps. <p> The flux values are in the native BAT survey units of counts/sec/detector. The detector is an individual piece of CZT in the BAT array with an area of 1.6 x 10^-7m<sup>2</sub>. <p> While the Swift mission is primarily designed to follow gamma-ray bursts, the random distribution of bursts in the sky means that these survey's sky coverage is relatively uniform with the exposure at any point varying between about 6 to 16 megaseconds.

The survey limits for source detection are about 10^-11 ergs/s/cm² over about half the sky and 1.3x10^-11 ergs/s/cm² over 90%. <p> These data replace the 9-month BAT datasets which we have retired. If you wish access to the older data please let us know. Note that for the 9-month data we provided access through the web page to the flux data and gave links to the signal-to-noise maps.

Since the existence of sources is most easily seen in the SNR maps, we decided to invert that for this release. <p> For the 8 band data, the source data were provided by the BAT team as 6 FITS files. Each of these contained the 8 bands in separate image extensions for a region centered at l=0,b=+/-90 or l=0,90,180,270,b=0, the centers of 6 cubic facets. However these data are not the classical cube-faced projections, e.g., as used in COBE data.

The data on the facets overlap, so that this is just a convenient way to tile the sky. <i>SkyView</i> separated each of the FITS image extensions into a separate file, but no other modifications were made to the data. The summed image was provided as six separate files. Provenance: NASA BAT Team.

This is a service of NASA HEASARC.