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Description
GLEAM, the GaLactic and Extragalactic All-sky MWA survey, is a survey of
the entire radio sky south of declination 30 degrees at frequencies
between 72 and 231 MHz. It was made with the Murchison Widefield Array
(MWA) using a drift scan method that makes efficient use of the MWA's very
large field-of-view. The survey is described in Wayth et al. (2015) and
the <a href="https://www.mwatelescope.org/gleam">website</a> at https://www.mwatelescope.org/gleam.
<p>
The data presented here are from the first year of GLEAM observing, published in:
<ul>
<li> Hurley-Walker et al. (2017): 25,000 square degrees of extragalactic sky
<li> For et al. (2018): the Large and Small Magellanic Clouds
<li> Hurley-Walker et al. (2019c): 8,000 square degrees of the Galactic plane
</ul>
A region around Centaurus A, a few other small regions described by Hurley-Walker et al. (2017), and the Galactic plane between 180 < l < 345 degrees, are not available.
<p>
The most sensitive and highest-resolution image is the 170-231MHz image
which was used for all source-finding in generating the catalogue. It has
a resolution of approximately 2.2 x 2.2/cos (dec + 26.7) arcmin at this
frequency. However, due to ionospheric distortions, the final resolution
of the survey varies by ~10% over the sky, with a direction-dependent PSF.
<p>
The <i>SkyView</i> data for the GLEAM surveys was extracted using the team's
cutout server, into small (3 degree) raw cutouts over the region covered
by the GLEAM survey. These cutouts have somewhat variable size and resolution. The
default scale (i.e., pixel size) used for <i>SkyView</i> images is given in the table
below. Since the GLEAM cutout server will not create an appropriately sized tile for the Sourth Pole, a
larger tile offset from the pole is used.
<p>
<i>SkyView</i> resamples the cutouts retreived from the GLEAM website into the image
geometry requested by the user. Only four wide-band datasets are included.
The table below gives the frequency range, central frequency and a typical pixel
scale for each of these bands.
<table border>
<tr><th colspan=5> GLEAM Bands In <i>SkyView</i> </th></tr>
<tr><th>Band</th>
<th>f<sub>min</sub> (MHz)</th>
<th>f<sub>max</sub> (MHz)</th>
<th>f<sub>C</sub> (MHz)</tg>
<th>Pixel scale (") </th>
</tr>
<tr> <td> 1 </td><td> 72 </td><td>103 </td><td> 88 </td> <td> 56 </td></tr>
<tr> <td> 2 </td><td>103 </td><td>134 </td><td>118 </td> <td> 44 </td></tr>
<tr> <td> 3 </td><td>138 </td><td>170 </td><td>155 </td> <td> 34 </td></tr>
<tr> <td> 4 </td><td>170 </td><td>231 </td><td>200 </td> <td> 28 </td></tr>
</table>
These data and 20 narrower bands are available through the team website.
<p>
To minimize resampling artifacts, this survey defaults to the Lanczos third order resampler.
SkyView tracks the size and orientation of the beam as given in each of the tiles and includes
the averaged value (i.e., the average of the input images weighted by the output pixels sampled
from each input) in the BMAJ, BMIN, and BPA keywords of any result FITS file. Provenance: Source data extracted as cutouts from <a href="http://gleam-vo.icrar.org/gleam_postage/q/form">GLEAM cutout server</a> in March 2020 with updates in July 2020.. This is a service of NASA HEASARC.
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