LOFAR observations of the XMM-LSS field
  We present observations of the XMM Large-Scale Structure (XMM-LSS) field
observed with the LOw Frequency ARray (LOFAR) at 120-168 MHz. Centred at a
J2000 declination of $-4.5^{\circ}$, this is a challenging field to observe
with LOFAR because of its low elevation with respect to the array. The low
elevation of this field reduces the effective collecting area of the telescope,
thereby reducing sensitivity. This low elevation also causes the primary beam
to be elongated in the north-south direction, which can introduce side lobes in
the synthesised beam in this direction. However the XMM-LSS field is a key
field to study because of the wealth of ancillary information, encompassing
most of the electromagnetic spectrum. The field was observed for a total of 12
hours from three four-hour LOFAR tracks using the Dutch array. The final image
presented encompasses $\sim 27$ deg$^2$, which is the region of the
observations with a $>$50\% primary beam response. Once combined, the
observations reach a central rms of 280 $\mu$Jy beam$^{-1}$ at 144 MHz and have
an angular resolution of $7.5 \times \ 8.5$". We present our catalogue of
detected sources and investigate how our observations compare to previous radio
observations. This includes investigating the flux scale calibration of these
observations compared to previous measurements, the implied spectral indices of
the sources, the observed source counts and corrections to obtain the true
source counts, and finally the clustering of the observed radio sources.
