We present results from a study of twelve X-ray bright clusters at 1.4 GHz with the 100-m Green Bank Telescope .
After subtraction of point sources using existing interferometer data , we reach a median ( best ) 1 \sigma rms sensitivity level of 0.01 ( 0.006 ) \mu Jy arcsec ^ { -2 } , and find a significant excess of diffuse , low surface brightness emission in eleven of twelve Abell clusters observed .
We also present initial results at 1.4 GHz of Abell 2319 from the Very Large Array .
In particular , we find : ( a ) four new detections of diffuse structures tentatively classified as two halos ( A2065 , A2069 ) and two relics ( A2067 , A2073 ) ; ( b ) the first detection of the radio halo in A2061 at 1.4 GHz , which qualifies this as a possible ultra-steep spectrum halo source with a synchrotron spectral index of \alpha \sim 1.8 between 327 MHz and 1.4 GHz ; ( c ) a \sim 2 Mpc radio halo in the sloshing , minor-merger cluster A2142 ; ( d ) a > 2 \times increase of the giant radio halo extent and luminosity in the merging cluster A2319 ; ( e ) a \sim 7 \times increase to the integrated radio flux and > 4 \times increase to the observed extent of the peripheral radio relic in A1367 to \sim 600 kpc , which we also observe to be polarized on a similar scale ; ( f ) significant excess emission of ambiguous nature in three clusters with embedded tailed radio galaxies ( A119 , A400 , A3744 ) .
Our radio halo detections agree with the well-known X-ray/radio luminosity correlation , but they are larger and fainter than current radio power correlation studies would predict .
The corresponding volume averaged synchrotron emissivities are 1-2 orders of magnitude below the characteristic value found in previous studies .
Some of the halo-like detections may be some type of previously unseen , low surface brightness radio halo or blend of unresolved shock structures and sub-Mpc scale turbulent regions associated with their respective cluster merging activity .
Four of the five tentative halos contain one or more X-ray cold fronts , suggesting a possible connection between gas sloshing and particle acceleration on large scales in some of these clusters .
Additionally , we see evidence for a possible inter-cluster filament between A2061 and A2067 .
For our faintest detections , we note the possibility of residual contamination from faint radio galaxies not accounted for in our confusion subtraction procedure .
We also quantify the sensitivity of the NVSS to extended emission as a function of size .