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Description
This table contains the source list from Low Frequency Array (LOFAR) Low Band observations of the Bootes field at 62 MHz. The images of this field and the 3C 295 field made at 62 MHz reach a noise level of 5 mJy beam<sup>-1</sup>, making them the deepest images ever obtained at this frequency. In total, the authors detect 329 sources in the Bootes 62-MHz field image, covering an area of 19.4 square degrees out to a primary-beam attenuation factor of 0.4. From the observations, the authors derive Euclidean-normalized differential source counts. The 62-MHz source counts agree with previous GMRT 153 MHz and Very Large Array 74 MHz differential source counts, scaling with a spectral index of -0.7. The authors find that a spectral index scaling of -0.5 is required to match up the LOFAR 34 MHz source counts. This result is also in agreement with source counts from the 38 MHz 8C survey, indicating that the average spectral index of radio sources flattens toward lower frequencies. The authors also find evidence for spectral flattening using the individual flux measurements of sources between 34 and 1400 MHz and by calculating the spectral index averaged over the source population. To select ultra-steep spectrum (alpha < -1.1) radio sources that could be associated with massive high-redshift radio galaxies, the authors compute spectral indices between 62 MHz, 153 MHz, and 1.4 GHz for sources in the Bootes field. They cross-correlate these radio sources with optical and infrared catalogs and fit the spectral energy distribution to obtain photometric redshifts. They find that most of these ultra-steep spectrum sources are located in the 0.7 <~ z <~ 2.5 range. The Bootes and 3C 295 fields were simultaneously observed on 2012 April 12 as part of a multi-beam observation with the LOFAR LBA stations. The idea behind the multi-beam setup was to use the 3C 295 observations as a calibrator field to transfer the gain amplitudes to the (target) Bootes field (pointing center of J2000.0 RA and Dec of 14<sup>h</sup> 32<sup>m</sup> 03.0<sup>s</sup>, +34<sup>o</sup> 16' 33"). The total integration time on both fields was 10.25 hr. The observing band for the Bootes field observations was centered at 62 MHz, with a bandwidth of 16 MHz. The synthesized beam for this observation had dimensions of 31 arcseconds x 19 arcseconds. An overview of the observations is given in Table 1 of the reference paper, and an overview of the image characteristics in Table 2 of the reference paper. This table was created by the HEASARC in January 2015 based on some of the contents of the machine-readable version of Table 3 from the reference paper, namely the 329 entries listing sources in the Bootes field detected at 62 MHz. The remaining entries in this table listing the sources detected in the 3C295 field at frequencies of 34, 46 and 62 MHz are available as the HEASARC tables LOF3C29534, LOF3C29546 and LOF3C29562, respectively. This is a service provided by NASA HEASARC .
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