Historically , the blazar population has been poorly understood at low frequencies because survey sensitivity and angular resolution limitations have made it difficult to identify megahertz counterparts .
We used the LOFAR Two-Metre Sky Survey ( LoTSS ) first data release value-added catalogue ( LDR1 ) to study blazars in the low-frequency regime with unprecedented sensitivity and resolution .
We identified radio counterparts to all 98 known sources from the Third Fermi -LAT Point Source Catalogue ( 3FGL ) or Roma-BZCAT Multi-frequency Catalogue of Blazars ( 5 ^ { \mathrm { th } } edition ) that fall within the LDR1 footprint .
Only the 3FGL unidentified \gamma -ray sources ( UGS ) could not be firmly associated with an LDR1 source ; this was due to source confusion .
We examined the redshift and radio luminosity distributions of our sample , finding flat-spectrum radio quasars ( FSRQs ) to be more distant and more luminous than BL Lacertae objects ( BL Lacs ) on average .
Blazars are known to have flat spectra in the gigahertz regime but we found this to extend down to \SI 144 \mega \hertz , where the radio spectral index , \alpha , of our sample is -0.17 \pm 0.14 .
For BL Lacs , \alpha = -0.13 \pm 0.16 and for FSRQs , \alpha = -0.15 \pm 0.17 .
We also investigated the radio-to- \gamma -ray connection for the 30 \gamma -ray-detected sources in our sample .
We find Pearson ’ s correlation coefficient is 0.45 ( p = 0.069 ) .
This tentative correlation and the flatness of the spectral index suggest that the beamed core emission contributes to the low-frequency flux density .
We compare our sample distribution with that of the full LDR1 on colour-colour diagrams , and we use this information to identify possible radio counterparts to two of the four UGS within the LDR1 field .
We will refine our results as LoTSS continues .