The LOFAR long baseline snapshot calibrator survey

With a current maximum baseline of 1300 km, the International LOFAR array is capable of attaining an angular resolution of 0.4 arcsec at a frequency of 140 MHz, opening for the first time the possibility of true subarcsecond imaging at wavelengths longer than 1 m. We used the multibeaming capability of LOFAR to conduct a fast and computationally inexpensive survey to inspect 630 sources in two hours to determine if they possess a sufficiently bright compact component to be usable as LOFAR delay calibrators. Here we summarize the characteristics of the survey, and its main results. In particular we have obtained the density of calibrators on the sky that are sufficiently bright to calibrate dispersive and non-dispersive delays for the International LOFAR. \ua9 Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike Licence