A Search for Fast Radio Bursts with the GBNCC Pulsar Survey

We report on a search for fast radio bursts (FRBs) with the Green BankNorthern Celestial Cap (GBNCC) Pulsar Survey at 350 MHz. Pointingsamounting to a total on-sky time of 61 days were searched to adispersion measure (DM) of 3000 pc cm-3, while the rest(23 days; 29% of the total time) were searched to a DM of 500 pccm-3. No FRBs were detected in the pointings observedthrough 2016 May. We estimate a 95% confidence upper limit on the FRBrate of 3.6× {10}3 FRBs sky-1day-1 above a peak flux density of 0.63 Jy at 350 MHzfor an intrinsic pulse width of 5 ms. We place constraints on thespectral index α by running simulations for differentastrophysical scenarios and cumulative flux density distributions. Thenondetection with GBNCC is consistent with the 1.4 GHz rate reported forthe Parkes surveys for α > +0.35 in the absence of scatteringand free-free absorption and α > -0.3 in thepresence of scattering, for a Euclidean flux distribution. Theconstraints imply that FRBs exhibit either a flat spectrum or a spectralturnover at frequencies above 400 MHz. These constraints also allowestimation of the number of bursts that can be detected with current andupcoming surveys. We predict that CHIME may detect anywhere from severalto ˜50 FRBs per day (depending on model assumptions), making it wellsuited for interesting constraints on spectral index, the logN-log S slope, and pulse profile evolution across its bandwidth(400-800 MHz).