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The North American Nanohertz Observatory for Gravitational Waves (NANOGrav)project currently observes 43 pulsars using the Green Bank and Arecibo radiotelescopes. In this work we use a subset of 17 pulsars timed for a span ofroughly five years (2005--2010). We analyze these data using standard pulsartiming models, with the addition of time-variable dispersion measure andfrequency-variable pulse shape terms. Within the timing data, we perform asearch for continuous gravitational waves from individual supermassive blackhole binaries in circular orbits using robust frequentist and Bayesiantechniques. We find that there is no evidence for the presence of a detectablecontinuous gravitational wave; however, we can use these data to place the mostconstraining upper limits to date on the strength of such gravitational waves.Using the full 17 pulsar dataset we place a 95% upper limit on the sky-averagedstrain amplitude of $h_0\lesssim 3.8\times 10^{-14}$ at a frequency of 10 nHz.Furthermore, we place 95% \emph{all sky} lower limits on the luminositydistance to such gravitational wave sources finding that the $d_L \gtrsim 425$Mpc for sources at a frequency of 10 nHz and chirp mass $10^{10}{\rmM}_{\odot}$. We find that for gravitational wave sources near our best timedpulsars in the sky, the sensitivity of the pulsar timing array is increased bya factor of $\sim$4 over the sky-averaged sensitivity. Finally we place limitson the coalescence rate of the most massive supermassive black hole binaries.

NANOGrav Limits on Gravitational Waves from Individual Supermassive Black Hole Binaries in Circular Orbits