We present an analysis of high-precision pulsar timing data taken as part of the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) project. We have observed 17 pulsars for a span of roughly five years using the Green Bank and Arecibo radio telescopes. We analyze these data using standard pulsar timing models, with the addition of time-variable dispersion measure and frequency-variable pulse shape terms. Sub-microsecond timing residuals are obtained in nearly all cases, and the best rms timing residuals in this set are similar to 30-50 ns. We present methods for analyzing post-fit timing residuals for the presence of a gravitational wave signal with a specified spectral shape. These optimally take into account the timing fluctuation power removed by the model fit, and can be applied to either data from a single pulsar, or to a set of pulsars to detect a correlated signal. We apply these methods to our data set to set an upper limit on the strength of the nHz-frequency stochastic supermassive black hole gravitational wave background of h(c)(1 yr(-1)) <7 x 10(-15) (95%). This result is dominated by the timing of the two best pulsars in the set, PSRs J1713+0747 and J1909-3744.
- gravitational waves
- data analysis methods
- general pulsars
- individual pulsars (J0030+0451, J0613-0200, J1012+5307, J1455-3330, J1600-3053, J1640+2224, J1643-1224, J1713+0747, J1744-1134, J1853+1308, B1855+09, J1909-3744, J1910+1256, J1918-0642, B1953+29, J2145-0750, J2317+1439)