Limits on the strength of individual gravitational wave sources using high-cadence observations of PSR B1937+21

TL;DR

This study used high-cadence pulsar observations to set new upper limits on gravitational wave strains from individual sources at very low frequencies, extending the sensitivity of pulsar timing arrays.

Contribution

It demonstrates the effectiveness of high-cadence observations in probing lower GW frequencies and provides new constraints on GW strains from individual sources.

Findings

Achieved sensitivity to GWs up to 4.98×10^{-6} Hz.

Placed upper limits on GW strain at 10^{-7} Hz: 1.53×10^{-11} and 4.99×10^{-14}.

Identified unmodeled periodic noise likely due to pulsar rotational behavior.

Abstract

We present the results of a search for gravitational waves (GWs) from individual sources using high cadence observations of PSR B1937+21. The data were acquired from an intensive observation campaign with the Lovell telescope at Jodrell Bank, between June 2011 and May 2013. The almost daily cadence achieved, allowed us to be sensitive to GWs with frequencies up to $4.98\times10^{-6}\,\rm {Hz}$, extending the upper bound of the typical frequency range probed by Pulsar Timing Arrays. We used observations taken at three different radio frequencies with the Westerbork Synthesis Radio Telescope in order to correct for dispersion measure effects and scattering variances. The corrected timing residuals exhibited an unmodeled periodic noise with an amplitude $~150\,\rm {ns}$ and a frequency of $3.4\rm {yr}^{-1}$. As the signal is not present in the entire data set, we attributed it to the rotational behaviour of the pulsar, ruling out the possibilities of being either due to a GW or an asteroid as the cause. After removing this noise component, we placed limits on the GW strain of individual sources equaling to $h_{\rm s}=1.53\times10^{-11}$ and $h_{\rm s}=4.99\times10^{-14}$ at $10^{-7}\,\rm {Hz}$ for random and optimal sources locations respectively.