Upper limits on microhertz gravitational waves from supermassive black-hole binaries using PSR J1909-3744 data from the second IPTA data release

TL;DR

This paper sets upper limits on gravitational wave strains from supermassive black-hole binaries using pulsar timing data, improving previous constraints and demonstrating the sensitivity of the IPTA-DR2 dataset.

Contribution

The study provides the first upper limits on gravitational waves from individual sources using the IPTA second data release, with improved sensitivity over previous results.

Findings

Upper limits on GW strain at 71 nHz and 1 μHz frequencies.

Detection sensitivity improved by a factor of 1.52 over previous studies.

Precise corrections for dispersion and scattering effects enhanced data quality.

Abstract

We present the results of a search for gravitational waves (GWs) from individual sources using high-cadence observations of PSR J1909\(-\)3744 obtained during an intensive observing campaign with the International Pulsar Timing Array second data release (IPTA-DR2) between July 2010 and November 2012. The observations, conducted at three different radio frequencies with the Nan\c{c}ay Radio Telescope (NRT) and Parkes Telescope (PKS) and five frequencies with the Green Bank Telescope (GBT), enabled precise corrections for dispersion measure effects and scattering variations. After these corrections, the timing residuals showed an unmodeled periodic noise component with an amplitude of 340 ns. Our analysis yields upper limits on the GW strain from individual sources, constraining it to be below \(1.9 \times 10^{-14}\) at 71 nHz and \(2.3 \times 10^{-13}\) at 1 \textmu Hz for average sky locations, while for optimal source locations the limits improve to \(6.2 \times 10^{-15}\) and \(8.9 \times 10^{-14}\) at the same frequencies, respectively. Our new limits are about a factor of 1.52 more stringent than those of Perera et al. based on an earlier EPTA data.