Expected properties of the first gravitational wave signal detected with pulsar timing arrays

Abstract

In this paper we attempt to investigate the nature of the first gravitational wave (GW) signal to be detected by pulsar timing arrays (PTAs): will it be an individual, resolved supermassive black hole binary (SBHB), or a stochastic background made by the superposition of GWs produced by an ensemble of SBHBs? To address this issue, we analyse a broad set of simulations of the cosmological population of SBHBs, that cover the entire parameter space allowed by current electromagnetic observations in an unbiased way. For each simulation, we construct the expected GW signal and identify the loudest individual sources. We then employ appropriate detection statistics to evaluate the relative probability of detecting each type of source as a function of time for a variety of PTAs; we consider the current International PTA, and speculate into the era of the Square Kilometre Array. The main properties of the first detectable individual SBHBs are also investigated. Contrary to previous work, we cast our results in terms of the detection probability (DP), since the commonly adopted criterion based on a signal-to-noise ratio threshold is statistic-dependent and may result in misleading conclusions for the statistics adopted here. Our results confirm quantitatively that a stochastic signal is more likely to be detected first (with between 75 to 93 per cent probability, depending on the array), but the DP of single-sources is not negligible. Our framework is very flexible and can be easily extended to more realistic arrays and to signal models including environmental coupling and SBHB eccentricity.

Selection bias in dynamically measured supermassive black hole samples: consequences for pulsar timing arrays

“…To investigate the consequences for PTA detection we follow Rosado et al (2015) (hereinafter R15). We consider an ideal IPTAtype array with N = 50 pulsars, timed with an rms residual σrms = 200 ns at intervals ∆t = 2 weeks.…”

Detecting Eccentric Supermassive Black Hole Binaries With Pulsar Timing Arrays: Resolvable Source Strategies

“…Hence, binary parameter measurement precisions become non-trivial once the Bayes factor favoring the presence of a signal exceeds our threshold value of 100. Rosado et al (2015) investigated the likely properties of the first detectable continuous GW source in IPTA and SKA (Janssen et al 2015) data, observing that the detection probability favored massive, nearby binaries with orbital frequencies 10 nHz. However, the authors did not consider eccentricity.…”

“…We choose a cutoff value of the tolerance S/N equal to 10 since this may correspond to realistic values of the S/Ns of first PTA detections of single GW sources after ∼10 years of IPTA and SKA1 activity (Rosado et al 2015). If our model can be successfully applied to real signals above this cutoff value, then we conclude that the treatment used in this paper is valid well into the era of first PTA detections.…”

Implications of the gravitational wave event GW150914

“…At very low frequencies ∼ 10 −17 − 10 −16 Hz, B-mode polarization in the cosmic microwave background would be a signal of primordial gravitational waves [170,171]. At higher frequencies ∼ 10 −9 − 10 −6 Hz, pulsar timing arrays are improving their sensitivity; their first detection is likely to be of the stochastic background formed by a large set of supermassive black hole binaries, but there is some prospect for individual detections [172]. At yet higher frequencies ∼ 10 −4 − 10 −1 Hz, eLISA is an ESA mission planned for launch in 2034 [13] that will involve three freely-falling test masses some millions of kilometers apart.…”