Gravitational wave astronomy with the SKA (1501.00127v1)

Abstract: On a time scale of years to decades, gravitational wave (GW) astronomy will become a reality. Low frequency (nanoHz) GWs are detectable through long-term timing observations of the most stable pulsars. Radio observatories worldwide are currently carrying out observing programmes to detect GWs, with data sets being shared through the International Pulsar Timing Array project. One of the most likely sources of low frequency GWs are supermassive black hole binaries (SMBHBs), detectable as a background due to a large number of binaries, or as continuous or burst emission from individual sources. No GW signal has yet been detected, but stringent constraints are already being placed on galaxy evolution models. The SKA will bring this research to fruition. In this chapter, we describe how timing observations using SKA1 will contribute to detecting GWs, or can confirm a detection if a first signal already has been identified when SKA1 commences observations. We describe how SKA observations will identify the source(s) of a GW signal, search for anisotropies in the background, improve models of galaxy evolution, test theories of gravity, and characterise the early inspiral phase of a SMBHB system. We describe the impact of the large number of millisecond pulsars to be discovered by the SKA; and the observing cadence, observation durations, and instrumentation required to reach the necessary sensitivity. We describe the noise processes that will influence the achievable precision with the SKA. We assume a long-term timing programme using the SKA1-MID array and consider the implications of modifications to the current design. We describe the possible benefits from observations using SKA1-LOW. Finally, we describe GW detection prospects with SKA1 and SKA2, and end with a description of the expectations of GW astronomy.

• The paper demonstrates that SKA’s exceptional sensitivity and pulsar timing arrays enable precise detection of low-frequency gravitational waves.
• It details methodologies for mitigating noise sources such as pulse jitter and interstellar medium effects to improve signal clarity.
• It reveals that improved waveform characterization of supermassive black hole binaries can significantly refine models of galaxy evolution and cosmology.

Gravitational Wave Astronomy with the Square Kilometre Array

Gravitational wave (GW) astronomy is poised to become a significant branch of astrophysics, leveraging the detection of low-frequency gravitational waves via pulsar timing arrays (PTAs). The Square Kilometre Array (SKA) is expected to play a pivotal role in this domain, facilitating both the initial detection and subsequent detailed paper of GWs. This paper underlines the potentials and challenges associated with integrating the SKA into the global framework of GW detection efforts.

Detecting Low-Frequency Gravitational Waves

Central to GW detection with the SKA is the exploitation of millisecond pulsars' highly stable emissions. Variations in the timing residuals, affected by passing gravitational waves, offer a means to directly detect these cosmic ripples. The SKA's unprecedented sensitivity will enhance our ability to time these pulsars with high precision, expanding the pool of observable pulsars and extending the frequency range of detectable GWs.

A key challenge will be distinguishing GW signals amidst noise. Known noise sources include pulse jitter, interstellar medium effects, and intrinsic pulsar timing noise. The SKA's high sensitivity and large sample of pulsars will allow for improved noise characterization and mitigation, enhancing GW detection prospects.

Expected Sources and Significance

The primary GW sources detectable at the low frequencies relevant to PTAs are supermassive black hole binaries (SMBHBs), potentially revealing insights into galaxy evolution models. Other scenarios include cosmic strings and potential signals from the inflationary epoch. SKA observations are anticipated to significantly constrain these models, testing theories of gravity and refining our understanding of cosmic history.

By characterizing the GW spectrum, the SKA will enable us to dissect the stochastic GW background's properties, identifying individual GW sources and interpreting their effects on galaxy development. The complementary nature of PTA observations ensures that they probe unique source classes compared to other GW observatories such as LIGO and eLISA.

Advancing Gravitational Wave Science

With the capabilities of the SKA, GW astronomy will transition from detection to analysis, enabling the exploration of anisotropies in the GW background and characterizing individual GW events. These advancements will allow for more precise tests of general relativity and other gravitational theories, particularly in the radiative regime, by detailing the dynamics of gravitating bodies as they emit GWs.

The SKA's ability to detect GW-induced perturbations in the timing residuals will provide unprecedented accuracy in measuring cosmic phenomena, such as the masses and structures of SMBHBs. PTA observations can merge the GW signal across multiple pulsar lines of sight, granting astronomers a potent method to investigate mergers' astrophysical environments and broader implications for cosmology.

Conclusion and Future Prospects

As the SKA realizes its potential in GW astronomy, it will catalyze discoveries impacting both fundamental physics and cosmology. The amalgamation of high-sensitivity timing, vast pulsar databases, and advanced noise mitigation strategies ensures the SKA's pivotal position in the future tapestry of GW research. This global endeavor will not only illuminate features of the GW landscape but also enhance our comprehension of the universe's structure and evolution.