Answers to frequently asked questions about the pulsar timing array Hellings and Downs curve
arXiv (Cornell University)(2023)
摘要
We answer frequently asked questions (FAQs) about the Hellings and Downs
correlation curve – the "smoking-gun" signature that pulsar timing arrays
(PTAs) have detected gravitational waves (GWs). Many of these questions arise
from inadvertently applying intuition about the effects of GWs on LIGO-like
detectors to the case of pulsar timing, where not all of that intuition
applies. This is because Earth-based detectors, like LIGO and Virgo, have arms
that are short (km scale) compared to the wavelengths of the GWs that they
detect (approximately 100-10,000 km). In contrast, PTAs respond to GWs whose
wavelengths (tens of light-years) are much shorter than their arms (a typical
PTA pulsar is hundreds to thousands of light-years from Earth). To demonstrate
this, we calculate the time delay induced by a passing GW along an Earth-pulsar
baseline (a "one-arm, one-way" detector) and compare it in the "short-arm"
(LIGO-like) and "long-arm" (PTA) limits. This provides qualitative and
quantitative answers to many questions about the Hellings and Downs curve. The
resulting FAQ sheet should help in understanding the "evidence for GWs"
recently announced by several PTA collaborations.
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关键词
pulsar timing array
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