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Astrophysics, Instrumentation and Methods for Astrophysics, astro-ph.IM
Abstract:
The highly stable spin of neutron stars can be exploited for a variety of
(astro-)physical investigations. In particular arrays of pulsars with
rotational periods of the order of milliseconds can be used to detect
correlated signals such as those caused by gravitational waves. Three such
"Pulsar Timing Arrays" (PTAs) have been set up around the world over the past
decades and collectively form the "International" PTA (IPTA). In this paper, we
describe the first joint analysis of the data from the three regional PTAs,
i.e. of the first IPTA data set. We describe the available PTA data, the
approach presently followed for its combination and suggest improvements for
future PTA research. Particular attention is paid to subtle details (such as
underestimation of measurement uncertainty and long-period noise) that have
often been ignored but which become important in this unprecedentedly large and
inhomogeneous data set. We identify and describe in detail several factors that
complicate IPTA research and provide recommendations for future pulsar timing
efforts. The first IPTA data release presented here (and available online) is
used to demonstrate the IPTA's potential of improving upon gravitational-wave
limits placed by individual PTAs by a factor of ~2 and provides a 2-sigma limit
on the dimensionless amplitude of a stochastic GWB of 1.7x10^{-15} at a
frequency of 1 yr^{-1}. This is 1.7 times less constraining than the limit
placed by (Shannon et al. 2015), due mostly to the more recent, high-quality
data they used.
