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General Relativity and Quantum Cosmology, gr-qc
Abstract:
We perform an unmodeled search for persistent, directional gravitational wave
(GW) sources using data from the first and second observing runs of Advanced
LIGO. We do not find evidence for any GW signals. We place limits on the
broadband GW flux emitted at 25~Hz from point sources with a power law spectrum
at $F_{\alpha,\Theta} <(0.05-25)\times 10^{-8} ~{\rm
erg\,cm^{-2}\,s^{-1}\,Hz^{-1}}$ and the (normalized) energy density spectrum in
GWs at 25 Hz from extended sources at $\Omega_{\alpha}(\Theta)
<(0.19-2.89)\times 10^{-8} ~{\rm sr^{-1}}$ where $\alpha$ is the spectral index
of the energy density spectrum. These represent improvements of $2.5-3\times$
over previous limits. We also consider point sources emitting GWs at a single
frequency, targeting the directions of Sco X-1, SN 1987A, and the Galactic
Center. The best upper limits on the strain amplitude of a potential source in
these three directions range from $h_0 < (3.6-4.7)\times 10^{-25}$, 1.5$\times$
better than previous limits set with the same analysis method. We also report
on a marginally significant outlier at 36.06~Hz. This outlier is not consistent
with a persistent gravitational-wave source as its significance diminishes when
combining all of the available data.
