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Abstract

We perform a search for continuous nearly monochromatic gravitational waves
from the central compact objects associated with the supernova remnants Vela
Jr. and G347.3 using LIGO O2 and O3 public data. Over $10^{18}$ different
waveforms are considered, covering signal frequencies between 20-1300 Hz
(20-400 Hz) for G347.3-0.5 (Vela Jr) and a very broad range of frequency
derivatives. Thousands of volunteers donating compute cycles through the
computing project Einstein@Home have made this endeavour possible. Following
the Einstein@Home search, we perform multi-stage follow-ups of over 5 million
waveforms. The selection threshold is set so that a signal could be confirmed
using the first half of the LIGO O3 data. We find no significant signal
candidate for either targets. Based on this null result, for G347.3-0.5, we set
the most constraining upper limits to date on the amplitude of gravitational
wave signals, corresponding to deformations below $10^{-6}$ in a large part of
the search band. At the frequency of best strain sensitivity, near $161$ Hz, we
set 90\%\ confidence upper limits on the gravitational wave intrinsic amplitude
of $h_0^{90\%}\approx 6.2\times10^{-26}$. Over most of the frequency range our
upper limits are a factor of 10 smaller than the indirect age-based upper
limit. For Vela Jr., near $163$ Hz, we set $h_0^{90\%}\approx
6.4\times10^{-26}$. Over most of the frequency range our upper limits are a
factor of 15 smaller than the indirect age-based upper limit. The Vela Jr.
upper limits presented here are slightly less constraining than the most recent
upper limits of \cite{ligo_o3a_c_v} but they apply to a broader set of signals.