Probing three supernova remnants with Einstein@Home
The volunteer distributed computing project enables a close look at central compact objects in Cassiopeia A, Vela Jr., and G347.3-0.5.
Searching for weak, continuous gravitational-wave emissions from rotating neutron stars is computationally demanding. However, limiting the search to a specific region or point in the sky allows for a broad range of frequencies and frequency derivatives to be searched deeply for faint signals. In earlier work, researchers from the permanent independent Max Planck research group “Continuous Gravitational Waves” at the AEI in Hannover, identified three young supernova remnants – Vela Jr., Cassiopeia A, and G347.3-0.5 – as promising targets. They have now published their results from targeted, deep searches of these objects using public LIGO O3 and O4a data. These results achieved by harnessing the computing power of Einstein@Home and the Atlas computer cluster surpass indirect limits on gravitational-wave emission by more than an order of magnitude. Although no detection was made, these results provide the most stringent constraints on neutron star ellipticity, r-mode amplitude, and, for the first time ever, anisotropy of the neutron stars’ crusts. Additionally, one signal candidate remains after follow-up investigations of three independent data sets. Whether it is of astrophysical origin can only be decided by analyzing additional data that is not yet publicly available.
Paper abstract
We carry out the deepest and broadest search for continuous gravitational-wave signals with frequencies between 20-1500 Hz, from three neutron stars at the center of the supernova remnants Cassiopeia A, Vela Jr., and G347.3-0.5. This search was made possible by the computing power shared by thousands of Einstein@Home volunteers. After the initial Einstein@Home search, we perform a multi-stage follow-up of the most promising ≈ 45 million signal candidates. In the last stages, we use independent data to further investigate the remaining candidates from the previous stages. We set the most stringent constraints to date on the gravitational-wave amplitude, equatorial ellipticity, r-mode saturation amplitude, and – for the first time – the neutron-star crustal anisotropy. For spin periods lower than 2 ms we constrain the ellipticity to be smaller than 4×10-7 for all targets. We exclude the crustal anisotropy to be smaller than 5×10-3 for spin periods between 1.3-100 ms. Only one candidate – from the low frequency G347.3 search – survives all follow-ups. We illustrate properties of this candidate. Investigations on new data will aid in clarifying its nature. Such “new” data exists and would be optimal for this purpose, but they are not publicly accessible at the time of writing. In the appendix we provide our estimate of the candidate parameters.
