New semicoherent targeted search for continuous gravitational waves from pulsars in binary systems
We present a novel semicoherent targeted search method for continuous gravitational waves (CWs) emitted by pulsars in binary systems. The method is based on a custom optimization of the coherence time, which is tailored according to the orbital parameters and their uncertainties, as provided by electromagnetic observations. While rotating pulsars are expected to produce quasimonochromatic CWs in their reference frame, their orbital motion introduces additional modulation in the observer's frame, alongside the modulation caused by the Earth's motion. As a result, the received signal is spread across a frequency range, and demodulation techniques must be used to improve sensitivity. However, Doppler corrections can, in some cases, vary significantly within the uncertainties of the orbital parameters, potentially lowering the detection chances of single-template, fully coherent searches. To exploit the constraints derived from electromagnetic observations, we implement a semicoherent search that is more robust than other methods. In this approach, the coherence time is evaluated for each source, taking into account the uncertainties in its orbital parameters. This method was tested and applied to a set of thirteen targets from the ATNF catalog. The search identified one outlier, whose astrophysical origin has been confidently excluded. For the first time to our knowledge, we then set upper limits on the signal strain from these 12 pulsars, with the lowest limit being $h_{UL}\sim9.01\times 10^{-26}$ for PSR~J1326-4728B.