Coherent search for binary pulsars across all Five Keplerian parameters in radio observations using the template-bank algorithm

Abstract

Relativistic binary pulsars orbiting white-dwarfs and neutron stars have already provided excellent tests of gravity. However, despite observational efforts, a pulsar orbiting a black hole has remained elusive. One possible explanation is the extreme Doppler smearing caused by the pulsar’s orbital motion which changes its apparent spin frequency during an observation. The classical solution to this problem has been to assume a constant acceleration/jerk for the entire observation. However, this assumption breaks down when the observation samples a large fraction of the orbit. This limits the length of search observations, and hence their sensitivity. This provides a strong motivation to develop techniques that can find compact binaries in longer observations. Here we present a GPU-based radio pulsar search pipeline that can perform a coherent search for binary pulsars by directly searching over three or five Keplerian parameters using the template-bank algorithm. We compare the sensitivity obtained from our pipeline with acceleration and jerk search pipelines for simulated pulsar-stellar-mass black hole binaries and observations of PSR J0737-3039A. We also discuss the computational feasibility of our pipeline for untargeted pulsar surveys and targeted searches. Our benchmarks indicate that circular orbit searches for P-BH binaries with spin-period Pspin ≥ 20ms covering the 3-10 Tobs regime are feasible for the High Time Resolution Universe pulsar survey. Additionally, an elliptical orbit search in Globular clusters for Pspin ≥ 20ms pulsars orbiting intermediate-mass black holes in the 5-10 Tobs regime is feasible for observations shorter than 2 hours with an eccentricity limit of 0.1.

4–8 GHz Fourier-domain Searches for Galactic Center Pulsars

“…Our N MSP estimate is a factor of 20 smaller than that derived by Wharton et al (2012), possibly due to our lack of sensitivity to tight MSP orbits. Sideband searches (Ransom et al 2003) and coherent full-orbit demodulation algorithms (Allen et al 2013;Balakrishnan et al 2022) will both provide sensitivity to short binary orbital periods (P b = T), thereby yielding stronger constraints on the GC MSP population in the near future. Alternatively, our nondetection of GC pulsars can be attributed to complex pulsar orbital dynamics arising from plausible close encounters with other neutron stars, stellar-mass BHs, and intermediate-mass BHs in the dense GC environment.…”

Missing for 20 yr: MeerKAT Redetects the Elusive Binary Pulsar M30B

“…First is PULSAR_MINER, 16 a user-friendly wrapper of PRESTO, 17 which is a Fourier-domain acceleration search pipeline sensitive to binary pulsars in constant acceleration (P orb  10 T obs ; Ransom et al 2002Ransom et al , 2003. Our second pipeline called 3D/5D_PEASOUP 18 uses the template-bank algorithm to search for pulsars in compact circular orbit binaries by coherently searching across three Keplerian parameters in the time domain (Balakrishnan et al 2022).…”

“…Here we searched for orbits between 4 and 10 hr in the 60 minute observation and between 2 and 5 hr in the 30 minute chunks, with an initial orbital phase between 0 and 2 π, mismatch of 10%, and a coverage of 90% assuming a minimum pulsar spin period of 2 ms, minimum pulsar mass of 1.4 M e , and a maximum companion mass of 8 M e . We refer interested readers to Section 3 of Ridolfi et al (2021) and Section 2 of Balakrishnan et al (2022) for a more in-depth review of the PULSAR_MINER and the 3D/5D_PEASOUP pipelines, respectively. On average, we folded approximately 350 pulsar candidates per beam for all our acceleration searches and 1000 pulsar candidates per beam for our template-bank searches.…”

TRAPUM discovery of 13 new pulsars in NGC 1851 using MeerKAT

“…This could reveal, for instance, systems that may have been ejected from the core during secondary exchange interactions, and that have not had time yet to sink back in the core (these types of objects are more common in GCs with a large γ, see Verbunt & Freire 2014). To complement this, all the beams, starting from the inner ones, will also be searched using more sophisticated (but often more computationally demanding) methods, such as jerk searches (Andersen & Ransom 2018), phase-modulation searches (Ransom et al 2003), template-banking algorithms over 3 or 5 Keplerian parameters (Balakrishnan et al 2022), as well as fast-folding algorithms (Morello et al 2020); the first three have a higher potential of unveiling fast pulsars in extremely compact binaries, while the latter is more sensitive to very slow, isolated pulsars. With such searches, we will know whether the intriguing lack of spiders is real, or a result of current limitations in our search techniques.…”