Resolving Multiple Gravitational Wave Sources in Pulsar Timing Array Data

Mohanty, Soumya D.; Qian, Yi-Qian; Wang, Yan

Resolving Multiple Gravitational Wave Sources in Pulsar Timing Array Data

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Date

2022-09-29

Authors

Mohanty, Soumya D.

Qian, Yi-Qian

Wang, Yan

Abstract

Timing the arrival of radio pulses from an array of rapidly spinning neutron stars (Pulsars) is a promising method for detecting gravitational waves (GWs) in the ultra-low frequency regime (10!" Hz to 10!# Hz), primarily from supermassive (billion solar mass and above) black hole binaries . It is expected that next-generation radio telescopes, namely, the Five-Hundred-Meter Aperture Spherical Radio Telescope (FAST) and the Square Kilometer Array (SKA), will grow the number of well-timed pulsars to 𝑂(10 $). T h i s w i l l r e s u l t i n g r e a t e r d i s t a n c e r e a c h f o r G W s o u r c e s, u n c o v e r i n g m u l t i p l e r e s o l v a b l e G W s o u r c e s i n a d d i t i o n t o a n u n r e s o l v e d p o p u l a t i o n . T h e m u l t i s o u r c e r e s o l u t i o n p r o b l e m f o r P T A s p o s e s a u n i q u e s e t o f d a t a a n a l y s i s c h a l l e n g e s s u c h a s n o n u n i f o r m l y s a m p l e d d a t a, a l a r g e n u m b e r o f s o − c a l l e d p u l s a r p h a s e p a r a m e t e r s t h a t a r i s e f r o m t h e i n a c c u r a t e l y m e a s u r e d d i s t a n c e s t o t h e p u l s a r s, a n d p o o r s e p a r a t i o n o f s i g n a l s i n t h e F o u r i e r d o m a i n d u e t o a s m a l l n u m b e r o f c y c l e s i n t h e o b s e r v e d w a v e f o r m s . W e a r e d e v e l o p i n g a n e n d − t o − e n d s o f t w a r e p i p e l i n e f o r a d d r e s s i n g t h e s e c h a l l e n g e s . T h e c o r e i d e a i s t h e i t e r a t i v e s u b t r a c t i o n o f i n d i v i d u a l l y e s t i m a t e d G W s o u r c e s f r o m t h e d a t a . H o w e v e r, m u l t i p l e s t a g e s o f r e f i n e m e n t a r e n e e d e d i m p r o v e t h e s a m p l e o f i d e n t i f i e d s o u r c e s, i n c l u d i n g a n o v e l a p p r o a c h t h a t m i t i g a t e s s p u r i o u s s o u r c e s b y c r o s s − c h e c k i n g t h e o u t p u t s f r o m t w o s e m i − i n d e p e n d e n t r e f i n e m e n t s t e p s . T h e p e r f o r m a n c e o f t h e c u r r e n t v e r s i o n o f t h e p i p e l i n e w a s q u a n t i f i e d o n s i m u l a t e d d a t a f r o m P T A s c o n t a i n i n g 10$ pulsars, leading to state-of-the-art results in all cases. For example, the fraction of sources found by the method that correspond to true sources in the simulated data exceeds 78% and 93% for a large-scale (with 10$ pulsars and 200 sources) and a midscale (with 10% pulsars and 100 sources) PTA, respectively. The pipeline is currently implemented as a mix of Matlab and parallelized C-code running on TACC resources.