# Searching for Continuous Gravitational Waves

The primary goal of this permanent independent research group is to make the first direct detection of gravitational waves from spinning neutron stars, and thus to observe these stars via a completely different physical mechanism, which would carry important new information about their internal structure and composition.

Neutron stars, the targets of this research program, are extreme objects formed in supernova explosions. They typically have around 40 % more mass than the Sun, but are only about 20 kilometers in diameter: the only objects that are known to be more compact than this are black holes. Until now, the vast majority of neutron stars have been found via the pulsations that result from their beamed electromagnetic emission periodically sweeping past the Earth; for this reason they are often called pulsars. However, while it is believed that the Milky Way contains about a hundred million neutron stars, fewer than 3000 have been detected so far. Gravitational waves might well be the only way to unveil this invisible population of extreme objects.

In 2016, the LIGO Scientific Collaboration announced the first direct observations of short bursts of gravitational waves, emitted during the inspiral and merger of black holes of tens of solar masses. Here we target a different type of gravitational wave signal: the long continuous waveform expected from a rapidly spinning neutron star. Because the star's sky location, spin rate, and deformation from axisymmetry are unknown, there is a large parameter space to search, and the sensitivity is limited by the amount of computing power available. The Einstein@Home volunteer computing project provides the lion's share of our compute cycles and on it we deploy our state-of-the-art search techniques.

The direct detection of gravitational waves has opened a new window on the Universe, providing a new tool for astrophysical observation. The detection of continuous gravitational waves will provide glimpses in the invisible population of neutron stars that inhabits our Galaxy, improve our understanding of stellar evolution and populations and shed light on the internal structure and evolutionary history on these extraordinary objects.

## Recently published papers

1.

C. Dreissigacker, R. Prix, and K. Wette

Fast and Accurate Sensitivity Estimation for Continuous-Gravitational-Wave Searches

Phys. Rev. D 98, 084058 (2018)

2.

G. Ashton, R. Prix, and D. I. Jones

A semicoherent glitch-robust continuous-gravitational-wave search method

Phys. Rev. D 98, 063011 (2018)

3.

G. Ashton, D. I. Jones, and R. Prix

Advances in our understanding of the free precession candidate PSR B1828-11

Pulsar Astrophysics the Next Fifty Years, Proceedings of the International Astronomical Union, IAU Symposium, Volume 337, pp. 307-308 (2018)

4.

K. Wette , S. Walsh, R. Prix, and M.A. Papa

Implementing a semicoherent search for continuous gravitational waves using optimally-constructed template banks

Phys. Rev. D 97, 123016 (2018)

5.

The LIGO Scientific Collaboration and the Virgo Collaboration

Full Band All-sky Search for Periodic Gravitational Waves in the O1 LIGO Data

Phys. Rev. D 97, 102003 (2018)

6.

K. Wette, R. Prix, D. Keitel, M. Pitkin, C. Dreissigacker, J.T. Whelan, and P. Leaci

OctApps: a library of Octave functions for continuous gravitational-wave data analysis

Journal of Open Source Software, 3(26), 707 (2018)

7.

G. Ashton and R. Prix

Hierarchical multi-stage MCMC follow-up of continuous gravitational wave candidates

Phys. Rev. D 97, 103020 (2018)

8.

G. Ashton et al.

Coincident detection significance in multimessenger astronomy

The Astrophysical Journal, Volume 860, Number 1 (2018)

9.

Covas et al. and LSC instrument authors

Identification and mitigation of narrow spectral artifacts that degrade searches for persistent gravitational waves in the first two observing runs of Advanced LIGO

Phys. Rev. D 97, 082002 (2018)

10.

A. Mukherjee, C. Messenger, and K. Riles

Accretion-induced spin-wandering effects on the neutron star in Scorpius X-1: Implications for continuous gravitational wave searches

Phys. Rev. D 97, 043016 (2018)

11.

G. D. Meadors, B. Krishnan, M. A. Papa, J. T. Whelan, Y. Zhang

Resampling to accelerate cross-correlation searches for continuous gravitational waves from binary systems

Phys. Rev. D 97, 044017 (2018)

12.

J. Ming, M. A. Papa, B. Krishnan, R. Prix, C. Beer, S. J. Zhu, H.-B. Eggenstein, O. Bock, B. Machenschalk

Optimally setting up directed searches for continuous gravitational waves in Advanced LIGO O1 data

Phys. Rev. D 97, 024051 (2018)

13.

S. J. Zhu, M. A. Papa, S. Walsh

A new veto for continuous gravitational wave searches

Phys. Rev. D 96, 124007 (2017)

14.

The LIGO Scientific Collaboration and the Virgo Collaboration

First low-frequency Einstein@Home all-sky search for continuous gravitational waves in Advanced LIGO data

Phys. Rev. D 96, 122004 (2017)

15.

A. Singh, M. A. Papa, H.-B. Eggenstein, S. Walsh

An adaptive clustering procedure for continuous gravitational wave searches

Phys. Rev. D 96, 082003 (2017)

16.

G. Ashton, R. Prix, D. I. Jones

Statistical characterization of pulsar glitches and their potential impact on searches for continuous gravitational waves

Phys. Rev. D 96, 063004 (2017)

17.

LIGO Scientific Collaboration and Virgo Collaboration

All-sky search for periodic gravitational waves in the O1 LIGO data

Phys. Rev. D 96, 062002 (2017)

18.

D. I. Jones, G. Ashton, and R. Prix

Implications of the Occurrence of Glitches in Pulsar Free Precession Candidates

Phys.Rev.Lett. 118 (2017) no.26, 261101

19.

Grant David Meadors, Evan Goetz, Keith Riles, Teviet Creighton, Florent Robinet

Searches for continuous gravitational waves from Scorpius X-1 and XTE J1751-305 in LIGO's sixth science run

Phys. Rev. D 95, 042005 (2017)

20.

Avneet Singh

Gravitational wave transient signal emission via Ekman pumping in neutron stars during post-glitch relaxation phase

Phys. Rev. D 95, 024022 (2017)

21.

G. Ashton, D. I. Jones, and R. Prix

On the free-precession candidate PSR B1828-11: Evidence for increasing deformation

Mon Not R Astron Soc (2017) 467 (1): 164-178

22.

M.A. Papa et al.

Hierarchical follow-up of sub-threshold candidates of an all-sky Einstein@home search for continuous gravitational waves on LIGO S6 data

Phys. Rev. D 94, 122006 (2016)

23.

Karl Wette

Empirically extending the range of validity of parameter-space metrics for all-sky searches for gravitational-wave pulsars

Phys. Rev. D 94, 122002 (2016)

24.

Sinead Walsh et al.

A comparison of methods for the detection of gravitational waves from unknown neutron stars

Phys. Rev. D 94, 124010 (2016)

25.

LIGO Scientific Collaboration

Results of the deepest all-sky survey for continuous gravitational waves on LIGO S6 data running on the Einstein at Home volunteer distributed computing project

Phys. Rev. D 94, 102002 (2016)

26.

Sylvia J. Zhu et al.

Results of the deepest Einstein@Home search for continuous gravitational waves from CasA from the S6 LIGO Science Run

Phys. Rev. D 94, 082008 (2016)

27.

Avneet Singh et al.

Results of an all-sky high-frequency Einstein@Home search for continuous gravitational waves in LIGO 5th Science Run

Phys. Rev. D 94, 064061 (2016)

28.

Grant David Meadors, Evan Goetz, and Keith Riles

Tuning into Scorpius X-1: adapting a continuous gravitational-wave search for a known binary system

Class. Quantum Grav. 33 (2016)

29.

David Keitel

Robust semicoherent searches for continuous gravitational waves with noise and signal models including hours to days long transients

Phys. Rev. D 93, 084024 (2016)

30.

Jing Ming, Badri Krishnan, Maria Alessandra Papa, Carsten Aulbert, and Henning Fehrmann

Optimal directed searches for continuous gravitational waves

Phys. Rev. D 93, 064011 (2016)

31.

Miroslav Shaltev

Optimizing StackSlide setup and data selection for continuous-gravitational-wave searches in realistic detector data

Phys. Rev. D 93, 044058 (2016)

32.

G. Ashton, D. I. Jones, and R. Prix

Comparing models of the periodic variations in spin-down and beamwidth for PSR B1828-11

Mon Not R Astron Soc (2016) 458 (1): 881-899