# 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 submitted papers

1.

L. Nieder et al.

Discovery of a Gamma-ray Black Widow Pulsar by GPU-accelerated Einstein@Home

arXiv:2009.01513 (2020)

2.

V. Dergachev, M. A. Papa

Results from the first all-sky search for continuous gravitational waves from small-ellipticity sources

arXiv:2004.08334 (2020)

for “Results from the first all-sky search for continuous gravitational waves from small-ellipticity sources”

## Recently published papers

3.

S. J. Zhu, M. Baryakhtar, M. A. Papa, D. Tsuna, N. Kawanaka, H.-B. Eggenstein

Characterizing the continuous gravitational-wave signal from boson clouds around Galactic isolated black holes

Phys. Rev. D 102, 063020 (2020)

for the publication “Characterizing the continuous gravitational-wave signal from boson clouds around Galactic isolated black holes”

4.

C. Dreissigacker, R. Prix

Deep-Learning Continuous Gravitational Waves: Multiple detectors and realistic noise

Phys. Rev. D 102, 022005 (2020)

5.

M.A. Papa, J. Ming, E.V. Gotthelf, B. Allen, R. Prix, V. Dergachev, H.-B. Eggenstein, A. Singh, S.J. Zhu

Search for Continuous Gravitational Waves from the Central Compact Objects in Supernova Remnants Cassiopeia A, Vela Jr. and G347.3-0.5

The Astrophysical Journal, Volume 897, Number 1 (2020)

for the publication “Search for Continuous Gravitational Waves from the Central Compact Objects in Supernova Remnants Cassiopeia A, Vela Jr. and G347.3-0.5”

6.

L. Fesik, M. A. Papa

First search for r-mode gravitational waves from J0537-6910

The Astrophysical Journal, Volume 895, Number 1 (2020)

for the publication “First search for r-mode gravitational waves from PSR J0537-6910”

7.

B. Beheshtipour, M. A. Papa

Deep learning for clustering of continuous gravitational wave candidates

Phys. Rev. D 101, 064009 (2020)

8.

V. Dergachev, M. A. Papa

Results from an extended Falcon all-sky survey for continuous gravitational waves

Phys. Rev. D 101, 022001 (2020)

for the publication “Results from an extended Falcon all-sky survey for continuous gravitational waves”

9.

C. J. Horowitz, M. A. Papa, S. Reddy

Search for compact dark matter objects in the solar system with LIGO data

Physics Letters B, Volume 800, 135072 (2020)

## 2019

10.

L. Nieder, C. J. Clark, C. G. Bassa, J. Wu, A. Singh, J. Y. Donner, B. Allen, R. P. Breton, V. S. Dhillon, H.-B. Eggenstein, J. W. T. Hessels, M. R. Kennedy, M. Kerr, S. Littlefair, T. R. Marsh, D. Mata Sánchez, M. A. Papa, P. S. Ray, B. Steltner, and J. P. W. Verbiest

Detection and timing of gamma-ray pulsations from the 707-Hz pulsar J0952−0607

The Astrophysical Journal, Volume 883, Number 1 (2019)

11.

V. Dergachev and M. A. Papa

Sensitivity Improvements in the Search for Periodic Gravitational Waves Using O1 LIGO Data

Phys. Rev. Lett. 123, 101101 (2019)

for “Sensitivity Improvements in the Search for Periodic Gravitational Waves Using O1 LIGO Data”

12.

C. Dreissigacker, R. Sharma, C. Messenger, Chris, and R. Prix

Deep-Learning Continuous Gravitational Waves

Phys. Rev. D 100, 044009 (2019)

13.

Jing Ming, Maria Alessandra Papa, Avneet Singh, Heinz-Bernd Eggenstein, Sylvia J. Zhu, Vladimir Dergachev, Yi-Ming Hu, Reinhard Prix, Bernd Machenschalk, Christian Beer, Oliver Behnke, and Bruce Allen

Results from an Einstein@Home search for continuous gravitational waves from Cassiopeia A, Vela Jr. and G347.3

Phys. Rev. D 100, 024063 (2019)

for “Results from an Einstein@Home search for continuous gravitational waves from Cassiopeia A, Vela Jr. and G347.3”

14.

Avneet Singh, Maria Alessandra Papa, and Vladimir Dergachev

Characterizing the sensitivity of isolated continuous gravitational wave searches to binary orbits

Phys. Rev. D 100, 024058 (2019)

15.

Vladimir Dergachev, Maria Alessandra Papa, Benjamin Steltner, and Heinz-Bernd Eggenstein

Loosely coherent search in LIGO O1 data for continuous gravitational waves from Terzan 5 and the Galactic center

Phys. Rev. D 99, 084048 (2019)

for “Loosely coherent search in LIGO O1 data for continuous gravitational waves from Terzan 5 and the galactic center”

16.

Sinead Walsh, Karl Wette, Maria Alessandra Papa, and Reinhard Prix

Optimizing the choice of analysis method for all-sky searches for continuous gravitational waves with Einstein@Home

Phys. Rev. D 99, 082004 (2019)

17.

Orion Sauter, Vladimir Dergachev, and Keith Riles

Efficient estimation of barycentered relative time delays for distant gravitational wave sources

Phys. Rev. D 99, 044006 (2019)

18.

V. Dergachev

Loosely coherent searches for medium scale coherence lengths

arXiv:1807.02351 (2019)

## 2018

19.

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

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

Phys. Rev. D 98, 084058 (2018)

20.

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

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

Phys. Rev. D 98, 063011 (2018)

21.

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)

22.

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)

23.

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)

24.

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)

25.

G. Ashton and R. Prix

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

Phys. Rev. D 97, 103020 (2018)

26.

G. Ashton et al.

Coincident detection significance in multimessenger astronomy

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

27.

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)

28.

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)

29.

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)

30.

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)

## 2017

31.

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

A new veto for continuous gravitational wave searches

Phys. Rev. D 96, 124007 (2017)

32.

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)

33.

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

Adaptive clustering procedure for continuous gravitational wave searches

Phys. Rev. D 96, 082003 (2017)

34.

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)

35.

LIGO Scientific Collaboration and Virgo Collaboration

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

Phys. Rev. D 96, 062002 (2017)

36.

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

37.

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)

38.

Avneet Singh

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

Phys. Rev. D 95, 024022 (2017)

39.

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

## 2016

40.

M.A. Papa et al.

Hierarchical follow-up of subthreshold candidates of an all-sky Einstein@Home search for continuous gravitational waves on LIGO sixth science run data

Phys. Rev. D 94, 122006 (2016)

41.

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)

42.

Sinead Walsh et al.

Comparison of methods for the detection of gravitational waves from unknown neutron stars

Phys. Rev. D 94, 124010 (2016)

43.

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)

44.

Sylvia J. Zhu et al.

Einstein@Home search for continuous gravitational waves from Cassiopeia A

Phys. Rev. D 94, 082008 (2016)

45.

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)

46.

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)

47.

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)

48.

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)

49.

Miroslav Shaltev

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

Phys. Rev. D 93, 044058 (2016)

50.

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