From spin noise to systematics: stochastic processes in the first International Pulsar Timing Array data release

L Lentati (1) , R. M. Shannon (2) , W. A. Coles (3) , J. P. W. Verbiest (4) , R van Haasteren (5) , J.A. Ellis (5) , R. N. Caballero (4) , R. N. Manchester (2) , Z. Arzoumanian (6) , S. Babak (7) , C.G Bassa (8) , N.D.R. Bhat (9) , P. Brem (7) , M. Burgay (10) , S. Burke-Spolaor (11) , D. Champion (4) , S. Chatterjee (12) , Ismaël Cognard (13) , J. M. Cordes (14) , S. Dai (2) , P. Demorest (14) , G. Desvignes (13) , T. Dolch (15) , R. D. Ferdman (16) , E. Fonseca (17) , J. R. Gair (1) , M.E. Gonzalez (18) , E. Graikou (4) , Lucas Guillemot (13) , J. w. t. Hessels (8) , G Hobbs (19) , G. H. Janssen (20) , G Jones (21) , R Karuppusamy (4) , M Keith (22) , M Kerr (19) , M Kramer (23) , M.T Lam (14) , P. D. Lasky (19) , A Lassus (13) , P Lazarus (7) , T. J. W. Lazio (5) , K.J. Lee (24) , L. Levin (22) , K. Liu (4) , R. S. Lynch (8) , D. R. Madison (25) , J. Mckee (26) , M A Mclaughlin (27) , S. T. Mcwilliams (27) , C.M.F. Mingarelli (28) , D.J. Nice (29) , S. Osłowski (4) , T. Pennucci (30) , B. B. P. Perera (22) , D. Perrodin (10) , A Petiteau (31) , P. Possenti (32) , S.M. Ransom (25) , D Reardon (19) , P. A. Rosado (33) , S. A. Sanidas (34) , A Sesana (7) , G. Shaifullah (4) , X Siemens (35) , R. Smits (20) , I. Stairs (36) , B. Stappers (22) , D.R. Stinebring (37) , K. Stowall (38) , J.J. Swiggum (39) , S.R. Taylor (5) , Gilles Theureau (16) , C. Tiburzi (10) , L Toomey (19) , M Vallisneri (5) , W. van Straten (4) , A Vecchio (40) , J.B. Wang (41) , Y. Wang (42) , X.P. You (43) , W.W. Zhu (13) , X.-J Zhu (44)

1 Cavendish Laboratory
2 CSIRO Astronomy and Space Science
3 University of California
4 MPIFR - Max-Planck-Institut für Radioastronomie
5 JPL - Jet Propulsion Laboratory
6 GSFC - NASA Goddard Space Flight Center
7 AEI - Max-Planck-Institut für Gravitationsphysik ( Albert-Einstein-Institut )
8 ASTRON - Netherlands Institute for Radio Astronomy
9 Curtin University [Perth]
10 OAC - INAF - Osservatorio Astronomico di Cagliari
11 NRAO - National Radio Astronomy Observatory
12 CRSR - Center for Radiophysics and Space Research [Ithaca]
13 LPC2E - Laboratoire de Physique et Chimie de l'Environnement et de l'Espace
14 Department of Astronomy [Ithaca]
15 Department of Physics, Hillsdale College
16 USN - Unité Scientifique de la Station de Nançay
17 UBC - University of British Columbia
18 Vancouver Coastal Health, Department of Nuclear Medicine
19 CSIRO Astronomy and Space Science
20 Netherlands Institute for Radio Astronomy ( ASTRON )
21 CoralCoE - ARC Centre of Excellence for Coral Reef Studies
22 Jodrell Bank Centre for Astrophysics
23 VUMC - Vrije Universiteit Medical Centre
24 KIAA-PKU - Kavli Institute for Astronomy and Astrophysics [Beijing]
25 NRAO - National Radio Astronomy Observatory [Green Bank]
26 JBCA - Jodrell Bank Centre for Astrophysics
27 Department of Physics, West Virginia University
28 TAPIR - Theoretical Astrophysics [Pasadena]
29 Physics Department, Lafayette College
30 Department of Astronomy [Charlottesville]
31 APC-Gravitation - APC - Gravitation
32 LGGE - Laboratoire de glaciologie et géophysique de l'environnement
33 CAS - Centre for Astrophysics and Supercomputing [Swinburne]
34 Anton Pannekoek Institute for Astronomy
35 University of Wisconsin - Milwaukee
36 Department of Physics and Astronomy, University of British Columbia
37 Department of Physics and Astronomy [Oberlin]
38 IOM - Institute of Meteoritics [Albuquerque]
39 Department of Physics and Astronomy, West Virginia University
40 BCU - Birmingham City University
41 Xinjiang Astronomical Observatory
42 HUST - Huazhong University of Science and Technology [Wuhan]
43 School of Physical Science and Technology
44 West Virginia University [Morgantown]

We analyse the stochastic properties of the 49 pulsars that comprise the first International Pulsar Timing Array (IPTA) data release. We use Bayesian methodology, performing model selection to determine the optimal description of the stochastic signals present in each pulsar. In addition to spin-noise and dispersion-measure (DM) variations, these models can include timing noise unique to a single observing system, or frequency band. We show the improved radio-frequency coverage and presence of overlapping data from different observing systems in the IPTA data set enables us to separate both system and band-dependent effects with much greater efficacy than in the individual PTA data sets. For example, we show that PSR J1643−1224 has, in addition to DM variations, significant band-dependent noise that is coherent between PTAs which we interpret as coming from time-variable scattering or refraction in the ionised interstellar medium. Failing to model these different contributions appropriately can dramatically alter the astrophysical interpretation of the stochastic signals observed in the residuals. In some cases, the spectral exponent of the spin noise signal can vary from 1.6 to 4 depending upon the model, which has direct implications for the long-term sensitivity of the pulsar to a stochastic gravitational-wave (GW) background. By using a more appropriate model, however, we can greatly improve a pulsar's sensitivity to GWs. For example, including system and band-dependent signals in the PSR J0437−4715 data set improves the upper limit on a fiducial GW background by ∼ 60% compared to a model that includes DM variations and spin-noise only.

Keywords: methods: data analysis; pulsars:individual; pulsars: general

Domains: Sciences of the Universe [physics]

L Lentati, R. M. Shannon, W. A. Coles, J. P. W. Verbiest, R van Haasteren, et al.. From spin noise to systematics: stochastic processes in the first International Pulsar Timing Array data release. Monthly Notices of the Royal Astronomical Society, 2016, 458 (2), pp.2161-2187. ⟨10.1093/mnras/stw395⟩. ⟨insu-01327914⟩