Main meetings/events from April 2017 until July 2017

Spring is a favourite time for meetings and the members of the SKA Pulsar Science Working Group (SKA-PSWG) have had various opportunities for attending meetings during this period.

Among those, we list the following:

1) 21st EPTA meeting

Universiteits Biblitheek, Amsterdam, The Netherlands, April 3-5, 2017

Amsterdam hosted the 21st meeting of the members of the European Pulsar Timing Array (EPTA), a large fraction of whom are also members of the SKA-PSWG. The ongoing projects and the plans for future research on the way to SKA were in the focus of the meeting.

2) Fundamental Physics with the Square Kilometre Array Conference

La Pirogue Resort & Spa, Flic en Flac, Mauritius, May 1–5, 2017

Several pulsar-related invited and contributed talks were in the focus of the “Gravity and Gravitational radiation” session in the context of a general conference about the SKA as a tool to probe fundamental physics, which took place at Mauritius.

3) The Broad Impact of Low Frequency Observing

CNR Conference Centre in Bologna, Italy, 19-23 June, 2017

Eight talks highlighted the impact of low frequency observations on pulsar science, with particular reference to the contribution of LOFAR and other low-frequency facilities, including the MWA, LWA, GMRT, VLITE, PAPER, CHIME, and 21CMA, on the way to SKA-low.

The venue of the conference during one of the session

4) EWASS 2017: Scientific Synergies enabled by the SKA, CTA and Athena

Faculty of Law, Charles University, Prague, Czech Republic, 26–30 June, 2017

The talks in this Symposium focused on outstanding but still unanswered scientific questions where the fully-fledged multi-wavelength and multi-messenger astronomy enabled by SKA, CTA and Athena will lead to a big step forward in our knowledge.

5) IPTA science meeting

Centre International d’Etudes Pédagogiques, Sèvres, France, 03-07 July 2017

The International Pulsar Timing Array (IPTA) is a worldwide collaboration, made of the contributions of three continental consortia: EPTA in Europe, PPTA in Australia and NanoGRAV in US. Its primary goal is to detect gravitational waves (GW) in the Nanohertz regime using radio pulsar timing observations. The 2017 IPTA conference was held in France the first week of July. The defining moments were the open day dedicated to multi-messenger gravitational wave astronomy and the long slots reserved for discussions, concerning in particular the status of a “first detection” publication and the future PTA organization in the framework of SKA.

The picture shows Di Li, project scientist of FAST, presenting the last news from the newborn giant radio telescope in China.

Publications related to the PSWG from April 2017 to July 2017

During the 4 aforementioned months, the members of the PSWG and their collaborators have published and/or submitted to international refereed journals many tens of papers dealing with the researches of interest for the SKA-PSWG. A selection of some of the papers is below.

  1. a) Wang, J.B., Coles, W.A., Hobbs, G., Shannon, R.M., Manchester, R.N., Kerr, M., Yuan, J.P., Wang, N., Bailes, M., Bhat, N.D.R., Dai, S., Dempsey, J., Keith, M.J., Lasky, P.D., Levin, Y., Oslowski, S., Ravi, V., Reardon, D.J., Rosado, P.A., Russell, C.J., Spiewak, R., van Straten, W., Toomey, L., Wen, L., You, X.-P., and Zhu, X.-J.: 2017, Comparison of pulsar positions from timing and very long baseline astrometry. http://cdsads.u-strasbg.fr/abs/2017MNRAS.469..425W Monthly Notices of the Royal Astronomical Society 469, 425-434.

This paper compares two different approaches for obtaining astrometric determination of the pulsar positions: pulsar timing methods and very long baseline interferometry (VLBI). The accuracy with which one can relate the two frames is limited by the current uncertainties in the VLBI reference source positions and in matching the pulsars to their reference source. Both these issues are relevant in the perspective of the much improved pulsar positional capabilities of SKA1-mid.

  1. b) Yao, J.M., Manchester, R.N., and Wang, N.: 2017, Determination of the Sun’s offset from the Galactic plane using pulsars. http://cdsads.u-strasbg.fr/abs/2017MNRAS.468.3289Y Monthly Notices of the Royal Astronomical Society 468, 3289-3294.

The authors derive the Sun’s vertical offset from the local mean Galactic plane by using the observed vertical distribution of young pulsars. From a sample of 115 pulsars, the estimated scale-heights are in agreement with those as OB stars and open clusters. SKA1-MID and SKA1-LOW will allow us to largely increase the sample of young pulsars in the solar surroundings, thus finally shedding light on the distribution of the post-supernova velocities of the newborn neutron stars.

  1. c) Wang, Y., Keith, M.J., Stappers, B., and Zheng, W.: 2017, Robust fitting for pulsar timing analysis. http://cdsads.u-strasbg.fr/abs/2017MNRAS.468.2637W Monthly Notices of the Royal Astronomical Society 468, 2637-2644.

In this paper a new robust fitting method (M-estimator) for pulsar timing analysis is presented. It is shown that the fitting results of M-estimators are more accurate than those of the mostly used Least Square method and, when dealing with positional parameters, they are closer to the result of very long baseline interferometry. The new method promises to have large application for pulsar timing analysis based on SKA1 data.

  1. d) Cameron, A.D., Barr, E.D., Champion, D.J., Kramer, M., and Zhu, W.W.: 2017, An investigation of pulsar searching techniques with the fast folding algorithm. http://cdsads.u-strasbg.fr/abs/2017MNRAS.468.1994C Monthly Notices of the Royal Astronomical Society 468, 1994-2010.

A comprehensive study of the fast folding algorithm (FFA) is on the focus of this paper. FFA is a pulsar searching technique alternative to the fast Fourier transform (FFT), It is in particular demonstrated that the FFA outperforms the FFT under ideal white noise conditions, and provides significant improvement in sensitivity to long-period pulsars in real red-noise corrupted observational data. FFA will be routinely used in pulsar search algorithm implemented in SKA1 large scale pulsar surveys.

  1. e) Dexter, J., Degenaar, N., Kerr, M., Deller, A., Deneva, J., Lazarus, P., Kramer, M., Champion, D., and Karuppusamy, R.: 2017, A transient, flat spectrum radio pulsar near the Galactic Centre. http://cdsads.u-strasbg.fr/abs/2017MNRAS.468.1486D Monthly Notices of the Royal Astronomical Society 468, 1486-1492.

The authors discuss the peculiarities of one of the radio pulsars in the Galactic Centre (GC) region, PSR J1746-2850, which has timing properties implying a large magnetic field strength and a young age, as well as a flat spectrum. They show that this pulsar is also transient in the radio. As such, this source, either a transient magnetar without any detected X-ray counterpart or a young, strongly magnetized radio pulsar producing magnetar-like radio emission, further blurs the line between the magnetars and the high magnetic field ordinary pulsars. The study of the relation among these two categories of neutron stars will be a distinct aim for SKA1.

  1. f) Freire, P.C.C., Ridolfi, A., Kramer, M., Jordan, C., Manchester, R.N., Torne, P., Sarkissian, J., Heinke, C.O., D’Amico, N., Camilo, F., Lorimer, D.R., and Lyne, A.G.: 2017, Long-term observations of the pulsars in 47 Tucanae – II. Proper motions, accelerations and jerks. http://cdsads.u-strasbg.fr/abs/2017arXiv170604908F ArXiv e-prints arXiv:1706.04908.

This paper deals with the results of a long-term timing of the millisecond pulsars in the globular cluster 47 Tucanae. The obtained improved timing parameters have provided additional information for studies of the cluster dynamics. No evidence is found in favour of the presence of an intermediate mass black hole (IMBH) at the centre of the cluster. SKA1-MID will revolutionize this field of research, allowing to put unprecedented constraints on the properties of many globular clusters and finally assessing the long debated issue of the existence of IMBH in this stellar systems.

  1. g) Keane, E.F., Barr, E.D., Jameson, A., Morello, V., Caleb, M., Bhandari, S., Petroff, E., Possenti, A., Burgay, M., Tiburzi, C., Bailes, M., Bhat, N.D.R., Burke-Spolaor, S., Eatough, R.P., Flynn, C., Jankowski, F., Johnston, S., Kramer, M., Levin, L., Ng, C., van Straten, W., and Venkatraman Krishnan, V.: 2017, The SUrvey for Pulsars and Extragalactic Radio Bursts I: Survey Description and Overview. http://cdsads.u-strasbg.fr/abs/2017arXiv170604459K ArXiv e-prints arXiv:1706.04459.

This is the reference paper for the Survey for Pulsars and Extragalactic Radio Bursts (SUPERB), an ongoing pulsar and fast transient survey running at the Parkes radio telescope. SUPERB involves real-time acceleration searches for pulsars and single pulse searches for pulsars and fast radio bursts (FRBs) and has been the most effective FRB experiment over the last 4 four years. Some of the concepts developed in the context of SUPERB (i.e. real time triggers for the follow-ups of the FRBs and the implementation of a real-time pulsar search) will be widely applied to the SKA1 experiments.

  1. h) Johnston, S. and Karastergiou, A.: 2017, Pulsar braking and the P-Pdot diagram. http://cdsads.u-strasbg.fr/abs/2017MNRAS.467.3493J Monthly Notices of the Royal Astronomical Society 467, 3493-3499.

The focus is here on the decay of the so-called inclination angle α, representing the angle between the magnetic and rotation axes of a radio pulsar. The authors show that it is possible to reproduce the observational P-Pdot diagram (i.e. the spin period vs spin period derivative diagram for the pulsars), without invoking for either pulsars with long birth periods or magnetic field decay. The implied birth rate equals to one ordinary pulsar per century, for a total Galactic population of about 20000 pulsars beaming towards Earth. The occurrence (or not) of a spontaneous decay of the surface magnetic field of a pulsar (and the related decay timescale) is a primary topic for SKA1, since it relates an observational property to the physics of the otherwise inaccessible neutron star crust and interior.

  1. i) van Heerden, E., Karastergiou, A., and Roberts, S.J.: 2017, A framework for assessing the performance of pulsar search pipelines. http://cdsads.ustrasbg.fr/abs/2017MNRAS.467.1661V Monthly Notices of the Royal Astronomical Society 467, 1661-1677.

The authors introduce a framework for assessing the effect of non-stationary Gaussian noise and radio frequency interference (RFI) on the sensitivity of standard pulsar search pipelines. The results (which are very important in the perspective of optimizing the SKA1 pulsar searches) indicate the need to develop new algorithms capable to remove non-stationary variations from the data before RFI excision and periodicity searching are performed.

  1. j) Lentati, L., Kerr, M., Dai, S., Hobson, M.P., Shannon, R.M., Hobbs, G., Bailes, M., Bhat, N.D.R., Burke-Spolaor, S., Coles, W., Dempsey, J., Lasky, P.D., Levin, Y., Manchester, R.N., Oslowski, S., Ravi, V., Reardon, D.J., Rosado, P.A., Spiewak, R., van Straten, W., Toomey, L., Wang, J., Wen, L., You, X., and Zhu, X.: 2017, Wide-band profile domain pulsar timing analysis. http://cdsads.u-strasbg.fr/abs/2017MNRAS.466.3706L Monthly Notices of the Royal Astronomical Society 466, 3706-3727.

The profile domain pulsar timing is here extended to incorporate frequency-dependent profile evolution and broad-band shape variation in the pulse profile, as well as variations in both pulse width and in the separation in phase of the main pulse and interpulse. It is shown that large improvements in timing precision are possible when compared to the usually adopted methodologies. For PSR J1713+0747 (one of the targets for the high precision timing made available by SKA1-MID) it is calculated that unaccounted shape variation biases the measured arrival times at the level of about 30 ns, the same order of magnitude as the expected shift due to gravitational waves in the pulsar timing band.

  1. k) Egron, E., Pellizzoni, A., Pollock, A., Iacolina, M.N., Ikhsanov, N.R., Possenti, A., and Marongiu, M.: 2017, Long-term Study of the Double Pulsar J0737-3039 with XMM-Newton: Spectral Analysis. http://cdsads.u-strasbg.fr/abs/2017ApJ…838..120E The Astrophysical Journal 838, 120.

This paper confirms the occurrence of an excess in the hard X-ray spectrum of the Double Pulsar, most likely ascribed to iron line emission. The Fe Kα emission line at 6.4-6.97 keV was previously unheard of in non-accreting binary systems and could testify to the presence of a relic disk that survived the supernova explosions that terminated the lives of the Double Pulsar’s stellar progenitors. This kind of studies anticipates the very fruitful synergies made available by the coordinated observations of SKA1 (for which the Double Pulsar will be an outstanding target) with those of planned high-energy satellites, alike Athena.

  1. l) Smits, R., Bassa, C.G., Janssen, G.H., Karuppusamy, R., Kramer, M., Lee, K.J., Liu, K., McKee, J., Perrodin, D., Purver, M., Sanidas, S., Stappers, B.W., and Zhu, W.W.: 2017, The beamformer and correlator for the Large European Array for Pulsars. http://cdsads.ustrasbg.fr/abs/2017A%26C….19…66S Astronomy and Computing 19, 66-74.

This paper reports on the “software correlator” and “beamformer” which enable the formation of a tied-array beam from the raw voltages captured at the 5 largest radio telescopes in Europe, in the context of the Large European Array for Pulsars (LEAP). The objective is to provide high signal-to-noise observations of millisecond pulsars in order to increase the sensitivity to the direct detection of low-frequency gravitational waves. The software developed in this job will be widely used in SKA1 pathfinders and precursors.

  1. m) Abbott, B. P. et al.: 2017, First Search for Gravitational Waves from Known Pulsars with Advanced LIGO. http://cdsads.u-strasbg.fr/abs/2017ApJ…839…12A The Astrophysical Journal 839, 12.

The focus is on searches for gravitational waves from 200 pulsars using data from the first observing run of the Advanced LIGO detectors. No gravitational-wave detection was obtained, but these new results improve on previous limits by more than a factor of two. Moreover, the new data led to set the most constraining upper limits yet on the gravitational-wave amplitudes and ellipticities for few pulsars. The synergic combination of the capabilities of SKA1 and of the Advanced LIGO and VIRGO detectors promises to finally shed light on the fraction of the pulsar spin-down energy, which is released in the form of gravitational waves.

  1. n) Tauris, T. M.; Kramer, M.; Freire, P. C. C.; Wex, N.; Janka, H.-T.; Langer, N.; Podsiadlowski, Ph.; Bozzo, E.; Chaty, S.; Kruckow, M. U.; van den Heuvel, E. P. J.; Antoniadis, J.; Breton, R. P.; Champion, D. J.: 2017, Formation of Double Neutron Star Systems http://adsabs.harvard.edu/abs/2017arXiv170609438T ArXiv e-prints arXiv:1706.09438.

In this paper, the authors make predictions of the properties of Double Neutron Star (DNS) systems, which can be tested with SKA1 data. The anticipated increase in known DNS sources (factor 5-10, with full SKA) will greatly improve the population statistics and thus our knowledge on DNS formation. SKA will also improve the pulsar timing significantly, which is important to derive NS masses, distances and proper motions of these systems, and thereby enable testing the proposed theoretical models.

  1. o) Perera, B. B. P.; Stappers, B. W.; Lyne, A. G.; Bassa, C. G.; Cognard, I.; Guillemot, L.; Kramer, M.; Theureau, G.; Desvignes, G.: 2017, Evidence for an intermediate-mass black hole in the globular cluster NGC 6624, http://cdsads.u-strasbg.fr/abs/2017MNRAS.468.2114P Monthly Notices of the Royal Astronomical Society, 468, 2114-2127

The investigation of more than 25 yr of high-precision timing observations of the millisecond pulsar PSR B1820-30A (located in the globular cluster NGC 6624) led the authors to propose that the pulsar is in either a low-eccentricity (0.33 ≲ e ≲ 0.4) smaller orbit with a low-mass companion or in a high-eccentricity (e ≳ 0.9) larger orbit with a massive companion. The high-eccentricity solution would imply that the pulsar is most likely orbiting around an intermediate-mass black hole of mass larger than 7500 solar masses located at the cluster centre. These results suggest that other globular clusters may also contain central black holes, which could be revealed by the discovery and subsequent timing study of new pulsars found with SKA1 and located sufficiently close to the globular cluster centre.

Report provided by the Pulsars SWG