Main meetings/events from August 2017 to November 2017
The members of the SKA Pulsar Science Working Group (SKA-PSWG) met at various meetings during this period. Among those, the largest and most prominent event was the IAU Symposium 337, which was held at the Jodrell Bank Observatory from Monday 4th September to Friday 9th September. In fact, 2017 marked the 50th anniversary of the discovery of pulsars and the conference was an exciting opportunity to reflect on what we have learnt from these unique physical laboratories and to look forward to the intriguing perspectives opened by their study in the next half century. The title of the conference was “Pulsar Astrophysics: The Next Fifty Years”, and over 200 scientists from all over the world participated. They presented a wealth of new results – some of them made public for the first time – and described how new facilities, among which SKA1 stands in a primary position, will be able to produce a new revolutionary phase in pulsar astrophysics in the near and mid term future.
Publications related to the PSWG from August 2017 through November 2017
During this period, the members of the PSWG and their collaborators have published and/or submitted to international refereed journals many tens of papers relevant to the scientific objectives of SKA1. A selection of some of the papers is below.
a) Graikou, E., Verbiest, J. P. W., Oslowski, S., Champion, D. J., Tauris, T. M., Jankowski, F., Kramer, M., 2017, Limits on the mass, velocity and orbit of PSR J1933-6211, Monthly Notices of the Royal Astronomical Society, http://cdsads.u-strasbg.fr/abs/2017MNRAS.471.4579G, MNRAS, 471, 4579G This paper reports on high-precision timing analysis of PSR J1933-6211 using data from the Parkes radio telescope. The authors have accurately measured the polarization properties of this pulsar and then applied the matrix template matching approach in which the times of arrival are measured using full polarimetric information. With this technique, they achieved timing residuals with a weighted root-mean-square of 1.23 μs, corresponding to a 15.5 % improvement compared to the total intensity timing analysis. This result is very promising for the precision timing capability of SKA1, the sensitivity of which will enable application of full polarimetric info to a very large sample of pulsars.
b) Kelley, L. Z., Blecha, L., Hernquist, L., Sesana, A., Taylor, S. R., 2017, The gravitational wave background from massive black hole binaries in Illustris: spectral features and time to detection with pulsar timing arrays, Monthly Notices of the Royal Astronomical Society, http://cdsads.u-strasbg.fr/abs/2017MNRAS.471.4508K, MNRAS, 471, 4508K The authors of this work use comprehensive massive black hole merger models based on cosmological hydrodynamic simulations to predict the spectrum of the stochastic gravitational wave background (GWB) and apply real time-of-arrival specifications from the International Pulsar Timing Array (IPTA) to calculate realistic times to detection of the GWB across a wide range of model parameters. Even with merger models that use pessimistic parameters, if the current rate of PTA expansion continues, the authors found that the IPTA is highly likely to make a detection within about 10 yr. This will enhance even more the capabilities of SKA1 to exploit the observations of a suitable number of millisecond pulsars in order to perform gravitational wave astrophysics.
c) Archibald, R. F., Burgay, M., Lyutikov, M., Kaspi, V. M., Esposito, P., Israel, G., Kerr, M., Possenti, A., Rea, N., Sarkissian, J., Scholz, P., Tendulkar, S. P., 2017, Magnetar-like X-Ray Bursts Suppress Pulsar Radio Emission, The Astrophysical Journal, http://cdsads.u-strasbg.fr/abs/2017ApJ…849L..20A, ApJ, 849L, 20A This paper deals with simultaneous observations of the high-magnetic-field radio pulsar PSR J1119-6127 at X-ray and at radio bands, during a period of magnetar-like bursts. Coincident with the occurrence of multiple X-ray bursts, rotationally powered radio emission ceases and then recovers on a timescale of ∼70 s. These observations of related radio and X-ray phenomena further solidify the connection between radio pulsars and magnetars. SKA1 is expected to find and study many objects like this and will discriminate among the proposed models for the link between X-ray and radio emission.
d) Zhang, F., Saha, P., 2017, Probing the Spinning of the Massive Black Hole in the Galactic Center via Pulsar Timing: A Full Relativistic Treatment, The Astrophysical Journal, http://cdsads.u-strasbg.fr/abs/2017ApJ…849…33Z, ApJ, 849, 33Z SKA is expected to reveal pulsars around the massive black hole (MBH) in the Galactic center (GC). Using a full relativistic framework with the pulsar approximated as a test particle, this paper investigates the constraints on the spin of the MBH by monitoring the timing of surrounding pulsars. For GC pulsars orbiting closely around the MBH (e.g., ≲1000 au), the authors find that full relativistic treatment is necessary to accurately account for their timing signals. Although usually there is degeneracy among MBH spin parameters, the achievable constraints on the spin of the MBH are still very tight.
e) Ambrosino, F., Papitto, A., Stella, L., Meddi, F., Cretaro, P., Burderi, L., Di Salvo, T., Israel, G. L., Ghedina, A., Di Fabrizio, L., Riverol, L., 2017, Optical pulsations from a transitional millisecond pulsar, Nature Astronomy, http://cdsads.u-strasbg.fr/abs/2017NatAs…1E.266A, NatAs, 1E, 266A A few transitional millisecond pulsars that swing between an accretion-powered X-ray pulsar regime and a rotationally powered radio pulsar regime in response to variations of the mass in-flow rate have been recently identified. They are interesting targets for the high instantaneous sensitivity of SKA1.. This paper focuses on the first detection of optical pulsations from a transitional millisecond pulsar.
f) Dyks, J., 2017, The geometry of a radio pulsar beam, Monthly Notices of the Royal Astronomical Society, http://cdsads.u-strasbg.fr/abs/2017MNRAS.471L.131D, MNRAS, 471L, 131D A full understanding of the still unclear mechanism(s) of the pulsar radio emission and the related origin of the large variety of pulse profiles seen from these objects is one of the aims of SKA1. In this paper, it is proposed that the underlying geometry is that of a flaring spiral that makes several revolutions around the pulsar magnetic dipole axis on its way to leave the magnetosphere. Such geometry is consistent with a stream of out-flowing and laterally drifting plasma.
g) Rajwade, K. M., Lorimer, D. R., Anderson, L. D., 2017, Detecting pulsars in the Galactic Centre, Monthly Notices of the Royal Astronomical Society, http://cdsads.u-strasbg.fr/abs/2017MNRAS.471.730R, MNRAS, 471, 730R In this paper a detailed analysis of both the canonical and millisecond pulsar populations in the Galactic Centre is presented. The authors consider free-free absorption and multipath scattering to be the two main causes of flux density mitigation. They demonstrate that the sensitivity limits of previous surveys are not sufficient to detect the Galactic Centre pulsar population and that the optimum frequency for future surveys is in the range of 9-13 GHz. In particular, future deeper surveys with SKA1 will probe a significant portion of the existing radio pulsar population in the Galactic Centre, which could consist of up to 52 canonical pulsars and 10 000 millisecond pulsars.
h) Berezina, M., Champion, D. J., Freire, P. C. C., Tauris, T. M., Kramer, M., Lyne, A. G., Stappers, B. W., Guillemot, L., Cognard, I., Barr, E. D., Eatough, R. P., Karuppusamy, R., Spitler, L. G., Desvignes, G., 2017, The discovery of two mildly recycled binary pulsars in the Northern High Time Resolution Universe pulsar survey, Monthly Notices of the Royal Astronomical Society, http://cdsads.u-strasbg.fr/abs/2017MNRAS.470.4421B, MNRAS, 470, 4421B This work focuses on the discovery and timing observations of PSR J2045+3633 and PSR J2053+4650, two binary pulsars found in the Northern High Time Resolution Universe pulsar survey being carried out with the Effelsberg radio telescope. Both pulsars belong to the still sparse population of mildly recycled pulsars. SKA1 is expected to largely increase the number of known objects of this class and thus address the many unanswered questions related to their evolution.
i) Geyer, M., Karastergiou, A., Kondratiev, V. I., Zagkouris, K., Kramer, M., Stappers, B. W., Grieszligmeier, J.-M., Hessels, J. W. T., Michilli, D., Pilia, M., Sobey, C., 2017, Scattering analysis of LOFAR pulsar observations, Monthly Notices of the Royal Astronomical Society, http://cdsads.u-strasbg.fr/abs/2017MNRAS.470.2659G, MNRAS, 470, 2659G Using LOFAR observations at frequencies between 110 and 190 MHz, the authors measured the effects of interstellar scattering on the average pulse profiles of 13 radio pulsars with simple pulse shapes. Such investigations of the turbulent interstellar medium using pulsars will greatly benefit from full exploitation of SKA1-LOW.
j) Bassa, C. G., Pleunis, Z., Hessels, J. W. T., Ferrara, E. C., Breton, R. P., Gusinskaia, N. V., Kondratiev, V. I., Sanidas, S., Nieder, L., Clark, C. J., Li, T., van Amesfoort, A. S., Burnett, T. H., Camilo, F., Michelson, P. F., Ransom, S. M., Ray, P. S., Wood, K., 2017, LOFAR Discovery of the Fastest-spinning Millisecond Pulsar in the Galactic Field, The Astrophysical Journal, http://cdsads.u-strasbg.fr/abs/2017ApJ…846L..20B, ApJ, 846L, 20B The paper describes the discovery of PSR J0952-0607, a 707 Hz binary millisecond pulsar that is now the fastest-spinning neutron star known in the Galactic field. It was found by using LOFAR at a central observing frequency of 135 MHz, thus strongly supporting the scientific potential of a large-scale pulsar search performed with SKA1-LOW. In fact, the authors additionally discuss the growing evidence that the fastest-spinning radio pulsars have exceptionally steep radio spectra, as well as the prospects for finding more sources like PSR J0952-0607.
k) Prager, B. J., Ransom, S. M., Freire, P. C. C., Hessels, J. W. T., Stairs, I. H., Arras, P., Cadelano, M., 2017, Using Long-term Millisecond Pulsar Timing to Obtain Physical Characteristics of the Bulge Globular Cluster Terzan 5, The Astrophysical Journal, http://cdsads.u-strasbg.fr/abs/2017ApJ…845..148P, ApJ, 845, 148P Using long-term radio pulsar timing observations of 36 millisecond pulsars in the core of the globular cluster Terzan 5, this paper presents new measurements of key physical properties of this stellar system. In particular, pulsar accelerations allow the researchers to study the intrinsic characteristics of the cluster, independent of reddening and stellar crowding. The observations probe the mass density profile without needing to quantify the mass-to-light ratio, and yield an upper limit on the mass of a possible black hole at the core of the cluster (about 30000 solar masses in this case). The exquisite timing capabilities of SKA1-MID will be able to strongly improve on these measurements and extend the technique to many globular clusters.
l) Mingarelli, C. M. F., Lazio, T. J. W., Sesana, A., Greene, J. E., Ellis, J. A, Ma, C.-P., Croft, S., Burke-Spolaor, S., Taylor, S. R., 2017, The Local Nanohertz Gravitational-Wave Landscape From Supermassive Black Hole Binaries, Nature Astronomy, doi:10.1038/s41550-017-0299-6, http://adsabs.harvard.edu/abs/2017arXiv170803491M, published online Nov. 13. The authors use the 2MASS all-sky catalogue and galaxy merger rates from the Illustris simulation to predict the number of continuous-wave gravitational-wave sources in the local Universe and to estimate their detectability by the International Pulsar Timing Array project. They find that these local sources can provide up to 20% anisotropy in the gravitational-wave background and predict that the IPTA could detect at least one of these sources within 10 years. Adding in the sensitivity of the SKA1 will greatly help the prospects for this science.
m) Lam, M. T, McLaughlin, M. A., Cordes, J. M., Chatterjee, S., Lazio, T. J. W., Optimal Frequency Ranges for Sub-Microsecond Precision Pulsar Timing, 2017, https://arxiv.org/abs/1710.02272, submitted to the Astrophysical Journal. The authors optimize pulse time-of-arrival precision as a function of observing frequency and observing bandwidth, incorporating information about the interstellar medium and pulse profile evolution. They find that the optimal centre frequencies depend on the individual pulsars and the telescopes employed. Wideband receivers centred at high frequencies will improve the arrival-time precisions and allow the use of more pulsars with high dispersion measures.