A. Corongiu

The Parkes Multibeam Pulsar Survey - VI. Discovery and timing of 142 pulsars and a Galactic population analysis

We present the discovery and follow-up observations of 142 pulsars found in the Parkes 20-cm multibeam pulsar survey of the Galactic plane. These new discoveries bring the total number of pulsars found by the survey to 742. In addition to tabulating spin and astrometric parameters, along with pulse width and flux density information, we present orbital characteristics for 13 binary pulsars which form part of the new sample. Combining these results from another recent Parkes multibeam survey at high Galactic latitudes, we have a sample of 1008 normal pulsars which we use to carry out a determination of their Galactic distribution and birth rate. We infer a total Galactic population of 30 000 ± 1100 potentially detectable pulsars (i.e. those beaming towards us) having 1.4-GHz luminosities above 0.1 mJy kpc 2 . Adopting the Tauris & Manchester beaming model, this translates to a total of 155 000 ± 6000 active radio pulsars in the Galaxy above this luminosity limit. Using a pulsar current analysis, we derive the birth rate of this population to be 1.4 ± 0.2 pulsars per century. An important conclusion from our work is that the inferred radial density function of pulsars depends strongly on the assumed distribution of free electrons in the Galaxy. As a result, any analyses using the most recent electron model of Cordes & Lazio predict a dearth of pulsars in the inner Galaxy. We show that this model can also bias the inferred pulsar scaleheight with respect to the Galactic plane. Combining our results with other Parkes multibeam surveys we find that the population is best described by an exponential distribution with a scaleheight of 330 pc. Surveys underway at Parkes and Arecibo are expected to improve the knowledge of the radial distribution outside the solar circle, and to discover several hundred new pulsars in the inner Galaxy.

Placing Limits on the Stochastic Gravitational-Wave Background Using European Pulsar Timing Array Data

The paper ‘Placing limits on the stochastic gravitational-wave background using European Pulsar Timing Array data’ was published in Mon. Not. R. Astron. Soc. 414, 3117–3128 (2011).

The Parkes multibeam pulsar survey - VII. Timing of four millisecond pulsars and the underlying spin-period distribution of the Galactic millisecond pulsar population

We present timing observations of 4-ms pulsars discovered in the Parkes 20-cm multibeam pulsar survey of the Galactic plane. PSRs J1552−4937 and J1843−1448 are isolated objects with spin periods of 6.28 and 5.47 ms, respectively. PSR J1727−2946 is in a 40-d binary orbit and has a spin period of 27 ms. The 4.43-ms pulsar J1813−2621 is in a circular 8.16-d binary orbit around a low-mass companion star with a minimum companion mass of 0.2 M� . Combining these results with detections from five other Parkes multibeam surveys, gives a well-defined sample of 56 pulsars with spin periods below 20 ms. We develop a likelihood analysis to constrain the functional form which best describes the underlying distribution of spin periods for millisecond pulsars. The best results were obtained with a lognormal distribution. A gamma distribution is less favoured, but still compatible with the observations. Uniform, power-law and Gaussian distributions are found to be inconsistent with the data. Galactic millisecond pulsars being found by current surveys appear to be in agreement with a lognormal distribution which allows for the existence of pulsars with periods below 1.5 ms.

Sardinia Radio Telescope wide-band spectral-polarimetric observations of the galaxy cluster 3C 129

We present new observations of the galaxy cluster 3C 129 obtained with the Sardinia Radio Telescope in the frequency range 6000-7200 MHz, with the aim to image the large-angular-scale emission at high-frequency of the radio sources located in this cluster of galaxies. The data were acquired using the recently-commissioned ROACH2-based backend to produce full-Stokes image cubes of an area of 1 deg x 1 deg centered on the radio source 3C 129. We modeled and deconvolved the telescope beam pattern from the data. We also measured the instrumental polarization beam patterns to correct the polarization images for off-axis instrumental polarization. Total intensity images at an angular resolution of 2.9 arcmin were obtained for the tailed radio galaxy 3C 129 and for 13 more sources in the field, including 3C 129.1 at the galaxy cluster center. These data were used, in combination with literature data at lower frequencies, to derive the variation of the synchrotron spectrum of 3C 129 along the tail of the radio source. If the magnetic field is at the equipartition value, we showed that the lifetimes of radiating electrons result in a radiative age for 3C 129 of t_syn = 267 +/- 26 Myrs. Assuming a linear projected length of 488 kpc for the tail, we deduced that 3C 129 is moving supersonically with a Mach number of M=v_gal/c_s=1.47. Linearly polarized emission was clearly detected for both 3C 129 and 3C 129.1. The linear polarization measured for 3C 129 reaches levels as high as 70% in the faintest region of the source where the magnetic field is aligned with the direction of the tail.

A multifeed S-band cryogenic receiver for the Sardinia Radio Telescope primary focus

The noise temperature of existing radio telescope receivers has actually achieved very low values. In any case, there are other practical ways to increase the observational speed of a single dish antennas without using longer integration time: observe with multi-beam and large bandwidth receiver. In this paper we present the front end and the cryogenic dewar design of the 5 beams FPA double linear polarization receiver for the primary focus of the 64 m Sardinia Radio Telescope.

Pulsar observations with European telescopes for testing gravity and detecting gravitational waves

A background of nanohertz gravitational waves from supermassive black hole binaries could soon be detected by pulsar timing arrays, which measure the times-of-arrival of radio pulses from millisecond pulsars with very high precision. The European Pulsar Timing Array uses five large European radio telescopes to monitor high-precision millisecond pulsars, imposing in this way strong constraints on a gravitational wave background. To achieve the necessary precision needed to detect gravitational waves, the Large European Array for Pulsars (LEAP) performs simultaneous observations of pulsars with all five telescopes, which allows us to coherently add the radio pulses, maximize the signal-to-noise of pulsar signals and increase the precision of times-of-arrival. We report on the progress made and results obtained by the LEAP collaboration, and in particular on the addition of the Sardinia Radio Telescope to the LEAP observations during its scientific validation phase. In addition, we discuss how LEAP can be used to monitor strong-gravity systems such as double neutron star systems and impose strong constraints on post-keplerian parameters.

The Sardinia Radio Telescope (SRT): A large modern radio telescope for observations from meter to mm wavelengths

The Sardinia Radio Telescope (SRT) is a new 64-m across radio astronomical facility located in Sardinia, Italy, and operated by the National Institute for Astrophysics (INAF). It can operate on a broad frequency range −300 MHz to 115 GHz, and is equipped with three different focus solutions: a primary, a Gregorian, and four Beam Wave Guide foci. The primary mirror is an active surface able to compensate the gravitational stress variations at different elevations and keeps the antenna gain flat and optimal at any elevation, as proven by regular observations of the 20-GHz system of the telescope. The optics is shaped and designed to minimise bandpass ripples that can jeopardise deep spectroscopic observations. Tests have delivered stunning results making SRT a world-class instrument for spectro-scopic astrophysical research. Currently, the receiver fleet comprises a P-L-band co-axial receiver (300–410 MHz and 1300–1800 MHz), a C–band system (5.7–7.7 GHz), and a K-band 7-beam array (18–26 GHz). A second C-band receiver (4.2–5.6 GHz), a 7-beam S-band array (3.0–4.5 GHz) and a 19-beam Q-band array (33–50 GHz) are being developed. The P-L-band package has an ultra-broad frequency coverage and its extension to 300 MHz at the low frequency end makes it a unique pulsar research machine in the current international radio astronomical context. The telescope has officially commenced its single-dish operations on 1 February 2016 with the start of an Early Science Program (ESP) that has been delivering stunning results. In this talk we will present the telescope, its main features that make it a unique radio astronomical instrument for several types of astrophysical observations, and results from its ESP campaign.

ERRATUM: “A SHAPIRO DELAY DETECTION IN THE BINARY SYSTEM HOSTING THE MILLISECOND PULSAR PSR J1910–5959A” (2012, ApJ, 760, 100)

PSR J1910−5959A is a binary pulsar with a helium white dwarf (HeWD) companion located about 6 arcmin from the center of the globular cluster NGC 6752. Based on 12 years of observations at the Parkes radio telescope, the relativistic Shapiro delay has been detected in this system. We obtain a companion mass MC = 0.180 ± 0.018 M (1σ ) implying that the pulsar mass lies in the range 1.1 M MP 1.5 M . We compare our results with previous optical determinations of the companion mass and examine prospects for using this new measurement for calibrating the mass–radius relation for HeWDs and for investigating their evolution in a pulsar binary system. Finally, we examine the set of binary systems hosting a millisecond pulsar and a low-mass HeWD for which the mass of both stars has been measured. We confirm that the correlation between the companion mass and the orbital period predicted by Tauris & Savonije reproduces the observed values but find that the predicted MP –PB correlation overestimates the neutron star mass by about 0.5 M in the orbital period range covered by the observations. Moreover, a few systems do not obey the observed MP –PB correlation. We discuss these results in the framework of the mechanisms that inhibit the accretion of matter by a neutron star during its evolution in a low-mass X-ray binary.

Infrared observations of the candidate double neutron star system PSR J1811-1736

PSR J1811-1736 (Ps = 104 ms) is an old (~1.89 Gyr) binary pulsar (Porb = 18.8 d) in a highly eccentric orbit (e = 0.828) with an unidentified companion. Interestingly, the pulsar timing solution yields an estimated companion mass of 0.93 M⊙ ≤ MC ≤ 1.5 M⊙, compatible with that of a neutron star. As such, it is possible that PSR J1811-1736 is a double neutron star (DNS) system, one of the very few discovered so far. This scenario can be investigated through deep optical/infrared (IR) observations. We used J- H- and K-band images, obtained as part of the UK Infrared Telescope (UKIRT) Infrared Deep Sky Survey (UKIDSS), and available in the recent Data Release 9 Plus, to search for the undetected companion of the PSR J1811-1736 binary pulsar. We detected a possible companion star to PSR J1811-1736 within the 3σ radio position uncertainty (1.32 arcsec), with magnitudes J = 18.61 ± 0.07, H = 16.65 ± 0.03 and K = 15.46 ± 0.02. The star colours are consistent with either a main sequence (MS) star close to the turn-off or a lower red giant branch (RGB) star, at a pulsar distance of ~5.5 kpc and with a reddening of E(B - V) ~4.9. The star mass and radius would be compatible with the constraints on the masses and orbital inclination of the binary system inferred from the mass function and with the lack of radio eclipses near superior conjunction. Thus, it is possible that it is the companion to PSR J1811-1736. However, based on the star density in the field, we estimated quite a large chance coincidence probability of ~0.27 between the pulsar and the star, which makes the association unlikely. No other star is detected within the 3σ pulsar radio position down to J ~ 20.5, H ~19.4 and K ~18.6, which allows us to rule out a MS companion star earlier than a mid-to-late M spectral type.

Parkes Observations of Radio Pulsars in Globular Clusters

Millisecond pulsars in southern globular clusters have been regularly observed for timing pourposes with the Parkes radio telescope. To date, several pulsars have data spanning more than 6 years, and their peculiarities are now recognisable via their timing analysis. In this paper we briefly summarise the state of the art of the timing for the eclipsing binary PSR J1701‐3006B in the clobular cluster NGC6266 and for all the millisecond pulsars in the globualr cluster NGC6752.