Nichi DAmico

Transient radio bursts from rotating neutron stars

The radio sky is relatively unexplored for transient signals, although the potential of radio-transient searches is high. This was demonstrated recently by the discovery of a previously unknown type of source, varying on timescales of minutes to hours. Here we report a search for radio sources that vary on much shorter timescales. We found eleven objects characterized by single, dispersed bursts having durations between 2 and 30 ms. The average time intervals between bursts range from 4 min to 3 h with radio emission typically detectable for <1 s per day. From an analysis of the burst arrival times, we have identified periodicities in the range 0.4–7 s for ten of the eleven sources, suggesting origins in rotating neutron stars. Despite the small number of sources detected at present, their ephemeral nature implies a total Galactic population significantly exceeding that of the regularly pulsing radio pulsars. Five of the ten sources have periods >4 s, and the rate of change of the pulse period has been measured for three of them; for one source, we have inferred a high magnetic field strength of 5 × 1013 G. This suggests that the new population is related to other classes of isolated neutron stars observed at X-ray and γ-ray wavelengths.

A Radio-loud Magnetar in X-ray Quiescence

As part of a survey for radio pulsars with the Parkes 64 m telescope, we have discovered PSR J1622-4950, a pulsar with a 4.3 s rotation period. Follow-up observations show that the pulsar has the highest inferred surface magnetic field of the known radio pulsars (B {approx}3 x 10{sup 14} G), and it exhibits significant timing noise and appears to have an inverted spectrum. Unlike the vast majority of the known pulsar population, PSR J1622-4950 appears to switch off for many hundreds of days and even in its on-state exhibits extreme variability in its flux density. Furthermore, the integrated pulse profile changes shape with epoch. All of these properties are remarkably similar to the only two magnetars previously known to emit radio pulsations. The position of PSR J1622-4950 is coincident with an X-ray source that, unlike the other radio pulsating magnetars, was found to be in quiescence. We conclude that our newly discovered pulsar is a magnetar-the first to be discovered via its radio emission.

DISCOVERY OF NEW GAMMA-RAY PULSARS WITH AGILE

Using gamma-ray data collected by the Astro-rivelatore Gamma ad Immagini LEggero (AGILE) satellite over a period of almost one year (from 2007 July to 2008 June), we searched for pulsed signals from 35 potentially interesting radio pulsars, ordered according to Fγ ∝ √ ˙ Ed −2 and for which contemporary or recent radio data were available. AGILE detected three new top-ranking nearby and Vela-like pulsars with good confidence both through timing and spatial analysis. Among the newcomers we find pulsars with very high rotational energy losses, such as the remarkable PSR B1509−58 with a magnetic field in excess of 10 13 Gauss, and PSR J2229+6114 providing a reliable identification for the previously unidentified EGRET source 3EG 2227+6122. Moreover, the powerful millisecond pulsar B1821−24, in the globular cluster M28, is detected during a fraction of the observations. Four other promising gamma-ray pulsar candidates, among which is the notable J2043+2740 with an age in excess of 1 million years, show a possible detection in the timing analysis only and deserve confirmation.

Pulsed high-energy gamma rays from PSR 1055-52

The Energetic Gamma Ray Experiment Telescope (EGRET) aboard the Compton Gamma Ray Observatory has detected a high-energy gamma-ray source at a position coincident with that of the radio pulsar PSR 1055-52. Analysis of the EGRET data at the radio pulsar period of 197 ms has revealed pulsed gamma-radiation at energies above 300 MeV, making PSR 1055-52 the fifth detected high-energy gamma-ray pulsar. The pulsed radiation from PSR 1055-52 has a very hard photon spectral index of -1.18 +/- 0.16 and a high efficiency for converting its rotational energy into gamma-rays. No unpulsed emission was observed.

The parkes observatory pulsar data archive

The Parkes pulsar data archive currently provides access to 144044 data files obtained from observations carried out at the Parkes observatory since the year 1991. Around 105 files are from surveys of the sky, the remainder are observations of 775 individual pulsars and their corresponding calibration signals. Survey observations are included from the Parkes 70 cm and the Swinburne Intermediate Latitude surveys. Individual pulsar observations are included from young pulsar timing projects, the Parkes Pulsar Timing Array and from the PULSE@Parkes outreach program. The data files and access methods are compatible with Virtual Observatory protocols. This paper describes the data currently stored in the archive and presents ways in which these data can be searched and downloaded.

Status of the Sardinia Radio Telescope project

We present the status of the Sardinia Radio Telescope (SRT) project, a new general purpose, fully steerable 64 m diameter parabolic radiotelescope capable to operate with high efficiency in the 0.3-116 GHz frequency range. The instrument is the result of a scientific and technical collaboration among three Structures of the Italian National Institute for Astrophysics (INAF): the Institute of Radio Astronomy of Bologna, the Cagliari Astronomy Observatory (in Sardinia,) and the Arcetri Astrophysical Observatory in Florence. Funding agencies are the Italian Ministry of Education and Scientific Research, the Sardinia Regional Government, and the Italian Space Agency (ASI,) that has recently rejoined the project. The telescope site is about 35 km North of Cagliari. The radio telescope has a shaped Gregorian optical configuration with a 7.9 m diameter secondary mirror and supplementary Beam-WaveGuide (BWG) mirrors. With four possible focal positions (primary, Gregorian, and two BWGs), SRT will be able to allocate up to 20 remotely controllable receivers. One of the most advanced technical features of the SRT is the active surface: the primary mirror will be composed by 1008 panels supported by electromechanical actuators digitally controlled to compensate for gravitational deformations. With the completion of the foundation on spring 2006 the SRT project entered its final construction phase. This paper reports on the latest advances on the SRT project.

The High Time Resolution Universe Pulsar Survey - VI. An artificial neural network and timing of 75 pulsars

We present 75 pulsars discovered in the mid-latitude portion of the High Time Resolution Universe survey, 54 of which have full timing solutions. All the pulsars have spin periods greater than 100 ms, and none of those with timing solutions are in binaries. Two display particularly interesting behaviour; PSR J1054{5944 is found to be an intermittent pulsar, and PSR J1809{0119 has glitched twice since its discovery. In the second half of the paper we discuss the development and application of an articial neural network in the data-processing pipeline for the survey. We discuss the tests that were used to generate scores and nd that our neural network was able to reject over 99% of the candidates produced in the data processing, and able to blindly detect 85% of pulsars. We suggest that improvements to the accuracy should be possible if further care is taken when training an articial

Population Synthesis of Millisecond and Submillisecond Pulsars

Known millisecond pulsars have periods longer than 1.558 ms. Recycled in binary systems, neutron stars can attain very short spin periods. In this Letter, we investigate the expected properties of the millisecond pulsar distribution by simulating synthetic populations under different assumptions for the neutron star equation of state and the decay of the magnetic field. We find evidence that a tail in the distribution of millisecond pulsars may exist at periods shorter than those observed.

The High Time Resolution Universe: The latest survey for pulsars at Parkes

The High Time Resolution Universe survey for radio pulsars and transients is the largest such survey yet undertaken with the Parkes radio telescope. We use the 13‐beam multibeam receiver centred at 1352 MHz, connected to BPSR, our new all‐digital backend. This system provides us with 340 MHz of usable band split into 870 channels, each sampled with two bits every 64 μs. The factor of eight improvement in frequency resolution over previous Parkes multibeam surveys allows us to probe further into the galactic plane for short duration signals, such as those from fast transients and millisecond pulsars. The survey is split into low, mid and high Galactic latitude regions, each covered with integration times of 4300, 540 and 270 s respectively. To date we have almost completed the mid latitude survey, discovering 65 previously unknown pulsars, including 15 millisecond pulsars. Upon completion we expect to discover some 400 pulsars, of which 75 will be millisecond pulsars.

The Radio‐loud Magnetar PSR J1622−4950

The High Time Resolution Universe survey for pulsars and fast transients has yielded the discovery of a slow radio pulsar, PSR J1622−4950, that despite its high dispersion measure exhibited a highly variable flux density and integrated pulse profile. The pulsar shares many properties with the two previously known magnetars that emit radio pulsations, including a similarly high inferred magnetic field strength. In contrast to other magnetars, PSR J1622−4950 shows no observed variations in X‐ray emission.