Pulsar microstructure and its quasi-periodicities with the S2 VLBI system at a resolution of 62.5 nanoseconds

We report on a study of microstructure and its quasi-periodicities of three pulsars at 1.65 GHz with the S2 VLBI system at a resolution of 62.5 ns, by far the highest for any such statistical study yet. For PSR B1929+10 we found in the average cross-correlation function (CCF) broad microstructure with a characteristic timescale of 95+-10 mcs and confirmed microstructure with characteristic timescales between 100 and 450 mcs for PSRs B0950+08 and B1133+16. On a finer scale PSRs B0950+08, B1133+16 (component II) and B1929+10 show narrow microstructure with a characteristic timescale in the CCFs of ~10 mcs, the shortest found in the average CCF or autocorrelation function (ACF) for any pulsar, apart perhaps for the Crab pulsar. Histograms of microstructure widths are skewed heavily toward shorter timescales but display a sharp cutoff. The shortest micropulses have widths between 2 and 7 mcs. No nanopulses or unresolved pulse spikes were detected. Cross-power spectra of single pulses show a large range of complexity with single spectral features representing classic quasi-periodicities and broad and overlapping features with essentially no periodicities at all. Significant differences were found for the two components of PSR B1133+16 in every aspect of our statistical analysis of micropulses and their quasi-periodicities. Asymmetries in the magnetosphere and the hollow cone of emission above the polar cap of the neutron star may be responsible for these differences.Comment: 18 pages, 11 figures, 3 tables, A&A, 2001, accepte

The characteristics of millisecond pulsar emission: II. Polarimetry

We have made polarimetric monitoring observations of millisecond pulsars visible from the northern hemisphere at 1410 MHz. Their emission properties are compared with those of normal pulsars. Although we demonstrated in paper I that millisecond pulsars exhibit the same flux density spectra and similar profile complexity, our results presented here suggest that millisecond pulsar profiles do not comply with the predictions of classification schemes based on ``normal'' pulsars. The frequency development of a large number of millisecond pulsar profiles is abnormal when compared with the development seen for normal pulsars. Moreover, the polarization characteristics suggest that millisecond-pulsar magnetospheres might not simply represent scaled versions of the magnetospheres of normal pulsars, supporting results of paper I. However, phenomena such as mode-changing activity in both intensity and polarization are recognized here for the first time (e.g., J1730--2304). This suggests that while the basic emission mechanism remains insensitive to rotational period, the conditions that, according to the canonical pulsar model, regulate the radio emission, might be satisfied at different regions in millisecond pulsar magnetospheres. At least three types of model have been proposed to describe the millisecond pulsar magnetospheres. A comparison of the predictions of these models with the observations suggests that individual cases are better explained by different processes. However, we show that millisecond pulsars can be grouped according to common emission properties, a grouping that awaits verification from future multifrequency observations.Comment: 38 pages, 8 figures, accepted for publication in ApJ, (see astro-ph/9801177 for paper I

La observación del cometa Halley desde el IAR

El cometa Halley fue observado con el radiotelescopio del IAR, entre el 6 de febrero y el 1º de mayo de 1986, en la línea de 1667 MHz (λ=18 cm) del radical OH. La línea fue detectada en absorción entre el 23 de marzo y el 23 de abril. No se observaron asimetrías significativas en los perfiles. El número total de moléculas de OH, calculado en base a los perfiles observados y al modelo utilizado por Scloerb y Gerard (1985), muestra variaciones semi-periódicas con relaciones entre máximos y mínimos del orden de 1,7 y su valor medio es 2,5 veces mayor que el valor predicho por dichos autores.The Halley Comet was observed with the IAR radio telescope, between the 6th of February and the 1st of May, 1986 in the OH-1667 MHz line. The line was detected in absorption between the 23rd of March and the 23rd of April. No significative asymmetries were observed. The total number of OH molecules, as derived from the profiles and the model used by Schloerb and Gerard (1985), shows quasi-periodic varlations wlth maximum-to-minimum ratios of about 1.7 and its average is about 2.5 times larger than the predicted valué.Asociación Argentina de Astronomí

Binary and Millisecond Pulsars at the New Millennium

We review the properties and applications of binary and millisecond pulsars. Our knowledge of these exciting objects has greatly increased in recent years, mainly due to successful surveys which have brought the known pulsar population to over 1300. There are now 56 binary and millisecond pulsars in the Galactic disk and a further 47 in globular clusters. This review is concerned primarily with the results and spin-offs from these surveys which are of particular interest to the relativity community.Comment: 59 pages, 26 figures, 5 tables. Accepted for publication in Living Reviews in Relativity (http://www.livingreviews.org

Binary and Millisecond Pulsars

We review the main properties, demographics and applications of binary and millisecond radio pulsars. Our knowledge of these exciting objects has greatly increased in recent years, mainly due to successful surveys which have brought the known pulsar population to over 1700. There are now 80 binary and millisecond pulsars associated with the disk of our Galaxy, and a further 103 pulsars in 24 of the Galactic globular clusters. Recent highlights have been the discovery of the first ever double pulsar system and a recent flurry of discoveries in globular clusters, in particular Terzan 5.Comment: 77 pages, 30 figures, available on-line at http://www.livingreviews.org/lrr-2005-

An upper limit on the power-law index of the radio spectrum of Geminga

Among the similar to 20 isolated neutron stars that emit in more than one energy band, only Geminga was radio quiet. Very recently, three groups at the Pushchino Radio Astronomy Observatory reported independently the detection of a weak pulsed radio emission from this source at similar to 100 MHz, bringing Geminga back into the standard group of radio-loud, isolated neutron stars. Here we report a series of observations of Geminga performed with the Arecibo radio telescope at various frequencies between 318 and 1400 MHz, performed from 1982 to 1984. No pulsed emission was detected. The high sensitivity of the Arecibo telescope allowed us to put a stringent upper limit to the spectral index in the radio band: alpha less than or equal to -3.6. If the 100 MHz pulsed emission is confirmed, Geminga will retain its peculiar nature of a radio pulsar with an extremely steep radio spectrum. This would severely constrain the models for the radio emission from isolated rotating neutron stars