Richard Wielebinski

The Characteristics of Millisecond Pulsar Emission. I. Spectra, Pulse Shapes, and the Beaming Fraction

The extreme physical conditions in millisecond pulsar magnetospheres, as well as an evolutionary history that differs from that of normal pulsars, raise the question whether these objects also differ in their radio emission properties. We have monitored a large sample of millisecond pulsars for a period of 3 yr using the 100 m Effelsberg radio telescope in order to compare the radio emission properties of these two pulsar populations. Our sample comprises a homogeneous data set of very high quality. With some notable exceptions, our findings suggest that the two groups of objects share many common properties. A comparison of the spectral indices between samples of normal and millisecond pulsars demonstrates that millisecond pulsar spectra are not significantly different from those of normal pulsars. This is contrary to what has previously been thought. There is evidence, however, that millisecond pulsars are slightly less luminous and less efficient radio emitters than normal pulsars. We confirm recent suggestions that a diversity exists among the luminosities of millisecond pulsars, with the isolated millisecond pulsars being less luminous than the binary millisecond pulsars, implying that the different evolutionary history has an influence on the emission properties. There are indications that old millisecond pulsars exhibit somewhat flatter spectra than the presumably younger ones. We present evidence that, contrary to common belief, the millisecond pulsar profiles are only marginally more complex than those found among the normal pulsar population. Moreover, the development of the profiles with frequency is rather slow, suggesting very compact magnetospheres. The profile development seems to anticorrelate with the companion mass and the spin period, again suggesting that the amount of mass transfer in a binary system might directly influence the emission properties. The angular radius of radio beams of millisecond pulsars does not follow the scaling predicted from a canonical pulsar model applicable for normal pulsars. Instead, they are systematically smaller, supporting the concept of a critical rotational period below which such a scaling ceases to exist. The smaller inferred luminosity and narrower emission beams will need to be considered in future calculations of the birthrate of the Galactic population.

Pulsar spectra of radio emission

We have collected pulsar flux density observa- tions and compiled spectra of 281 objects. The database of Lorimer et al. (1995) has been extended to frequencies higher than 1.4 GHz and lower than 300 MHz. Our results show that above 100 MHz the spectra of the majority of pulsars can be described by a simple power law with av- erage value of spectral index = 1:8 0:2. A rigorous analysis of spectral tting revealed only about 10% of spectra which can be modelled by the two power law. Thus, it seems that single power law is a rule and the two power law spectrum is a rather rare exception, of an unknown origin, to this rule. We have recognized a small number of pulsars with almost flat spectrum ( 1:0) in the wide frequency range (from 300 MHz to 20 GHz) as well as few pulsars with a turn-over at unusually high frequency ( 1G Hz).

The diffuse radio emission from the Coma cluster at 2.675 GHz and 4.85 GHz

We present new measurements of the diffuse radio halo emission from the Coma cluster of galaxies at 2.675 GHz and 4.85 GHz using the Effelsberg 100--m telescope. After correction for the contribution from point sources we derive the integrated flux densities for the halo source (Coma C),

Molecular Gas in the Andromeda Galaxy

S_{2.675 GHz}=(107\pm 28)mJy

Systematic bias in interstellar magnetic field estimates

and

The Characteristics of Millisecond Pulsar Emission. II. Polarimetry

S_{4.85 GHz}=(26\pm 12)mJy

The Characteristics of Millisecond Pulsar Emission. III. From Low to High Frequencies

. These values verify the strong steepening of the radio spectrum of Coma C at high frequencies. Its extent strongly depends on frequency, at 4.85 GHz it is only marginally visible. The measurement at 4.85 GHz is the first flux density determination for Coma C at this high frequency. In order to quantify the spectral steepening we compare the expectations for the spectrum of Coma C with the observations, resorting to basic models for radio halo formation. The in--situ acceleration model provides the best fit to the data. From equipartition assumptions we estimate a magnetic field strength

The Cygnus superbubble revisited

B_{eq}=0.57 (1+k)^{0.26}\mu G

Discovery of Radio Pulsations from the X-Ray Pulsar J0205+6449 in Supernova Remnant 3C 58 with the Green Bank Telescope

in the intracluster medium of Coma, where k is the energy ratio of the positively and negatively charged particles. As a by--product of the 2.675 GHz observation we present a new flux density for the diffuse emission of the extended source 1253+275 (

Milestones in the Observations of Cosmic Magnetic Fields

S_{2.675GHz}=112\pm 10