Mean Pulse Profile Research Articles

The ultraviolet pulsations of the cataclysmic variable AE Aquarii as observed with the Hubble Space Telescope

We present the results of high time resolution UV spectroscopy and simultaneous high-speed UBVR photometry of AE Aqr. The UV spectra were obtained with the Faint Object Spectrograph aboard the Hubble Space Telescope (HST), and the photometry was carried out with the 82 sec telescope at McDonald Observatory. Our study focuses on the coherent 33 sceond oscillations, whose amplitude is found to be very large in the UV (40% of the mean quiescent level). The mean pulse profile has two broad unequal peaks spaced by half an oscillation cycle. The pulse profiles in the UV and optical bands appear quite similar in shape, with no discernible shifts. The orbital delay curve of the UV pulses establishes the white dwarf as their origin. The (UV+optical) spectrum of the pulsations is well described by a white dwarf atmosphere model with a temperature of about 26,000 K. We find no oscillations in the UV emission-line fluxes, nor in their velocities, down to a limit of 800 km/s. Based on the properties of the UV and optical pulsations we suggest that they originate in the X-ray heated magnetic polar caps of the white dwarf. Under this assumption we produce maximum entropy maps of the brightness distribution of the white dwarf surface. Using this model we are able to reproduce the observed mean pulse profile and interpret fluctuations in the oscillation amplitude as small fluctuations in the accretion rate. We find that the amplitudes and profiles of the pulses are not strongly affectd by the large aperiodic flares exhibited by the system. This suggests that the large flares are not related to the process of depositing material onto the white dwarf and argues against models that place their origin at the white dwarf magnetosphere.

Mean pulse polarization of southern pulsars at 1560 MHz

Mean pulse total intensity and polarization data at 1560 MHz are presented for 45 southern pulsars. The observations were made during 1988 at Parkes using a filter-bank polarimeter system. The results are discussed in terms of the rotating vector model for pulse polarization. Notable results include a highly polarized interpulse pulsar and several pulsars with very wide mean pulse profiles

On the Separation of the Components in the Mean Pulse Profile of PSR 1451-68 and their Spectral Behavior

AbstractWe have developed a method to understand the detailed structure of the mean pulse profile of pulsars, namely, the Gaussian fit separation of the average profile (GFSAP) method, in which we assume the total profile is the superposition of several individual Gaussian-distributed components. Linear polarization data is used to simplify the fitting. The components of PSR 1451–68 are separated and their spectral indices calculated. We find that the profile of PSR 1451–68 is actually quintuple instead of triple, which is in agreement with the idea that quintuple is the prototype shape of pulsar profiles. The core component is shown to have the steepest spectrum, while the inner cone has the flattest. Another conclusion from PSR 1451–68 is that the core width does not change with frequency.

The shape of pulsar radio beams

All available data on the mean pulse profiles of pulsars and their polarization, including a large body of previously unpublished material, have been analysed in order to determine the two-dimensional form of the radio beams emitted by pulsars. The differing properties of core and conal emission discussed by Rankin are confirmed but it is suggested that the observations are best described by a gradual change in emission characteristics from the core or axial region to the outer edge of the emission beam rather than two distinct emission processes. The spectral index difference between the core and conal regions is shown to be a function of pulsar period and is greatest for short-period pulsars. It is shown that the emission within the beam boundary is often patchy and that the distribution of component locations within the beam is essentially random. The polarization properties of pulsars with interpulses are analysed and it is shown that these pulsars fall into two groups, those where the interpulse is from the opposite pole and those where all the emission is from one pole. It is proposed that only the former group be known as interpulses. The latter group forms part of a larger set having wide profiles which are believed to originate from pulsars in which the magnetic axis is nearly aligned with the rotation axis. Evidence relating to the shape of the beam boundary is considered and it is concluded that the data are consistent with circular beams. Observational evidence suggests that the beam radius is large for short-period pulsars and is approximately proportional to P−1/3, where P is the pulsar period. Based on this relation for beam radius, the inclination angle of the magnetic axis is computed for pulsars where complete conal emission is observed. It is shown that for young pulsars the distribution of inclination angle is uniform whereas old pulsars have preferentially aligned fields. The time-scale for alignment is similar to the time-scale for field decay, that is, about 107 yr. We discuss the implications of the period dependence of beam radius, patchy emission beams and alignment of the magnetic axis on the pulsar beaming fraction, that is, the proportion of pulsars beaming towards us.

Mode-Changing, Drifting Subpulses, and Interpulse Emission in PSR 1822-09

PSR 1822–09 is a nearby galactic disk pulsar with a typical .769 s period. Its large period derivative indicates a young timing age of 250,000 yrs and a strong estimated surface magnetic field of 6.4 × 1012 G. We have observed this pulsar at frequencies around 1700 MHz and 2650 MHz. The mean pulse profile at these frequencies consists of a double peaked main pulse with two dissimilar components and a weak interpulse 185° of pulse longitude after the main pulse second component. The interpulse is detected in both frequency ranges, and the main pulse - interpulse separation does not change between these frequencies and the low frequencies around 327 MHz where the interpulse was discovered by Cady and Ritchings (1977).

Integrated pulse profiles and mean fluxes of 24 pulsars at 2.388 gigahertz

view Abstract Citations (17) References (13) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Integrated pulse profiles and mean fluxes of 24 pulsars at 2.388 gigahertz. Downs, G. S. Abstract Integrated pulse profiles are presented which represent the superposition of several hundred thousand pulses and approximate the true mean pulse profiles at 2.388 GHz for 24 pulsars. Observed interpulses are examined, the mean pulse energy associated with each integrated pulse profile is determined, and peak pulse fluxes are estimated. Comparison with later observations at 2.7 GHz indicates significant differences between the mean pulse energies measured at 2.388 and 2.7 GHz in several cases. Publication: The Astrophysical Journal Supplement Series Pub Date: June 1979 DOI: 10.1086/190591 Bibcode: 1979ApJS...40..365D Keywords: Microwave Emission; Pulsars; Pulse Duration; Pulsed Radiation; Radio Astronomy; Pulse Amplitude; Radiant Flux Density; Astrophysics; Pulsars:Pulse Structure full text sources ADS | data products SIMBAD (24)

Orthogonal Polarization in Pulsar Radio Emission

For many pulsars the integrated or mean pulse profile is highly polarized. Generally linear polarization dominates over circular and there is a continuous variation of position angle through the profile (e.g. Manchester 1971). In most models for the emission process the angle of polarization is related to the (projected) direction of magnetic fields in the source region. Several of the observed properties of pulsars, for example, the mode-changing phenomenon (Backer 1970) and the different spectral index of different components of the intergrated profile (Manchester 1971), suggest that different parts of the integrated profile are emitted in different (though closely related) parts of the source. The different observed position angles across the integrated profile would then result from different projected magnetic field directions in these different parts of the source. For many pulsars the observed position angle variations are closely represented by a path through a radial set of projected field directions such as would be obtained in the vicinity of a magnetic pole (cf. Radhakrishnan and Cooke 1969).