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Added by
Alexander Tchekhovskoy
Publication date
2015
fields
Physics
and research's language is
English
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Almost 50 years after radio pulsars were discovered in 1967, our understanding of these objects remains incomplete. On the one hand, within a few years it became clear that neutron star rotation gives rise to the extremely stable sequence of radio pulses, that the kinetic energy of rotation provides the reservoir of energy, and that electromagnetic fields are the braking mechanism. On the other hand, no consensus regarding the mechanism of coherent radio emission or the conversion of electromagnetic energy to particle energy yet exists. In this review, we report on three aspects of pulsar structure that have seen recent progress: the self-consistent theory of the magnetosphere of an oblique magnetic rotator; the location, geometry, and optics of radio emission; and evolution of the angle between spin and magnetic axes. These allow us to take the next step in understanding the physical nature of the pulsar activity.
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Pulsars play a crucial astrophysical role as the highly energetic compact radio, X-ray, and gamma-ray sources. Our previous works show that the radio pulsars found as the pulsing gamma sources by the Large Area Telescope (LAT) on the board of the Fermi Gamma-Ray Space Telescope have high values of magnetic field near the light cylinder, two-three orders of magnitude stronger comparing with the magnetic fields of radio pulsars: $log B_{lc}$ (G) are 3.60-3.95 and 1.75. Moreover, their losses of the rotation energy are also three orders higher than the corresponding values for the main group of radio pulsars on average:$log dot E$ (erg/s) = 35.37-35.53 and 32.64. The correlation between gamma-ray luminosities and radio luminosities is found. It allows us to select those objects from all set of the known radio pulsars that can be detected as gamma pulsars with the high probability. We give the list of such radio pulsars and propose to search for gamma emisson from these objects. On the other hand, the known catalog of gamma pulsars contains some sources which are not known as radio pulsars at this moment. Some of them have the large values of gamma luminosities and according to the obtained correlation, we can expect marked radio emission from these objects. We give the list of such pulsars and expected flux densities to search for radiation at frequencies 1400 and 111 MHz.
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L. Guillemot (for the Fermi LAT Collaboration
, for the Fermi Pulsarn Search Consortium
,
2012
Observations of pulsars with the Large Area Telescope (LAT) on the Fermi satellite have revolutionized our view of the gamma-ray pulsar population. For the first time, a large number of young gamma-ray pulsars have been discovered in blind searches of the LAT data. More generally, the LAT has discovered many new gamma-ray sources whose properties suggest that they are powered by unknown pulsars. Radio observations of gamma-ray sources have been key to the success of pulsar studies with the LAT. For example, radio observations of LAT-discovered pulsars provide constraints on the relative beaming fractions, which are crucial for pulsar population studies. Also, radio searches of LAT sources with no known counterparts have been very efficient, with the discovery of over forty millisecond pulsars. I review radio follow-up studies of LAT-discovered pulsars and unidentified sources, and discuss some of the implications of the results.
We present a study of the spectral properties of 441 pulsars observed with the Parkes radio telescope near the centre frequencies of 728, 1382 and 3100 MHz. The observations at 728 and 3100 MHz were conducted simultaneously using the dual-band 10-50cm receiver. These high-sensitivity, multi-frequency observations provide a systematic and uniform sample of pulsar flux densities. We combine our measurements with spectral data from the literature in order to derive the spectral properties of these pulsars. Using techniques from robust regression and information theory we classify the observed spectra in an objective, robust and unbiased way into five morphological classes: simple or broken power law, power law with either low or high-frequency cut-off and log-parabolic spectrum. While about $79 %$ of the pulsars that could be classified have simple power law spectra, we find significant deviations in 73 pulsars, 35 of which have curved spectra, 25 with a spectral break and 10 with a low-frequency turn-over. We identify 11 gigahertz-peaked spectrum (GPS) pulsars, with 3 newly identified in this work and 8 confirmations of known GPS pulsars; 3 others show tentative evidence of GPS, but require further low-frequency measurements to support this classification. The weighted mean spectral index of all pulsars with simple power law spectra is $-1.60 pm 0.03$. The observed spectral indices are well described by a shifted log-normal distribution. The strongest correlations of spectral index are with spin-down luminosity, magnetic field at the light-cylinder and spin-down rate. We also investigate the physical origin of the observed spectral features and determine emission altitudes for three pulsars.
Data are gathered from the Parkes pulsar data archive of twelve young radio pulsars, with the intervals of data for each pulsar ranged between 2.8 years and 6.8 years. 31 glitches are identified by using phase connection from pulsar timing technology, ranging from $1.7times10^{-9}$ to $8.5times10^{-6}$ at the change in relative glitch sizes $Delta u/ u$, where $ u=1/P$ is the pulse frequency. 8 post-glitch behaviours of 13 published glitches are updated with 4 exponential recoveries observed. Detecting 18 new glitches has great significance, but only one exponential relaxation was discovered in these new glitches. The bimodal distribution of $Delta u/ u$, as before, is validated with peaks at $sim 10^{-6}$ and $sim 10^{-9}$. Moreover, all exponential decays were observed in large glitches, and have very low $Q$. It takes short time toward the extrapolation of the pre-glitch pulse frequency with the timescale of 40 or 80 days. Besides, most glitches exhibit a linear decrease in slow-down rate $|dot{ u}|$ and a permanent change in $ddot{ u}$ after glitch. In special, PSR J1341-6220 was detected 4 new glitches to compose a total of 27 glitches, rising in third place of the most actively glitching pulsars known with a glitch rate of $1.17$ glitches per year. Unusual post-glitch behaviours demonstrate long-lasting increase of $ u$ for hundreds of days in PSR J1112--6103 and PSR J1614--5048.
The analysis of distributions of some parameters of radio pulsars emitting X-ray radiation was carried out. The majority of such pulsars has short spin periods with the average value $< P >$ = 133 msec. The distribution of period derivatives reveals a bimodality, dividing millisecond ($< log dfrac{dP}{dt}>$ = -19.69) and normal ($< log dfrac{dP}{dt}> $ = -13.29) pulsars. Magnetic fields at the surface of the neutron star are characterized by the bimodal distribution as well. The mean values of $<log B_s>$ are $8.48$ and $12.41$ for millisecond pulsars and normal ones, respectively. The distribution of magnetic fields near the light cylinder, it does not show the noticeable bimodality. The median value of $log B_{lc}$ = 4.43 is almost three orders higher comparing with this quantity ($<log B_{lc}>$ = 1.75) for radio pulsars without registered X-ray emission. Losses of rotational energy ($<log dfrac{dE}{dt}>$ = 35.24) are also three orders higher than corresponding values for normal pulsars. There is the strong correlation between X-ray luminosities and losses of rotational energies. The dependence of the X-ray luminosity on the magnetic field at the light cylinder has been detected. It shows that the generation of the non-thermal X-ray emission takes place at the periphery of the magnetosphere and is caused by the synchrotron mechanism. We detected the positive correlations between luminosities in radio, X-ray and gamma -ray ranges. Such correlations give the possibility to carry out a purposeful search for pulsars in one of these ranges if they radiate in other one.
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