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Scienctific Articles |
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| Evidence
for Free Precession in the Pulsar B1642-03 |
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T.V.
Shabanova, A.G. Lyne, J.O. Urama
Astrophysical Journal, 552,
321-325 (2001)
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| Abstract.
We present an analysis of the
timing data of the pulsar B1642-03, collected over
a span of 30 years between 1969 and 1999. During
this interval, the timing residuals exhibit cyclical
changes with amplitude varying from 15 to 80 ms
and spacing of maxima varying from 3 to 7 yr. Interpretation
of these observed cyclical changes in terms of free
precession suggests a wobble angle of about 0.8
degrees. |
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A.D. Kuzmin and
B.Ya. Losovsky
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| Abstract.
We present the results of the first low frequency
measurements of the flux densities of a large sample
of millisecond pulsars (MSPs) at 102 and 111 MHz.
Combining our observations with data at higher frequencies
borrowed from the literature, we constructed the
spectra of 30 MSPs in the 0.1 to 4.8 GHz frequency
range. Our flux density measurements extend the
known spectra of MSPs to the lowest frequency to
date. The coverage of a low frequency range allows
us to search for low frequency turn-over, which
is often observed for normal pulsars. We find that
spectra of MSPs differ from those of normal pulsars,
showing no low-frequency turn-over typical of normal
pulsars. We suggest that the geometry of the radio
emission region of MSPs differs from that of normal
pulsars: the magnetic field configuration in MSPs'
magnetospheres may deviate from that of a pure dipole
and/or the radio emission region may be radially
compressed. Monochromatic luminosities at this low
frequency and the integral luminosity over the 0.1-4.8
GHz frequency range were determined and their dependence
on other pulsar parameters analyzed. |
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T. V. Shabanova
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| Abstract.
Two glitches have been detected in the pulsar PSR
B1822-09. The first glitch occured around MJD 49615
and was characterized by a fractional increase in
rotational frequency of 2*10^{-10}. The second glitch
occured 325 days after the first one and caused
a fractional change in frequency of 5*10^{-9}. Of
interest was the post-glitch behaviour. The rotational
frequency immediately after the second glitch began
slowly, gradually increasing which lasted ~620 days.
As a result of the slow increase a fractional change
in rotation frequency for this period of time made
up 7*10^{-9}. This event was accompanied by a decrease
in the frequency derivative, which having reached
minimum magnitude ~0.4 percentage less than the
original value, returned to its initial value. |
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T. V. Shabanova, J.O.Urama
Astron. Astrophys. 354, 960-964 (2000)
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| Abstract.
An analysis of four glitches observed in the pulsar
B1822-09 during the period 1994 - 1999 is presented.
The main distinguishing feature of these glitches
is that the sudden increase in rotational frequency
is accompanied by a decrease in the frequency derivative.
The largest change of the frequency derivative was
measured in the fourth glitch. This glitch occured
around MJD 51054 and was characterized by rather
a small increase in rotational frequency of Delta_nu/nu=7*10^{-9},
but a large decrease in the frequency derivative
by ~2.4 percent. The first two glitches were observed
practically simultaneously at two frequencies of
0.1 GHz in Pushchino, Russia and 1.6/2.3 GHz at
HartRAO, South Africa. An analysis of the high-
and low frequency timing data showed that glitches
did not affect the pulse arrival times at different
frequencies within 2 ms. Glitch signature was identical
in the wide frequency range from 0.1 to 2.3 GHz.
In addition, a more exact value of the dispersion
measure was measured to be 19.383(3) pc*cm^{-3}. |
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T. V. Shabanova
Astrophysical Journal, 453, 779-782 (1995)
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| Abstract.
The data set of available pulse arrival times of
the pulsar PSR B0329+54, including the JPL timing
data between 1968 and 1983 and the Pushchino timing
data between 1978 and 1994, is analyzed. It is shown
that a quasi-sinusoidal modulation with a period
of 16.9 years exists in the timing residuals. This
periodicity can be interpreted as evidence for the
existence of a planet-like body orbiting the pulsar
PSR B0329+54 with the 16.9-yr orbital period. The
planet has the minimum mass of about twice the mass
of the Earth, and moves in eccentric orbit (e=0.23)
with the semimajor axis 7.3 AU. The existence of
3-yr periodicity in arrival times, claimed by Demianski
and Proszynski in 1979, is verified. It manifested
itself distinctly in the JPL data only after removing
the main 16.9-yr periodicity. |
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