559 research outputs found
Multifrequency Observations of Giant Radio Pulses from the Millisecond Pulsar B1937+21
Giant pulses are short, intense outbursts of radio emission with a power-law
intensity distribution that have been observed from the Crab Pulsar and PSR
B1937+21. We have undertaken a systematic study of giant pulses from PSR
B1937+21 using the Arecibo telescope at 430, 1420, and 2380 MHz. At 430 MHz,
interstellar scattering broadens giant pulses to durations of secs,
but at higher frequencies the pulses are very short, typically lasting only
-secs. At each frequency, giant pulses are emitted only in narrow
(\lsim10 \mus) windows of pulse phase located -sec after the
main and interpulse peaks. Although some pulse-to-pulse jitter in arrival times
is observed, the mean arrival phase appears stable; a timing analysis of the
giant pulses yields precision competitive with the best average profile timing
studies. We have measured the intensity distribution of the giant pulses,
confirming a roughly power-law distribution with approximate index of -1.8,
contributing \gsim0.1% to the total flux at each frequency. We also find that
the intensity of giant pulses falls off with a slightly steeper power of
frequency than the ordinary radio emission.Comment: 21 pages, 10 Postscript figures; LaTeX with aaspp4.sty and epsf.tex;
submitted to Ap
Simultaneous Dual Frequency Observations of Giant Pulses from the Crab Pulsar
Simultaneous measurements of giant pulses from the Crab pulsar were taken at
two widely spaced frequencies using the real-time detection of a giant pulse at
1.4 GHz at the Very Large Array to trigger the observation of that same pulse
at 0.6 GHz at a 25-m telescope in Green Bank, WV. Interstellar dispersion of
the signals provided the necessary time to communicate the trigger across the
country via the Internet. About 70% of the pulses are seen at both 1.4 GHz and
0.6 GHz, implying an emission mechanism bandwidth of at least 0.8 GHz at 1 GHz
for pulse structure on time scales of one to ten microseconds.
The arrival times at both frequencies display a jitter of 100 microseconds
within the window defined by the average main pulse profile and are tightly
correlated. This tight correlation places limits on both the emission mechanism
and on frequency dependent propagation within the magnetosphere.
At 1.4 GHz the giant pulses are resolved into several, closely spaced
components. Simultaneous observations at 1.4 GHz and 4.9 GHz show that the
component splitting is frequency independent. We conclude that the multiplicity
of components is intrinsic to the emission from the pulsar, and reject the
hypothesis that this is the result of multiple imaging as the signal propagates
through the perturbed thermal plasma in the surrounding nebula. At both 1.4 GHz
and 0.6 GHz the pulses are characterized by a fast rise time and an exponential
decay time which are correlated. The pulse broadening with its exponential
decay form is most likely the result of multipath propagation in intervening
ionized gas.Comment: LaTeX, 18 pages, 7 figures, accepted for publication in The
Astrophysical Journa
Giant Radio Pulses from the Crab Pulsar
Individual giant radio pulses (GRPs) from the Crab pulsar last only a few
microseconds. However, during that time they rank among the brightest objects
in the radio sky reaching peak flux densities of up to 1500 Jy even at high
radio frequencies. Our observations show that GRPs can be found in all phases
of ordinary radio emission including the two high frequency components (HFCs)
visible only between 5 and 9 GHz (Moffett & Hankins, 1996). This leads us to
believe that there is no difference in the emission mechanism of the main pulse
(MP), inter pulse (IP) and HFCs. High resolution dynamic spectra from our
recent observations of giant pulses with the Effelsberg telescope at a center
frequency of 8.35 GHz show distinct spectral maxima within our observational
bandwidth of 500 MHz for individual pulses. Their narrow band components appear
to be brighter at higher frequencies (8.6 GHz) than at lower ones (8.1 GHz).
Moreover, there is an evidence for spectral evolution within and between those
structures. High frequency features occur earlier than low frequency ones.
Strong plasma turbulence might be a feasible mechanism for the creation of the
high energy densities of ~6.7 x 10^4 erg cm^-3 and brightness temperatures of
10^31 K.Comment: accepted by Advances in Space Research, to appear in the 35th COSPAR
assembly proceeding
Phase and Intensity Distributions of Individual Pulses of PSR B0950+08
The distribution of the intensities of individual pulses of PSR B0950+08 as a
function of the longitudes at which they appear is analyzed. The flux density
of the pulsar at 111 MHz varies strongly from day to day (by up to a factor of
13) due to the passage of the radiation through the interstellar plasma
(interstellar scintillation). The intensities of individual pulses can exceed
the amplitude of the mean pulse profile, obtained by accumulating 770 pulses,
by more than an order of magnitude. The intensity distribution along the mean
profile is very different for weak and strong pulses. The differential
distribution function for the intensities is a power law with index n = -1.1 +-
0.06 up to peak flux densities for individual pulses of the order of 160 Jy
Multifrequency Radio Observations of the Crab Pulsar
Previously unseen profile components of the Crab pulsar have been discovered
in a study of the frequency-dependent behavior of its average pulse profile
between 0.33 and 8.4 GHz. One new component, 36 degrees ahead of the main pulse
at 1.4 GHz, is not coincident with the position of the precursor at lower
frequencies. Two additional, flat-spectrum components appear after the
interpulse between 1.4 and 8.4 GHz. The normal interpulse undergoes a
transition in phase and spectrum by disappearing near 2.7 GHz, and reappearing
10 degrees earlier in phase at 4.8 and 8.4 GHz with a new spectral index. The
radio frequency main disappears for frequencies above 4.8 GHz, even though it
is seen at infrared, optical, and higher energies. The existence of the
additional components at high frequency and the strange, frequency-dependent
behavior is unlike anything seen in other pulsars, and cannot easily be
explained by emission from a simple dipole field geometry.Comment: 13 pages. Source is single LaTeX file with 3 figures, using aaspp and
epsf style files (included). To appear in The Astrophysical Journal,
September 1996. Paper can also be found at http://www.ee.nmt.edu
Statistical Studies of Giant Pulse Emission from the Crab Pulsar
We have observed the Crab pulsar with the Deep Space Network (DSN) Goldstone
70 m antenna at 1664 MHz during three observing epochs for a total of 4 hours.
Our data analysis has detected more than 2500 giant pulses, with flux densities
ranging from 0.1 kJy to 150 kJy and pulse widths from 125 ns (limited by our
bandwidth) to as long as 100 microseconds, with median power amplitudes and
widths of 1 kJy and 2 microseconds respectively. The most energetic pulses in
our sample have energy fluxes of approximately 100 kJy-microsecond. We have
used this large sample to investigate a number of giant-pulse emission
properties in the Crab pulsar, including correlations among pulse flux density,
width, energy flux, phase and time of arrival. We present a consistent
accounting of the probability distributions and threshold cuts in order to
reduce pulse-width biases. The excellent sensitivity obtained has allowed us to
probe further into the population of giant pulses. We find that a significant
portion, no less than 50%, of the overall pulsed energy flux at our observing
frequency is emitted in the form of giant pulses.Comment: 19 pages, 17 figures; to be published in Astrophysical Journa
- …