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DIAGNOSTIC OF INTERMITTENT RADIO EMISSION FROM PULSARS
Losovsky B.
Pushchino Radio Astronomy Observatory, Astro Space Centre, Lebedev Physical Institute, Russian Academy of Sciences, Pushchio. Moscow region, Russia
Losovsky A.
Mosvow Region Government, Krasnogorsk, Moscow region, Russia
ABSTRACT
The following types of anomalous phenomena of radio emission from pulsars are considered: variations in residual deviations, changes in the pulse shape, switching on and off radio emission, period failures, changes in the measure of dispersion and scattering. Numerous data from observations of radio emission from pulsars, including observations of the pulsar in the Crab Nebula, indicate that they are all caused by processes occurring in the pulsar's magnetosphere. The considered phenomena do not require the involvement of a starquake model. A technique for probing active processes in the Crab Nebula by observing giant pulses and measuring their scattering is proposed and tested.
Keywords: pulsars, timing noise, glitches, magnetosphere, pulsar wind.
I. INTRODUCTION
A topical area of research in astrophysics at present is the study of the effect of fast rotation on the properties of various physical systems [1]. Pulsars can also be referred to such physical systems. Pulsars are magnetized neutron stars that are formed as a result of supernova explosions [2]. Observations of pulsars show that these are rapidly rotating objects with a period from hundredths to several tens of seconds. Rapid rotation of pulsars is a consequence of the law of conservation of angular momentum during the collapse of a star. A magnetized spinning neutron star creates a powerful electric field. Moving along closed magnetic
lines of force, charged particles create a pulsar magnetosphere, which extends up to the light cylinder, where the speed of rotation is equal to the speed of light. Within the limits of the light cylinder, the plasma rotates with the pulsar. On the contrary, charges in open lines of force, accelerated by an electric field to relativ-istic energies, leave the magnetosphere and stimulate synchrotron radio emission of curvature. The angle between the axis of rotation and the magnetic axis turns the pulsar into a cosmic beacon. A characteristic property of pulsars is pulsed periodic radio emission with high period stability. (Fig.1)
Figure 1. Diagram of the radio emission of the pulsar. The radio beam, magnetic and rotation axes open and closed lines offorce are shown. On the surface of the light cylinder, the speed of rotation is equal to the speed of
light.
Pulsars gradually slow down as a result of the conversion of rotational energy into the energy of charged particles and electromagnetic waves. As a simple model, the rotation period Pa (or rotation frequency t>), the first derivative of the period P (or the first derivative of the rotation frequency u) and the epoch of measurements in Julian days JD are used. The actual moments of arrival of a certain pulse of the observed pulsar at the telescope in the universal time scale (UTC) to are recalculated to the barycenter of the Solar system in dynamic barycentric time (TDB) ts, taking into account a number of corrections (relativistic, dispersive, etc.) [3]. Theoretical moments of arrival td of the same pulse to the barycenter, assuming a quadratic dependence of the pulse arrival time on the pulse number N, is calculated by the formula:
ta = to + N +1/2 P N2,
where l'„ and P are the period and derivative of
the period at the initial time tQ, corresponding to the
epoch JD0. The parameters Pa and P are taken from the
pulsar catalog. The difference between the actual arrival time (ts) and the calculated time (td) is called the residual deviation. Despite the high stability of the pulsar emission periods, control over the pulse arrival time (timing) shows the presence of different types of irregularities: variations in residual deviations, changes in the pulse shape (mode), nonstationary operation (termination and resumption of radio emission), period failures (glitches). Below we will consider the indicated types of irregularities, and show , that all of them are
caused by disturbances in the pulsar magnetosphere. The considered phenomena do not require the use of a starquake model. A technique for probing active processes in the Crab nebula by observing giant pulses and measuring their scattering is proposed and tested.
2. QUASIPERIODIC IRREGULARITIES OF ROTATION OF PULSARS
In [4], an exhaustive analysis of the temporal instabilities of 366 pulsars in the interval from 10 to 36 years was performed at the 76th radio telescope of the Jodrell Bank Observatory. The observations were carried out at various frequencies from 235 MHz up to 1630 MHz. The arrival time of pulses at each frequency was determined according to a standard procedure using a template. Timing was carried out according to the TEMRO-2 program. Domestic analogue is TIMAPR [5].The analysis included both conventional and regenerated pulsars. Analysis of the measurement results shows that variations in the arrival time are quasi-periodic in nature with characteristic periods from one to ten years and are not associated with errors in the observation and data processing system. With an increase in the observation interval, new periodicities appear. Quasiperiodic structures in residual deviations are clearly visible in the pulsars B1540-06, B1826-17, B1828-11, B2148 + 63 and are characteristic of many other pulsars. The assumptions that quasiperiodic structures (timing noisy) are caused by low-frequency noise processes, hypothetical satellites of pulsars, or free precession of neutron stars do not agree with observations.
A separate class is made up of mode-switching pulsars, in which the middle profile appears in two, and
sometimes in three forms. A detailed analysis of the observations of such pulsars, carried out at the 76-m radio telescope of the Jodrell Bank Observatory, is given in [6]. The cross-correlation function confirms the high degree of correlation between the width of the pulse profile and the parameter u. The spectra of the parameter u and quasiperiodic structures of residual deviations are similar. It follows that the quasi-periodic variations of the residual deviations, the derivative of the rotation frequency and the pulse shape are interdependent, which indicates that they are apparently controlled by a single mechanism.
Recently, many observations of non-stationary radio pulsars have appeared. These are, first of all, switching off pulsars. For example, the pulsar PSR B1931 + 24 (J1933 + 2421) emits like a normal radio pulsar for 5-10 days, then turns off for less than 10 seconds for 25-30 days, and then turns on again [7]. This process is repeated quasi-periodically. It should be noted that during radio emission, the deceleration of the pulsar occurs faster than in the absence of radio emission. This pulsar can be viewed as an example of the interaction between the pulsar and the magnetosphere, in which the flow of charged particles controls the deceleration of the pulsar.
According to existing concepts, the magnetosphere of a neutron star-pulsar is filled with electron-positron plasma, and radio emission is generated by a stream of these charged particles. The termination of radio emission can be associated with the termination of plasma generation in the magnetosphere, and the onset of radio emission - with the resumption of plasma generation [8].
In addition to switching off radio pulsars, a group of so-called nulling pulsars is known, which also do not observe radio emission for a certain period of time, but not as regularly as switched off ones, and for which the difference in rotation deceleration has not yet been measured. Nulling lasts from seconds to hours and even days. Wang et al. [9] assumed, that nulling pulsars are a type of mode switching pulsars, in which, after a change in the distribution of currents in the magnetosphere, the radiation direction and intensity change, and, as a result, the radiation pattern (mode) changes. Most of the nulling pulsars in the (Pa vs P) diagram are
located near the "death line" (cessation of radio emission) [10]. Therefore, the presence of nulling may also indicate the aging of the pulsar, leading to a malfunction of the radio emission mechanism [11]. According to Kramer et al. [7], the flux density in the nulling is
less than 1% of the average intensity, and according to Esamdin et al. [12] for the pulsar PSR B0826-34, the flux density in the passive phase was 2% of the density in the active phase.
3 JUMPING IRREGULARITIES IN THE ROTATION OF PULSAR
Jumping irregularities in the rotation of the pulsar (glitches) can be of two types: discrete glitches and slow glitches. Both types of glitches cause accelerated rotation of the pulsar, which occurs against the background of secular deceleration of the neutron star. With discrete faults, the frequency increases suddenly, and then follows an exponential decrease in frequency to the previous value. Slow failures are associated with slow frequency fluctuations. Espinoza et al. (13) report that by the time of publication of their article in 2011 at the Jodrell Bank Observatory, more than 700 pulsars were observed using a 76-meter radio telescope, and 128 new glitches were recorded in 63 pulsars. Taking into account the previously published data, this amounted to 315 glitches in 102 pulsars.
Shabanova et al. [14] presented the timing results for 27 pulsars at the Pushchino Observatory for 33.5 years from 1978 to 2012 and 10 pulsars from the Jet Propulsion Laboratory archive for 43.5 years. The presence of the above irregularities is confirmed: discrete failures, slow failures and quasi-periodic oscillations. Zau et al. [15] confirmed the report of Shabanova and Urama [16] about slow failures for the pulsar B1822-09 and also for J1825-0935. But since the observed residual deviations of these pulsars during glitches are similar to timing variations in other pulsars, they believe that slow glitches are not unique, but are caused by the same reasons as timing variations. The authors of the above-mentioned work [4] came to the same conclusion.
Cadez et al.[17] devoted their work to the study of the pulsar in the Crab Nebula using radio data from the Jodrell Bank Observatory from 1988 to 2014. in conjunction with optical observations of the pulsar using an ultrafast photon counter installed on the Copernicus telescope at the Astrophysical Observatory in Aziago (Italy) in October 2008 and on the telescope of the European South Observatory in La Silla (Chile) in 2009. Analysis of the data showed that jumps in the inhibition index n = urn / u2 are mainly associated with large glitches, when the relative change in the rotational speed u exceeds 1.0 * 10-8 (Fig. 2). A similar conclusion about the relationship between the inhibition index and glitches was made in [18].
Figure 2. Dependence between the dispersion measure DM (points, scale on the left) and the braking index n (dashed line, horizontal segments, scale on the right). The vertical segments of the dash line represent glitches. The solid line shows the braking index with a shift of 1010 days. Time in the abscissa in MJD = JD-2400000. The correlation coefficient between braking index n and dispersion measure DM is 0.7.
The delay of variations in the measure of dispersion relative to variations in the braking index ~ 1010 days and is explained by the time of ionization of the nebula by the pulsar wind. Glitches and the following variations in the braking index are caused by instability in the magnetosphere, which changes the configuration of the magnetic field and currents in the plasma through which the pulsar interacts with the nebula. It should be recalled that the hypothesis of a connection between period disruptions and processes in the magnetosphere was expressed in the book by R. Manchester and J. Taylor [19]. There are several models describing the origin of period glitches. One model views glitches as star-quakes caused by a flattened crust rearranging that tends to become spherical as the star's rotation slows down. Another model considers a neutron star as a reservoir filled with a superfluid liquid with many vortices, the mass of which, when the pulsar's rotation slows down, transfers angular momentum to the crust, which leads to a glitch. [13]. The above model of Cadez et al.[17] assumes that instabilities in the magnetosphere
itself can lead to glitches. The various considered tipes of anomalous phenomena , thus as variations of residual deviation, changes in the pulse shape, switching on and off radio emission, glitches are connected and cased be magnetosphere processes . So there is no need to explain glitches by processes occurring inside the pulsar (starquake hypothesis).
Large Phased Array Pushchino Radio Astronomy Observatory also monitors the radio emission from the pulsar in the Crab Nebula. [20]. Giant pulses are analyzed using a special program that allows you to determine the amount of scattering by simulating the passage of a pulse through a scattering medium [21]. Our data do not yet allow us to draw a definite conclusion about the effect of glitches on the measure of dispersion and scattering, but do not exclude such a dependance (Fig. 3). As for gamma-ray bursts [17], according to our data, they tend to concentrate during the period of enhanced disturbances in the Crab Nebula, which also confirms the proposed hypothesis.
Figure.3 Changes in the scattering of the pulsar in the Crab Nebula at a frequency of 111 MHz in the period 2002 - 2020. Vertical segments show the moments of glitches (short segments - strong glitches, shortened segments - weak glitches) and gamma bursts (long segments) *. The abscissa shows the observation epoch in modified Julian days MJD = JD-2450000 and the corresponding years.
*http://www.jb.man.ac.uk/pulsar/glitches.html)
4. CONCLUSION
Disturbances in the magnetosphere cause powerful fluxes of relativistic particles in the form of pulsar wind and polar jets. Monitoring the radio emission of giant pulses from the pulsar makes it possible to control these phenomena. The results of the analysis of the scattering parameter of the giant impulses are compared with the variations in the dispersion measure according to the data of the Jodrell Bank observatory*).
The connection between scattering and dispersion measure is well traced (Fig. 4)[22]. Thus, scattering measurements can serve as a basis for monitoring the activity of the Crab Nebula.
Dispersion measure is well traced (Fig. 4) [22]. Thus, scattering measurements can serve as a basis for monitoring the activity of the Crab Nebula.
*http://www.jb.man.ac.uk/pulsar/crab/crab2.txt
MJD 2920 3650 4380 5110 5840 6570 7300 8030 8760 9490 2003 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 2020 Figure.4 Comparison of scattering variations in ms (scale on the left) and dispersion conditional measure dm (DM-56.7) * 1000 (scale on the right). The abscissa is the same as at Fig.3.
The following types of anomalous phenomena of radio emission from pulsars are considered: variations in residual deviations, changes in the pulse shape, switching on and off radio emission, period fail-ures(glitches), changes in the dispersion measure and scattering. The connection established between them indicates a common mechanism of their generation in the pulsar magnetosphere and the propagation of disturbances in the environment. The considered phenomena do not require the involvement of a starquake model.
The results of long-term sounding of the Crab Nebula at the PRAO ASC FIAN by monitoring the radio emission of giant pulses from the pulsar in the Crab Nebula are presented. A technique for probing active processes in the Crab Nebula by observing giant pulses and measuring their scattering is proposed and tested.
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DYNAMICS OF PLASMA PISTON IN PIPE FILLED BY A GAS-LIQUID MEDIUM
Fedun V.
Associate Professor of the Department of Physics Pryazovsky State Technical University, Ukraine
ABSTRACT
The work simulates the operation of a plasma generator, which creates elastic waves in a pipe filled with a two-phase fluid. Modeling is based on wave models of non-stationary gas dynamics. The nonlinear nature of the properties of such systems was taken into account in the simulation. A model of the expansion of a plasma formation in a waveguide is proposed, which made it possible to study the process of excitation of elastic pressure pulses. The time dependences of the rate of expansion of the cavity, sound pressure, and energy of acoustic radiation were obtained and analyzed at various values of the gas content and static pressure of the fluid.
Keywords: plasma formation, cavity, plasma piston, homogeneous model of a two-phase medium, gas content.
Introduction. A lot of technological processes in cryogenic devices, in the metallurgical, oil-producing and oil-refining industries are accompanied by the formation of vapor-liquid systems or proceed occur in gasliquid media. The intensification of such processes can be carried out using elastic waves [1,2]. One of the effective ways to create acoustic fields in a liquid is based on the pulsations of a vapor-gas cavity, which is formed by an electric discharge in a liquid [3]. A numerical experiment was carried out in [4] on the generation of elastic pulses by powerful plasma bunches in an acoustic waveguide filled with a single-phase liquid. In this
case, the discharge forms a gas-plasma cavity - a plasma piston, which causes translational motion of the gas-liquid interface. Therefore, there is no added mass, and the transformation efficiency of the discharge energy into the energy of elastic vibrations increases. Since liquids in technological processes contain gas bubbles, the previously obtained results [4] require clarification.
The aim of this work is to simulate the generation of elastic waves by a plasma piston - a vapor-gas cavity,
