A 12-Year Periodicity in the Pulse Arrival Times for the Pulsar PSR B0943+10

An analysis of observations obtained over 26 years beginning in 1992 have indicated the appearance of sinusoidal variations with a period of about 12 years in the residual deviations of the pulse arrival times (PATs) for the pulsar PSR B0943+10. This behavior in the PAT residuals could be due to the influence of a planet orbiting the pulsar. These observations were carried out on the Large Scanning Antenna of the Pushchino Radio Astronomy Observatory at 112 MHz.

     

The character of pulse delays during radio bursts in the pulsar B0943+10

Results of a new series of observations of the anomalous pulsar B0943+10 carried out on the Large Scanning Antenna and DKR-1000 radio telescope of the Pushchino Radio Astronomy Observatory at 112 and 62 MHz, respectively, are presented. Several hundred pulse-arrival times (PATs) obtained on various days in 2013–2016 that correspond to the burst (B) mode emission are analyzed. A method for establishing the many-hour pulse shift in the emission window from 3.5-minute fragments is proposed. The delay of the mean pulse relative to the pre-calculated value follows an exponential law with a relaxation time of about 47 minutes. The pulse delay grows by 6 ms during the five hours following the onset of a burst. The random scatter of the residual PAT deviations is comparable to the amplitude of the systematic variations in these times over the lifetime of the B mode. These observations show that the character of the pulse delay as a function of time is the same at 112 and 62 MHz.     

Detection of the new rotating radio transient pulsar PSR J2225+35

We have detected the new pulsar PSR J2225+35, which displays the properties of the new class of radio sources “Rotating Radio Transients” (RRATs). RRATs are distinguished by isolated bursts of radio emission and long quiet periods. Throughout 45 observations with a total duration of about 3 hr, only two bursts of radio emission lasting a total of about 10 min were detected in two observations. The temporal and frequency delay of the pulses corresponds to the dispersion measure DM = 51.8 pc/cm³ and the distance d = 3.05 kpc. The period of the pulses is P = 0.94 s. The emission is polarized, with the rotation measure being RM = 49.8 rad/m².     

Radio emission of RRAT pulsars at 111 MHz

Observations of the RRAT pulsars J0627+16, J0628+09, J1819?1458, J1826?1419, J1839?01, J1840?1419, J1846?0257, J1848?12, J1850+15, J1854+0306, J1919+06, J1913+1330, J1919+17, J1946+24, and J2033+00 observed earlier on the 64-m Parkes telescope (Australia) and the 300-m Arecibo radio telescope (Puerto Rico) at 1400 MHz were conducted at 111 MHz on the LSA radio telescope of the Pushchino Radio Astronomy observatory in 2010–2012. A characteristic feature of these pulsars is their sporadic radio emission during rare active epochs and the absence of radio emission during long time intervals. No appreciable flare activity of these pulsars was detected in the Pushchino observations. However, processing the observations using the Fast Folding Algorithm taking into account known information about the pulsar dispersion measures and periods shows that, even during quiescent intervals, the majority of the studied pulsars generate weak radio pulses with a period corresponding to that of the radio emission of the sporadic pulses observed at active epochs. The flux of this radio emission does not exceed 100 mJy at the pulse peak, even at the low frequency of 111 MHz. This considerably hinders detection of the radio emission of RRAT pulsars at high frequencies, since the radio fluxes of RRAT pulsars decreases with increasing frequency.     

On the existence of planets around the pulsar PSR B0329+54

Results of timing measurements of the pulsar PSR B0329+54 obtained in 1968–2012 using the Big Scanning Antenna of the Pushchino Radio Astronomy Observatory (at 102 and 111 MHz), the DSS 13 and DSS 14 telescopes of the Jet Propulsion Laboratory (2388 MHz), and the 64 m telescope of the Kalyazin Radio Astronomy Observatory (610 MHz) are presented. The astrometric and rotational parameters of the pulsar are derived at a new epoch. Periodic variations in the barycentric timing residuals have been found, which can be explained by the presence of a planet orbiting the pulsar, with an orbital period P₁ = 27.8 yr, mass m _c sin i = 2M_?, and orbital semi-major axis a = 10.26 AU. The results of this study do not confirm existence of a proposed second planet with orbital period P₂ = 3 yr.     

The radio pulsar J0205+6449 in the supernova remnant 3C 58

The detection of pulsed radio emission from the recently discovered X-ray pulsar J0205+6449 in the young supernova remnant 3C 58 is reported together with the results of first studies of this emission. The observations were carried out at 111 and 88 MHz on radio telescopes of the Pushchino Observatory. The pulsar period, 65.68 ms, and period derivative, \(\dot P = 1.9 \times 10^{ - 13} \), have been confirmed. The integrated pulse profile at 111 MHz has been obtained and the flux density and spectral index α=2.8 measured. The pulsar dispersion measure DM=141 pc cm^?3 has been confirmed. This dispersion measure yields a distance to the pulsar of d=6.4 kpc, a factor of two or more greater than the previously favored distance to the supernova remnant 3C 58 (2.6 kpc). The problem of the age and distance of the pulsar-SNR system is discussed. If the age of the pulsar J0205+6449 is equal to that of the SNR (820 years), this pulsar is the youngest known radio pulsar. The synchrotron mechanism for the radio and X-ray emission is proposed to explain the lower radio and X-ray luminosity of this new pulsar compared to the Crab pulsar, which is similar to it in many ways. Optical emission with luminosity L_opt=10³¹ erg/s and gamma-ray emission with L_γ=7×10³⁵ erg/s are predicted, and the steep radio spectrum (α≈3) can be explained.     

Energy of anomalously intense pulsar pulses at decameter wavelengths

Cumulative and differential energy distributions are derived for the subpulse radio emission from the pulsars B0809+74, B0943+10, B0950+08, and B1133+16 at decameter wavelengths. The obtained cumulative distributions are compared with the analogous characteristic distributions for giant pulsar pulses. The analysis suggests that the amplification mechanisms in pulsar magnetospheres producing giant pulses and anomalously intense pulses may be similar.     

Observations of giant pulses from B1237+25 (J1239+2453) at 111 MHz. Detection and classification

An analysis of data from monitoring of individual pulses of the second-period pulsar PSR B1237+25 (J1239+2453) carried out on the Large Phased Array (LPA) of the Pushchino Radio Astronomy Observatory at 111 MHz during 2012–2015 is presented. The aim of this observing program is a search for anomalously strong and giant pulses. The regular generation of powerful individual pulses at the longitudes of three of five components in the main profile of PSR B1237+25 has been detected. The distribution of these strong pulses in flux density is bimodal, and has the power-law form characteristic for giant pulses, with power-law indices n = ?1.26 ± 0.05 and ?3.36 ± 0.34, which differentiates them from the regular pulses of pulsars, having a log–normal distribution. The characteristic pulse widths at the half-intensity level are 3–5 ms, which comprises 50–100% of the width of the corresponding component in the mean profile. The most powerful of the detected pulses had a peak flux density of 900 ± 160 Jy, and the strongest pulse exceeded the session-mean profile by a factor of 65.     

The parameters of pulsar subpulse emission at decameter wavelengths

An original method for determining the main parameters of the radio emission of pulsar subpulses at decameter wavelengths is proposed. The method involves the combined use of spectral and correlation analyses for the recorded signals. The novelty of the method is connected with two conditions that must be fulfilled to determine all the characteristics of the subpulse decameter emission. First, the signal-to-noise ratio in the output data must be increased, which can be done only by accumulating more data. Second, the phase characteristics of the subpulse component in the main pulse window must be preserved during the accumulation process. The method proposed makes it possible to fulfill these conditions simultaneously. A reference transfer function obtained from a spectral analysis of data with a relatively high number of individual detected pulses is used in the correlation analysis. The method is used to determine the drift rate, subpulse component width, individual subpulse width, secondary periods P ₂ and P ₃, and the subpulse structure coherence timescale recorded for the pulsar PSR B0809+74 at the central frequency 23.7 MHz. Perspectives for future application of the method are discussed.     

Simultaneous dual-frequency observations of giant radio pulses from the millisecond pulsar B1937+21

Simultaneous dual-frequency observations of giant radio pulses from the millisecond pulsar B1937+21 were performed for the first time in January–February 2002 on the Westerbork Synthesis Radio Telescope (2210–2250 MHz) and the 64-m Kalyazin radio telescope (1414–1446 MHz). The total observing time was about three hours. Ten giant pulses with peak flux densities from 600 to 1800 Jy were detected at 2210–2250 MHz, and fifteen giant pulses with peak flux densities from 3000 to 10000 Jy were observed at 1414–1446 MHz. No events were found to occur simultaneously at both frequencies. Thus, the observed radio spectra of individual giant pulses of this pulsar are limited in frequency to scales of about \(\frac{{\Delta v}}{v} < 0.5\). The duration of the giant pulses is less than 100 ns and is consistent with the expected scattering timescale in these frequency ranges. Instantaneous radio spectra of the detected giant pulses were compared with the diffractive spectra obtained from ordinary pulses of the pulsar. In some cases, considerable deviations of the radio spectra of the giant pulses from the diffractive spectrum were revealed, which can be interpreted as indicating temporal structure of the giant pulses on timescales of 10–100 ns.     

Two scales for the frequency dependence of the scattering of pulsar radio emission

We have measured the pulse broadening by scattering at 40, 60, and 111 MHz for the pulsars PSR B0809+74, B0950+08, B1919+21, and B2303+30. The frequency dependence of the scatter-broadening parameter is analyzed based on these measurements and data from the literature. The dependence obtained purely from the literature data is not consistent with the theory, and the scattering magnitudes differs considerably from the data of the catalog of 706 pulsars of Taylor et al. A two-component model for the frequency dependence of the scattering of the pulsar radio emission in the interstellar medium is proposed. Allowing for the presence of two scattering scales removes both inconsistencies between the observational data for these four pulsars and differences between the observed and theoretical frequency dependences for the scattering, as well as the need to invoke anomalous scattering magnitudes. The data of the catalog of Taylor et al. need to be corrected for the difference in the scattering magnitudes in the two branches of the frequency dependence.     

The pulsar PSR B1931+24 as an orthogonal rotator

The angles of the magnetic moment μ and the line of sight L to the rotation axis Ω are estimated for the pulsar PSR B1921+24, which displays “on” and “off” periods in its radio emission. It is shown that this object is an orthogonal rotator, i.e., the angle β between μ and Ω is equal to 88°.2 and the angle between L and Ω is ζ = 98.7°, and that its rotation period should be twice the usually adopted value (P = 1.626 s). One possible reason for the peculiarities of this pulsar could be the precession of a relic disk in the equatorial region of the object. Further observations (in particular, in the infrared) are required to confirm the existence of such a disk. Polarization data for other pulsars whose radiation switches on and off (transients) are also required, to determine if they are likewise orthogonal rotators. Calculations for PSR B0656+14 show that β ∼ 20°, and the sharp increase of its pulse intensities is due to intrinsic reasons, and is not associated with a relic disk. Original Russian Text ? I.F. Malov, 2007, published in Astronomicheskiĭ Zhurnal, 2007, Vol. 84, No. 6, pp. 531–535.     

The pulsar J1852+0040 in Kes 79 and the nature of central compact objects in supernova remnants

A possible model for the pulsar PSR J1852+0040 associated with the supernova remnant Kes 79 and detected in place of a central compact object in this remnant is discussed. The main observational properties of the pulsar can be understood as consequences of its weak surface magnetic field (B _s < 3 × 10¹¹ G) and short rotational period (P ～ 0.1 s). Its X-ray emission is thermal, and is generated in a small region near the surface of the neutron star due to cooling of the surface as the surface accretes matter from a relict disk surrounding the pulsar. The radio emission is generated in the outer layers of the pulsar magnetosphere by the synchrotron (cyclotron) mechanism. The optical luminosity of J1852+0040 is estimated to be L _opt < 10²⁸ erg/s. If the spectral features in another central compact object, 1E 1207.4+5209, are interpreted as electron cyclotron lines, this provides evidence for a weak surface magnetic field for this neutron star as well (B < 6 × 10¹⁰ G). The hypothesis that all central compact objects have weak surface fields makes it possible to explain the number of detected central compact objects, the absence of pulsar-wind nebulae associated with these objects, and the fact that no pulsar has yet been detected at the position of SN 1987a. We suggest that, after the supernova remnant has dissipated, the central compact object becomes a weak X-ray source (XDINS), whose weak emission is also due to the weakness of its magnetic field.     

The turbulence spectrum of the interstellar plasma toward the pulsars PSR B0809+74 and B0950+08

The interstellar scintillation of the pulsars PSR B0809+74 and B0950+08 have been studied using observations at low radio frequencies (41, 62, 89, and 112 MHz), and the characteristic temporal and frequency scales for diffractive scintillations at these frequencies determined. A comprehensive analysis of the frequency and temporal structure functions reduced to a single frequency shows that the spectra of the inhomogeneities of the interstellar plasma toward both pulsars are described by a power law. The index of the interstellar plasma fluctuation spectrum toward PSR B0950+08 (n = 3.00 ± 0.05) differs appreciably from the Kolmogorov index. The spectrum toward PSR B0809+74 is a power law with index n = 3.7 ± 0.1. Strong angular refraction has been detected toward PSR B0950+08. Analysis of the distribution of inhomogeneities along the line of sight indicates that the scintillations of PSR B0950+08 take place in a turbulent layer with an enhanced electron density localized approximately 10 pc from the observer. The distribution of inhomogeneities for PSR B0809+74 is quasi-uniform. The mean square fluctuations of the electron density are estimated for inhomogeneities with characteristic scale ρ ₀ = 10⁷ m along the directions toward four pulsars. The local turbulence in the 10-pc layer is a factor of 20 higher on this scale than in the extended region responsible for the scintillations of PSR B0809+74.     

Giant pulses—The main component of the radio emission of the crab pulsar

The paper presents an analysis of dual-polarization observations of the Crab pulsar obtained on the 64-m Kalyazin radio telescope at 600 MHz with a time resolution of 250 ns. A lower limit for the intensities of giant pulses is estimated by assuming that the pulsar radio emission in the main pulse and interpulse consists entirely of giant radio pulses; this yields estimates of 100 and 35 Jy for the peak flux densities of giant pulses arising in the main pulse and interpulse, respectively. This assumes that the normal radio emission of the pulse occurs in the precursor pulse. In this case, the longitudes of the giant radio pulses relative to the profile of the normal radio emission turn out to be the same for the Crab pulsar and the millisecond pulsar B1937+21, namely, the giant pulses arise at the trailing edge of the profile of the normal radio emission. Analysis of the distribution of the degree of circular polarization for the giant pulses suggests that they can consist of a random mixture of nanopulses with 100% circular polarization of either sign, with, on average, hundreds of such nanopulses within a single giant pulse.     

Behavior of pulsar B0329+54 pulse characteristics in the immediate vicinity of mode switch times at 111.4 MHz

Times of switches from the normal to the abnormal radiation mode have been recorded in observations of individual pulses of pulsar B0329+54 using the Large Phased Array of the Pushchino Radio Astronomy Observatory at 111.4 MHz. The variations in the amplitudes of the outer components that accompany the switch to the abnormal pulse profile occurred simultaneously in only half the cases. The phase of component IV of the integrated pulse does not vary during mode switches. In half the cases, instantaneous variations of the phases of component I and the central component during mode switches may be preceeded by additional smooth variations of the phases of individual pulses occuring over several minutes. We detected a decrease in the linear polarization of the central component by, on average, 8% in the abnormal mode for the integrated pulse, due to variations in the relative intensities of two orthogonally polarized modes of the pulsar radiation.     

Refinement of the parameters of the binary pulsar B0655+64 based on 111 MHz observations

An analysis of monitoring observations for the pulsar PSR B0655+64, which is located in a binary system, at 111 MHz during 2002–2015 are presented. The Keplerian parameters of the pulsar have been refived: the longitude of periastron ω = 276_.^°5785 ± 0_.^°0005 and the orbital semi-major axis is a_p sin i = 4.124976± 0.000003 s. The parameters of the perturbed motion have been determined: the motion of periastron ω = 0_.^°315 ± 0_.^°005/ year, and the derivative of the period of the binary system ? = (-1.66 ± 0.11) × 10^-14 s/s = (-0.524 ± 0.038) µs/year. The estimated time scale for the decay of the PSR 0655+64 system is (1.7 ± 0.1) × 10¹¹ yrs.     

Refractive shift in the position of the pulsar PSR B0329+54, measured at 111, 610, and 2300 MHz

The results of an analysis of timing data for the pulsar PSR B0329+54 obtained in 1968–2012 on the Large Scanning Antenna of the Pushchino Radio Astronomy Observatory at 111 MHz, the 64 m DSS-14 telescope of the Jet Propulsion Laboratory at 2.3 GHz, and the 64 m telescope of the Kalyazin Radio Astronomy Observatory at 610 MHz are presented. The astrometric and spin parameters of the pulsar are derived at a new epoch. The coordinates of the pulsar and its proper motion measured at the three frequencies differ. These differences have a systematic character, and are interpreted as a secular, refractive shift in the apparent position of the pulsar that arises because it is observed through large-scale inhomogeneities of the interstellar medium, leading to variations in the angle of refraction.     

Distribution of inhomogeneities in the interstellar plasma in the directions of three distant pulsars from observations with the RadioAstron ground–space interferometer

The RadioAstron ground–space interferometer has been used to measure the angular sizes of the scattering disks of the three distant pulsars B1641–45, B1749–28, and B1933+16. The observations were carried out with the participation of the Westerbork Synthesis Radio Telescope; two 32-m telescopes at Torun, Poland and Svetloe, Russia (the latter being one antenna of the KVAZAR network); the Saint Croix VLBA antenna; the Arecibo radio telescope; the Parkes, Narrabri (ATCA), Mopra, Hobart, and Ceduna Australian radio telescopes; and the Hartebeesthoek radio telescope in South Africa. The full widths at half maximum of the scattering disks were 27 mas at 1668 MHz for B1641–45, 0.5 mas at 1668 MHz for B1749–28, and 12.3 at 316 MHz and 0.84 mas at 1668 MHz for B1933+16. The characteristic time scales for scatter-broadening of the pulses on inhomogeneities in the interstellar plasma τ_sc were also measured for these pulsars using various methods. Joint knowledge of the size of the scattering disk and the scatter-broadening time scale enables estimation of the distance to the effective scattering screen d. For B1641–45, d = 3.0 kpc for a distance to the pulsar D = 4.9 kpc, and for B1749–28, d = 0.95 kpc for D = 1.3 kpc. Observations of B1933+16 were carried out simultaneously at 316 and 1668 MHz. The positions of the screen derived using the measurements at the two frequencies agree: d ₁ = 2.6 and d ₂ = 2.7 kpc, for a distance to the pulsar of 3.7 kpc. Two screens were detected for this pulsar from an analysis of parabolic arcs in the secondary dynamic spectrum at 1668 MHz, at 1.3 and 3.1 kpc. The scattering screens for two of the pulsars are identified with real physical objects located along the lines of sight toward the pulsars: G339.1–04 (B1641–45) and G0.55–0.85 (B1749–28).     

Distribution of interstellar plasma in the direction of PSR B0525+21 from data obtained on a ground–space interferometer

Observations on the RadioAstron ground–space interferometer with the participation of the Green Bank and Arecibo ground telescopes at 1668 MHz have enabled studies of the characteristics of the interstellar plasma in the direction of the pulsar PSR B0525+21. The maximum projected baseline for the ground–space interferometer was 233 600 km. The scintillations in these observations were strong, and the spectrum of inhomogeneties in the interstellar plasma was a power law with index n = 3.74, corresponding to a Kolmogorov spectrum. A new method for estimating the size of the scattering disk was applied to estimate the scattering angle (scattering disk radius) in the direction toward PSR B0525+21, θ _scat = 0.028 ± 0.002 milliarcsecond. The scattering in this direction occurs in a plasma layer located at a distance of 0.1Z from the pulsar, where Z is the distance from the pulsar to the observer. For the adopted distance Z = 1.6 kpc, the screen is located at a distance of 1.44 kpc from the observer.