Characteristics of the pulsed emission of the peculiar pulsar B1822-09 at low radio frequencies

The pulse structure of the pulsar B1822-09 has been studied at 112, 62, and 42 MHz. The observations were conducted in 2010 on the Large Scanning Antenna and the DKR-1000 radio telescope of the Pushchino Radio Astronomy Observatory. The shape of the main pulse and interpulse undergo considerable changes at low radio frequencies. In the main pulse, the precursor disappears and is replaced by a new component that trails 50 ms behind the main component. At 62 MHz, the interpulse acquires a pronounced two-peaked shape. At 62 and 112 MHz, as well as at higher frequencies, the brighter second component of the interpulse follows the main pulse at 185° and has a relative amplitude of about 5%. The main pulse width changes with frequency according to the power law W _0.5 ∼ ν ^−0.15 in the frequency range 42–4750-MHz. The interpulse width follows this law only in the range 325–4750 MHz; at 112, 102, and 62 MHz, the interpulse is almost a factor of three broader than themain pulse. The parameters of the pulse’s scattering on interstellar plasma inhomogeneities and the initial pulse width before it enters the scattering medium have been measured at 62 and 42 MHz. The frequency dependence of the characteristic scale for scattering of the pulses of B1822-09 corresponds to a Kolmogorov spectrum for the electron-density fluctuations in the interstellar medium in the direction toward this pulsar.     

Detection of regular variations in the intensity and pulse time of arrival of the anomalous pulsar PSR B0943+10

Timing of the anomalous pulsar PSR B0943+10 during 2007–2013 was carried out on the Large Phased Array radio telescope of the Pushchino Radio Astronomy Observatory at 112 MHz. The astrometric and rotational parameters for epoch MJD=56 500 have been determined. Considerable deviations of the pulse times of arrival from the precalculated values with a characteristic period of several years due to the presence of correlated low-frequency noise in the pulsar spin phase have been detected. These deviations can be explained in a planetary model by the presence of two companions of the pulsar, whose orbital parameters have been determined. A continuous increase in the longitude of the pulse maximum within the emission window, the pulse width, and the intensity have been detected after each switch to the burst mode. Together with the changes in pulse shape, degree of linear polarization of the pulse, and drift rate of individual pulses detected earlier, this indicates that all the main parameters of the radio emission in the B mode are unstable. This distinguishes PSR B0943+10 from all other modes-witching pulsars. The origin of the observed properties of this pulsar are probably associated with the interaction of its extended magnetosphere with the surrounding medium.     

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.

     

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.     

Microstructure of pulsar radio pulses measured with a time resolution of 62.5 ns at 1650 MHz

We present an analysis of pulsar observations carried out on two frequency channels at 1634 MHz and 1650 MHz with a time resolution of 62.5 ns on the 70-m radio telescope of the NASA Deep Space Network in Tidbinbilla. The data were recorded using the S2 system, intended primarily for VLBI observations. Microstructure with characteristic timescales of 270, 80, and 150 µs was detected in pulsars B0833-45, B1749-28, and B1933 + 16, respectively. The distribution of microstructure timescales for the Vela pulsar (B0833-45) is characterized by a gradual growth with decreasing timescale to 200 µs; the distribution has a maximum at 20–200 µs and falls off sharply for timescales below 20 µs. The statistical relation between the microstructure modulation index m and the corresponding timescale τ_µ can be approximated by the power law dependence R∝τ _⊙ ^0.5 ; i.e., the intensity is higher for micropulses with longer durations. This contradicts the predictions of nonlinear models for the formation of micropulses by supercompact soliton wave packets. In all the pulsars studied, the time delays of the micropulses between the two frequency channels deviate from the expected dispersion laws for the interstellar plasma. In particular, the micropulses in the low-frequency channel arrive earlier than predicted by the dispersion measures derived previously from the mean pulse profiles. The deviation from the dispersion delay is determined most accurately for B0833-45, and is 4.9±0.2 µs. Such anomalous delays are probably associated with the effects of propagation of the radio emission within the pulsar magnetosphere.     

Polarization of individual pulses of radio pulsars at the low frequencies 40, 60, and 103 MHz

Measurements of the linear polarization of individual pulses at 40, 60, and 103 MHz are presented for ten pulsars. The degree and position angle of a linear polarization were measured with a temporal resolution of 1–7 ms, and the longitudinal distributions of these parameters were constructed for each pulsar at one or more of these frequencies. These are the first such measurements for pulsars B0031-07, B0320 + 39, B0628-28, and B2217 + 47. Apart from B0628-28, all the pulsars are characterized by the simultaneous presence of orthogonal polarization modes in at least one component of the integral profile. The secondary polarization mode increases at frequencies ≤100 MHz for pulsars whose integrated pulses contain pairs of conal components (B0031-07, B0329 + 54, B0834 + 06, B1133 + 16, B2020 + 28). This is manifested both as an expansion of the longitudinal range where the secondary polarization mode is observed and an increase in its contribution to the emission at a given longitude. New data confirming the dependence of the linear polarization of individual pulses on the intensity and mode of the pulsar emission have been obtained.     

Giant pulses from the pulsar PSR B0950+08

Analysis of individual pulses of the pulsar B0950+08 at 112 MHz has shown that giant pulses with intensities exceeding the peak amplitude of the mean profile at these longitudes by two orders of magnitude are observed at the longitudes of all three components of the mean pulsar profile (the precursor and two-component main pulse). The maximum peak flux density of a recorded pulse is 15 240 Jy, and the energy of this pulse exceeds the mean pulse energy by a factor of 153. Strong but infrequent pulses at the longitude of the first component (precursor) can reach peak flux densities of 5750 Jy, exceeding the amplitude of the mean profile at this longitude by a factor of 490. It is shown that the emission at the precursor longitudes is virtually absent when giant pulses appear at the main-pulse longitudes, and vice versa: the presence of giant pulses at the precursor longitude results in the absence or considerable attenuation of the emission at other longitudes. The analysis shows that the cumulative probability function of the pulse peak flux densities has a piecewise power-law form. The power-law index for pulses with intensities exceeding 600 Jy appearing at the longitudes of the main pulse in the mean profile varies from n ₁ = ?1.25 ± 0.04 to n ₂ = ?1.84 ± 0.07. The obtained pulse energy distribution also has an inflection at E > 3000 Jy ms and a power-law form with the same index. The distribution of the pulse intensities at the precursor longitude was obtained, and forms a power law with index n = ?1.5 ± 0.1. The studied properties of the pulses at various longitudes of the mean profile are interpreted in the framework of induced scattering of the main-pulse emission by particles of ultrarelativistic, strongly magnetized plasma in the pulsar magnetosphere.     

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.     

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.     

The unusual profile of the radio pulsar Geminga

The results of observations of the radio emission profiles of the Geminga pulsar at 102.5, 87, 58, and 39 MHz are reported. Individual pulses are presented for the first time, and rare occasions of strong emission over the entire pulsar rotation period have been detected. A detailed analysis of the shapes, durations, and arrival phases of the pulses at 102.5 MHz is presented. These data reflect the unique character of the radio emission of Geminga.     

Radio emission from two anomalous X-ray pulsars

Observations of the anomalous X-ray pulsar (AXP) 1E 2259+586 and the AXP candidate 1RXS J1308.6+212708 at 111, 87, and 61 MHz are reported. The observations were carried out on two high-sensitivity radio telescopes of the Pushchino Radio Astronomy Observatory. Mean pulse profiles are presented, and the dispersion measures, distances, spectral indices, and integrated radio luminosities of both objects are estimated. Comparison with X-ray data shows large differences in the mean pulse widths and luminosities. The detection of radio emission from these two AXPs, together with other data, suggests the need to revise the radio-emission mechanisms in the magnetar model or the magnetar model itself.     

New observations of anomalous X-ray pulsars at low frequencies

We report the results of new observations of three anomalous X-ray pulsars: 1E 2259+586, 4U 0142+61, and XTE J1810-197. The observations were carried out on high-sensitivity radio telescopes of the Pushchino Radio Astronomy Observatory: the Large Phased Array at 111MHz and the DKR-1000 at 62 MHz. New, digital, multi-channel receivers designed for pulsar observations were used. Pulse profiles and dynamical spectra for the three pulsars are presented. The mean flux density for XTE J1810-197 is estimated to be ∼160 mJy at 62 MHz. An estimated spectral index for this pulsar is also presented.     

Interferometric observations of 4C 21.53 and PSR 1937+214 at decameter wavelengths

Preliminary resuts of interferometric observations of 4C 21.53 and PSR 1937+214 at 25 and 20 MHz are presented. The observations were obtained using the URAN-1 and URAN-2 interferometers, with baselines of 42.4 and 152.3 km. In addition to the pulsar radiation, which provides about 70% of the total flux of the object, radio emission from extended components with dimensions of several tens arcseconds has been detected for the first time. The angular size of the pulsar is 3″ at 25 MHz and 4″.8 at 20 MHz. The pulsar’s low-frequency spectrum deviates appreciably from the power law derived at higher frequencies.     

Anisotropic Scattering of the Radio Emission of the Pulsar B0833–45 in the Vela Supernova Remnant

Very Long Baseline Interferometry (VLBI) observations of the pulsar B0833–45 have been carried out as part of the scientific program of the RadioAstron mission. Ground support was provided by the Long Baseline Array, which includes radio telescopes in Australia and other countries in the southern hemisphere. The VLBI observations of the pulsar are analyzed in order to derive the parameters characterizing the scattering of the pulsar radio emission: the angular size of the scattering disk, the spatial scale of the diffraction pattern, the drift velocity of this pattern relative to the observer, the pulse scattering time scale, and the characteristic scintillation time and frequency scales, as well as the index of the electrondensity fluctuation spectrum. Comparison of these values with the predictions of the theory of scattering on a thin screen enables the determination of the position of the effective screen along the line of sight. Estimates made using various methods give distances to the screen from the observer of 0.79 to 0.87 times the total distance to the pulsar. Although the position of the screen is beyond the boundary of the Vela supernova remnant, this object may play the dominant role in the scattering. The scattering disk is an ellipse with a 2:1 axis ratio and with the inferred position angle of the major axis being ≈ 50°, based on the changes in the visibility-function amplitude for various orientations of the projected baseline. This conclusion is supported by the shape of the visibility-function amplitude as a function of the delay.

     

Giant pulses of PSR B0531+21 at 112 MHz

Three series of 111.88 MHz observations of giant pulses of PSR B0531+21 have been carried out in 2005 and 2007. The scattering of pulses observed in various series varies by a factor of 1.7: 10.6±0.5 ms in November 2005, 18±1 ms in January 2007, and 16±0.8 ms in June 2007. The cumulative probability distribution for the peak intensities of the giant pulses for each of these series shows that the distribution is stable and is a power law with a single slope (n = 2.3). This testifies to stability of the mechanism generating the giant pulses. The distribution functions for the 2005 and 2007 data can be superposed after correcting the intensities with a coefficient equal to the ratio of the effective pulse widths. Consequently, in the range of 23MHz-9GHz the energy in the pulses is conserved; i.e., the increase in the pulse intensity is proportional to the decrease in the scattering. Refractive scintillations at low frequencies in measurements with large time separation lead to variations in the number of giant pulses exceeding a given amplitude, proportional to the ratio of the mean flux densities of the pulsar in the corresponding observational series. The maximum energy of the recorded giant pulses is 2.5 × 10⁷ Jy µs. A comparison with the statistical properties of the giant pulses observed at other frequencies shows that the frequency dependence of the maximum energy of the giant pulses in the range of 23 MHz-9GHz is a power-law with index 2.2±0.2. The degree of linear polarization of the giant pulses at 112 MHz does not exceed 12%.     

Measurement of the inner turbulence scale of the interstellar plasma toward the pulsar PSR B2111+46

The pulsar PSR B2111+46 has been observed at 112 MHz, and a new approach to analyzing pulsar pulses scattered in turbulent interstellar plasma applied. This method is based on the dependence of the normalized energy in the trailing part of a pulse on the intrapulse time. Since the trailing edge of a pulse follow exponential law to high accuracy, the inner turbulence scale of the interstellar plasma exceeds the field coherence scale. The measured scattering parameter is τ _sc = 147 ± 1 ms. Analysis of the parameters of diffractive and refractive scintillations of the pulsar at 610 MHz together with the 112 MHz data shows that the spectrum of the interstellar plasma toward PSR B2111+46 is a piecewise power law: on scales of 10¹³–10¹⁴ cm, the exponent of the turbulence spectrum is n ≃ 4, whereas n = 3.5 on scales of 2 × 10⁸−10¹³ cm. The spectrum flattens with approach to the inner turbulence scale l: n = 3–3.2. The obtained inner turbulence scale is l = (3.5 ± 1.5) × 10⁷ cm. The distribution of the interstellar plasma toward the pulsar is close to statistically homogeneous. The local density (N _e = 0.4 cm⁻³) and filling factor (F = 0.04) of the interstellar plasma have been estimated. The similarity of N _e estimates obtained from the inner scale of the inhomogeneities and the ratio of the emission measure to the dispersion measure provides evidence that the inner turbulence scale corresponds to the ion inertial length.     

Detection of radio emission from the AXP 4U 0142+61

The detection of pulsed radio emission from the X-ray pulsar AXP 4U 0142+61 with a period of P = 8.68832935(6) s and a period derivative of $ \dot P $ \dot P = 18.713(4) × 10⁻¹³ s/s is reported. The observations were carried out on two high-sensitivity radio telescopes of the Pushchino Radio Astronomy Observatory: the Large Phased Array at 111MHz and the DKR-1000 at 40MHz.Mean pulse profiles are presented; the measured flux density is S ₁₁₁ = 30 ± 20 mJy. The estimated distance derived from the dispersion measure, 27 pc/cm³, is 1.4 kpc, and the integrated radio luminosity is L _R = 1.5 × 10²⁷ erg/cm. Comparison with X-ray data shows an appreciable difference in the pulse duration (the radio pulse is about a factor of 20 more narrow) and strong variations in the flux density.     

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.     

Polarization observations of circumstellar OH masers

Results of observations of circumstellar OH masers in lines with wavelengths near 18 cm are reported. The observations were carried out on the radio telescope of the Nan cay Radio Astronomy Observatory (France). In 2007–2009, 70 late-type stars were observed (including Mira and semi-regular variables). For 53 of these, emission was detected in at least one of three OH lines (1612, 1665, or 1667 MHz). Circular and linear polarization of the maser emission was measured, yielding all four Stokes parameters. Polarized emission features were detected in the OH line spectra of 41 stars. A summary of all the observations is given. The results obtained for T Lep, R LMi, and R Crt are discussed. Emission in the 1665 and 1667 MHz OH lines was detected in T Lep for the first time. Features probably due to Zeeman splitting were detected in the OH line profiles of all three stars. Estimates of the magnetic-field strengths in the maser sources were obtained (0.46–2.32 mG). Variability of the polarization characteristics of the maser emission of the stars on time intervals of several months was found.     

Solar 3.04 cm hydrogen line emission revealed in observations of the active region NOAA 10105

RATAN-600 observations of a microwave source located above the active region NOAA 10105 obtained on September 7–20, 2002 with a frequency resolution of ～10% have revealed a spectral feature near 3.04 cm that can be interpreted as a neutral hydrogen line. This feature was observed September 11, 2002, in both absorption and emission, and was detected in the spectra of various portions of the source (sunspot, flocculus, and background). The maximum line depth of (35 ± 5)% of the source brightness was observed at the start of the observations (9.2^h UT) in the flocculus in absorption. The line intensity decreased rapidly with time, becoming less than the measurement errors by 9.7^h UT. It is most likely that the 3.04 cm emission is related to a 2B chromospheric flare (M2.2 X-ray burst) observed at ～7.5^h UT in the floccular field, near the main sunspot of NOAA 10105. In this case, the total duration of the event was about two hours. These observations are consistent with earlier statistical studies, and refines these based on data with higher spatial resolution. Recommendations for further observational studies of the solar 3.04-cm hydrogen line are presented; requirements for theories of the 3.04 cm line taking into account nonequilibrium states of the active-region plasma are indicated.