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.     

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%.     

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.     

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.     

Studies of cosmic plasma using radioastron VLBI observations of giant pulses of the pulsar B0531+21

The structure of the interstellar plasma in the direction of the pulsar in the Crab Nebula is studied using several sets of space-VLBI observations obtained with networks of ground telescopes and the RadioAstron space antenna at 18 and 92 cm. Six observing sessions spanning two years are analyzed. Giant pulses are used to probe the cosmic plasma, making it possible to measure the scattering parameters without averaging. More than 4000 giant pulses were detected. The interferometer responses (visibility functions) on ground and ground–space baselines are analyzed. On the ground baselines, the visibility function as a function of delay is dominated by a narrow feature at zero delay with a width of δ_τ ~ 1/B, where B is the receiver bandwidth. This is typical for compact continuum sources. On the ground–space baselines, the visibility function contains a set of features superposed on each other and distributed within a certain interval of delays, which we identify with the scattering time for the interfering rays τ. The amplitude of the visibility function on ground baselines falls with increasing baseline; the scattering disk is partially resolved at 18 cmand fully resolved at 92 cm. Estimates of the scattering angle ? give 0.5–1.3mas at 18 cm and 14.0 mas at 92 cm. The measured values of ? and τ are compared to estimate the distance from the source to the effective scattering screen, which is found at various epochs to be located at distances from 0.33 to 0.96 of the distance from the observer to the pulsar, about 2 kpc. The screen is close to the Crab Nebula at epochs of strong scattering, confirming that scattering on inhomogeneities in the plasma in the vicinity of the nebula itself dominates at these epochs.     

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.     

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.     

Studies of Giant Pulses from the Pulsar B0301+19 (J0304+1932) at 111 MHz

Astronomy Reports - The results of observations of the pulsar B0301+19 (J0304+1932) carried out on the Large Scanning Antenna of the Pushchino Radio Astronomy Observatory at 111 MHz during...     

The spin-down mechanism of the X-ray pulsar 4U 2206+54

Observations of the X-ray pulsar 4U 2206+54 obtrained over 15 years show that its period, which is now 5555 ± 9 s, is increasing dramatically. This behavior is difficult to explain using traditional scenarios for the spin evolution of compact stars. The observed spin-down rate of the neutron star in 4U 2206+54 is in good agreement with the value expected in a magnetic-accretion scenario, taking into account that, under certain conditions, the magnetic field of the accretion stream can affect the geometry and type of flow. The neutron star in this case accretes material from a dense gaseous slab with small angular momentum, which is kept in equilibrium by the magnetic field of the flow itself. A magnetic-accretion scenario can be realized in 4U 2206+54 if the magnetic-field strength at the surface of the optical counterpart to the neutron star is higher than 70 G. The magnetic field at the surface of the neutron star is 4 × 10¹² G in this scenario, in agreement with estimates based on an analysis of X-ray spectra of the pulsar.     

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.     

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.     

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.     

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.     

Monitoring of the radio emission of the Crab Nebula pulsar at low frequencies

Results of long-term (2002–2010) monitoring of giant radio pulses of the pulsar PSR B0531+21 in the Crab Nebula at ν = 44, 63, and 111 MHz are reported. The observations were conducted on the LPA and DKR-1000 radio telescopes of the Lebedev Physical Institute. The giant pulses were analyzed using specialized software for calculating the magnitude of the scattering τ _sc , signal-to-noise ratio, and other required parameters by modeling the propagation of a pulse in the scattering interstellar medium. Three pronounced sharp increases in the scattering were recorded in 2002–2010. Analysis of the dependence between the variations of the scattering and dispersion measure (data of Jodrell Bank Observatory) shows a strong correlation at all frequencies, ≈0.9. During periods of anomalous increase in scattering and the dispersion measure, the index γ in the frequency dependence of the scattering in the Crab Nebula, τ _sc (ν) ∝ ν ^−γ , was smaller than the generally accepted values γ = 4.0 for a Gaussian and γ = 4.4 for a Kolmogorov distribution. This difference in combination with the piece-wise power-law spectrum may be due to the presence of a dense plasma structure with developed Langmuir turbulence in the nebula, along the pulsar’s line of sight. The magnetic field in the Crab Nebula estimated from measurements of the rotation measure toward the pulsar is 100 μG.     

Detection of new pulsars at 111 MHz

The first results of a search for pulsars using the Large Phased Array of the Lebedev Physical Institute at 111 MHz for right ascensions 0^h-24^h and declinations 21°-42° are reported. Data with a time resolution of 100 ms in six frequency channels within a 2.5-MHz frequency band have been processed. Thirty-four pulsars have been detected, of which seventeen were observed on this telescope earlier; ten known pulsars had not been observed earlier. Seven new pulsars have been discovered.     

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.     

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.