ION-CYCLOTRON ABSORPTION OF FAST WAVES IN A CYLINDRICAL CURRENT-CARRYING PLASMA

Influence of a longitudinal stationary current on the absorption and the radial structure of fast waves in a cylindrical current-carrying plasma is discussed. To evaluate the dispersion equation for fast waves, there was used the dielectric tensor taking into account the radial current structure and geometry of the confining helical magnetic field by the plasma safety factor. It is shown that the damping rate of fast waves in a non-equilibrium current-carrying plasma differ from those for an equilibrium plasma column in a homogeneous magnetic field nearby the cutoffs and resonances due to the rotational transformation (including shear-effects) of the helical magnetic field lines.

Генерация периодической последовательности ультракоротких электромагнитных импульсов в схеме с двумя параллельными излучающим и поглощающим электронными пучками

We demonstrate the possibility of generating periodical trains of ultrashort microwave pulses based on the effect of passive mode-locking in a scheme with two parallel coaxial electron beams formed by a single cathode and transported in a single vacuum volume. The external tubular beam provides amplification of radiation during rectilinear motion along a periodic slow-wave structure, while the internal paraxial beam provides nonlinear cyclotron absorption.

New measurements of the cyclotron line energy in Cen X-3

ABSTRACT We report results from the analysis of data from two observations of the accreting binary X-ray pulsar Cen X-3 carried out with the broad-band X-ray observatories Suzaku and NuSTAR. The pulse profile is dominated by a broad single peak and show some energy dependence with two additional weak pulse peaks at energies below 15 and 25 keV, respectively. The broad-band X-ray spectrum for 0.8–60.0 keV for Suzaku and 3.0–60.0 keV for NuSTAR is fitted well with high-energy cut-off power-law model along with soft-excess, multiple iron emission lines and a cyclotron absorption. The cyclotron line energy is found to be $30.29^{+0.68}_{-0.61}$ and $29.22^{+0.28}_{-0.27}$ keV, respectively, in the Suzaku and NuSTAR spectra. We make a comparison of these two measurements with four previous measurements of Cyclotron Resonant Scattering Feature (CRSF) in Cen X-3 obtained with Ginga, BeppoSAX, and RXTE. We find no evidence for a dependence of the CRSF on luminosity. Except for one CRSF measurement with BeppoSAX , the remaining measurements are consistent with a CRSF energy in the range of 29.5–30.0 keV over a luminosity range of 1.1–5.4 × 1037 erg s−1 different from several other sources that show considerable CRSF variation in the same luminosity range.

Redshifted absorption lines from an isolated neutron star

The solid crust constituting the outer layers of a hot neutron star is wrapped by an mm-to-cm thin atmosphere. Even if the atmosphere is so thin, it substantially affects the blackbody spectrum emitted by the surface, resulting in an overall hardening of the emitted spectrum. The composition of the atmosphere has so far remained elusive. Several narrow absorption features have been detected and interpreted as arising from proton (or electron) resonant cyclotron absorption in the neutron star magnetic field. Apart from these, for a Hydrogen atmosphere no spectral features are expected, whereas when it is polluted with metals, absorption features start appearing in soft X-ray spectra. Absorption edges and features have been possibly observed during thermonuclear explosions onto the neutron star surface. Isolated neutron stars represent a breeding ground where to look for absorption features, thanks to their simple X-ray spectra. Here we report on the detection of redshifted Nitrogen and Oxygen absorption features from the closest and brightest isolated neutron star. The lines are ~50 eV wide and their intensity is incompatible from originating in the interstellar path to the neutron star. Lines are redshifted by a common gravitational redshift of z_g=0.216±0.004.

Revisiting the spectral and timing properties of 4U 1909+07 with NuSTAR and Astrosat

ABSTRACT We present the results obtained from the analysis of high-mass X-ray binary pulsar 4U 1909+07 using NuSTAR and Astrosat observations in July 2015 and 2017, respectively. X-ray pulsations at ≈604 s are clearly detected in our study. Based on the long-term spin-frequency evolution, the source is found to spun-up in the last 17 yr. We observed a strongly energy-dependent pulse profile that evolved from a complex broad structure in soft X-rays into a profile with a narrow emission peak followed by a plateau in energy ranges above 20 keV. This behaviour ensured a positive correlation between the energy and pulse fraction. The pulse profile morphology and its energy evolution are almost similar during both the observations, suggesting a persistent emission geometry of the pulsar over time. The broad-band energy spectrum of the pulsar is approximated by an absorbed high-energy exponential cut-off power-law model with iron emission lines. In contrast to the previous report, we found no statistical evidence for the presence of cyclotron absorption features in the X-ray spectra. We performed phase-resolved spectroscopy using data from the NuSTAR observation. Our results showed a clear signature of absorbing material at certain pulse phases of the pulsar. These findings are discussed in terms of stellar wind distribution and its effect on the beam geometry of this wind-fed accreting neutron star. We also reviewed the subsonic quasi-spherical accretion theory and its implication on the magnetic field of 4U 1909+07 depending on the global spin-up rate.

The giant outburst of 4U 0115+634 in 2011 with Suzaku and RXTE

We present an analysis of X-ray spectra of the high-mass X-ray binary 4U 0115+634 as observed with Suzaku and RXTE in 2011 July, during the fading phase of a giant X-ray outburst. We used a continuum model consisting of an absorbed cutoff power law and an ad hoc Gaussian emission feature centered around 8.5 keV, which we attribute to cyclotron emission. Our results are consistent with a fundamental cyclotron absorption line centered at ∼10.2 keV for all observed flux ranges. At the same time we rule out significant influence of the 8.5 kev Gaussian on the parameters of the cyclotron resonant scattering feature, which are not consistent with the cyclotron line energies or the depths of previously reported flux-dependent descriptions. We also show that some continuum models can lead to artificial line-like residuals in the analyzed spectra, which are then misinterpreted as unphysically strong cyclotron lines. Specifically, our results do not support the existence of a previously claimed additional cyclotron feature at ∼15 keV. Apart from these features, we find for the first time evidence for a He-like Fe XXV emission line at ∼6.7 keV and weak H-like Fe XXVI emission close to ∼7.0 keV.

Long-term variability of a black widow’s eclipses – A decade of PSR J2051$-$0827

ABSTRACT In this paper we report on $\sim 10$ yr of observations of PSR J2051$-$0827, at radio frequencies in the range 110–4032 MHz. We investigate the eclipse phenomena of this black widow pulsar using model fits of increased dispersion and scattering of the pulsed radio emission as it traverses the eclipse medium. These model fits reveal variability in dispersion features on time-scales as short as the orbital period, and previously unknown trends on time-scales of months–years. No clear patterns are found between the low-frequency eclipse widths, orbital period variations, and trends in the intrabinary material density. Using polarization calibrated observations we present the first available limits on the strength of magnetic fields within the eclipse region of this system; the average line of sight field is constrained to be $10^{-4}$ G $\lesssim B_{||} \lesssim 10^2$ G, while for the case of a field directed near-perpendicular to the line of sight we find $B_{\perp } \lesssim 0.3$ G. Depolarization of the linearly polarized pulses during the eclipse is detected and attributed to rapid rotation measure fluctuations of $\sigma _{\text{RM}} \gtrsim 100$ rad m$^{-2}$ along, or across, the line of sights averaged over during a subintegration. The results are considered in the context of eclipse mechanisms, and we find scattering and/or cyclotron absorption provide the most promising explanation, while dispersion smearing is conclusively ruled out. Finally, we estimate the mass-loss rate from the companion to be $\dot{M}_{\text{C}} \sim 10^{-12}\, \mathrm{M}_\odot$ yr$^{-1}$, suggesting that the companion will not be fully evaporated on any reasonable time-scale

Properties of the transient X-ray pulsar Swift J1816.7–1613 and its optical companion

We present results of investigation of the poorly studied X-ray pulsar Swift J1816.7–1613 during its transition from the type I outburst to the quiescent state. Our studies are based on the data obtained from X-ray observatories Swift, NuSTAR, and Chandra alongside with the latest IR data from UKIDSS/GPS and Spitzer/GLIMPSE surveys. The aim of the work is to determine the parameters of the system, namely the strength of the neutron star magnetic field and the distance to the source, which are required for the interpretation of the source behaviour in the framework of physically motivated models. No cyclotron absorption line was detected in the broad-band energy spectrum. However, the timing analysis hints at the typical for the X-ray pulsars magnetic field from a few ×1011 to a few ×1012 G. We also estimated the type of the IR-companion as a B0-2e star located at a distance of 7–13 kpc.