Публикации

We report on the monitoring of the final stage of the outburst from the first Galactic ultraluminous X-ray pulsar Swift J0243.6+6124, which reached ˜40 Eddington luminosities. The main aim of the monitoring program with the Swift/XRT telescope was to measure the magnetic field of the neutron star using the luminosity of transition to the `propeller' state. The visibility constraints, unfortunately, did not permit us to observe the source down to the fluxes low enough to detect such a transition. The tight upper limit on the propeller luminosity Lprop < 6.8 × 1035 erg s-1 implies the dipole component of the magnetic field B < 1013 G. On the other hand, the observed evolution of the pulse profile and of the pulsed fraction with flux points to a change of the emission region geometry at the critical luminosity Lcrit ˜ 3 × 1038 erg s-1 both in the rising and declining parts of the outburst. We associate the observed change with the onset of the accretion column, which allows us to get an independent estimate of the magnetic field strength close to the neutron stars surface of B > 1013 G. Given the existing uncertainty in the effective magnetosphere size, we conclude that both estimates are marginally compatible with each other.

The luminosity of accreting magnetized neutron stars can largely exceed the Eddington value due to appearance of accretion columns. The height of the columns can be comparable to the neutron star radius. The columns produce the X-rays detected by the observer directly and illuminate the stellar surface, which reprocesses the X-rays and causes additional component of the observed flux. The geometry of the column and the illuminated part of the surface determine the radiation beaming. Curved space-time affects the angular flux distribution. We construct a simple model of the beam patterns formed by direct and reflected flux from the column. We take into account the possibility of appearance of accretion columns, whose height is comparable to the neutron star radius. We argue that depending on the compactness of the star, the flux from the column can be either strongly amplified due to gravitational lensing, or significantly reduced due to column eclipse by the star. The eclipses of high accretion columns result in specific features in pulse profiles. Their detection can put constraints on the neutron star radius. We speculate that column eclipses are observed in X-ray pulsar V 0332+53, leading us to the conclusion of large neutron star radius in this system (˜15 km if M ˜ 1.4 M⊙). We point out that the beam pattern can be strongly affected by scattering in the accretion channel at high luminosity, which has to be taken into account in the models reproducing the pulse profiles.

This paper describes a space experiment that is planned to be performed within the framework of

the Russian project of the microsatellite CHIBIS AI to meaure ionospheric signal delays to determine the

electron density and spatial fluctuations of the ionospheric and magnetospheric plasma. The measurements

will be conducted by the phase interferometer method at two levels using signals from the onboard in-phase

transmitters and GPS/GLONASS signals. The location of the radiation sources at two levels will make it pos-

sible to separate plasma variations in the ionosphere and inner magnetosphere–plasmasphere. The experi-

mental results are of interest both for solving fundamental problems of near-Earth plasma physics and applied

problems to improve positioning accuracy using global navigation systems.

Открытие планеты земной группы, вращающейся вокруг Проксимы Центавра, привело к множеству работ, обсуждающих возможные условия на этой планете. Поскольку в солнечной системе основные факторы, определяющие космическую погоду,—это солнечный ветер и космические лучи (КЛ), представляется важным понять, каковы параметры звездного ветра, галактических и звездных КЛ около экзопланет. На основе имеющихся данных представлены оценки скорости и плотности звездного ветра, возможных потоков и флюенсов космических лучей около Проксимы b. Получено, что вследствие модуляции галактические КЛ практически отсутствуют в районе орбиты Проксимы b, вплотьдо энергий частиц порядка 1 ТэВ. Тем не менее более мощные и частые по сравнению с Солнцем вспышки на Проксиме Центавра могут ускорятьч астицы до максимальных энергий порядка 3150αβ ГэВ (параметры α, β < 1), поэтому интенсивностьзв ездных космических лучей в астросфере может оказаться сравнимой с интенсивностью низкоэнергичных КЛ в гелиосфере.

Выполнено исследование формирования U -образного спектра (U -shaped spectrum) – одного из необычных волновых явлений, наблюдавшегося на приэкваториальной части орбиты спутника DEMETER. Впервые дано объяснение этого волнового явления, основанное на предположении, что данное излучение формируется волнами, генерируемыми молниевыми разрядами, в то время как форма спектра определяется особенностями распространения и затухания волн в приэкваториальной области верхней ионосферы.