134 research outputs found
Cyclotron emission, absorption, and the two faces of X-ray pulsar A 0535+262
Deep NuSTAR observation of X-ray pulsar A 0535+262, performed at a very low
luminosity of erg s, revealed the presence of two
spectral components. We argue that the high-energy component is associated with
cyclotron emission from recombination of electrons collisionally excited to the
upper Landau levels. The cyclotron line energy of keV
was measured at the luminosity of almost an order of magnitude lower than what
was achieved before. The data firmly exclude a positive correlation of the
cyclotron energy with the mass accretion rate in this source.Comment: 5 pages, 3 figures, accepted by MNRAS Letter
Luminosity dependence of the cyclotron line and evidence for the accretion regime transition in V 0332+53
We report on the analysis of NuSTAR observations of the Be-transient X-ray
pulsar V 0332+53 during the giant outburst in 2015 and another minor outburst
in 2016. We confirm the cyclotron-line energy-luminosity correlation previously
reported in the source and the line energy decrease during the giant outburst.
Based on 2016 observations, we find that a year later the line energy has
increased again essentially reaching the pre-outburst values. We discuss this
behaviour and conclude that it is likely caused by a change of the emission
region geometry rather than previously suggested accretion-induced decay of the
neutron stars magnetic field. At lower luminosities, we find for the first time
a hint of departure from the anticorrelation of line energy with flux, which we
interpret as a transition from super- to sub-critical accretion associated with
the disappearance of the accretion column. Finally, we confirm and briefly
discuss the orbital modulation observed in the outburst light curve of the
source.Comment: added journal reference&doi for proper indexin
Dramatic spectral transition of X-ray pulsar GX 304-1 in low luminous state
We report on the discovery of a dramatic change in the energy spectrum of the
X-ray pulsar GX 304-1 appearing at low luminosity. Particularly, we found that
the cutoff power-law spectrum typical for accreting pulsars, including GX 304-1
at higher luminosities of erg s,
transformed at lower luminosity of erg s to a
two-component spectrum peaking around 5 and 40 keV. We suggest that the
observed transition corresponds to a change of the dominant mechanism
responsible for the deceleration of the accretion flow. We argue that the
accretion flow energy at low accretion rates is released in the atmosphere of
the neutron star, and the low-energy component in the source spectrum
corresponds to the thermal emission of the optically thick, heated atmospheric
layers. The most plausible explanations for the high-energy component are
either the cyclotron emission reprocessed by the magnetic Compton scattering or
the thermal radiation of deep atmospheric layers partly Comptonized in the
overheated upper layers. Alternative scenarios are also discussed.Comment: 5 pages, 2 figures, accepted by MNRAS Letter
Mechanics and Mathematical Modeling of Class III Treatment with Orthodontic Appliances with a Movable Ramp
Treatment of class III is a current problem in orthodontics that requires constant improvement of its methods, development of new or modifications of known methods and techniques. We have developed and studied the modification of removable functionally-directing orthodontic appliances for treatment of Class III, which consists of a plastic base, vestibular arc, retaining clasps, ramp, which is connected with the base by means of two torsion springs. Its usage ensures a prolonged contact of ramp with the teeth. We studied two types of club-shaped springs (torsion springs): one spring, which create an amortization effect during the action of the ramp, but do not change its inclination angle and second one – spring that seek to increase the angle of the ramp inclination due to the disclosure of its curl
MECHANICS AND MATHEMATICAL MODELING OF CLASS III TREATMENT WITH ORTHODONTIC APPLIANCES WITH A MOVABLE RAMP
Treatment of class III is a current problem in orthodontics that requires constant improvement of its methods, development of new or modifications of known methods and techniques. We have developed and studied the modification of removable functionally-directing orthodontic appliances for treatment of Class III, which consists of a plastic base, vestibular arc, retaining clasps, ramp, which is connected with the base by means of two torsion springs. Its usage ensures a prolonged contact of ramp with the teeth.We studied two types of club-shaped springs (torsion springs): one spring, which create an amortization effect during the action of the ramp, but do not change its inclination angle and second one – spring that seek to increase the angle of the ramp inclination due to the disclosure of its curl
RX J0440.9+4431: another supercritical X-ray pulsar
In the beginning of 2023 the Be transient X-ray pulsar RX J0440.9+4431
underwent a fist-ever giant outburst observed from the source peaking in the
beginning of February and reaching peak luminosity of
erg s. Here we present the results of a detailed spectral and temporal
study of the source based on NuSTAR, INTEGRAL, Swift, and NICER observations
performed during this period and covering wide range of energies and
luminosities. We find that both the pulse profile shape and spectral hardness
change abruptly around erg s, which we associate
with a transition to super-critical accretion regime and erection of the
accretion column. The observed pulsed fraction decreases gradually with energy
up to 20 keV (with a local minimum around fluorescence iron line), which is
unusual for an X-ray pulsar, and then rises rapidly at higher energies with the
pulsations significantly detected up to keV. The broadband energy
spectra of RX J0440.9+4431 at different luminosity states can be approximated
with a two-hump model with peaks at energies of about 10-20 and 50-70 keV
previously suggested for other pulsars without additional features. In
particular an absorption feature around 30 keV previously reported and
interpreted as a cyclotron line in the literature appears to be absent when
using this model, so the question regarding the magnetic field strength of the
neutron star remains open. Instead, we attempted to estimate field using
several indirect methods and conclude that all of them point to a relatively
strong field of around G.Comment: 11 pages, 10 figures, 2 tables. Submitted to MNRA
Constraints on the magnetic field structure in accreting compact objects from aperiodic variability
We investigate the aperiodic variability for a relatively large sample of
accreting neutron stars and intermediate polars, focusing on the properties of
the characteristic break commonly observed in power spectra of accreting
objects. In particular, we investigate the relation of the break frequency and
the magnetic field strength, both of which are connected to the size of the
magnetosphere. We find that for the majority of objects in our sample the
measured break frequency values indeed agree with estimated inner radii of the
accretion disc, which allows to use observed break frequencies to independently
assess the magnetic field strength and structure in accreting compact objects.
As a special case, we focus on Hercules X-1 which is a persistent,
medium-luminosity X-ray pulsar accreting from its low-mass companion. In the
literature, it has been suggested that the complex pulse profiles, the spin-up
behaviour and the luminosity-correlation of the cyclotron energy seen in Her
X-1 can be explained with a complex magnetic field structure of the neutron
star. Here, we connect the measured break frequency to the magnetospheric
radius and show that the magnetic field strength derived assuming a dipole
configuration is nearly an order of magnitude smaller than the magnetic field
strength corresponding to the cyclotron energy. Accordingly, this discrepancy
can be explained with the magnetic field having strong multipole components.
The multipolar structure would also increase the accreting area on the neutron
star surface, explaining why the critical luminosity for accretion column
formation is puzzlingly high in this source.Comment: 10 pages, 3 figure
Study of the X-ray pulsar IGR J19294+1816 with NuSTAR: Detection of cyclotron line and transition to accretion from the cold disk
In the work we present the results of two deep broadband observations of the poorly studied X-ray pulsar IGR J19294+1816 obtained with the NuSTAR observatory. The source was observed during Type I outburst and in the quiescent state. In the bright state a cyclotron absorption line in the energy spectrum was discovered at E-cyc = 42.8 +/- 0.7 keV. Spectral and timing analysis prove the ongoing accretion also during the quiescent state of the source. Based on the long-term flux evolution, particularly on the transition of the source to the bright quiescent state with luminosity around 10(35) erg s(-1), we conclude that IGR J19294+1816 switched to the accretion from the "cold" accretion disk between Type I outbursts. We also report the updated orbital period of the system
- …