arXiv subjects

V. L. Plokhotnichenko

Publications and source records attributed to V. L. Plokhotnichenko.

5 recordsLinked to original sources

arXiv2026

There and back again: Mysterious optical pulse profile behavior of the transitional millisecond pulsar PSR J1023+0038

Neutron stars in close binary systems have the potential to spin up to millisecond periods due to the accretion of matter and angular momentum from their low-mass companions. In later stages of this process, they sometimes start to swing between the accretion-powered and rotation-powered regimes, manifesting themselves as low-mass X-ray binaries and millisecond radio pulsars, respectively. Such systems are known as transitional millisecond pulsars. PSR J1023+0038 was the first one of this kind to be discovered and the first to show optical pulsations at the rotation frequency of the neutron star during a peculiar low accretion state. The optical pulse profile is characterized by a smooth double-peaked shape resembling thermal light curves of X-ray pulsars, but more likely emerging from re-emission of the pulsar wind energy by charged particles in the surrounding medium. Although the amplitudes of the peaks show strong variability, the overall structure of the pulse profile was observed to be fixed, with the optical pulsed fraction less than 1 percent. Here, we report time-resolved observation of a dramatic violation of this permanence during our high temporal resolution observations of PSR J1023+0038 with the 6-m BTA telescope of the Special Astrophysical Observatory. On a timescale of a few seconds the pulse profile took a single-peaked, nearly sinusoidal shape, with synchronous magnification of the pulsed fraction up to about 5 percent. After spending about 220 seconds in this new regime, accompanied by flaring activity, the system returned to its normal state. We discuss a number of possible explanations of this peculiar behavior in the context of the physics and geometry of interactions between the pulsar wind and surrounding matter. However, a complete picture is yet to be revealed.

astro-ph.HE↗

arXiv2024

SRGe J194401.8+284452 -- an X-ray Cataclysmic Variable in the Field of the Gamma-Ray Source 4FGL J1943.9+2841

SRGe J194401.8+284452 is the brightest point-like X-ray object within the position uncertainty ellipse of an unidentified $γ$-ray source 4FGL J1943.9+2841. We performed multi-wavelength spectral and photometric studies to determine its nature and possible association with the $γ$-ray source. We firmly established its optical counterpart with the Gaia based distance of about 415 pc. Our data show that the object is a cataclysmic variable with an orbital period of about 1.5 hours. SRGe J194401.8+284452 exhibits fast spontaneous transitions between the high and low luminosity states simultaneously in the optical and X-rays, remaining relatively stable between the transitions on scales of several months/years. This can be caused by an order of magnitude changes in the accretion rate. The brightness of the source is about 17 mag and 20 mag in the optical range and $5\times 10^{-12}$ and $5\times 10^{-13}$ erg/cm$^2$/s in the $0.3- 10$ keV range in the high and low states, respectively. We constrained the mass of the white dwarf ($0.3 - 0.9$ $M_\odot$) and its temperature in the low state (14750 $\pm$ 1250 K), the mass of the donor star ($\leq$ 0.08 $\pm$ 0.01 $M_ \odot$). In the low state, we detected regular optical pulsations with an amplitude of 0.2 mag and a period of 8 min. They are likely associated with the spin of the white dwarf, rather than with its non-radial pulsations. In the high state, the object demonstrates only stochastic optical brightness variations on time scales of $1 - 15$~minutes with amplitudes of $0.2 - 0.6$~mag. We conclude, that SRGe J194401.8+284452 can be classified as an intermediate polar, and its association with the $γ$-ray source is very unlikely.

astro-ph.HE↗

arXiv2000

High Speed Phase-Resolved 2-d UBV Photometry of the Crab pulsar

We report a phase-resolved photometric and morphological analysis of UBV data of the Crab pulsar obtained with the 2-d TRIFFID high speed optical photometer mounted on the Russian 6m telescope. By being able to accurately isolate the pulsar from the nebular background at an unprecedented temporal resolution (1 μs), the various light curve components were accurately fluxed via phase-resolved photometry. Within the $UBV$ range, our datasets are consistent with the existing trends reported elsewhere in the literature. In terms of flux and phase duration, both the peak Full Width Half Maxima and Half Width Half Maxima decrease as a function of photon energy. This is similarly the case for the flux associated with the bridge of emission. Power-law fits to the various light curve components are as follows; α= 0.07 \pm 0.19 (peak 1), α= -0.06 \pm 0.19 (peak 2) and α= -0.44 \pm 0.19 (bridge) - the uncertainty here being dominated by the integrated CCD photometry used to independently reference the TRIFFID data. Temporally, the main peaks are coincident to \le 10 μs although an accurate phase lag with respect to the radio main peak is compromised by radio timing uncertainties. The plateau on the Crab's main peak was definitively determined to be \leq 55 μs in extent and may decrease as a function of photon energy. There is no evidence for non-stochastic activity over the light curves or within various phase regions, nor is there evidence of anything akin to the giant pulses noted in the radio. Finally, there is no evidence to support the existence of a reported 60 second modulation suggested to be as a consequence of free precession.

astro-ph↗

arXiv1998

A Search for the Optical Counterpart of PSR B1951+32 in the Supernova Remnant CTB 80

Using time-resolved two-dimensional aperture photometry we have put upper limits on the pulsed emission from two proposed optical counterparts for PSR B1951+32. Our pulsed upper limits of m_{vpulsed}>23.3, m_{bpulsed}>24.4$, for the first candidate and m_{vpulsed}>23.6$, m_{bpulsed}>24.3 for the second, make it unlikely that either of these is, in fact, the pulsar. We discuss three further candidates, but also reject these on the basis of timing results. A search of a 5.5arcs x 5.5arcs area centred close to these stars failed to find any significant pulsations at the reported pulsar period.

astro-ph↗

arXiv1998

Pulsed optical emission from Geminga

We present optical data which shows that G", the optical counterpart of the gamma-ray pulsar Geminga, pulses in B with a period of 0.237 seconds. The similarity between the optical pulse shape and the gamma-ray light curve indicates that a large fraction of the optical emission is non-thermal in origin - contrary to recent suggestions based upon the total optical flux. The derived magnitude of the pulsed emission is m_B = 26.0 +/- 0.4. Whilst it is not possible to give an accurate figure for the pulsed fraction (due to variations in the sky background) we can give an upper limit of m_B ~ 27 for the unpulsed fraction.

astro-ph↗