11 research outputs found
Poissonian resetting of subdiffusion in a linear potential
Resetting a stochastic process is an important problem describing the
evolution of physical, biological and other systems which are continually
returned to their some fixed point different from their initial position. We
consider the motion of a subdiffusive particle with a constant drift under
Poissonian resetting. In this model the stochastic process is Brownian motion
subordinated by an inverse infinitely divisible process (subordinator).
Although this approach includes a wide class of subdiffusive system with
Poissonian resetting by using different subordinators, each of such systems has
a stationary state with the asymmetric Laplace distribution in which the scale
and asymmetric parameters depend on the Laplace exponent of used subordinators.
Moreover, the mean time for the particle to reach a target is finite and has a
minimum, optimal with respect to the resetting rate. Features of Levy motion
under this resetting and the influence of a linear potential are discussed.Comment: 14 pages, 5 figure
Free-free absorption parameters of Cassiopeia A from low-frequency interferometric observations
Context. Cassiopeia A is one of the most extensively studied supernova
remnants (SNRs) in our Galaxy. The analysis of its spectral features with the
help of low frequency observations plays an important role for understanding
the evolution of the radio source through the propagation of synchrotron
emission to observers through the SNR environment and the interstellar medium.
Aims. In this paper we present measurements of the integrated spectrum of Cas A
to characterize the properties of free-free absorption towards this SNR. We
also add new measurements to track its slowly evolving and decreasing
integrated flux density. Methods. We use the Giant Ukrainian radio telescope
(GURT) for measuring the continuum spectrum of Cassiopeia A within the
frequency range of 16-72 MHz. The radio flux density of Cassiopeia A relative
to the reference source of the radio galaxy Cygnus A has been measured on
May-October, 2019 with two subarrays of the GURT, used as a two-element
correlation interferometer. Results. We determine magnitudes of emission
measure, electron temperature and an average number of charges of the ions for
both internal and external absorbing ionized gas towards in Cassiopeia A.
Generally, their values are close to the ones suggested by Arias et al. (2018),
although for some there are slight differences. In the absence of clumping we
find the unshocked ejecta of M = 2.61 solar mass at the electron density of
15.3 cm^-3 has a gas temperature of T=100 K. If the clumping factor is 0.67,
then the unshocked ejecta of 0.96 solar mass the electron density of 18.7
cm^-3. Conclusions. The integrated flux density spectrum of Cassiopeia A
obtained with the GURT interferometric observations is consistent with the
theoretical model within measurement errors and also reasonably consistent with
other recent results in the literature.Comment: 9 pages, 9 figures, 2 table
Twist of fractional oscillations
Using the method of the Laplace transform, we consider fractional
oscillations. They are obtained by the time-clock randomization of ordinary
harmonic vibrations. In contrast to sine and cosine, the functions describing
the fractional oscillations exhibit a finite number of damped oscillations with
an algebraic decay. Their fractional differential equation is derived.Comment: 12 pages, 2 figure
Multi-antenna probing of absorbing regions inside and outside Cassiopeia A
International audienceContext. Cassiopeia A occupies an important place among supernova remnants (SNRs) in low-frequency radio astronomy. The analysis of its continuum spectrum from low frequency observations reveals the evolution of the SNR absorption properties over time and suggests a method for probing unshocked ejecta and the SNR interaction with the circumstellar medium (CSM). Aims. In this paper we present low-frequency measurements of the integrated spectrum of Cassiopeia A to find the typical values of free-free absorption parameters towards this SNR in the middle of 2023. We also add new results to track its slowly evolving and decreasing integrated flux density. Methods. We used the New Extension in Nançay Upgrading LOFAR (NenuFAR) and the Ukrainian Radio Interferometer of NASU (URAN-2, Poltava) for measuring the continuum spectrum of Cassiopeia A within the frequency range of 8-66 MHz. The radio flux density of Cassiopeia A has been obtained on June-July, 2023 with two sub-arrays for each radio telescope, used as a two-element correlation interferometer. Results. We measured magnitudes of emission measure, electron temperature and an average number of charges of the ions for both internal and external absorbing ionized gas towards Cassiopeia A from its integrated spectrum. Generally, their values are comparable to those presented by Stanislavsky et al. (2023), but their slight changes show the evolution of free-free absorption parameters in this SNR. Based on high accuracy of the measurements, we have detected the SNR-CSM interaction. Conclusions. The integrated flux-density spectrum of Cassiopeia A obtained with the NenuFAR and URAN-2 interferometric observations opens up new possibilities for continuous monitoring the ionized gas properties in and around Cassiopeia A to observe theevolution of unshocked ejecta and the SNR-CSM interaction in future studies
Multi-antenna probing of absorbing regions inside and outside Cassiopeia A
International audienceContext. Cassiopeia A occupies an important place among supernova remnants (SNRs) in low-frequency radio astronomy. The analysis of its continuum spectrum from low frequency observations reveals the evolution of the SNR absorption properties over time and suggests a method for probing unshocked ejecta and the SNR interaction with the circumstellar medium (CSM). Aims. In this paper we present low-frequency measurements of the integrated spectrum of Cassiopeia A to find the typical values of free-free absorption parameters towards this SNR in the middle of 2023. We also add new results to track its slowly evolving and decreasing integrated flux density. Methods. We used the New Extension in Nançay Upgrading LOFAR (NenuFAR) and the Ukrainian Radio Interferometer of NASU (URAN-2, Poltava) for measuring the continuum spectrum of Cassiopeia A within the frequency range of 8-66 MHz. The radio flux density of Cassiopeia A has been obtained on June-July, 2023 with two sub-arrays for each radio telescope, used as a two-element correlation interferometer. Results. We measured magnitudes of emission measure, electron temperature and an average number of charges of the ions for both internal and external absorbing ionized gas towards Cassiopeia A from its integrated spectrum. Generally, their values are comparable to those presented by Stanislavsky et al. (2023), but their slight changes show the evolution of free-free absorption parameters in this SNR. Based on high accuracy of the measurements, we have detected the SNR-CSM interaction. Conclusions. The integrated flux-density spectrum of Cassiopeia A obtained with the NenuFAR and URAN-2 interferometric observations opens up new possibilities for continuous monitoring the ionized gas properties in and around Cassiopeia A to observe theevolution of unshocked ejecta and the SNR-CSM interaction in future studies
Parker Solar Probe detects solar radio bursts related with a behindâtheâlimb active region
Context. The interpretation of solar radio bursts observed by Parker Solar Probe (PSP) in the encounter phase plays a key role in understanding intrinsic properties of the emission mechanism in the solar corona. Lower timeâfrequency resolution of the PSP receiver can be overcome by simultaneous groundâbased observations using more advanced antennas and receivers.
Aims. In this paper we present such observations for which the active active region 12 765, begetter of type III, J, and U solar bursts, was within sight of groundâbased instruments and behind the solar limb of the PSP spacecraft.
Methods. We used a subarray of the Giant Ukrainian Radio Telescope to get the spectral properties of radio bursts at the frequency range of 8â80 MHz, as well as the PSP radio instruments with a bandwidth of 10.5 kHzâ19.2 MHz, during solar observations on June 5, 2020.
Results. We directly detected the radio events initiated by the active region behind the solar limb of the PSP spacecraft, using special conditions in the solar corona, due to the absence of active regions from the PSP side. Following the generation mechanism of solar radio emission, we refined the density model for the solar corona above the active region 12765 responsible for the radio bursts. Based on the PSP spacecraft position near the Sun and delays of radio waves between spaceâ and groundâbased records, we found the corresponding radio responses on the PSP spectrogram.
Conclusions. The absence of sunspots from the PSP side contributes to the propagation of radio waves from a dense loop of the Sun to quiet regions with low densities, through which PSP instruments can detect the radiation