arXiv subjects

Priyesh Kumar Tripathi

Publications and source records attributed to Priyesh Kumar Tripathi.

8 recordsLinked to original sources

arXiv2026

Effect of Multi-Species Plasma on Fanaroff-Riley Radio Jets

The Fanaroff-Riley (FR) dichotomy observed in extragalactic radio jets has been attributed to a range of possible mechanisms, including intrinsic jet properties such as the presence of different species in the plasma. Jet material may span from a pure electron-positron pair plasma to mixed plasmas containing electrons, positrons, and protons, or even to hadronic jets made up of electrons and protons only. To investigate this aspect, we present results from three-dimensional simulations of low-power, supersonic, magnetized jets at kiloparsec scales in a magnetohydrodynamic framework. By varying the plasma composition, we show its impact on jet stability and on the development of diffuse structures typical of core-brightened FR type I sources. Our results indicate that the growth of non-axisymmetric instabilities plays a key role in disrupting the jet head.

astro-ph.HE↗

arXiv2026

Outflow Behavior from the Transonic Advective Disks: A Hydrodynamical Simulation Study

We investigate the properties of outflows from the transonic advective accretion disk using hydrodynamical numerical simulations. We consider two different disk temperatures with an order-of-magnitude difference. For the hotter disk, we adopt initial conditions for velocity, specific angular momentum, and temperature from analytical solutions. In the colder disk case, the velocity and angular momentum profiles are kept identical, while an order of magnitude reduction in the temperature. The simulations are performed in the presence of viscosity and radiative cooling, considering bremsstrahlung and synchrotron processes. In both disk models, the outflow rate increases with viscosity. We also examine the poloidal velocity structures for both cases. We analyze the influence of viscosity on the mass flux-weighted energy and momentum fluxes of the outflows. Our results show that both energy and momentum fluxes increase with higher viscosity and may play a significant role in accretion feedback mechanisms.

astro-ph.HE↗

arXiv2026

QPOs from the Viscous Transonic Accretion Flow Around a Spinning Black Hole

We investigate the dynamics of transonic advective accretion flows around spinning black holes in the presence of viscosity. The spacetime of a Kerr black hole is approximated using a pseudo-potential. We study viscously driven shock oscillations over a range of black hole spin parameters. Our results show that the frequency range of quasi-periodic oscillations (QPOs) obtained from the power density spectra depends strongly on the black hole spin. Low-spin systems predominantly exhibit low-frequency QPOs, whereas rapidly rotating black holes (greater than 0.9 Kerr parameter) produce QPOs spanning a broad range from low to high frequencies, comparable to those observed in black hole X-ray binaries. We further obtain a correlation between the QPO frequency and the power-law photon index by computing the spectrum for a 10 solar mass black hole.

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arXiv2026

How Plasma Properties of the Fanaroff-Riley Jet can Shape its Morphology

Extragalactic jets are broadly classified into two categories based on radio observations: core-brightened jets, known as Fanaroff-Riley Type I (FR I), and edge-brightened jets, classified as Type II (FR II). This FR dichotomy may arise due to variation in the ambient medium and/or the properties of the jet itself, such as injection speed, temperature, composition, magnetization, etc. To investigate this, we perform large-scale three-dimensional magnetohydrodynamic (3D-MHD) simulations of low-power, supersonic jets extending to kiloparsec scales. We inject a jet beam carrying an initially toroidal magnetic field into a denser, unmagnetized, and stratified ambient medium through a cylindrical nozzle. Our simulations explore jets with varying injection parameters to investigate their impact on morphology and emission properties. Furthermore, we examine jets with significantly different plasma compositions, such as hadronic and mixed electron-positron-proton configurations, to study the conditions that may drive transitions between FR I and FR II morphologies. We find that, under the same injection parameters, mixed plasma composition jets tend to evolve into FR I structures. In contrast, electron-proton jets exhibit a transition between FR I and FR II morphologies at different stages of their evolution.

astro-ph.HE↗

arXiv2025

Dynamical properties of oscillating, viscous, transonic accretion disks around black holes

We investigate the time evolution of sub-Keplerian transonic accretion flow onto a non-rotating black hole using axisymmetric viscous hydrodynamic simulations. We simulate the accretion flow using boundary values from semi-analytical analysis and set up three different models. Two of the models do not predict accretion shocks from the semi-analytic analysis, while one of them does. We also consider radiative cooling along with viscosity in the simulation. Our two-dimensional simulation deviated from the one-dimensional semi-analytical solution and admitted shocks in all three models. Viscous dissipation tends to push the shock front outward, and radiative cooling will push it in. Additionally, gravity is attractive. Depending on the competing strengths of all three processes, it may trigger shock oscillation. Different rates of angular-momentum transport in various layers may trigger eddies, which will enhance the shock oscillation. We show that any simple power law cannot approximate these solutions. We find that hot and higher angular-momentum flow requires higher viscosity to produce oscillatory shocks. From the temporal variation of the luminosity, shock oscillations generate QPOs in the range of sub-Hertz to a few Hertz frequencies if a ten solar mass black hole is assumed.

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arXiv2024

On Disk Formation around Isolated Black Holes via Stream Accretion

We investigate accretion onto an isolated black hole from uniform winds. If the winds are directed towards the black hole, then the accretion process can be well described by the classical Bondi-Hoyle Lyttleton or BHL accretion. If the wind is not directed towards the black hole and flows past it, then a smaller fraction of the flow can be attracted by the black hole, and this type of accretion cannot be described by the classical BHL, and we coin the second kind as the lateral BHL. We show that the classical BHL cannot form an accretion disk, while lateral BHL can form transient accretion disks. To describe the thermodynamics of the flow, we have used a variable adiabatic index equation of state which depends on the temperature of the flow as well as the composition of the gas. We show that the electron-proton gas forms an accretion disk, which disappears and forms a shock cone, only to form the disk again at a later time, while for flows with less protons, the accretion disk, once lost, does not reappear again. Only when the flow is pair-dominated does it form a persistent accretion disk. We also show that a shock cone is less luminous than the accretion disk.

astro-ph.HE↗

arXiv2024

Radiative acceleration of relativistic jets from accretion discs around black holes

Matter falling onto black holes, {also called} accretion discs, emit intense high-energy radiation. Accretion discs during {hard to hard intermediate} spectral states also emit bipolar outflows. Radiation drag was supposed to impose the upper limit on the terminal speed. It was later shown that a radiation field around an advective accretion disc imposes no upper limit on speed, about a few hundred of Schwarzschild radius from the disc surface. We {study radiatively driven electron-proton and electron-positron jets, for gemeotrically thick and slim transonic discs} by using numerical simulation. We show that pair-dominated jets can reach ultra-relativistic speeds by radiation driving. We also discuss at what limits radiative acceleration may fail.

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arXiv2024

Numerical Simulation of Radiatively driven Transonic Relativistic Jets

We perform the numerical simulations of axisymmetric, relativistic, optically thin jets under the influence of the radiation field of an accretion disk. We show that starting from a very low injection velocity at the base, jets can be accelerated to relativistic terminal speeds when traveling through the radiation field. The jet gains momentum through the interaction with the radiation field. We use a relativistic equation of state for multi-species plasma, which self-consistently calculates the adiabatic index for the jet material. All the jet solutions obtained are transonic in nature. In addition to the acceleration of the jet to relativistic speeds, our results show that the radiation field also acts as a collimating agent. The jets remain well collimated under the effect of radiation pressure. We also show that if the jet starts with a rotational velocity, the radiation field will reduce the angular momentum of the jet beam.

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