Conveners
Spectral and temporal properties of accretion flows and jets around compact objects and the theoretical models: Thursday block 1
- Banibrata Mukhopadhyay (Indian Institute of Science)
Spectral and temporal properties of accretion flows and jets around compact objects and the theoretical models: Thursday block 2
- Banibrata Mukhopadhyay (Indian Institute of Science)
Spectral and temporal properties of accretion flows and jets around compact objects and the theoretical models: Friday block 1
- Banibrata Mukhopadhyay (Indian Institute of Science)
Spectral and temporal properties of accretion flows and jets around compact objects and the theoretical models: Friday block 2
- Banibrata Mukhopadhyay (Indian Institute of Science)
Description
This session brings together all the scientists who are interested in relativistic astrophysics around galactic, extra-galactic and intermediate mass black holes, as well other compact objects. We welcome papers on the following topics and other from related topics:
1. Theory of accretion disks, outflows and jets and underlying magneto-hydrodynamic (MHD)
2. Emission processes from the disks and jets, including that of gravitational waves
3. Polarization properties of radiations from disks and jets
4. Fitting of satellite data by theoretical models
5. Evidences for disk-jet connections
6. General relativistic MHD (GRMHD), or otherwise as appropriate, simulations of flows in curved spacetime (e.g. black hole) geometry.
I will first plan to review the accretion phenomenology and underlying
models, mostly for a black hole. I will attempt to touch upon, how over the decades with the evolution of observations with newer data, newer models are proposed to explain them: standard Shakura-Sunyaev Keplerian disk, advective sub-Keplerian disk, magnetically arrested (advective) disk, etc. Finally, I will aim to...
Multifrequency polarimetry is emerging as a powerful probe of blazar jets, especially due to the advent of the Imaging X-ray Polarimetry Explorer (IXPE) space observatory.
We study the polarization of High-Synchrotron Peaked (HSP) blazars, where both optical and X-ray emission can be attributed to synchrotron radiation from a population of non-thermal electrons. We adopt an axisymmetric...
The Blandford-Znajek (BZ) mechanism is an electromagnetic manifestation of the Penrose process that currently constitutes the best theoretical candidate to explain the launching of relativistic jets by black holes.
In this talk we offer a modern review about the BZ mechanism and the analytic construction of black hole magnetospheres. Higher order perturbative corrections are crucial in order...
General Relativity has been extensively tested within the weak-field regime across various experiments. Recent years have seen significant progress in exploring the strong-field domain, now made possible through gravitational waves, X-ray data, and radio images of supermassive black holes like SgrA and M87. In this talk, I will discuss recent efforts to test General Relativity using black...
Using a set of general-relativistic magnetohydrodynamics simulations that include proper neutrino transfer, we assess for the first time the role played by the fallback accretion onto the remnant from a binary neutron-star merger over a timescale of hundreds of seconds. In particular, we find that, independently of the equation of state, the properties of the binary, and the fate of the...
We develop a model formalism to study the structure of a relativistic, viscous, optically thin, advective accretion flow around a rotating black hole in presence of radiative coolings. We use this model to examine the physical parameters of four black hole Ultra-luminous X-ray sources (BH-ULXs), namely mass ($M_{\rm BH}$), spin ($a_{\rm k}$) and accretion rate (${\dot m}$), respectively. While...
Low angular momentum flows around black holes are likely to form standing shocks during the accretion processes. The shocks possibly encounter instabilities leading to various observational signatures associated with inflows and outflows. In our work, we address a range of issues like flaring in under-luminous Sgr A* with supermassive black hole and outflow properties in super-accretors like...
In this talk, I will describe the results of the most extensive multiwavelength observational campaign ever carried out on the prototype of the class of transitional millisecond pulsars, PSR J1023+0038. The campaign aimed to find an explanation once and for all for the peculiar variability pattern shown by the source during its current active X-ray state. The results of the data analysis...
Ultraluminous X-ray sources (ULXs) have captivated researchers for decades due to their exceptionally high luminosities and unique spectral characteristics. Some of these sources defy expectations by exhibiting super-Eddington luminosities with respect to stellar mass sources even in their low-hard state. Numerical steady-state calculations suggest that ULXs in this state can be explained as...
An optically thin advective accretion disk appears to be indispensable in explaining the hard spectral state of black hole sources. We explore, with the help of general relativistic magnetohydrodynamic (GRMHD) simulations, how a large scale stronger magnetic field helps in transporting angular momentum in disk and outflow/jet, depending on the field geometry and plasma-β parameter, basically...
GRB jets are launched from rapidly spinning black holes (BHs), anchored by a strong magnetic field, a process known as the Blandford–Znajek (BZ) mechanism. However, most BHs from core collapse are likely born slowly spinning, raising the question of what type of transients emerge in those cases. With the upcoming launch of LSST, it is imperative to map the wide spectrum of transients from...
A thin circular structure vibrating in the central plane of a black hole will be investigated. This circular ring (string loop) can be considered a simplified model for thin magnetic flux tubes (in plasma physics), and connections to accreting fluid structures around the black hole will be demonstrated. The stability of the string loop and the frequencies of its vibrational modes will be...
The electromagnetic field of a particle moving in the vicinity of a Schwarzschild black hole is calculated. The energy emitted by the particle is calculated using the multipole expansion approach. The particle is considered as it approaches the event horizon of the black hole. The electromagnetic field of this particle is calculated in the limit of the event horizon approach. It is shown that...
In this work, we investigate the global structure of shock-induced general relativistic magneto-hydrodynamic (GRMHD) accretion flows around a Kerr black hole, where the disk is threaded by the radial ($b^r$) and the toroidal ($b^\phi$) magnetic fields. In doing so, we consider an advective, axisymmetric, and optically thin accretion flow that is confined in the disk mid-plane. In addition, we...
The Einstein–Maxwell and the electrodynamical equations are written for a (d+1)-dimensional FRW-like spacetime in the presence of plasma with the help of a wellknown (3 + 1) decomposition formalism given by Thorne and Macdonald. Actually this work is the generalisation of earlier one by Holcomb and Tajima[2].
We have studied the propagation of an electromagnetic wave in cold plasma in...
Using a set of general-relativistic magnetohydrodynamics simulations that include proper neutrino transfer, we assess for the first time the role played by the fallback accretion onto the remnant from a binary neutron-star merger over a timescale of hundreds of seconds. In particular, we find that, independently of the equation of state, the properties of the binary, and the fate of the...
As the last student of Prof. Malheiro I would like to talk about him and present my work which he was involved in his last year of his life:
The study of Active Galactic Nuclei (AGN) has garnered significant attention due to their structures and dynamic behaviors. Understanding AGN feedback mechanisms and their impact on host galaxies is of paramount importance. In this context, the TWIST...
Understanding the intricate network of nonlinear interactions crucial for the development and sustenance of turbulence induced by magnetorotational instability (MRI) has proven challenging. A large-scale dynamo, generating dominant azimuthal magnetic fields, emerges as a pivotal component of this turbulence. Direct numerical simulations of MRI dynamo have revealed statistical self-organization...
We present the results of a comprehensive spectro-polarimetric analysis of nine black hole X-ray binaries namely Cyg X$-1$, 4U 1630$-47$, 4U 1957$+115$, Cyg X$-3$, LMC X$-1$, LMC X$-3$, Swift J1727.8$-1613$, Swift J151857.0$-572147$ and GX 339$-4$ using quasi-simultaneous IXPE, NICER and NuSTAR observations. Polarimetric measurements with IXPE confirm the detection of a significant degree of...
We develop a framework to study the properties of mass outflows from a relativistic, viscous, magnetized, advective accretion flow around a rotating black hole (BH). While doing so, we assume that the disk is mainly threaded by the toroidal component of magnetic field and consider synchrotron radiation as the main cooling mechanism within the accretion disk. With this, we self consistently...
The aim of our work is to study the origin of the spectral transitions of transient black hole binaries. In this work, we find signatures of spectral state transition (hard to soft state) while studying the radiative shock forthe accretion flow. The gradient of the energy dissipation curve shows a sudden break for certain critical flow parameters when the post-shock dissipation is maximum....
We investigate the properties of relativistic accretion flow in a Kerr-Taub-NUT (KTN) spacetime in presence or absence of shock waves. This spacetime, characterized by the spin parameter or Kerr parameter ($a_{\rm k}$) and the gravitomagnetic charge or NUT parameter ($n$), can represent either a black hole or a naked singularity depending on the suitable choice of their values. By solving the...
The fast variability properties of Galactic black holes binaries can be satisfactorily explained by considering multiple physical mechanisms, such as Comptonization, reflection, variation in accretion geometry, focusing due to gravitational bending, and the effect of disk-jet connections. The nature of variability i.e., soft/hard time lag in Black Hole Transients, is complex due to the...
