arXiv subjects

Deepika A. Bollimpalli

Publications and source records attributed to Deepika A. Bollimpalli.

4 recordsLinked to original sources

arXiv2026

The nature of tilted supercritical accretion discs

In this paper, we report on the first 3D general relativistic radiation magnetohydrodynamic simulations of large supercritical accretion discs that are tilted with respect to the black hole spin axis. We explore a range of black hole spin parameters (from $a_* = -0.9$ to 0.9), initial tilts (in the range from $β_0 = 0^\circ$ to $30^\circ$), and target mass accretion rates. We first confirm that, for all the untilted simulations, the Eddington accretion limit is obeyed ($\dot{M}_\mathrm{BH} \lesssim \dot{M}_\mathrm{Edd}$), consistent with our previous findings. However, for tilted discs we find that the mass accretion rate can be enhanced by up to a factor of ten and that factor depends linearly on tilt $\dot{M}_\mathrm{BH} \propto β_0 \ge \dot{M}_\mathrm{Edd}$. This could be an important aspect in solving the puzzle of the growth of the first supermassive black holes. We also find that for a given tilt, the mass accretion rate enhancement is proportional to the magnitude of the spin. Additionally, we find that tilted supercritical accretion discs are more advective than their untilted counterparts. We attribute all of these differences to the presence of standing shocks in the inner regions of the accretion flow, a feature unique to tilted discs.

astro-ph.HE↗

arXiv2025

Polarization Signatures of Quasi-Periodic Oscillations in Simulated Tilted, Truncated Disks

We utilize the Monte Carlo radiation transport code, Pandurata, to create images, spectra, polarization maps, and light curves from a set of general relativistic magnetohydrodynamic simulations of tilted, truncated, black hole accretion disks. Truncation can have spectral and polarization signatures all its own; tilt introduces both inclination and azimuthal dependencies into the spectra and polarization; and precession and oscillations of the tilted accretion flow inside the truncation radius introduce time dependencies or periodicity to all of this. We use the ray-traced results from our simulations to evaluate the feasibility of measuring these effects, particularly in the context of current and future X-ray polarization observatories. Such detections could greatly improve our understanding of the geometry of accretion disks and coronae in the hard state, the physics of quasi-periodic oscillations (QPOs), and how system properties evolve as sources approach the hard-to-soft state transition.

astro-ph.HE↗

arXiv2025

Long timescale numerical simulations of large, super-critical accretion discs

In this paper, we report on three of the largest (in terms of simulation domain size) and longest (in terms of duration) 3D general relativistic radiation magnetohydrodynamic simulations of super-critical accretion onto black holes. The simulations are all set for a rapidly rotating ($a_* = 0.9$), stellar-mass ($M_\mathrm{BH} = 6.62 M_\odot$) black hole. The simulations vary in their initial target mass accretion rates (assumed measured at large radius), with values sampled in the range $\dot{m}=\dot{M}/\dot{M}_\mathrm{Edd} = 1-10$. We find in practice, though, that all of our simulations settle close to a net accretion rate of $\dot{m}_\mathrm{net} = \dot{m}_\mathrm{in}-\dot{m}_\mathrm{out} \approx 1$ (over the radii where our simulations have reached equilibrium), even though the inward mass flux (measured at large radii) $\dot{m}_\mathrm{in}$ can exceed 1,000 in some cases. This is possible because the outflowing mass flux $\dot{m}_\mathrm{out}$ adjusts itself to very nearly cancel out $\dot{m}_\mathrm{in}$, so that at all radii $\dot{M}_\mathrm{net} \approx \dot{M}_\mathrm{Edd}$. In other words, these simulated discs obey the Eddington limit. We compare our results with the predictions of the slim disc (advection-dominated) and critical disc (wind/outflow-dominated) models, finding that they agree quite well with the critical disc model both qualitatively and quantitatively. We also speculate as to why our results appear to contradict most previous numerical studies of super-critical accretion.

astro-ph.HE↗

arXiv2020

Asymmetric Jet launching

In resistive and viscous magnetohydrodynamical (MHD) simulations we obtain axial jets launched from the innermost magnetosphere of a star-disk system. We found that in a part of the parameter space continuous asymmetric jets, which are propagating in opposite directions, are launched. We compare the speed of propagation and rotation of obtained jets with recent observational results.

astro-ph.HE↗