Geometry of the comptonization region of MAXI J1348$-$630 through type-C quasi-periodic oscillations with NICER

TL;DR

This study models the corona regions in MAXI J1348$-$630 using QPO data, revealing two interacting coronae with specific sizes and behaviors during different outburst states, advancing understanding of accretion physics.

Contribution

It introduces a detailed physical model of two interacting coronae during different states of the outburst, supported by simultaneous spectral and timing analysis.

Findings

Two coronae of different sizes are identified and modeled.

The coronae's properties are consistent across outburst and reflare phases.

Changes in phase-lag and coherence are explained by corona geometry.

Abstract

We use the rms and lag spectra of the type-C quasi-periodic oscillation (QPO) to study the properties of the Comptonisation region (aka corona) during the low/hard and hard-intermediate states of the main outburst and reflare of MAXI J1348$-$630. We simultaneously fit the time-averaged energy spectrum of the source and the fractional rms and phase-lag spectra of the QPO with the time-dependent Comptonization model vKompth. The data can be explained by two physically connected coronae interacting with the accretion disc via a feedback loop of X-ray photons. The best-fitting model consists of a corona of $\sim$10$^3$ km located at the inner edge of the disc and a second corona of $\sim$10$^4$ km horizontally extended and covering the inner parts of the accretion disc. The properties of both coronae during the reflare are similar to those during the low/hard state of the main outburst, reinforcing the idea that both the outburst and the reflare are driven by the same physical mechanisms. We combine our results for the type-C QPO with those from previous work focused on the study of type-A and type-B QPOs with the same model to study the evolution of the geometry of the corona through the whole outburst, including the reflare of MAXI J1348$-$630. Finally, we show that the sudden increase in the phase-lag frequency spectrum and the sharp drop in the coherence function previously observed in MAXI J1348$-$630 are due to the type-C QPO during the decay of the outburst and can be explained in terms of the geometry of the coronae.