2025/04/12 by Seshadri Majumder, Majumder, Seshadri, Santabrata Das +3
Chemistry · Medicine · Physics and Astronomy · #Astrophysics of Galaxies (astro-ph.GA) #Cardiovascular Syncope and Autonomic Disorders #FOS: Physical sciences #High Energy Astrophysical Phenomena (astro-ph.HE) #Instrumentation and Methods for Astrophysics (astro-ph.IM) #Molecular spectroscopy and chirality #Stellar, planetary, and galactic studies
paper · pdf · doi:10.48550/arxiv.2504.09070
openalex publication_date 2025/04/12 · openalex created_date 2025/10/14 · openalex updated_date 2026/07/28
We present the long-term spectral evolution of eight black hole ultra-luminous X-ray sources (BH-ULXs), namely NGC1313 X-1, NGC5408 X-1, NGC6946 X-1, IC342 X-1, NGC55 ULX1, NGC4395 ULX1, NGC5204 X-1 and NGC4190 ULX1 using \it XMM-Newton monitoring data spanning over a decade or more. An in-depth spectral modeling with thermal Comptonization (\it nthComp) and standard disc (\it diskbb) components reveals NGC5204 X-1, IC342 X-1, NGC4190 ULX1 and NGC1313 X-1 exhibiting harder spectral characteristics with dominant effect of Comptonization (Fnth>Fdisc, Γnth\lesssim2). However, NGC6946 X-1 and NGC55 ULX1 remain in a disc-dominated state (Fdisc∼2Fnth, Γnth\gtrsim2), while NGC5408 X-1 shows intermediate spectral characteristics. The spectral analyses indicate an anti-correlation between disc luminosity (Ldisc) and temperature (Tcol) for all sources except NGC5204 X-1. These anti-correlations follow a relation Ldisc∝ Tcolα with steeper exponents of α=-6.01±0.25 (NGC55 ULX1), -8.93±0.11 (NGC6946 X-1), and -10.31±0.10 (NGC5408 X-1) for sources with softer or intermediate spectral characteristics. For harder sources, NGC1313 X-1 and IC342 X-1, the combined results provide α=-3.58±0.04. However, for NGC5204 X-1, a positive correlation is found, yielding α=1.4±0.1, suggesting that the emission mechanism is associated with the transition from the `standard disc' to the `slim disc' scenario. These findings suggest that the observed Ldisc-Tcol correlations, along with the overall spectro-temporal properties of BH-ULXs, seems to be governed by disc-corona-wind driven accretion processes at various inclinations. Finally, we report a QPO-like feature (∼20 mHz) with rms%∼6.6, Q-factor ∼6.7 and significant 2.8σ in NGC55 ULX1.