Long-term evolution of BH-ULX candidates: An `unusual' $L_{\rm disc}$-$T_{\rm col}$ correlation associated with spectral states
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2025
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| author | Majumder, Seshadri Das, Santabrata Nandi, Anuj |
| author_facet | Majumder, Seshadri Das, Santabrata Nandi, Anuj |
| contents | 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 ($F_{nth}>F_{disc}$, $Γ_{nth}\lesssim2$). However, NGC6946 X-1 and NGC55 ULX1 remain in a disc-dominated state ($F_{disc}\sim2F_{nth}$, $Γ_{nth}\gtrsim2$), while NGC5408 X-1 shows intermediate spectral characteristics. The spectral analyses indicate an anti-correlation between disc luminosity ($L_{disc}$) and temperature ($T_{col}$) for all sources except NGC5204 X-1. These anti-correlations follow a relation $L_{disc}\propto T_{col}^α$ with steeper exponents of $α=-6.01\pm0.25$ (NGC55 ULX1), $-8.93\pm0.11$ (NGC6946 X-1), and $-10.31\pm0.10$ (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 $α=-3.58\pm0.04$. However, for NGC5204 X-1, a positive correlation is found, yielding $α=1.4\pm0.1$, 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 $L_{disc}-T_{col}$ 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 ($\sim20$ mHz) with $rms\%\sim6.6$, Q-factor $\sim6.7$ and significant $2.8σ$ in NGC55 ULX1. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2504_09070 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Long-term evolution of BH-ULX candidates: An `unusual' $L_{\rm disc}$-$T_{\rm col}$ correlation associated with spectral states Majumder, Seshadri Das, Santabrata Nandi, Anuj High Energy Astrophysical Phenomena Astrophysics of Galaxies Instrumentation and Methods for Astrophysics 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 ($F_{nth}>F_{disc}$, $Γ_{nth}\lesssim2$). However, NGC6946 X-1 and NGC55 ULX1 remain in a disc-dominated state ($F_{disc}\sim2F_{nth}$, $Γ_{nth}\gtrsim2$), while NGC5408 X-1 shows intermediate spectral characteristics. The spectral analyses indicate an anti-correlation between disc luminosity ($L_{disc}$) and temperature ($T_{col}$) for all sources except NGC5204 X-1. These anti-correlations follow a relation $L_{disc}\propto T_{col}^α$ with steeper exponents of $α=-6.01\pm0.25$ (NGC55 ULX1), $-8.93\pm0.11$ (NGC6946 X-1), and $-10.31\pm0.10$ (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 $α=-3.58\pm0.04$. However, for NGC5204 X-1, a positive correlation is found, yielding $α=1.4\pm0.1$, 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 $L_{disc}-T_{col}$ 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 ($\sim20$ mHz) with $rms\%\sim6.6$, Q-factor $\sim6.7$ and significant $2.8σ$ in NGC55 ULX1. |
| title | Long-term evolution of BH-ULX candidates: An `unusual' $L_{\rm disc}$-$T_{\rm col}$ correlation associated with spectral states |
| topic | High Energy Astrophysical Phenomena Astrophysics of Galaxies Instrumentation and Methods for Astrophysics |
| url | https://arxiv.org/abs/2504.09070 |