# XMM-Newton observation of V1504 Cyg as a probe for the existence of an evaporated corona

**Authors:** A. Dobrotka, J. -U. Ness, A. A. Nucita, M. Melicherčík  
**arXiv:** [2304.11162](https://arxiv.org/abs/2304.11162)  
**Date:** 2023-04-12  
**Summary page:** https://www.summarizepaper.com/en/paper/2304.11162v1/

## Key points

- The article analyzes an XMM-Newton observation of the dwarf novae V1504 Cyg during its decline from an outburst.
- The aim is to search for evidence of an evaporated X-ray corona, which can be understood as an optically thin geometrically thick disc around a central part of an optically thick geometrically thin disc.
- Cooling flow model is used to analyze the evolution of the amplitude of variability and power density spectra in UV and X-rays to study the X-ray spectra.
- Results show that the X-ray (pn) count rate increases from initially around 0.03 cps to 0.17 cps with a harder spectrum and a higher degree of variability.
- OM/UVW1 light curve follows a slow decline with decreasing amplitude of variability.
- The authors split the X-ray data into two parts and analyzed them separately. Both parts are described by a cooling flow model, while the first low luminosity part requires an additional power law component suggesting presence of a wind.
- Timing analysis reveals a potential break frequency at log(f/Hz) = -3.02 during decline towards quiescence, which agrees with optical data from Kepler observations.
- The X-ray nature of this break frequency supports the innermost parts of the disc as source of variability.
- Similar frequencies were observed in several other cataclysmic variables, indicating that a sandwich model where a geometrically thick corona surrounds the geometrically thin disc is possible accretion configuration.
- This study provides new insights into understanding dwarf novae and their accretion processes through analyzing their X-ray spectra and variability patterns during outbursts and declines towards quiescence.

## Summary

This article presents an analysis of an XMM-Newton observation of the dwarf novae V1504 Cyg during its decline from an outburst. The aim of the study is to search for evidence of an evaporated X-ray corona, which can be understood as an optically thin geometrically thick disc around a central part of an optically thick geometrically thin disc. The authors use a cooling flow model and analyze the evolution of the amplitude of variability and power density spectra in UV and X-rays to study the X-ray spectra. The results show that the X-ray (pn) count rate increases from initially around 0.03 cps to 0.17 cps with a harder spectrum and a higher degree of variability. Meanwhile, the OM/UVW1 light curve follows a slow decline with decreasing amplitude of variability. To further investigate, the authors split the X-ray data into two parts and analyzed them separately. Both parts are described by a cooling flow model, while the first low luminosity part requires an additional power law component suggesting presence of a wind. Spectral fitting revealed a higher temperature during the second brighter part. Timing analysis reveals a potential break frequency at log(f/Hz) = -3.02 during decline towards quiescence, which agrees with optical data from Kepler observations. The X-ray nature of this break frequency supports the innermost parts of the disc as source of variability. Additionally, similar frequencies were observed in several other cataclysmic variables, indicating that a sandwich model where a geometrically thick corona surrounds the geometrically thin disc is possible accretion configuration. Overall, this study provides new insights into understanding dwarf novae and their accretion processes through analyzing their X-ray spectra and variability patterns during outbursts and declines towards quiescence.