Title:	Hard X-Ray Flares and Spectral Variability in NGC 4395 ULX1
Authors:	Ghosh, Tanuman Rana, Vikram Bachetti, Matteo
Keywords:	Ultraluminous x-ray sources X-ray binary stars Astrophysics - High Energy Astrophysical Phenomena
Issue Date:	10-Oct-2022
Publisher:	IOP Publishing Ltd for the American Astrophysical Society
Citation:	The Astrophysical Journal, 2022, Vol. 98, p76
Abstract:	We report the detection of flaring events in NGC 4395 ULX1, a nearby ultraluminous X-ray source (ULX), for the first time, using recent XMM-Newton observations. The flaring episodes are spectrally harder than the steady-emission intervals, resulting in higher fractional variability in the high-energy regime. A thin Keplerian and a slim accretion disk provide the best-fit continuum for XMM-Newton spectra. All observations show a broad hump-like feature around ∼0.9 keV, which can be associated with a collection of blended emission lines, and suggests the presence of a wind or outflow in this ULX through comparison with other ULXs that show a similar feature. The flaring spectra correspond to higher slim-disk temperatures due to a higher mass accretion rate under an advection-dominated accretion scenario. The luminosity–temperature (L-T) values in different flux states show a positive trend. When characterized with a power-law relation, the L-T profile is broadly consistent with both L ∝ T2 and L ∝ T4 relations for the analyzed data. The empirical predictions for a slim accretion disk in the case of super-Eddington accretion onto a stellar-mass compact object is L ∝ T2, which is a possible scenario in ULX1. The origin of the flaring events is understood as an intrinsic change in accretion rate or presence of variable clumpy wind in the inner region of the accretion disk.
Description:	Open Access
URI:	http://hdl.handle.net/2289/8006
ISSN:	0004-637X 1538-4357 (Online)
Alternative Location:	https://ui.adsabs.harvard.edu/abs/2022ApJ...938...76G/abstract https://arxiv.org/abs/2202.01432 https://doi.org/10.3847/1538-4357/ac8f8f
Copyright:	2022 The Author(s)
Appears in Collections:	Research Papers (A&A)

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