<p>In this paper, we report the detailed spectral and temporal properties of six non-nuclear X-ray point sources, namely X-1, X-2, X-3, X-4, X-5, and X-6, located in the Seyfert 2 galaxy, NGC 4602, utilising the archival XMM-Newton data. Spectral fitting was performed using two empirical models: an absorbed power-law model and an absorbed disk blackbody model. Based on the estimated bolometric luminosity, all six sources fall in the ultraluminous X-ray sources range, with three out of the six sources (X-1, X-3, and X-6) reaching the extreme-luminosity X-ray luminosity range, exceeding <InlineEquation ID="IEq1"> <EquationSource Format="TEX">$10^{40}$</EquationSource> <EquationSource Format="MATHML"><math> <msup> <mn>10</mn> <mn>40</mn> </msup> </math></EquationSource> </InlineEquation> erg s<InlineEquation ID="IEq2"> <EquationSource Format="TEX">$^{-1}$</EquationSource> <EquationSource Format="MATHML"><math> <mmultiscripts> <mrow /> <mrow /> <mrow> <mo>-</mo> <mn>1</mn> </mrow> </mmultiscripts> </math></EquationSource> </InlineEquation>, even in their lower limits. Detailed spectral analysis reveals distinct states among the sources. The sources, X-1, X-2, and X-4 exhibit hard spectral state with the powerlaw photon indices <InlineEquation ID="IEq3"> <EquationSource Format="TEX">$\Gamma $</EquationSource> <EquationSource Format="MATHML"><math> <mi mathvariant="normal">Γ</mi> </math></EquationSource> </InlineEquation> ranging from <InlineEquation ID="IEq4"> <EquationSource Format="TEX">$\sim $</EquationSource> <EquationSource Format="MATHML"><math> <mo>∼</mo> </math></EquationSource> </InlineEquation>1.69 to <InlineEquation ID="IEq5"> <EquationSource Format="TEX">$\sim $</EquationSource> <EquationSource Format="MATHML"><math> <mo>∼</mo> </math></EquationSource> </InlineEquation>1.79 and inner disk temperatures <InlineEquation ID="IEq6"> <EquationSource Format="TEX">$kT_{in}\sim 0.65$</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>k</mi> <msub> <mi>T</mi> <mrow> <mi mathvariant="italic">in</mi> </mrow> </msub> <mo>∼</mo> <mn>0.65</mn> </mrow> </math></EquationSource> </InlineEquation>–1.54 keV, within the error limits, while the sources, X-3, X-5, and X-6 display soft spectra with <InlineEquation ID="IEq7"> <EquationSource Format="TEX">$\Gamma \sim 1.97$</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi mathvariant="normal">Γ</mi> <mo>∼</mo> <mn>1.97</mn> </mrow> </math></EquationSource> </InlineEquation>–2.43 with the cooler disk temperatures lying between <InlineEquation ID="IEq8"> <EquationSource Format="TEX">$kT_{in} \sim 0.28$</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>k</mi> <msub> <mi>T</mi> <mrow> <mi mathvariant="italic">in</mi> </mrow> </msub> <mo>∼</mo> <mn>0.28</mn> </mrow> </math></EquationSource> </InlineEquation> and 0.44 keV. In this work, the Luminosity–Temperature relation could not be tightly constrained due to limited data availability, but the validity of <InlineEquation ID="IEq9"> <EquationSource Format="TEX">$\textrm{L} \sim \text {T}^{4}$</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mtext>L</mtext> <mo>∼</mo> <msup> <mtext>T</mtext> <mn>4</mn> </msup> </mrow> </math></EquationSource> </InlineEquation> relation was taken into account for the purpose of mass estimation. The hard spectral state of the sources (X-1, X-2, and X-4) may be attributed either due to the inverse comptonization of soft seed photons from the hot corona or due to the emission from the innermost region of the accretion flow while the soft spectra of the sources (X-3, X-5, and X-6) could be interpreted either as a thermal emission associated with an outflowing wind or emission from the accretion disk itself. The sources exhibit no short-term temporal variability as indicated by the Chi-square probability of constancy values, which is further complemented by the <InlineEquation ID="IEq10"> <EquationSource Format="TEX">$ 3\sigma $</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mn>3</mn> <mi>σ</mi> </mrow> </math></EquationSource> </InlineEquation> upper limit values of RMS fractional variability. Moreover, the power density spectra created show no sign of pulsations in these sources.</p>

Spectral and temporal properties of ultraluminous X-ray sources in NGC 4602 with XMM-Newton

期刊论文
发表日期：

2025年12月9日

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Dayananda Mayanglambam,
Praveen Kangjam,
A. Senorita Devi

摘要

In this paper, we report the detailed spectral and temporal properties of six non-nuclear X-ray point sources, namely X-1, X-2, X-3, X-4, X-5, and X-6, located in the Seyfert 2 galaxy, NGC 4602, utilising the archival XMM-Newton data. Spectral fitting was performed using two empirical models: an absorbed power-law model and an absorbed disk blackbody model. Based on the estimated bolometric luminosity, all six sources fall in the ultraluminous X-ray sources range, with three out of the six sources (X-1, X-3, and X-6) reaching the extreme-luminosity X-ray luminosity range, exceeding $10^{40}$ $10^{40}$ erg s $^{-1}$ $^{- 1}$ , even in their lower limits. Detailed spectral analysis reveals distinct states among the sources. The sources, X-1, X-2, and X-4 exhibit hard spectral state with the powerlaw photon indices $\Gamma $ $Γ$ ranging from $\sim $ $\sim$ 1.69 to $\sim $ $\sim$ 1.79 and inner disk temperatures $kT_{in}\sim 0.65$ $k T_{in} \sim 0.65$ –1.54 keV, within the error limits, while the sources, X-3, X-5, and X-6 display soft spectra with $\Gamma \sim 1.97$ $Γ \sim 1.97$ –2.43 with the cooler disk temperatures lying between $kT_{in} \sim 0.28$ $k T_{in} \sim 0.28$ and 0.44 keV. In this work, the Luminosity–Temperature relation could not be tightly constrained due to limited data availability, but the validity of $\textrm{L} \sim \text {T}^{4}$ $L \sim T^{4}$ relation was taken into account for the purpose of mass estimation. The hard spectral state of the sources (X-1, X-2, and X-4) may be attributed either due to the inverse comptonization of soft seed photons from the hot corona or due to the emission from the innermost region of the accretion flow while the soft spectra of the sources (X-3, X-5, and X-6) could be interpreted either as a thermal emission associated with an outflowing wind or emission from the accretion disk itself. The sources exhibit no short-term temporal variability as indicated by the Chi-square probability of constancy values, which is further complemented by the $ 3\sigma $ $3 σ$ upper limit values of RMS fractional variability. Moreover, the power density spectra created show no sign of pulsations in these sources.