<p>In this study, we investigated the spectral properties of the X-ray point sources in the giant elliptical galaxy NGC 4472 (M49), located at a distance of <InlineEquation ID="IEq1"> <EquationSource Format="TEX">\(\sim \)</EquationSource> <EquationSource Format="MATHML"><math> <mo>∼</mo> </math></EquationSource> </InlineEquation>16.7 Mpc in the equatorial constellation of Virgo. Utilizing all available Chandra data observed using the ACIS-S detector from the year 2000 to the year 2021, we identified a total of 57 X-ray point sources, each with data counts <InlineEquation ID="IEq2"> <EquationSource Format="TEX">\(\gtrsim \)</EquationSource> <EquationSource Format="MATHML"><math> <mo>≳</mo> </math></EquationSource> </InlineEquation>100. From the spectral study, we found 8 ultraluminous X-ray sources (ULXs) and 49 X-ray binaries (XRBs). Among the ULXs, source X-1 was found to be an extremely luminous X-ray source (ELXs) with bolometric luminosity, <InlineEquation ID="IEq3"> <EquationSource Format="TEX">\(L_x \sim 10^{40}\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mi>L</mi> <mi>x</mi> </msub> <mo>∼</mo> <msup> <mn>10</mn> <mn>40</mn> </msup> </mrow> </math></EquationSource> </InlineEquation> erg s<InlineEquation ID="IEq4"> <EquationSource Format="TEX">\(^{-1}\)</EquationSource> <EquationSource Format="MATHML"><math> <mmultiscripts> <mrow /> <mrow /> <mrow> <mo>-</mo> <mn>1</mn> </mrow> </mmultiscripts> </math></EquationSource> </InlineEquation>, probably accreting at a super-Eddington rate. We also detected a super-soft source, X-3, accreting at <InlineEquation ID="IEq5"> <EquationSource Format="TEX">\(\sim \)</EquationSource> <EquationSource Format="MATHML"><math> <mo>∼</mo> </math></EquationSource> </InlineEquation>0.05 times the Eddington limit, with a disk temperature of <InlineEquation ID="IEq6"> <EquationSource Format="TEX">\(KT_{in} \sim 0.25^{+0.06}_{-0.05}\)</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</mn> <mo>.</mo> <msubsup> <mn>25</mn> <mrow> <mo>-</mo> <mn>0.05</mn> </mrow> <mrow> <mo>+</mo> <mn>0.06</mn> </mrow> </msubsup> </mrow> </math></EquationSource> </InlineEquation> keV. Assuming a disk blackbody model, the estimated black hole mass is <InlineEquation ID="IEq7"> <EquationSource Format="TEX">\({\sim } 5.57^{+8.89}_{-3.10} \times 10^2 \ M_{\odot }\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mo>∼</mo> <mn>5</mn> <mo>.</mo> <msubsup> <mn>57</mn> <mrow> <mo>-</mo> <mn>3.10</mn> </mrow> <mrow> <mo>+</mo> <mn>8.89</mn> </mrow> </msubsup> <mo>×</mo> <msup> <mn>10</mn> <mn>2</mn> </msup> <mspace width="4pt" /> <msub> <mi>M</mi> <mo>⊙</mo> </msub> </mrow> </math></EquationSource> </InlineEquation>, placing it as a possible intermediate-mass black hole (IMBH) candidate. Source X-4 showed notable variability in luminosity, which closely correlated with changes in its inner disk temperature. Its luminosity increased as the disk temperature rose, and decreased as the temperature dropped. A similar trend was also observed in source X-14, although with comparatively less variation in luminosity. Most of the other ULXs in this study remained in a hard spectral state with consistent luminosity across observations, with the exception of source X-34, which displayed spectral variability, and source X-50, which was observed in a soft thermal state. Further, the majority of the detected X-ray binaries were found in a hard spectral state. While four of the XRBs exhibited a soft state and another four showed spectral transitions, their luminosities remained relatively stable. A color–color analysis of the X-ray sources revealed that both XRBs and ULXs generally reside within the low-mass X-ray binary (LMXB) region, albeit with enhanced spectral hardness. Notably, source X-1 displayed even greater hardness, potentially due to its higher luminosity.</p>

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Spectral study of the X-ray sources in NGC 4472

  • Thokchom Sanatombi,
  • A. Senorita Devi,
  • Akram Chandrajit Singha,
  • K. Yugindro Singh

摘要

In this study, we investigated the spectral properties of the X-ray point sources in the giant elliptical galaxy NGC 4472 (M49), located at a distance of \(\sim \) 16.7 Mpc in the equatorial constellation of Virgo. Utilizing all available Chandra data observed using the ACIS-S detector from the year 2000 to the year 2021, we identified a total of 57 X-ray point sources, each with data counts \(\gtrsim \) 100. From the spectral study, we found 8 ultraluminous X-ray sources (ULXs) and 49 X-ray binaries (XRBs). Among the ULXs, source X-1 was found to be an extremely luminous X-ray source (ELXs) with bolometric luminosity, \(L_x \sim 10^{40}\) L x 10 40 erg s \(^{-1}\) - 1 , probably accreting at a super-Eddington rate. We also detected a super-soft source, X-3, accreting at \(\sim \) 0.05 times the Eddington limit, with a disk temperature of \(KT_{in} \sim 0.25^{+0.06}_{-0.05}\) K T in 0 . 25 - 0.05 + 0.06 keV. Assuming a disk blackbody model, the estimated black hole mass is \({\sim } 5.57^{+8.89}_{-3.10} \times 10^2 \ M_{\odot }\) 5 . 57 - 3.10 + 8.89 × 10 2 M , placing it as a possible intermediate-mass black hole (IMBH) candidate. Source X-4 showed notable variability in luminosity, which closely correlated with changes in its inner disk temperature. Its luminosity increased as the disk temperature rose, and decreased as the temperature dropped. A similar trend was also observed in source X-14, although with comparatively less variation in luminosity. Most of the other ULXs in this study remained in a hard spectral state with consistent luminosity across observations, with the exception of source X-34, which displayed spectral variability, and source X-50, which was observed in a soft thermal state. Further, the majority of the detected X-ray binaries were found in a hard spectral state. While four of the XRBs exhibited a soft state and another four showed spectral transitions, their luminosities remained relatively stable. A color–color analysis of the X-ray sources revealed that both XRBs and ULXs generally reside within the low-mass X-ray binary (LMXB) region, albeit with enhanced spectral hardness. Notably, source X-1 displayed even greater hardness, potentially due to its higher luminosity.