The Luminosity Function of Low Mass X-Ray Binaries in the Globular Cluster System of NGC 1399
| Autor: | Giuseppe D'Ago, Giuseppina Fabbiano, Arunav Kundu, Thomas H. Puzia, Thomas J. Maccarone, Paul Goudfrooij, Maurizio Paolillo, Stephen E. Zepf |
|---|---|
| Přispěvatelé: | D’Ago, G., Paolillo, Maurizio, Fabbiano, G., Puzia, T. H., Maccarone, T. J., Kundu, A., Goudfrooij, P., Zepf, S. E. |
| Jazyk: | angličtina |
| Rok vydání: | 2014 |
| Předmět: |
Physics
High Energy Astrophysical Phenomena (astro-ph.HE) Detection threshold X-ray Order (ring theory) FOS: Physical sciences Astronomy and Astrophysics Type-cD galaxy Astrophysics Luminosity Galaxies: elliptical and lenticular cD Galaxies: individual: NGC 1399 X-rays: binaries X-rays: galaxies Space and Planetary Science Globular cluster Low Mass Astrophysics - High Energy Astrophysical Phenomena Luminosity function (astronomy) |
| Zdroj: | Astronomy & Astrophysics Artículos CONICYT CONICYT Chile instacron:CONICYT |
| Popis: | We present a study of the faint-end of the X-ray Luminosity Function of Low Mass X-ray binaries in the Globular Cluster system of the cD galaxy NGC 1399 by performing a stacking experiment on 618 X-ray undetected GCs, in order to verify the presence of faint LMXBs and to constrain the faint-end slope of the GC-LMXBs XLF below the individual detection threshold of $8\times10^{37}$ erg s$^{-1}$ in the $0.5-8$ keV band. We obtain a significant X-ray detection for the whole GC sample, as well as for the red and blue GC subpopulations, corresponding to an average luminosity per GC $_{GC}$ of $(3.6\pm1.0)\times10^{36}\ erg\ s^{-1}$, $(6.9\pm2.1)\times10^{36}\ erg\ s^{-1}$ and $(1.7\pm0.9)\times10^{36}\ erg\ s^{-1}$, respectively for all, red and blue GCs. If LMXBs in red and blue GCs have the same average intrinsic luminosity, we derive a red/blu ratio $\simeq 3$ of GCs hosting LMXBs ($2.5\pm1.0$ or $4.1\pm2.5$ depending on the surveyed region); alternatively, assuming the fractions observed for brighter sources, we measure an average X-ray luminosity of $L_{X}=(4.3\pm1.3)\times10^{37}\ erg\ s^{-1}$ and $L_{X}=(3.4\pm1.7)\times10^{37}\ erg\ s^{-1}$ per red and blue GC-LMXBs respectively. In the assumption that the XLF follows a power-law distribution, we find that a low-luminosity break is required at $L_{X}\leq 8\times10^{37}$ erg s$^{-1}$ both in the whole, as well as in the color-selected (red and blue) subsamples. Given the bright-end slopes measured above the X-ray completeness limit, this result is significant at $>3\sigma$ level. Our best estimates for the faint end slope are $\beta_{L}=-1.39/-1.38/-1.36$ for all/red/blue GC-LMXBs. We also find evidence that the luminosity function becomes steeper at luminosities $L_X\gtrsim 3\times 10^{39}$ erg s$^{-1}$, as observed in old ellipticals. Comment: In press on A&A |
| Databáze: | OpenAIRE |
| Externí odkaz: |
|