Archival Chandra and XMM-Newton observations reveal two transient X-ray sources in NGC 4552 exceeding 10^39 erg/s, classifying them as new transient ULXs.
The X-ray Globular Cluster Population in NGC 1399
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abstract
We report on the {\it Chandra} observations of the elliptical galaxy NGC 1399, concentrating on the X-ray sources identified with globular clusters (GCs). A large fraction of the 2-10 keV X-ray emission in the $8' \times 8'$ {\it Chandra} image is resolved into point sources with luminosities $\ge 5 \times 10^{37}$ \ergsec. These sources are most likely Low Mass X-ray Binaries (LMXBs). In a region imaged by {\it HST} about 70% of the X-ray sources are located within GCs. This association suggests that in giant elliptical galaxies luminous X-ray binaries preferentially form in GCs. Many of the GC sources have super-Eddington luminosities (for an accreting neutron star) and their average luminosity is higher than the non-GC sources. The X-ray spectral properties of both GC and non-GC sources are similar to those of LMXBs in our Galaxy. Two of the brightest sources, one of which is in a GC, have an ultra-soft spectrum, similar to that seen in the high state of black hole candidates. The ``apparent'' super-Eddington luminosity in many cases may be due to multiple LMXB systems within individual GCs, but with some of the most extremely luminous systems containing massive black holes.
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Transient and Variable Ultra-luminous X-ray Sources in NGC 4552
Archival Chandra and XMM-Newton observations reveal two transient X-ray sources in NGC 4552 exceeding 10^39 erg/s, classifying them as new transient ULXs.