Based on archival Chandra observations with a total exposure of 1.3 Ms, we study Xray point sources in the Fornax cluster of galaxies, with the primary aim of searching for intra-cluster X-ray source populations. We detect 1177 point sources out to a projected radius of ∼30 arcmin (∼180 kpc) from the cluster center and down to a limiting 0.5-8 keV luminosity of ∼ 3 × 10 37 erg s −1 . We construct source surface density profile, after excluding sources associated with foreground stars, known globular clusters, ultracompact dwarfs and galactic nuclei. From this profile we statistically identify ∼183 excess sources that are not associated with the bulk stellar content of the individual member galaxies of Fornax, nor with the cosmic X-ray background. Taking into account Poisson error and cosmic variance, the cumulative significance of this excess is at 2 σ level (with a maximum of 3.6 σ) outside three effective radii of the central giant elliptical, NGC 1399. The luminosity function of the excess sources is found to be Corresponding author: Zhiyuan Li xiangyu.jin@mail.mcgill.ca, lizy@nju.edu.cn 2 Jin et al.significantly steeper than that of the GC-hosting sources (presumably low-mass Xray binaries [LMXBs]), disfavoring the possibility that unidentified GCs are primarily responsible for the excess. We show that a large fraction of the excess can be related to the extended stellar halo of NGC 1399 and/or the diffuse intra-cluster light, thus providing strong evidence for the presence of intra-cluster X-ray sources in Fornax, the second unambiguous case for a galaxy cluster after Virgo. Other possible origins of the excess, including supernova-kicked LMXBs and stripped nucleated dwarf galaxies are discussed.

Previous X-ray observations toward the Nuclear Star Cluster (NSC) at the Galactic center have discovered thousands of point sources, most of which were believed to be cataclysmic variables (CVs), i.e., a white dwarf (WD) accreting from a low-mass companion. However, the population properties of these CVs remain unclear, which otherwise contain important information about the evolutionary history of the NSC. In this work we utilize ultradeep archival Chandra observations to study the spectral properties of the NSC CVs, in close comparison with those in the Solar vicinity. We find that the NSC CVs have strong Fe XXV and Fe XXVI lines (both of which show equivalent widths ∼ 200 − 300 eV), indicating metal-rich companions. Moreover, their Fe XXVI to Fe XXV line flux ratio is used to diagnose the characteristic white dwarf mass (M WD ) of NSC CVs. The results show that the CVs with L 2−10keV > 6 × 10 31 erg s −1 have a mean M WD of ∼ 0.6/1.0 M ⊙ if they are magnetic/non-magnetic CVs; while those with L 2−10keV between 1 − 6 × 10 31 erg s −1 have a mean xuxj@nju.edu.cn M WD of ∼ 0.8/1.2 M ⊙ if they are magnetic/non-magnetic CVs. All these Chandra-detected CVs collectively contribute ∼30-50% of the unresolved 20-40 keV X-ray emission from the NSC. The CV population with massive (i.e., M WD ∼ 1.2M ⊙ ) WDs have not been observed in the Solar vicinity or the Galactic bulge, and they might have been formed via dynamical encounters in the NSC.

One of the most unique phenomena in the Galactic center region is the existence of numerous long and narrow filamentary structures within a few hundred parsecs of Sgr A . While more than one than one hundred radio filaments have been revealed by MeerKAT, about two dozens X-ray filaments have been discovered so far. In this article, we report our analysis on the deep Chandra and NuSTAR observations of a non-thermal X-ray filament, G0.13-0.11, which is located adjacent to the Radio arc. Chandra revealed a unique morphology of G0.13-0.11, which is an elongated (0.1 pc in width and 3.2 pc in length) structure slightly bended towards the Radio arc. A pulsar candidate (Γ ∼ 1.4) is detected in the middle of the filament, with a tail of diffuse non-thermal X-ray emission on one side of the filament. The filament is detected by NuSTAR up to 79 keV, with the hard X-ray centroid consistent with the pulsar candidate. We found that the X-ray intensity decays along the filament farther away from the pulsar candidate, dropping to half of its peak value at 2.2 pc away. This system is mostly likely a Pulsar Wind Nebula interacting with ambient interstellar magnetic field, where the filaments are kinetic jets from PWN as recently proposed. The nature of this filament adds to complex origin of the X-ray filaments, which serve as powerful tools to probe local and global powerful particle accelerators in the Galactic center.