We have studied the X-ray point-source population of the 30 Doradus (30 Dor) star-forming complex in the Large Magellanic Cloud using high spatial resolution X-ray images and spatially resolved spectra obtained with the Advanced CCD Imaging Spectrometer (ACIS) on board the Chandra X-Ray Observatory. Here we describe the X-ray sources in a 17'x17' field centered on R136, the massive star cluster at the center of the main 30 Dor nebula. We detect 20 of the 32 Wolf-Rayet stars in the ACIS field. The cluster R136 is resolved at the subarcsecond level into almost 100 X-ray sources, including many typical O3-O5 stars, as well as a few bright X-ray sources previously reported.
ROSAT observations found no convincing evidence for X-ray sources located in local dwarf spheroidal galaxies (dSph). Now with more sensitive instruments on board Chandra and XMM-Newton we can reach fainter luminosity levels. We report on an observation of the Sagittarius (Sgr) dSph made using Chandra and an observation of the Carina (Car) dSph made using XMM-Newton. Our observations are sensitive to sources with X-ray luminosities in the 0.1-10keV band of ~1x10^32^erg/s and 3x10^34^erg/s for the Sgr and Car fields respectively. We have identified a total of 80 sources in the Sgr field and 53 sources in the Car field. Although the source numbers are roughly consistent with the expected number of background AGN, we found a small fraction of X-ray sources which were soft and could be located in the host dSph. Follow-up optical/IR observations may help to identify their optical counterparts and hence determine their nature.
We present data products from the 300ks Chandra survey in the AKARI North Ecliptic Pole (NEP) deep field. This field has a unique set of 9-band infrared photometry covering 2-24 micron from the AKARI Infrared Camera, including mid-infrared (MIR) bands not covered by Spitzer. The survey is one of the deepest ever achieved at ~15 micron, and is by far the widest among those with similar depths in the MIR. This makes this field unique for the MIR-selection of AGN at z~1. We design a source detection procedure, which performs joint Maximum Likelihood PSF fits on all of our 15 mosaicked Chandra pointings covering an area of 0.34 square degree. The procedure has been highly optimized and tested by simulations. We provide a point source catalog with photometry and Bayesian-based 90 per cent confidence upper limits in the 0.5-7, 0.5-2, 2-7, 2-4, and 4-7keV bands. The catalog contains 457 X-ray sources and the spurious fraction is estimated to be ~1.7 per cent. Sensitivity and 90 per cent confidence upper flux limits maps in all bands are provided as well. We search for optical MIR counterparts in the central 0.25 square degree, where deep Subaru Suprime-Cam multiband images exist. Among the 377 X-ray sources detected there, ~80 per cent have optical counterparts and ~60 per cent also have AKARI mid-IR counterparts. We cross-match our X-ray sources with MIR-selected AGN from Hanami et al. Around 30 per cent of all AGN that have MID-IR SEDs purely explainable by AGN activity are strong Compton-thick AGN candidates.
We have detected 300 X-ray sources within the half-mass radius (2.79') of the globular cluster 47 Tucanae in a deep (281ks) Chandra exposure. We perform photometry and simple spectral fitting for our detected sources and construct luminosity functions, X-ray color-magnitude, and color-color diagrams. Eighty-seven X-ray sources show variability on timescales from hours to years. Thirty-one of the new X-ray sources are identified with chromospherically active binaries from the catalogs of Albrow and coworkers (2001, Cat. <J/ApJ/559/1060>). We estimate that the total number of neutron stars in 47 Tuc is of order 300, reducing the discrepancy between theoretical neutron star retention rates and observed neutron star populations in globular clusters. Comprehensive tables of source properties and simple spectral fits are provided electronically.
We report on the first X-ray images of the Phoenix dwarf galaxy, taken with XMM-Newton in 2009 July. This Local Group dwarf galaxy shares similarities with the Small Magellanic Cloud (SMC) including a burst of star formation ~50Myr ago. The SMC has an abundance of high-mass X-ray binaries (HMXBs) and so we have investigated the possibility of an HMXB population in Phoenix with the intention of furthering the understanding of the HMXB-star formation rate relation. The data from the combined European Photon Imaging Cameras (EPIC) were used to distinguish between different source classes [foreground stars, background galaxies, active galactic nuclei (AGN) and supernova remnants] using EPIC hardness ratios and correlations with optical and radio catalogues.
The incidence of active galactic nuclei (AGNs) within the local environment is a potentially valuable probe of the mechanisms that trigger and provide fuel for accretion onto supermassive black holes. While the correlation between AGN fraction and environment has been well-studied in the local universe, AGN fractions have been measured for relatively few dense environments at high redshift. In this paper, we present a measurement of the X-ray AGN fraction in the USS 1558-003 protocluster associated with the z=2.53 radio galaxy 4C-00.62. Our measurement is based on a 100-ks Chandra observation, follow-up spectroscopy from the Multi-Object Double Spectrograph on the Large Binocular Telescope, and broad and narrowband photometry. These data are sensitive to AGNs more luminous than L_X_>2x10^43^erg/s in the rest-frame hard X-ray band (2-10keV). We have identified two X-ray AGNs at the redshift of USS 1558-003, one of which is the radio galaxy. We have determined that 2.0_-1.3_^+2.6^% of the H{alpha} emitters in the protocluster are X-ray AGNs. Unlike most other high-redshift cluster progenitors studied with similar techniques, USS1558-003 does not have a significantly higher fraction of AGNs than field galaxies at similar redshifts. This lower AGN fraction is inconsistent with the expectation that the higher gas fractions at high redshift, combined with the high galaxy densities and modest relative velocities in protoclusters, should produce higher AGN fractions.
About 20% of the >1000 known exoplanets are Jupiter analogs orbiting very close to their parent stars. It is still under debate to what detectable level such hot Jupiters possibly affect the activity of the host stars through tidal or magnetic star-planet interaction. In this paper we report on an 87ks Chandra observation of the hot Jupiter hosting star WASP-18. This system is composed of an F6 type star and a hot Jupiter of mass 10.4M_Jup_ orbiting in less than 20hr around the parent star. On the basis of an isochrone fitting, WASP-18 is thought to be 600Myr old and within the range of uncertainty of 0.5-2Gyr. The star is not detected in X-rays down to a luminosity limit of 4x10^26^erg/s, which is more than two orders of magnitude lower than expected for a star of this age and mass. This value proves an unusual lack of activity for a star with an estimated age around 600Myr. We argue that the massive planet can play a crucial role in disrupting the stellar magnetic dynamo created within its thin convective layers. Other additional 212 X-ray sources are detected in the Chandra image. We list them and briefly discuss their nature.
We investigate the nature of the X-ray point source population within the Young Massive Cluster Westerlund 1. Chandra observations of 18 ks and 42 ks were used to determine the X-ray properties of emitters within Wd 1, while a comprehensive multiwavelength dataset was employed to constrain their nature. We find X-ray emission from a multitude of different stellar sources within Wd 1, including both evolved high mass and low mass pre-MS stars.
We present Chandra ACIS-I X-ray observations of 0FGL J1311.9-3419 and 0FGL J1653.4-0200, the two brightest high Galactic latitude (|b|>10{deg}) {gamma}-ray sources from the three-month Fermi Large Area Telescope (LAT) bright source list that are still unidentified. Both were also detected previously by EGRET, and despite dedicated multi-wavelength follow-up, they are still not associated with established classes of {gamma}-ray emitters like pulsars or radio-loud active galactic nuclei. X-ray sources found in the ACIS-I fields of view are cataloged, and their basic properties are determined. These are discussed as candidate counterparts to 0FGL J1311.9-3419 and 0FGL J1653.4-0200, with particular emphasis on the brightest of the 9 and 13 Chandra sources detected within the respective Fermi-LAT 95% confidence regions. Further follow-up studies, including optical photometric and spectroscopic observations, are necessary to identify these X-ray candidate counterparts in order to ultimately reveal the nature of these enigmatic {gamma}-ray objects.
We have identified a large-scale structure traced by galaxies at z=0.8, within the Lockman Hole, by means of multi-object spectroscopic observations. By using deep XMM images we have investigated the soft X-ray emission from the Warm-Hot Intergalactic Medium (WHIM) expected to be associated with this large-scale structure and we set a tight upper limit to its flux in the very soft 0.2-0.4keV band. The non-detection requires the WHIM at these redshifts to be cooler than 0.1keV. Combined with the WHIM emission detections at lower redshift, our result indicates that the WHIM temperature rapidly decreases with redshift, as expected in popular cosmological models.
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