اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدChandra Observations of Unresolved X-ray Sources around two Clusters of Galaxies
92
0
0.0
(
0
)
تأليف
S.M. Molnar
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
We have searched for unresolved X-ray sources in the vicinity of two rich clusters of galaxies: Abell 1995 (A1995) and MS 0451.6-0305 (MS0451), using the Chandra X-ray observatory. We detected significantly more unresolved sources around A1995 than expected based on the number of X-ray sources to the same flux limit detected in deep CHANDRA observations of blank fields. Previous studies have also found excess X-ray sources in the vicinity of several nearby clusters of galaxies using ROSAT$ $, and recently in more distant ($z ~ 0.5$) clusters (RXJ0030 and 3C295) using Chandra. In contrast, we detect only 14 unresolved X-ray sources near MS0451, which is consistent with the number expected from a cluster-free background. We determine the luminosity functions of the extra sources under the assumption that they are at the distance of their respective clusters. The characteristic luminosity of the extra sources around A1995 must be an order of magnitude fainter than that of the extra sources around RXJ0030 and 3C295. The apparent lack of extra sources around MS0451 is consistent with its greater distance and the same characteristic luminosity as the A1995 sources. Hardness ratios suggest that, on average, the extra sources in A1995 may have harder spectra than those of RXJ0030 and 3C295. These results indicate that different classes of objects may dominate in different clusters, perhaps depending on the formation history and/or dynamical state of the accompanying cluster.
قيم البحث
اقرأ أيضاً
We report the results of a programme of dual-epoch Chandra ACIS-S observations of five ultraluminous X-ray sources (ULXs) in nearby spiral galaxies. All five ULXs are detected as unresolved, point-like X-ray sources by Chandra, though two have faded
below the 10^39 erg/s luminosity threshold used to first designate these sources as ULXs. Using this same criterion, we detect three further ULXs within the imaged regions of the galaxies. The ULXs appear to be related to the star forming regions of the galaxies, indicating that even in ``normal spiral galaxies the ULX population is predominantly associated with young stellar populations. A detailed study of the Chandra ACIS-S spectra of six of the ULXs shows that five are better described by a powerlaw continuum than a multi-colour disc blackbody model, though there is evidence for additional very soft components to two of the powerlaw continua. The measured photon indices in four out of five cases are consistent with the low/hard state in black hole binaries, contrary to the suggestion that powerlaw-dominated spectra of ULXs originate in the very high state. A simple interpretation of this is that we are observing accretion onto intermediate-mass black holes, though we might also be observing a spectral state unique to very high mass accretion rates in stellar-mass black hole systems. Short-term flux variability is only detected in one of two epochs for two of the ULXs, with the lack of this characteristic arguing that the X-ray emission of this sample of ULXs is not dominated by relativistically-beamed jets. The observational characteristics of this small sample suggest that ULXs are a distinctly heterogeneous source class.
We present results of a Chandra observation of a field in NGC 2264. The observations were taken with the ACIS-I camera with an exposure time of 48.1 ks. We present a catalog of 263 sources, which includes X-ray luminosity, optical and infrared photom
etry and X-ray variability information. We found 41 variable sources, 14 of which have a flare-like light curve, and 2 of which have a pattern of a steady increase or decrease over a 10 hour period. The optical and infrared photometry for the stars identified as X-ray sources are consistent with most of these objects being pre-main sequence stars with ages younger than 3 Myr.
The International Gamma-Ray Astrophysics Laboratory (INTEGRAL) satellite has detected in excess of 1000 sources in the ~20-100 keV band during its surveys of the sky over the past 17 years. We obtained 5 ks observations of 15 unclassified IGR sources
with the Chandra X-ray Observatory in order to localize them, to identify optical/IR counterparts, to measure their soft X-ray spectra, and to classify them. For 10 of the IGR sources, we detect Chandra sources that are likely (or in some cases certain) to be the counterparts. IGR J18007-4146 and IGR J15038-6021 both have Gaia parallax distances, placing them at 2.5+0.5-0.4 and 1.1+1.5-0.4 kpc, respectively. We tentatively classify both of them as intermediate polar-type Cataclysmic Variables. Also, IGR J17508-3219 is likely to be a Galactic source, but it is unclear if it is a Dwarf Nova or another type of transient. For IGR J17118-3155, we provide a Chandra localization, but it is unclear if the source is Galactic or extragalactic. Based on either near-IR/IR colors or the presence of extended near-IR emission, we classify four sources as Active Galactic Nuclei (IGR J16181-5407, IGR J16246-4556, IGR J17096-2527, and IGR J19294+1327), and IGR J20310+3835 and IGR J15541-5613 are AGN candidates. In addition, we identified an AGN in the INTEGRAL error circle of IGR J16120-3543 that is a possible counterpart.
We present a catalog of 9017 X-ray sources identified in Chandra observations of a 2 by 0.8 degree field around the Galactic center. We increase the number of known X-ray sources in the region by a factor of 2.5. The catalog incorporates all of the A
CIS-I observations as of 2007 August, which total 2.25 Msec of exposure. At the distance to the Galactic center (8 kpc), we are sensitive to sources with luminosities >4e32 erg/s (0.5-8.0 keV; 90% confidence) over an area of one square degree, and up to an order of magnitude more sensitive in the deepest exposure (1.0 Msec) around Sgr A*. The positions of 60% of our sources are accurate to <1 (95% confidence), and 20% have positions accurate to <0.5. We search for variable sources, and find that 3% exhibit flux variations within an observation, 10% exhibit variations from observation-to-observation. We also find one source, CXOUGC J174622.7-285218, with a periodic 1745 s signal (1.4% chance probability), which is probably a magnetically-accreting cataclysmic variable. We compare the spatial distribution of X-ray sources to a model for the stellar distribution, and find 2.8 sigma evidence for excesses in the numbers of X-ray sources in the region of recent star formation encompassed by the Arches, Quintuplet, and Galactic center star clusters. These excess sources are also seen in the luminosity distribution of the X-ray sources, which is flatter near the Arches and Quintuplet than elsewhere in the field. These excess point sources, along with a similar longitudinal asymmetry in the distribution of diffuse iron emission that has been reported by other authors, probably have their origin in the young stars that are prominent at l~0.1 degree.
X-ray observations of galaxy clusters potentially provide powerful cosmological probes if systematics due to our incomplete knowledge of the intracluster medium (ICM) physics are understood and controlled. In this paper, we study the effects of galax
y formation on the properties of the ICM and X-ray observable-mass relations using high-resolution self-consistent cosmological simulations of galaxy clusters and comparing their results with recent Chandra X-ray observations. We show that despite complexities of their formation and uncertainties in their modeling, clusters of galaxies both in observations and numerical simulations are remarkably regular outside of their cores, which holds great promise for their use as cosmological probes.
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
