Iron and nickel line properties in the X-ray-reflecting region of the Circinus galaxy     

Silvano Molendi  Stefano Bianchi  Giorgio Matt 《Monthly notices of the Royal Astronomical Society》2003,343(1):L1-L4

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A hard X-ray constraint on the presence of an AGN in the ultraluminous infrared galaxy Arp 220     

K. Iwasawa  G. Matt  M. Guainazzi  A.C. Fabian 《Monthly notices of the Royal Astronomical Society》2001,326(3):894-900

We present X-ray results on the ultraluminous infrared galaxy Arp 220 obtained with BeppoSAX . X-ray emission up to 10 keV is detected. No significant signal is detected with the PDS detector in the higher energy band. The 2–10 keV emission has a flat spectrum (Γ∼1.7) , similar to M82, and a luminosity of ∼ 1×10⁴¹ erg s⁻¹ . A population of X-ray binaries may be a major source of this X-ray emission. The upper limit of an iron K line equivalent width at 6.4 keV is ≃600 eV. This observation imposes the tightest constraint so far on an active nucleus if present in Arp 220. We find that a column density of X-ray absorption must exceed 10²⁵ cm⁻² for an obscured active nucleus to be significant in the energetics, and the covering factor of the absorption should be almost unity. The underluminous soft X-ray starburst emission may need a good explanation, if the bolometric luminosity is primarily powered by a starburst.  相似文献   

Superhumps in the helium dwarf nova KL Draconis     

Matt A. Wood  Matthew J. Casey †  Peter M. Garnavich  Brooke Haag ‡ 《Monthly notices of the Royal Astronomical Society》2002,334(1):87-93

We report on the discovery of a 25.5-min superhump period for the suspected helium dwarf nova system KL Draconis in a high state. The presence of superhumps combined with the previously observed helium spectrum and large-amplitude photometric variations confirm that KL Dra is an AM CVn system similar to CR Bootis, V803 Cen and CP Eridani. We also find a low-state photometric period at 25.0 min that we suggest may be the orbital period. With this assumption, we estimate   q =0.075  ,   M ₁=0.76 M_⊙  and   M ₂=0.057 M_⊙  .  相似文献   

An XMM–Newton observation of Ark 120: the X-ray spectrum of a 'bare' Seyfert 1 nucleus     

S. Vaughan  A. C. Fabian  D. R. Ballantyne  A. De Rosa  L. Piro  G. Matt 《Monthly notices of the Royal Astronomical Society》2004,351(1):193-205

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Molecular gas properties of 12-μm Seyfert galaxies – I. The southern sample     

Matt Strong  Alan Pedlar  Susanne Aalto  Rob J. Beswick  Stephen Curran  Roy Booth 《Monthly notices of the Royal Astronomical Society》2004,353(4):1151-1160

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Relativistic spectral features from X-ray-illuminated spots and the measure of the black hole mass in active galactic nuclei   总被引：1，自引：0，他引：1  

M. Dov&#;iak  S. Bianchi  M. Guainazzi  V. Karas  G. Matt 《Monthly notices of the Royal Astronomical Society》2004,350(2):745-755

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Elusive active galactic nuclei     

R. Maiolino  A. Comastri  R. Gilli  N. M. Nagar  S. Bianchi  T. Böker  E. Colbert  A. Krabbe  A. Marconi  G. Matt  M. Salvati 《Monthly notices of the Royal Astronomical Society》2003,344(4):L59-L64

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Contemporary patterns and issues of school segregation and white flight in U.S. metropolitan areas: towards spatial inquiries     

Zhang  Charlie H.  Ruther  Matt 《GeoJournal》2021,86(3):1511-1526

GeoJournal - The geography of education issues has long been an under-researched area in geography literature. This article reviews studies on school segregation and white flight and emphasizes the...  相似文献   

Are Models Too Simple? Arguments for Increased Parameterization   总被引：2，自引：0，他引：2  

Hunt RJ  Doherty J  Tonkin MJ 《Ground water》2007,45(3):254-262

The idea that models should be as simple as possible is often accepted without question. However, too much simplification and parsimony may degrade a model's utility. Models are often constructed to make predictions; yet, they are commonly parameterized with a focus on calibration, regardless of whether (1) the calibration data can constrain simulated predictions or (2) the number and type of calibration parameters are commensurate with the hydraulic property details on which key predictions may depend. Parameterization estimated through the calibration process is commonly limited by the necessity that the number of calibration parameters be smaller than the number of observations. This limitation largely stems from historical restrictions in calibration and computing capability; we argue here that better methods and computing capabilities are now available and should become more widely used. To make this case, two approaches to model calibration are contrasted: (1) a traditional approach based on a small number of homogeneous parameter zones defined by the modeler a priori and (2) regularized inversion, which includes many more parameters than the traditional approach. We discuss some advantages of regularized inversion, focusing on the increased insight that can be gained from calibration data. We present these issues using reasoning that we believe has a common sense appeal to modelers; knowledge of mathematics is not required to follow our arguments. We present equations in an Appendix, however, to illustrate the fundamental differences between traditional model calibration and a regularized inversion approach.  相似文献   

The XMM Cluster Survey: forecasting cosmological and cluster scaling-relation parameter constraints     

Martin Sahlén  Pedro T. P. Viana  rew R. Liddle  A. Kathy Romer  Michael Davidson  Mark Hosmer  Ed Lloyd-Davies  Kivanc Sabirli  Chris A. Collins  Peter E. Freeman  Matt Hilton  Ben Hoyle  Scott T. Kay  Robert G. Mann  Nicola Mehrtens  Christopher J. Miller  Robert C. Nichol  S. Adam Stanford  Michael J. West  † 《Monthly notices of the Royal Astronomical Society》2009,397(2):577-607

We forecast the constraints on the values of  σ₈, Ω_m  and cluster scaling-relation parameters which we expect to obtain from the XMM Cluster Survey (XCS). We assume a flat Λ cold dark matter Universe and perform a Monte Carlo Markov Chain analysis of the evolution of the number density of galaxy clusters that takes into account a detailed simulated selection function. Comparing our current observed number of clusters shows good agreement with predictions. We determine the expected degradation of the constraints as a result of self-calibrating the luminosity–temperature relation (with scatter), including temperature measurement errors, and relying on photometric methods for the estimation of galaxy cluster redshifts. We examine the effects of systematic errors in scaling relation and measurement error assumptions. Using only  ( T , z )  self-calibration, we expect to measure Ω_m to ±0.03 (and  Ω_Λ  to the same accuracy assuming flatness), and σ₈ to ±0.05, also constraining the normalization and slope of the luminosity–temperature relation to ±6 and ±13 per cent (at 1σ), respectively, in the process. Self-calibration fails to jointly constrain the scatter and redshift evolution of the luminosity–temperature relation significantly. Additional archival and/or follow-up data will improve on this. We do not expect measurement errors or imperfect knowledge of their distribution to degrade constraints significantly. Scaling-relation systematics can easily lead to cosmological constraints 2σ or more away from the fiducial model. Our treatment is the first exact treatment to this level of detail, and introduces a new 'smoothed ML' (Maximum Likelihood) estimate of expected constraints.  相似文献