710 research outputs found
The large-scale bias of the hard X-ray background
Recent deep X-ray surveys combined with spectroscopic identification of the
sources have allowed the determination of the rest-frame 2-8 keV luminosity as
a function of redshift. In addition, an analysis of the HEAO1 A2 2-10 keV
full-sky map of the X-ray background (XRB) reveals clustering on the scale of
several degrees. Combining these two results in the context of the currently
favored Lambda-CDM cosmological model implies an average X-ray bias factor,
b_x, of b_x^2 = 1.12 +- 0.33, i.e., b_x = 1.06 +- 0.16. These error estimates
include only statistical error; the systematic error sources, while comparable,
appear to be sub-dominant. This result is in contrast to the large biases of
some previous estimates and is more in line with current estimates of the
optical bias of L* galaxies.Comment: 6 pages, 3 eps figures, accepted for ApJ, vol. 612, 10 September 200
On the nature of the X-ray absorption in the Seyfert 2 galaxy NGC 4507
We present results of the ASCA observation of the Seyfert 2 galaxy NGC 4507.
The 0.5-10 keV spectrum is rather complex and consists of several components:
(1) a hard X-ray power law heavily absorbed by a column density of about 3
10^23 cm^-2, (2) a narrow Fe Kalpha line at 6.4 keV, (3) soft continuum
emission well above the extrapolation of the absorbed hard power law, (4) a
narrow emission line at about 0.9 keV. The line energy, consistent with highly
ionized Neon (NeIX), may indicate that the soft X-ray emission derives from a
combination of resonant scattering and fluorescence in a photoionized gas. Some
contribution to the soft X-ray spectrum from thermal emission, as a blend of Fe
L lines, by a starburst component in the host galaxy cannot be ruled out with
the present data.Comment: 8 pages, LateX, 5 figures (included). Uses mn.sty and epsfig.sty. To
appear in MNRA
The Changing AGN Population
We investigate how the fraction of broad-line sources in the AGN population
changes with X-ray luminosity and redshift. We first construct the rest-frame
hard-energy (2-8 keV) X-ray luminosity function (HXLF) at z=0.1-1 using Chandra
Lockman Hole-Northwest wide-area data, Chandra Deep Field-North 2 Ms data,
other Chandra deep field data, and the ASCA Large Sky Survey data. We find that
broad-line AGNs dominate above 3e43 ergs/s and have a mean luminosity of 1.3e44
ergs/s. Type II AGNs can only become an important component of the X-ray
population at Seyfert-like X-ray luminosities. We then construct z=0.1-0.5 and
z=0.5-1 HXLFs and compare them with both the local HXLF measured from HEAO-1 A2
survey data and the z=1.5-3 HXLF measured from soft-energy (0.5-2 keV) Chandra
and ROSAT data. We find that the number density of >1e44 ergs/s sources
(quasars) steadily declines with decreasing redshift, while the number density
of 1e43-1e44 ergs/s sources peaks at z=0.5-1. Strikingly, however, the number
density of broad-line AGNs remains roughly constant with redshift while their
average luminosities decline at the lower redshifts, showing another example of
cosmic downsizing.Comment: Accepted by The Astrophysical Journal Letters, 5 page
Atualização metodológica complementar para avaliação de germoplasma de forrageiras.
Esta publicação apresenta aos técnicos que trabalham nesta área informações detalhadas sobre os critérios qualitativos e quantitativos fundamentais na avaliação de germoplasma para introdução de espécies e validação da metodologia de avaliação de germoplasma de forrageiras. Esta metodologia, além de cobrir os aspectos básicos da avaliação de plantas forrageiras, trás no seu conteúdo um modelo matemático de simples aplicação que favorece o seu entendimento, permitindo eleger o germoplasma mais adaptado à região. Este documento teve o embasamento técnico nos trabalhos de introdução de forrageiras realizados pela Embrapa Pantanal nas sub-regiões da Nhecolândia e Paiaguás, localizadas no Pantanal Sul-Mato-Grossense. Pela praticidade será muito útil não somente para os pesquisadores, mas também aos extensionistas, técnicos agrícolas e a todos que se interessam pela introdução e avaliação de forrageiras.bitstream/CPAP-2009-09/56848/1/DOC97.pd
BeppoSAX observations of the Seyfert 1 Galaxy NGC 3516
We present the results of two observations of the bright Seyfert 1 galaxy NGC
3516, obtained with BeppoSAX in 1996 November and 1997 March. Useful signal is
detected between 0.2 and 60 keV, allowing for the first time the simultaneous
observation of all main spectral features. The source was brighter by a factor
2 at the second epoch of observation. Both spectra present a strong Fe Kalpha
line, and a reflection hump at high energy. An absorption edge at 0.8 keV is
visible in the later spectrum, but not in the earlier one, indicating that this
feature is strongly variable.Comment: to appear in : The Active X-ray Sky: Results from BeppoSAX and
Rossi-XTE, Nuclear Physics B Proceedings Supplements, L. Scarsi, H. Bradt, P.
Giommi and F. Fiore (eds.), Elsevier Science B.V. 4 pages LateX and 6 ps
figures, using espcrc2 and epsfi
The Xmm-Newton Spectrum of a Candidate Recoiling Supermassive Black Hole: An Elusive Inverted P-Cygni Profile
We present a detailed spectral analysis of new XMM-Newton data of the source CXOC J100043.1+020637, also known as CID-42, detected in the COSMOS survey at z = 0.359. Previous works suggested that CID-42 is a candidate recoiling supermassive black hole (SMBH) showing also an inverted P-Cygni profile in the X-ray spectra at ~6 keV (rest) with an iron emission line plus a redshifted absorption line (detected at 3σ in previous XMM-Newton and Chandra observations). Detailed analysis of the absorption line suggested the presence of ionized material flowing into the black hole at high velocity. In the new long XMM-Newton observation, while the overall spectral shape remains constant, the continuum 2-10 keV flux decrease of ~20% with respect to previous observation and the absorption line is undetected. The upper limit on the intensity of the absorption line is EW \u3c 162 eV. Extensive Monte Carlo simulations show that the nondetection of the line is solely due to variation in the properties of the inflowing material, in agreement with the transient nature of these features, and that the intensity of the line is lower than the previously measured with a probability of 98.8%. In the scenario of CID-42 as a recoiling SMBH, the absorption line can be interpreted as being due to an inflow of gas with variable density that is located in the proximity of the SMBH and recoiling with it. New monitoring observations will be requested to further characterize this line
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