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Register a new userOn the Simbol-X capability of detecting red/blue-shifted emission and absorption Fe K lines
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F. Tombesi
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The detection of red/blue-shifted iron lines in the spectra of astronomical X-ray sources is of great importance, as it allows to trace the environment around compact objects, like black holes in AGNs. We report on extensive simulations to test the Simbol-X capability of detecting such spectral features, focusing on the low energy detector (0.5-30 keV).
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We investigate the capability of detecting, with Simbol-X, non-thermal emission during stellar flares, and distinguishing it from hot thermal emission. We find that flare non-thermal emission is detectable when at least ~20 cts are detected with the CZT detector in the 20-80 keV band. Therefore Simbol-X will detect the non-thermal emission from some of the X-ray brightest nearby stars, whether the thermal vs. non-thermal relation, derived for solar flares, holds.
We have observed a sample of 22 luminous quasars, in the range 2.0<z<2.5, at 1.6 microns with the near-infrared (NIR) spectrograph FSPEC on the Multiple Mirror Telescope. Our sample contains 13 radio-loud and 9 radio-quiet objects. We have measured the systemic redshifts z_(sys) directly from the strong [O III]5007 line emitted from the narrow-line-region. From the same spectra, we have found that the non-resonance broad H$beta$ lines have a systematic mean redward shift of 520+/-80 km/s with respect to systemic. Such a shift was not found in our identical analysis of the low-redshift sample of Boroson & Green. The amplitude of this redshift is comparable to half the expected gravitational redshift and transverse Doppler effects, and is consistent with a correlation between redshift differences and quasar luminosity. From data in the literature, we confirm that the high-ionization rest-frame ultraviolet broad lines are blueshifted ~550-1050 km/s from systemic, and that these velocity shifts systematically increase with ionization potential. Our results allow us to quantify the known bias in estimating the ionizing flux from the inter-galactic-medium J_(IGM) via the Proximity Effect. Using redshift measurements commonly determined from strong broad line species, like Lyalpha or CIV1549, results in an over-estimation of J_(IGM) by factors of ~1.9-2.3. Similarly, corresponding lower limits on the density of baryon Omega_b will be over-estimated by factors of ~1.4-1.5. However, the low-ionization MgII2798 broad line is within ~50 km/s of systemic, and thus would be the line of choice for determining the true redshift of 1.0<z<2.2 quasars without NIR spectroscopy, and z>3.1 objects using NIR spectroscopy.
In recent years there have been many reported detections of highly redshifted or blueshifted narrow spectral lines (both emission or absorption) in the X-ray spectra of active galaxies, but these are all modest detections in terms of their statistical significance. The aim of this paper is to review the issue of the significance of these detections and, in particular, take account of publication bias. A literature search revealed 38 reported detections of narrow, strongly shifted (v/c >= 0.05) X-ray lines in the 1.5-20 keV spectra of Seyfert galaxies and quasars. These published data show a close, linear relationship between the estimated line strength and its uncertainty, in the sense that better observations (with smaller uncertainties) only ever show the smallest lines. This result is consistent with many of the reported lines being false detections resulting from random fluctuations, drawn from a large body of data and filtered by publication bias such that only the most `significant fluctuations are ever reported. The reality of many of these features, and certainly their prevalence in the population at large, therefore remains an open question that is best settled though uniform analysis (and reporting) of higher quality observations.
We present results from a 150 ksec Suzaku observation of the Seyfert 1.5 NGC 3516 in October 2005. The source was in a relatively highly absorbed state. Our best-fit model is consistent with the presence of a low-ionization absorber which has a column density near 5 * 10^{22} cm^{-2} and covers most of the X-ray continuum source (covering fraction 96-100%). A high-ionization absorbing component, which yields a narrow absorption feature consistent with Fe K XXVI, is confirmed. A relativistically broadened Fe K alpha line is required in all fits, even after the complex absorption is taken into account; an additional partial-covering component is an inadequate substitute for the continuum curvature associated with the broad Fe line. A narrow Fe K alpha emission line has a velocity width consistent with the Broad Line Region. The low-ionization absorber may be responsible for producing the narrow Fe K alpha line, though a contribution from additional material out of the line of sight is possible. We include in our model soft band emission lines from He- and H-like ions of N, O, Ne and Mg, consistent with photo-ionization, though a small contribution from collisionally-ionized emission is possible.
Measurements of the asymmetry of the emission peaks in the core of the Ca II H line for 105 giant stars are reported. The asymmetry is quantified with the parameter V/R, defined as the ratio between the maximum number of counts in the blueward peak and the redward peak of the emission profile. The Ca II H and K emission lines probe the differential motion of certain chromospheric layers in the stellar atmosphere. Data on V/R for the Ca II K line are drawn from previous papers and compared to the analogous H line ratio, the H and K spectra being from the same sets of observations. It is found that the H line V/R value is +0.04 larger, on average, than the equivalent K line ratio, however, the difference varies with B-V color. Red giants cooler than B-V = 1.2 are more likely to have the H line V/R larger than the K line V/R, whereas the opposite is true for giants hotter than B-V = 1.2. The differences between the Ca II H and K line asymmetries could be caused by the layers of chromospheric material from which these emission features arise moving with different velocities in an expanding outflow.
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