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Register a new userA Study of the High-Luminosity Quasar HS 1946+7658
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We study the variability of the quasar HS 1946+7658 on intra-night time scale based on both our own optical and archival X-ray data. We find the quasar non-variable during about 11 hours of optical monitoring. This is in accordance with the low intra-night variability duty cycle of radio-quiet quasars. Regarding the X-rays, we cannot make a firm conclusion about the quasar variability owing to the controversial results of the light curves statistical analysis. In addition, we calibrated Johnson-Cousins $BVRI$ magnitudes of 7 field stars that are to be used as secondary standards.
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We present the highest quality Lyman Alpha forest spectra published to date, from the QSO HS 1946+7658. The distribution of H I column densities is a power law of slope -1.5 from Log N = 12.1 - 14. This power law can extend to N = 0, because lines weaker than Log N = 12.1 do not have a large H I optical depth. Low column lines with Log N > 9 could account for all observed He II absorption, but lines with Log N > 12 alone are unlikely to do so. The b distribution between 20 and 60 km/sec is a Gaussian with a mean of 23 km/sec (less than reported in past at this z), and a sigma b of 14 km/sec. We report no evolution in the Lyman alpha forest (except the number of lines), because Lu et al. (1997) found the same N and b distributions at <z> = 3.7. We see lines with 14 < b < 20 km/sec and b > 80 km/sec that cannot be accounted for by noise or blending effects. We discover that the lower cutoff in the b distribution varies with N, from b = 14 km/sec at Log N = 12.5 to b = 22 km/sec at Log N = 14.0, but otherwise b and N are not correlated. We see no Lyman Alpha line clustering above 50 kms, in disagreement with previous results from lower signal to noise data, but we do see a 3 sigma clustering signal at 25 - 50 km/sec among lines with Log N > 13.6
PDS 456 is a nearby (z=0.184), luminous (L_bol ~10^47 erg/s) type I quasar. A deep 190 ks Suzaku observation in February 2007 revealed the complex, broad band X-ray spectrum of PDS 456. The Suzaku spectrum exhibits highly statistically significant absorption features near 9 keV in the quasar rest--frame. We show that the most plausible origin of the absorption is from blue-shifted resonance (1s-2p) transitions of hydrogen-like iron (at 6.97 keV in the rest frame). This indicates that a highly ionized outflow may be present moving at near relativistic velocities (~0.25c). A possible hard X-ray excess is detected above 15 keV with HXD (at 99.8% confidence), which may arise from high column density gas (Nh>10^24cm^-2) partially covering the X-ray emission, or through strong Compton reflection. Here we propose that the iron K-shell absorption in PDS 456 is associated with a thick, possibly clumpy outflow, covering about 20% of $4pi$ steradian solid angle. The outflow is likely launched from the inner accretion disk, within 15-100 gravitational radii of the black hole. The kinetic power of the outflow may be similar to the bolometric luminosity of PDS 456. Such a powerful wind could have a significant effect on the co-evolution of the host galaxy and its supermassive black hole, through feedback.
X-ray and multi-wavelength observations of the most luminous known local (z<0.3) AGN, the recently discovered radio-quiet quasar PDS 456, are presented. The spectral energy distribution shows that PDS 456 has a bolometric luminosity of 1e47 erg/s, peaking in the UV. The X-ray spectrum obtained by ASCA and RXTE shows considerable complexity. The most striking feature observed is a deep, highly-ionised, iron K edge (8.7 keV, rest-frame), originating via reprocessing from highly ionised material, possibly the inner accretion disk. PDS 456 was found to be remarkably variable for its luminosity; in one flare the X-ray flux doubled in just about 15 ksec. If confirmed this would be an unprecedented event in a high-luminosity source, with a light-crossing time corresponding to about 2RS. The implications are that either flaring occurs within the very central regions, or else that PDS 456 is a super-Eddington or relativistically beamed system.
We propose a new interpretation of the quasar luminosity function (LF), derived from physically motivated models of quasar lifetimes and light curves. In our picture, quasars evolve rapidly and their lifetime depends on both their instantaneous and peak luminosities. We study this model using simulations of galaxy mergers that successfully reproduce a wide range of observed quasar phenomena. With lifetimes inferred from the simulations, we deconvolve the observed quasar LF from the distribution of peak luminosities, and show that they differ qualitatively, unlike for the simple models of quasar lifetimes used previously. We find that the bright end of the LF traces the intrinsic peak quasar activity, but that the faint end consists of quasars which are either undergoing exponential growth to much larger masses and higher luminosities, or are in sub-Eddington quiescent states going into or coming out of a period of peak activity. The break in the LF corresponds directly to the maximum in the intrinsic distribution of peak luminosities, which falls off at both brighter and fainter luminosities. Our interpretation of the quasar LF provides a physical basis for the nature and slope of the faint-end distribution, as well as the location of the break luminosity.
We present arc-second-resolution data in the radio, IR, optical and X-ray for 4C+19.44 (=PKS 1354+195), the longest and straightest quasar jet with deep X-ray observations. We report results from radio images with half to one arc-second angular resolution at three frequencies, plus HST and Spitzer data. The Chandra data allow us to measure the X-ray spectral index in 10 distinct regions along the 18 arcsec jet and compare with the radio index. The radio and X-ray spectral indices of the jet regions are consistent with a value of $alpha =0.80$ throughout the jet, to within 2 sigma uncertainties. The X-ray jet structure to the south extends beyond the prominent radio jet and connects to the southern radio lobe, and there is extended X-ray emission in the direction of the unseen counter jet and coincident with the northern radio lobe. This jet is remarkable since its straight appearance over a large distance allows the geometry factors to be taken as fixed along the jet. Using the model of inverse Compton scattering of the cosmic microwave background (iC/CMB) by relativistic electrons, we find that the magnetic field strengths and Doppler factors are relatively constant along the jet. If instead the X-rays are synchrotron emission, they must arise from a population of electrons distinct from the particles producing the radio synchrotron spectrum.
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