Quasar Continuum Research Articles

A gravitational microlensing determination of continuum source size in Q2237+0305

Following the detection of a gravitational microlensing high-magnification event (HME) in Q2237+0305A, attempts have been made to place limits on the dimensions of the quasar continuum source. The analyses have studied either the observed event magnitude or the event duration. The latter approach has been hampered by lack of knowledge about the transverse velocity of the lensing galaxy. We obtain both upper and lower statistical limits on the size of the continuum source from the observed HME using determinations of transverse velocity obtained from the published monitoring data. Our calculations take account of the caustic orientation as well as the component of the caustic velocity that results from stellar proper motions. Our determination of the source size relies on an estimated duration of 52 d for the HME, and so will be refined when more HMEs are observed. We find that the upper and lower limits on the magnified region of the R-band continuum source are 6 × 1015 and 2 × 1013 cm, respectively (99 per cent confidence). Through consideration of the joint probability for source size and mean microlens mass we find that the mean mass lies between ∼0.01 and ∼1 M⊙ (95 per cent confidence).

The shape of the blue/UV continuum of B3-VLA radio quasars: dependence on redshift, blue/UV luminosity and radio power

We present UBVR photometry of a sample of 73 radio quasars, about 80 per cent complete, with redshifts 0.4–2.8. From these data the shape of the spectral energy distribution (SED) in the rest-frame blue/ultraviolet is analysed, using the individual sources as well as through broad-band composite SEDs. The SEDs of the individual sources are generally well fitted with power laws, with slopes α ranging from 0.4 to –1.7 (Sν∝να). Two sources with α 3000 A to αUV=−0.66 ± 0.15 at λ <3000 A. Although the broad-band spectral points are expected to include some masked contamination from emission lines/bumps, the break cannot be explained by line/bump emission, and most likely reflects an intrinsic trend in the continuum. The continuum shape is shown to depend on redshift. For the quasars with z 1.2, αUV is more flat, −0.48±0.12, and there are too few spectral points longward of 3000 A to obtain αblue and analyse the presence of the 3000-A break. A trend similar to that between αUV and z is found between αUV and luminosity at 2400 A, L2400, with luminous quasars exhibiting a harder spectrum. The data show an intrinsic correlation between L2400 and the radio power at 408 MHz, not related to selection effects or independent cosmic evolution. The correlations αUV–z, αUV–L2400 and L2400–z appear to be consistent with accretion disc models with approximately constant black hole mass and accretion rates decreasing with time. If the trends L2400–z and P408–z are predominantly related to a selection bias, rather than cosmic evolution, only one of the correlations αUV–L2400 or αUV–z needs to be intrinsic.

A Comparison of the Optical Properties of Radio‐loud and Radio‐quiet Quasars

We have made radio observations of 87 optically selected quasars at 5 GHz with the VLA in order to measure the radio power for these objects and hence determine how the fraction of radio-loud quasars varies with redshift and optical luminosity. The sample has been selected from the recently completed Edinburgh Quasar Survey and covers a redshift range of 0.3 < z < 1.5 and an optical absolute magnitude range of -26.5 < M_{B} < -23.5 (h, q_{0} = 1/2). We have also matched up other existing surveys with the FIRST and NVSS radio catalogues and combined these data so that the optical luminosity-redshift plane is now far better sampled than previously. We have fitted a model to the probability of a quasar being radio-loud as a function of absolute magnitude and redshift and from this model infer the radio-loud and radio-quiet optical luminosity functions. The radio-loud optical luminosity function is featureless and flatter than the radio-quiet one. It evolves at a marginally slower rate if quasars evolve by density evolution, but the difference in the rate of evolutions of the two different classes is much less than was previously thought. We show, using Monte-Carlo simulations, that the observed difference in the shape of the optical luminosity functions can be partly accounted for by Doppler boosting of the optical continuum of the radio-loud quasars and explain how this can be tested in the future.

Application of the contouring method to extended microlensed sources

The method devised by Lewis et al. (1993) for calculating the light curve of a microlensed point source is expanded to two dimensions to enable the calculation of light curves of extended sources. This method is significantly faster than the ray shooting method that has been used in the past. The increased efficiencyis used to obtain much higher resolution light curves over increased time scales. We investigate the signatures arising from different source geometries in a realistic microlensing model. We show that a large fraction of high magnification events (HMEs) in image A of Q2237+0305 involve only one caustic, and could therefore yield information on the structure of the quasar continuum through the recognition of a characteristic event shape. In addition, the cataloguing of HMEs into morphological type will, in theory, enable the direction of the transverse motion, as well as the source size to be obtained from long term monitoring.

On Quasar Masses and Quasar Host Galaxies

The mass of massive black holes in quasar cores can be deduced using the typical velocities of Hb-emitting clouds in the Broad Line Region (BLR) and the size of this region. However, this estimate depends on various assumptions and is susceptible to large systematic errors. The Hb-deduced black hole mass in a sample of 14 bright quasars is found here to correlate with the quasar host galaxy luminosity, as determined with the Hubble Space Telescope (HST). This correlation is similar to the black hole mass vs. bulge luminosity correlation found by Magorrian et al. in a sample of 32 nearby normal galaxies. The similarity of the two correlations is remarkable since the two samples involve apparently different types of objects and since the black hole mass estimates in quasars and in nearby galaxies are based on very different methods. This similarity provides a ``calibration'' of the Hb-deduced black hole mass estimate, suggesting it is accurate to +-0.5 on log scale. The similarity of the two correlations also suggests that quasars reside in otherwise normal galaxies, and that the luminosity of quasar hosts can be estimated to +-0.5 mag based on the quasar continuum luminosity and the Hb line width. Future imaging observations of additional broad-line active galaxies with the HST are required in order to explore the extent, slope, and scatter of the black hole mass vs. host bulge luminosity correlation in active galaxies.

The Neutral Hydrogen Column Density Towards Q1937-1009 From the Unabsorbed Intrinsic Continuum in the Lyman-alpha Forest.

view Abstract Citations (51) References (11) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Neutral Hydrogen Column Density Towards Q1937-1009 From the Unabsorbed Intrinsic Continuum in the Lyman-alpha Forest. Burles, Scott ; Tytler, David Abstract The absorption system at ζ=3.572 towards Q1937-1009 provides the best extragalactic measurement of the atomic deuterium to hydrogen ratio, D/H. We have obtained a new low-resolution, high signal-to-noise ratio (SNR) Keck spectrum to re-measure the total neutral hydrogen column density N(H I) using the amount of Lyman continuum absorption. We develop a new method to directly determine the intrinsic unabsorbed quasar continuum from low-resolution spectra of the Lyα forest for the first time. We use three types of spectra to measure N( H I): (1) A wide slit spectrum for flux calibration, (2) a high-resolution spectrum to determine the unabsorbed continuum between Lyα forest lines, and (3) a high SNR spectrum to measure the residual flux below the Lyman limit. We measure log[N(H I)]=17.86±0.02 cm-2, which is reliable because N(H I) is fully specified by the data. This result is consistent with the N(H I) measured by Tytler et al. (1996, Nature, 381, 207) from the Lyman series absorption lines, but not with absorption models proposed by Wampler (1996, Nature, 383, 308) nor estimates of the total N(H I) by Songaila et al. (1997, Nature, 385, 137), both of which suggested lower N(H I) and higher D/H. The Wampler models predict abundant flux below the Lyman limit which is absent from both our old and new spectra, taken with different instruments. The new Keck data is consistent with the data presented by Songaila et al. (1997). The results differ due to the different methods of analysis, and our measurement of the QSO continuum does not agree with the continuum models assumed by Songaila et al. Publication: The Astronomical Journal Pub Date: October 1997 DOI: 10.1086/118566 arXiv: arXiv:astro-ph/9707176 Bibcode: 1997AJ....114.1330B Keywords: QUASARS: ABSORPTION LINE; GALAXIES: ABUNDANCES; Astrophysics E-Print: 15 pages, 6 figures, To appear in the Astronomical Journal in October 1997 full text sources arXiv | ADS | data products SIMBAD (2) NED (2)

The Relationship between the High-Energy Continuum and Emission Lines in Quasars: A Low-Redshift Sample

view Abstract Citations (52) References (60) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Relationship between the High-Energy Continuum and Emission Lines in Quasars: A Low-Redshift Sample Green, Paul J. Abstract Photoionization models dictate that many prominent quasar emission lines are sensitive to both the luminosity and shape of the quasars high- energy continuum-primarily the extreme ultraviolet (EUV) and soft X-ray continuum. Unfortunately, the EUV band is severely obscured by Galactic absorption. Using data from the adjacent UV and soft X-ray bandpasses, we initiate the first large-scale, multiline investigation of correlations between the QSO soft X-ray continuum and line emission in a sample of QSOs observed by Einstein and IUE. We present a new error analysis for objective, automated line measurements, which enables us to include the information contained in weak or undetected lines. We tabulate more than 300 UV emission-line equivalent widths from IUE spectra of 85 QSOs in the atlas of Lanzetta, Turnshek, & Sandoval, then characterize the distributions of line equivalent and velocity widths (Wlambda_ and FWHM). We then compare these line parameters to the QSO continuum spectral energy distributions from optical through soft X-ray wavelengths, using survival analysis to incorporate any nondetections for X-ray flux and/or UV emission lines. Several correlations noted in previous studies are not reproduced here. However, we illustrate that the exclusion of undetected lines from such studies may spuriously enhance apparent correlations. We find significant correlations between Wlambda_ and UV luminosity (e.g., the well-studied Baldwin effect) for Lyα, C IV, He II, and C III]. Wlambda_(C III]) and Wlambda_(He II) also show previously unreported correlations with X-ray luminosity that, for C III], appears to be primary. The line ratios C III]/Lyα and He II/Lyα both show strongest dependence on l_x_. Wlambda_(Lyα) correlates strongly with spectral slopes α_UV_ and α_OX_ (between 2500 A and 2 keV), but not with X-ray luminosity. Using these results, we argue that one simple geometrical interpretation of the Baldwin effect (BEff) as a result of a distribution of disk inclinations is not plausible. We also provide evidence that the BEff weakens or disappears when the line emission is correctly compared to the luminosity in the continuum bandpass relevant to its production. We thus support the interpretation of the BEff as a change in spectral energy distribution with luminosity, and we predict that no BEff relative to X-ray luminosity should be found for Fe II or Mg II emission lines. Extensions of our method to samples of a wider redshift/ luminosity range will be presented in a later paper, which will test these predictions. Publication: The Astrophysical Journal Pub Date: August 1996 DOI: 10.1086/177584 arXiv: arXiv:astro-ph/9603099 Bibcode: 1996ApJ...467...61G Keywords: GALAXIES: ACTIVE; GALAXIES: QUASARS: EMISSION LINES; GALAXIES: QUASARS: GENERAL; ULTRAVIOLET: GALAXIES; X-RAYS: GALAXIES; Astrophysics E-Print: 31 pages including 3 figures, AAS latex, plus 6 tables totaling 8 pages, to appear in ApJ Vol. 468, September 1, 1996 full text sources arXiv | ADS | data products NED (85) SIMBAD (10) MAST (1) INES (1)

Radiative Transfer in a Clumpy Universe. II. The Ultraviolet Extragalactic Background

view Abstract Citations (1427) References (99) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Radiative Transfer in a Clumpy Universe. II. The Ultraviolet Extragalactic Background Haardt, Francesco ; Madau, Piero Abstract The integrated ultraviolet flux arising from QSOs and/or hot, massive stars in metal-producing young galaxies is likely responsible for maintaining the intergalactic diffuse gas and the Lyα forest clouds in a highly ionized state. The spectrum and intensity of such UV background have generally been obtained by modeling the reprocessing due to intervening material as a pure photoelectric absorption process. However, owing to the emission from radiative recombinations within the absorbing clouds, a photoionized clumpy medium could contribute substantially to the metagalactic flux. In other words, QSO absorption- line systems are sources, not just sinks of ionizing photons. We present a detailed calculation of the propagation of AGN-like ionizing radiation through the intergalactic space. We model the ionization state of absorbing clouds, and show that the universe will be more opaque above 4 Ry than previously estimated. Singly ionized helium in Lyα forest clouds and Lyman-limit systems is found to be very efficient in reprocessing soft X-ray, helium-ionizing photons into ultraviolet, hydrogen-ionizing ones. We demonstrate that a significant fraction of the absorbed primary photons (emitted, e.g., by quasar sources) will be reradiated by the photoionized gas through Lyα line emission, two-photon continuum, and recombination continuum radiation. In the light of new data and recent studies, we also reassess the contribution of the QSOs observed in optical surveys to the UV extragalactic background, and find that the stochastic reprocessing of quasar Lyman continuum radiation by hydrogen and helium along the line of sight will significantly affect the amplitude, spectral shape, and fluctuation properties of the metagalactic flux. In a scenario in which QSOs are the primary source of ionizing photons in the universe, the integrated H I Lyα emission at z = 0 from photoionized Lyα clouds and Lyman limit systems is found to be at a level of less than 5% of current observational limits on the far-UV extragalactic radiation flux. We show that J_912_ increases from ~10^-23^ ergs cm^-2^ s^-1^ Hz^- 1^ sr^-1^ at the present epoch to ~5 x 10^-22^ ergs cm^-2^ s^-1^ Hz^-1^ sr^-1^ at z = 2.5. The attenuated direct quasar emission plus recombination radiation from intergalactic gas appear to provide enough hydrogen-ionizing photons to satisfy the proximity effect at large redshift. The He II/H I ratio in the diffuse intergalactic medium and the Lyα clouds increases from ~25 at z = 0 to ~45 at z = 2.5, to decrease again below 30 for z >~ 4.5. The spectrum of the ionizing background at high redshift is shown to have a hump at energies below 40.8 eV due to redshift-smeared He Il Lyα line and two-photon continuum emission. We propose that observations of low-ionization species such as O II in metal-line absorption systems may be able to test the presence of such a prominent feature in the UV background spectrum. We also note that, if the metagalactic flux is dominated by QSOs, the suggested steep decline of their ionizing emissivity beyond z ~ 4 should produce an increase in the observed rate of incidence of Lyα forest clouds at these redshifts relative to an extrapolation from the intermediate-z regime, as observed by Williger et al. (1994). Publication: The Astrophysical Journal Pub Date: April 1996 DOI: 10.1086/177035 arXiv: arXiv:astro-ph/9509093 Bibcode: 1996ApJ...461...20H Keywords: COSMOLOGY: THEORY; COSMOLOGY: DIFFUSE RADIATION; GALAXIES: INTERGALACTIC MEDIUM; GALAXIES: QUASARS: ABSORPTION LINES; RADIATIVE TRANSFER; Astrophysics E-Print: revised version submitted to ApJ 20 sept 95, full text sources arXiv | ADS | data products SIMBAD (4) Related Materials (3) Part 1: 1995ApJ...441...18M Part 3: 1999ApJ...514..648M Part 4: 2012ApJ...746..125H

Broad NE 8 lambda 774 emission from quasars in the HST-FOS snapshot survey (ABSNAP)

We discuss the strength and frequency of broad Ne VIII lambda 774 emission from quasars measured in the Hubble Space Telescope Faint Object Spectrograph (HST-FOS) snapshot survey (Absnap). Five sources in the survey have suitable redshifts (0.86 less than or equal to Z(sub em) less than or equal to 1.31), signal-to-noise ratios and no Lyman limit absorptions. Three of the five sources have a strong broad emission line near 774 A (rest), and the remaining two sources have a less securely measured line near this wavelength. We identify these lines with Ne VIII lambda 774 based on the measured wavelengths and theoretical estimates of various line fluxes (Hamann et al. 1995a). Secure Ne VIII detections occur in both radio-loud and radio-quiet sources. We tentatively conclude that broad Ne VIII lambda 774 emission is common in quasars, with typical strengths between approximately 25% and approximately 200% of O VI lambda 1034. These Ne VIII lambda 774 measurements imply that the broad emission line regions have a much hotter and more highly ionized component than previously recognized. They also suggest that quasar continua have substantial ionizing flux out to energies greater than 207 eV (greater than 15.2 ryd, lambda less than 60 A). Photoionization calculations using standard incident spectra indicate that the Ne VIII emission requires ionization parameters U greater than or = 5, total column densities N(sub H) greater than or = 10(sub 22)/sq cm and covering factors greater than or = 25%. The temperatures could be as high as approximately 10(exp 5) K. If the gas is instead collisionally ionized, strong Ne VIII would imply equilibrium temperatures in the range approximately 400,000 less than or approximately = T(sub e) less than or approximately = 10(exp 6) K. In either case, the highly ionized Ne VIII emission regions would appear as X-ray 'warm absorbers' if they lie along our line of sight to the X-ray continuum source.

The X-ray and ultraviolet absorbing outflow in 3C 351

3C 351 (z = 0.371), and X-ray-'quiet' quasar, is one of the few quasars showing signs of a 'warm absorber' in its X-ray spectrum; i.e., partially ionized absorbing material in the line of sight whose opacity depends on its ionization structure. The main feature in the X-ray spectrum is a K-edge due to O VII or O VIII. 3C 351 also shows unusually strong, blueshifted, associated, absorption lines in the ultraviolet (Bahcall et al. 1993) including O VI (lambda lambda 1031, 1037). This high ionization state strongly suggests an identification with the X-ray absorber and a site within the active nucleus. In this paper we demonstrate that the X-ray and UV absorption is due to the same material. This is the first confirmed UV/X-ray absorber. Physical conditions of the absorber are determined through the combination of constraints derived from both the X-ray and UV analysis. This highly ionized, outflowing, low-density, high-column density absorber situated outside the broad emission line region (BELR) is a previously unknown component of nuclear material. We rule out the identification of the absorber with a BELR cloud as the physical conditions in the two regions are inconsistent with one another. The effect of the X-ray quietness and IR upturn in the 3C 351 continuum on the BELR is also investigated. The strengths of the high-ionization lines of C IV lambda-1549 and O VI lambda-1034 with respect to Lyman-alpha are systematically lower (up to a factor of 10) in the material ionized by the 3C 351 continuum as compared to those produced by the 'standard' quasar continuum, the strongest effect being on the strength of O VI lambda-1034. We find that for a 3C 351-like continuum, C III) lambda-1909 ceases to be a density indicator.

Continuum and line emission in Cygnus A

Continuum and line emission in Cygnus A

The intrinsic nuclear spectrum of NGC 1068

We have inferred the intrinsic optical, UV and X-ray continuum of the obscured Seyfert nucleus of NGC 1068, using small aperture and polarized flux data to separate host galaxy contamination from reflected nuclear light. In support of popular unification models, we find it to be similar to typical type 1 Seyfert galaxy and quasar continua. The bolometric luminosity of the active nucleus is 2.2 x 10(exp 11) (f(sub refl)/0.01)(exp -1)(D/22Mpc)(exp 2) L(sub sun), where f(sub refl) is the fraction of nuclear flux reflected into our line of sight and D is the distance to NGC 1068.

Measurements of D A for a Large QSO Sample and Determination of Evolution of Lyman-Alpha Clouds

We have measured D A , the mean relative depression of quasar continuum between Lyα and Lyβ emission, for a large sample of quasars. We have carried out the measurements by simply adding the Lyα lines (excluding the lines in identified systems) together. The big advantage of this approach over the conventional method is that the continuum is fitted locally by employing high S/N and relatively high resolution spectra, and this leads to a more reliable estimate of the continuum level in the Lyα forest region. Also, the contamination of D A by metal lines is easily removed. Extending the method proposed by Zuo (1993) and Lu & Zuo (1993), we have determined γ int , the intrinsic evolutionary rate exponent of Lyα forest lines

Properties of high-redshift Lyman-alpha clouds. I - Statistical analysis of the Schneider-Schmidt-Gunn quasars

Techniques for statistical analysis of the Lyman-α forest in high-redshift quasars are developed, and applied to the low-resolution (25 A) spectra of 29 of the 33 quasars in the Schneider-Schmidt-Gunn (SSG) sample. We extrapolate each quasar's continuum shortward of Lyman-α emission, then consider each spectral bin of each quasar to be an (approximately) independent measurement of the absorption due to the Lyman-α clouds. With several thousand such measurements thus available, we can obtain good determinations of some interesting properties of clouds in the redshift range 2.5 &lt;z &lt;4.3 without actually resolving any single cloud. We find that the mean absorption increases with z approximately as a power law (1 + Z)<SUP>gamma</SUP> + 1^ with γ = 2.46 +/- 0.37. The mean ratio of Lyman-α to Lyman-β absorption in the clouds is 0.476 +/- 0.054. We also detect, and obtain ratios, for Lyman-γ, δ, and possibly ɛ. We are also able to quantify the fluctuations of the absorption around its mean, and find that these are comparable to, or perhaps slightly larger than, that expected from an uncorrelated distribution of clouds. The techniques in this paper, which include the use of bootstrap resampling of the quasar sample to obtain estimated errors and error covariances, and a mathematical treatment of absorption from a (possibly nonuniform) stochastic distribution of lines, should be applicable to future, more extensive, data sets.

A dwarf galaxy near the sight line to PKS 0454+0356 - A fading 'faint blue galaxy'?

view Abstract Citations (15) References (22) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A Dwarf Galaxy near the Sight Line to PKS 0454+0356: A Fading ``Faint Blue Galaxy''? Steidel, Charles C. ; Dickinson, Mark ; Bowen, David V. Abstract We report the discovery of a dwarf galaxy (M_B_=-17.2 for H_0_=50 km s^-1^ Mpc^-1^) at z = 0.072 which is only 4" (3.7 h^-1^_100_ kpc) in projection from the line of sight to the bright quasar PKS 0454+0356 (Z_em_ = 1.345). The dwarf has very blue optical and optical/infrared colors and exhibits line emission indicative of ongoing or recent star formation. However, there is no detection of Ca II λλ3934, 3969 absorption at Z_abs_ = 0.072 to equivalent width limits (3 σ) of ~40 mA, which would suggest an H I column density along the line of sight of less than 5 X 10^19^ cm^-2^, if the Ca II/H I ratio is similar to sight lines in the Galaxy. Based on the absence of Ca II absorption and the unusually weak line emission given the very blue color of the dwarf, we speculate that it may be close to exhausting its supply of gas. As its star formation rate declines, the galaxy's blue magnitude should fade substantially, eventually reaching a quiescent state in accord with its K luminosity of ~0.005 L_sun_. Future observations of the sight line to PKS 0454+0356 using HST in search of Mg II resonance lines, or a search for 21 cm absorption against the quasar radio continuum, could place even more stringent limits on the extent of the gas associated with an intrinsically faint, star-forming dwarf. Publication: The Astrophysical Journal Pub Date: August 1993 DOI: 10.1086/186963 Bibcode: 1993ApJ...413L..77S Keywords: Blue Stars; Dwarf Galaxies; Emission Spectra; Quasars; Star Formation; Faint Objects; Line Of Sight; Astrophysics; GALAXIES: DISTANCES AND REDSHIFTS; GALAXIES: EVOLUTION; GALAXIES: QUASARS: ABSORPTION LINES full text sources ADS | data products SIMBAD (5) NED (3)

The nucleus of the Cygnus A galaxy

view Abstract Citations (26) References (38) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Nucleus of the Cygnus A Galaxy Vestergaard, M. ; Barthel, P. D. Abstract Newly obtained high resolution optical images of the prototypical luminous radio galaxy Cygnus A (3C 405) indicate an inhomogeneous distribution of obscuring dust and, in combination with previous data, three types of radiation (stellar and blue featureless continuum as well as luminous line emission) in its central regions. The galaxy should not be classified as a colliding pair of galaxies, nor as a dust-lane galaxy. The alleged double nucleus finds its origin in heavy obscuration coupled to excess line emission in the central regions of an otherwise normal giant elliptical galaxy. A strongly reddened nuclear component, coincident with the Cygnus A radio core, is found to emit faint but concentrated narrow line emission. All data appear consistent with identification of Cygnus A as a radio-loud quasar having its radio axis oriented at about 35^deg^ from the sky plane. The presumed dust torus obscuring the quasar continuum is inferred to be smaller than 800 parsecs. Publication: The Astronomical Journal Pub Date: February 1993 DOI: 10.1086/116443 Bibcode: 1993AJ....105..456V Keywords: Cosmic Dust; Cygnus Constellation; Elliptical Galaxies; Galactic Nuclei; Imaging Techniques; Radio Galaxies; Emission Spectra; High Resolution; Line Spectra; Luminosity; Astrophysics; GALAXIES: INDIVIDUAL: CYGNUS A (3C405); GALAXIES: NUCLEI; GALAXIES: ACTIVE full text sources ADS | data products SIMBAD (2) NED (1)

The role of Compton and Raman scattering in the quasar continuum

There are three ways in which an electromagnetic wave can undergo scattering in a plasma: (i) when the scattering of radiation occurs by a single electron, it is called Compton Scattering (CS); (ii) if it occurs by a longitudinal electron plasma mode, it is called Stimulated Raman Scattering (SRS), and (iii) if it occurs by a highly damped electron plasma mode, it is called Stimulated Compton Scattering (SCS). The non-thermal continuum of quasars is believed to be produced through the combined action of synchrotron and inverse Compton processes, which are essentially single-particle processes. Here, we investigate the role of SRS and SCS in the generation of continuum radiation from these compact objects. It is shown as an example that the complete spectrum of 3C 273 can be reproduced by suitably combining SCS and SRS. The differential contributions of SCS and SRS under different values of the plasma parameters are also calculated.

Interpreting the light curve of Q2237 + 0305

view Abstract Citations (41) References (29) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Interpreting the Light Curve of Q2237+0305 Webster, R. L. ; Ferguson, A. M. N. ; Corrigan, R. T. ; Irwin, M. J. Abstract Theoretical modeling of the mass distribution in the lens for Q2237+0305 will not give an accurate estimate of the microlensing parameters for each of the images. It will be possible to statistically estimate microlensing parameters from the data, however the timescales over which data must be collected, may be uncomfortably long. The required timescale depends on both the mean compact object mass and the apparent transverse velocity of the source, and is ~> 130(m/M_sun_)^0.5^ (5000 km s^-1^/v_t_) years. The observation of the quasar continuum source crossing a caustic or cusp line gives a good estimate of the source size. Our best estimate from the current data is <~4 X 10^-4^ (v_t_/5000 km s^-1^)pc. General characteristics of the light curves will tell us about the nature of cluster and halo dark matter. Preliminary indications, principally from the lensed quasar 0957+561, suggest that cluster dark matter comprises objects smaller than ~0.1M_sun_. A better understanding of the mass distribution in the principle lensing galaxy for these two gravitationally lensed quasars and careful monitoring of the individual images on a regular basis (weekly for Q2237+0305) would provide the required statistical base to better determine the quasar source size, the nature of dark matter, and the masses of compact objects responsible for microlensing. Publication: The Astronomical Journal Pub Date: December 1991 DOI: 10.1086/116015 Bibcode: 1991AJ....102.1939W Keywords: Dark Matter; Gravitational Lenses; Light Curve; Galactic Structure; Quasars; Astrophysics; GRAVITATIONAL LENSES; QUASARS full text sources ADS | data products NED (5) SIMBAD (2)

The shape of the ultraviolet continuum of quasars and intergalactic dust

Measurements are presented of the shape of the UV continuum of a large number of quasars. We investigate earlier claims that the near-UV spectral index α UV gets flatter with increasing look-back time. We also investigate the dependence of α UV on luminosity and radio type.

Models of the continuum of quasars and AGNs in the EUV and adjacent energy ranges

Abstract It is in the extreme ultraviolet band (1200 A − 1 keV) that the energy emitted by quasars and AGNs is most intense. No direct information however is yet available in this range. What constraints on the EUV continuum flux are set by the observations of the continuum in the optical, UV and X-ray ranges, and by the observations of optical/UV emission line intensity ratios? What constraints are set by plausible models of the UV/X spectrum? What are the signatures of an accretion disk in this range? We examine these questions and conclude that direct observations of the flux variations and the spectral shape of the EUV continuum are essential to make progress in this field.