scholarly journals The X-ray Emission of Quasars as Observed by Ginga

1994 ◽  
Vol 159 ◽  
pp. 123-125
Author(s):  
A.J. Lawson ◽  
M.J.L. Turner
Keyword(s):  
Spectral Index ◽  
Rest Frame ◽  
Line Emission ◽  
Adequate Description ◽  
Rank Tests ◽  
X Ray ◽  
Spectrum Radio ◽  
Show Evidence ◽  
The Mean ◽  
The Relationship

We present preliminary results on a spectal analysis of quasars observed by the X-ray observatory Ginga. Simple power-law models with fixed Galactic absorbtion provide an adequate description of the spectra for most of the sources in the 2–18 keV band. A small number of sources show evidence for a feature at 6.4 keV (in the source rest frame) due to Fe line emission. Maximum likelihood and Spearman rank tests were used to investigate the relationship between radio loudness and X-ray spectral index in this class of object. These tests showed, respectively, that the mean X-ray spectral index of radio quiet quasars (RQQs) is significantly different from that of flat spectrum radio loud quasars (FRSQs) at the >99% level, and that the dominant relationship with spectral index is radio loudness (not X-ray luminosity or redshift) at >99% significance. This last result has not previously been demonstrated in this band, but agrees with findings in the lower energy Einstein band (0.5–3.5 keV). These results are discussed in the context of current unified models.

scholarly journals The Relationship of Hard X‐Ray and Optical Line Emission in Low‐Redshift Active Galactic Nuclei

2005 ◽  
Vol 634 (1) ◽  
pp. 161-168 ◽  
Author(s):  
T. M. Heckman ◽  
A. Ptak ◽  
A. Hornschemeier ◽  
G. Kauffmann
Keyword(s):  
Active Galactic Nuclei ◽  
Line Emission ◽  
Galactic Nuclei ◽  
X Ray ◽  
Optical Line ◽  
Relationship Of ◽  
The Relationship

scholarly journals Spectral Properties of Fermi Blazars and their Unification Schemes

2020 ◽  
Vol 29 (1) ◽  
pp. 168-178
Author(s):  
Evaristus U. Iyida ◽  
Finbarr C. Odo ◽  
Augustine E. Chukwude ◽  
Augustine A. Ubachukwu
Keyword(s):  
Selection Effect ◽  
Spectral Indices ◽  
Bl Lac Objects ◽  
X Ray ◽  
Spectrum Radio ◽  
Significant Difference ◽  
Evolutionary Connection ◽  
Galaxy Populations ◽  
The Relationship ◽  
Bl Lacs

AbstractWe use the distributions of spectral indices (αv ) of a large homogenous sample of Fermi-detected blazars to re-investigate the relationship between flat spectrum radio quasars (FSRQs) and subclasses of BL Lac objects (BL Lacs). We compute the broadband synchrotron and Compton spectral indices from radio-to-X-ray and X-ray to y-ray bands, respectively. Analyses of our data show continuity in the distributions of the spectral indices from FSRQs to HSP through LSP and ISP subclasses of BL Lacs. We find from y-ray luminosity distribution that the jetted radio galaxies form the low-luminosity tail of the distribution, which is suggestive that the sequence can be extended to the young jetted galaxy populations. We observe a significant difference in the shape of Compton and synchrotron spectra: significant anti-correlation (r ∼−0.80) exists between the broadband Compton and synchrotron spectral indices. Furthermore, the broadband spectral indices vary significantly with redshift (z) at low redshift (z < 0.3) and remain fairly constant at high (z ≥ 0.3) redshift. The trend of the variations suggests a form of evolutionary connection between subclasses of blazars. Thus, while selection effect may be significant at low redshift, evolutionary sequence can also be important. Our results are not only consistent with a unified scheme for blazars and their young jetted galaxy counterparts but also suggest that the broadband spectral sequence of blazars is not a secondary effect of redshift dependence.

scholarly journals Fresnel scatter revisited – comparison of 50 MHz radar and radiosondes in the Arctic, the Tropics and Antarctica

2010 ◽  
Vol 28 (10) ◽  
pp. 1993-2005 ◽  
Author(s):  
S. Kirkwood ◽  
E. Belova ◽  
K. Satheesan ◽  
T. Narayana Rao ◽  
T. Rajendra Prasad ◽  
...  
Keyword(s):  
Refractive Index ◽  
The Arctic ◽  
Refractive Index Gradient ◽  
Upper Troposphere ◽  
Show Evidence ◽  
Index Gradient ◽  
The Mean ◽  
Distinct Layering ◽  
The Tropics ◽  
The Relationship

Abstract. High-resolution radiosondes and calibrated radars operating close to 50 MHz, are used to examine the relationship between the strength of radar scatter and refractive index gradient. Three radars are used, in Kiruna in Arctic Sweden, at Gadanki in southern India and at the Swedish/Finnish base Wasa/Aboa in Queen Maud Land, Antarctica. Calibration is accomplished using the daily variation of galactic noise measured at each site. Proportionality between radar scatter strength and the square of the mean gradient of potential refractive index, M2, is found in the upper troposphere and lower stratosphere at all three sites, confirming previously reported results from many VHF radars. If the radar scatter is interpreted as Fresnel scatter, the constant of proportionality between radar scatter and M2 is found to be the same, within the calibration uncertainties, for all three radars. The radiosondes show evidence of distinct layering with sharp gradients, extending over 10s of kilometers horizontally, but the scatter is found to be two orders of magnitude weaker than would be expected from true Fresnel scatter from such layers. Using radar reflectivities resolved to a few 100 ms, we show that this is due to strong temporal variability in the scattering conditions, possibly due to undulations of the scattering layers. The constancy of the radar scatter – M2 relationship between the different sites suggests an unexpected uniformity in these perturbations between very different regions of the globe.

scholarly journals Correlation of X-Ray and Infrared Emission of Radio-Quiet QSOs

1987 ◽  
Vol 124 ◽  
pp. 607-609
Author(s):  
D. M. Worrall
Keyword(s):  
Spectral Index ◽  
Infrared Emission ◽  
X Ray ◽  
Previous Claim ◽  
Standard Deviations ◽  
The Relationship ◽  
Best Fit ◽  
Better Than

A correlation of the form , with γ = 0.83, is found between 2 keV monochromatic X-ray luminosity and 1.65 μm monochromatic infrared luminosity for a sample of optically selected radio-quiet QSOs. This is equivalent to an average 1.65 μm to 2 keV spectral index of αir/x = 1.28+0.05 log(lir/1031 ergs s−1 Hz−1). The ratio of X-ray to infrared luminosity decreases with increasing infrared luminosity in a manner similar to the relationship between X-ray and optical luminosity. The standard deviations of the distributions of data about the best-fit functions are comparable for the X-ray versus infrared and X-ray versus optical fits. Thus, contrary to a previous claim, the infrared luminosity is not better than the optical luminosity at predicting the X-ray emission from QSOs.

scholarly journals Quasar Surveys

1986 ◽  
Vol 119 ◽  
pp. 17-32
Author(s):  
M. G. Smith
Keyword(s):  
Luminosity Function ◽  
Seyfert Galaxies ◽  
Radio Sources ◽  
Selection Effects ◽  
Spectral Evolution ◽  
X Ray ◽  
Spectrum Radio ◽  
Show Evidence ◽  
Optical Surveys ◽  
Radio Luminosity Function

A review is given of progress in surveys for quasars at frequencies from radio to x-ray. Radio results show evidence for a decline in the radio luminosity function for flat-spectrum radio sources at redshifts z > 2. The IRAS survey is uncovering hitherto unknown dusty Seyfert galaxies. Optical surveys, which yield the largest number of QSOs per square degree, may suffer from selection effects which depend on intrinsic luminosity, redshift, and spectral evolution - particularly above redshift 2. Below redshifts of about 2.3, the optical magnitude-redshift plane is being filled in to the point where the evolution of the luminosity function can be seen directly. The statistics of quasar pair separations provide the best evidence so far for quasar clustering.The existence of many potentially significant selection effects means that a multi-frequency approach to quasar surveys is likely to prove essential to an understanding of the evolutionary behaviour of the quasar population as a whole.

scholarly journals Strong gravity effects: X-ray spectra, variability and polarimetry

2006 ◽  
Vol 2 (S238) ◽  
pp. 129-138
Author(s):  
Andrew C. Fabian
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Line Emission ◽  
Disk Surface ◽  
Seyfert Galaxies ◽  
Iron Line ◽  
X Ray ◽  
Gravity Effects ◽  
Show Evidence ◽  
Iron Abundance

AbstractAccreting black holes often show iron line emission in their X-ray spectra. When this line emission is very broad or variable then it is likely to originate from close to the black hole. The theory and observations of such broad and variable iron lines are briefly reviewed here. In order for a clear broad line to be found, one or more of the following have to occur: high iron abundance, dense disk surface and minimal complex absorption.Several excellent examples are found from observations of Seyfert galaxies and Galactic Black Holes. In some cases there is strong evidence that the black hole is rapidly spinning. Further examples are expected as more long observations are made with XMM-Newton, Chandra and Suzaku. The X-ray spectra show evidence for the strong gravitational redshifts and light bending expected around black holes.

THE RELATIONSHIP AMONG XBLs, RBLs AND FSRQs

2010 ◽  
Vol 19 (06) ◽  
pp. 909-915
Author(s):  
HONG-GUANG WANG ◽  
JUN-HUI FAN ◽  
YONG HUANG ◽  
JING PAN ◽  
JIANG-HE YANG
Keyword(s):  
Black Hole ◽  
Emission Line ◽  
Central Black Hole ◽  
Bl Lacertae Objects ◽  
X Ray ◽  
Bolometric Luminosity ◽  
Bl Lacertae ◽  
Spectrum Radio ◽  
The Relationship ◽  
Black Hole Masses

In this work, we revisited the relationship between the subclasses of blazars (X–ray selected BL Lacertae objects (XBLs), radio selected BL Lacertae objects (RBLs), and flat spectrum radio quasars (FSRQs)) based on a sample of blazars. We found that the FSRQs–RBLs–XBLs relationship is clear in their bolometric luminosity, emission line luminosity and the accretion ratio with V FSRQs > V RBLs > V XBLs , where V stands for the three parameters. However, there is no clear difference amongst their central black hole masses. The bolometric luminosity is closely correlated with the emission line luminosity and the accretion ratio.

scholarly journals Exploratory X-Ray Monitoring of Luminous Radio-quiet Quasars at High Redshift: Extended Time-series Analyses and Stacked Imaging Spectroscopy

2021 ◽  
Vol 923 (1) ◽  
pp. 111
Author(s):  
Marcus O. Thomas ◽  
Ohad Shemmer ◽  
W. N. Brandt ◽  
Maurizio Paolillo ◽  
Shai Kaspi ◽  
...  
Keyword(s):  
Time Series ◽  
Rest Frame ◽  
High Redshift ◽  
Imaging Spectroscopy ◽  
Optical Monitoring ◽  
Spectral Slope ◽  
Mean Power ◽  
X Ray ◽  
Time Series Analyses ◽  
The Mean

Abstract We present three new Chandra X-ray epochs along with new ground-based optical–UV observations as the third installment in a time-series analysis of four high-redshift (z ≈ 4.1–4.4) radio-quiet quasars. In total, we present nine epochs for these sources with rest-frame temporal baselines of ∼1300–2000 days. We utilize the X-ray data to determine basic variability properties, as well as produce mean spectra and stacked images based on effective exposure times of ∼40–70 ks per source. We perform time-series analyses in the soft and hard bands, separately, and compare variability properties to those of sources at lower redshifts and luminosities. The magnitude of X-ray variability of our sources remains consistent with or lower than that of similar sources at lower redshifts, in agreement with the variability–luminosity anticorrelation. The mean power-law photon indices in the stacked Chandra spectra of our sources are consistent with the values measured from their archival XMM-Newton spectra separated by about 3 yr in the rest frame. Along with the X-ray observations, we provide near-simultaneous optical monitoring of the sources in the optical–UV regime. The overall variability in the optical-to-X-ray spectral slope is consistent with sources at lower redshifts, and the optical–UV observations display mild variability on monthly timescales.

scholarly journals ROSAT Observations of Bright BL Lacertae Objects

1994 ◽  
Vol 159 ◽  
pp. 377-377
Author(s):  
G. Lamer ◽  
H. Brunner ◽  
R. Staubert
Keyword(s):  
Power Laws ◽  
Spectral Indices ◽  
Bl Lacertae Objects ◽  
Mean Values ◽  
X Ray ◽  
Bl Lacertae ◽  
Spectrum Radio ◽  
Significant Difference ◽  
The Mean ◽  
5 Ghz

We have compiled a sample of 23 X-ray and radio selected BL Lacertae objects which have been observed with the Position Sensitive Proportional Counter (PSPC) on board of the ROSAT Satellite. The sample consists of three parts:In Table I results from 4 objects observed for their known rapid X-ray variability are presented. 5 objects are the BL Lac subset of a complete sample of flat spectrum radio sources with 5 GHz flux densities > 1 Jy. Detailed results from this sample will be published in Brunner et al. 1993. The data of the 14 remainig objects were collected from the ROSAT data archive to supplement the sample. The whole sample contains 7 X-ray selected objects (XBLs,αOX < 1.2) and 16 radio selected objects (RBLs).The X-ray spectra of the sources are well described by single power laws with galactic absorption. The X-ray energy indices αX are widely dispersed around a mean of 1.34. Significant X-ray flux variability and correlated spectral variability was detected on timescales down to hours. The object H 1218+304 was found to be rapidly variable within each of three observations. Its spectral hardness is correlated with the flux level (see Table I).We calculated the intrinsic distributions of the spectral indices αX for the XBL and RBL samples and of the differences between ROSAT and EXOSAT ME spectral indices αPSPC – αME (only XBL sample) using a maximum likelihood fit. There is no significant difference in the mean spectral indices between the X-ray and radio selected subsamples. The mean values < αX > are 1.34 for XBLs and 1.33 for RBLs. The spectra of the X-ray selected objects slightly steepen at higher X-ray energies (< αPSPC – αME > = −0.11). This supports the view that the X-ray emission of XBLs is supplied by synchrotron radiation. The steepening of the X-ray spectrum is then due to a cutoff in the energy distribution of the electrons.

A Search for Halo Binaries: the First Results

1984 ◽  
Vol 88 ◽  
pp. 381-384
Author(s):  
David W. Latham ◽  
Robert P. Stefanik ◽  
Bruce W. Carney
Keyword(s):  
Rest Frame ◽  
Radial Velocities ◽  
Mean Velocity ◽  
Local Standard ◽  
Show Evidence ◽  
First Results ◽  
The Mean ◽  
High Space ◽  
Local Standard Of Rest

AbstractHe report the first results from a program to monitor the stars in the Carney and Latham (1985) halo survey for velocity variations due to orbital motion. From the sample of 300 stars with high space velocities, 24 spectroscopie binaries candidates have been identified.The Halo Survey of Carney and Latham (1985) has identified approximately 300 stars with space velocities greater than 200 km sec−l compared to the local standard of rest. The radial velocities of these stars have been monitored for typically two years, and at least 24 show evidence of possible variation. These stars are listed in Table I, which gives the star name, the number of observations, the number of days between the first and last observations, the mean velocity, the RMS, the U, V, and W velocities, and the speed compared to the galactic rest frame.The error of a single measurement is perhaps ± 0.7 km sec−1, but depends to some extent on the metallicity and the quality of the spectrum. For a star to be included in Table I as a binary candidates we have chosen a threshold of ± 2.0 km sec−1 for the RMS, or approximately 3 sigma. We plan to monitor the radial velocities of these binary candidates closely over the next few years. We also plan to obtain b-y and V-K colors to search for the light of possible companions.

Sign in / Sign up

Export Citation Format

Share Document