scholarly journals Soft X-ray Emission of Quasars

1994 ◽  
Vol 159 ◽  
pp. 373-373
Author(s):  
N. Schartel ◽  
R. Walter ◽  
H.H. Fink
Keyword(s):  
Power Law ◽  
High Redshift ◽  
Spectral Band ◽  
Black Body ◽  
Spectral Slope ◽  
X Ray ◽  
Body Model ◽  
Sky Survey ◽  
Photon Index ◽  
The Mean

From a list of known quasars compiled from various catalogues we selected all sources detected by the PSPC (0.1 – 2.4 keV) aboard ROSAT with more than 80 counts during the all sky survey. A sample of 102 sources resulted. At higher redshifts most of the selected sources are radio-loud. At a redshift smaller than 0.50 we found 54 radio-quiet quasars and 30 radio-loud sources. For this reduced sample the mean spectral index of the radio-quiet sources (< Γ > = 2.53) and that of the radio-loud ones (< Γ > = 2.26) are clearly different with a significance of 3.3 σ.About 2/3 of the bright quasars observed with Einstein also belong to our sample. The spectra observed with ROSAT are sytematically steeper than the ones observed with Einstein yielding a < ΓROSAT – ΓEinstein > of 0.66 ± 0.18 for radio quiet and of 0.68 ± 0.19 for radio-loud sources, respectively.For radio loud quasars, the mean spectral slope decreases from 2.3 to 1.5 when the redshift increases beyond 0.5 (figure 1). The fact that high redshift sources show a photon index of about 1.5, which is similar to the mean index observed with Einstein for radio-loud sources, suggests that this decrease towards higher redshifts can be interpreted by the shift of the soft X-ray excess outside of the ROSAT spectral band when the redshift increases. The solid lines in figure 1 represent theoretical pathes of the photon index as a function of the redshift as derived from simulations assuming a power law plus black body model spectrum for the quasars X-ray emission. In curve No 1 the powerlaw index is fixed to 1.4. To be compatible with the observation the temperature of the blackbody component must range between 50 and 70 eV. Curve No 2 asssumes the same model with a powerlaw index fixed to 1.8 to account for radio quiet sources.

scholarly journals The inner view of NGC 1052 using multiple X-ray observations

2019 ◽  
Vol 491 (1) ◽  
pp. 29-38 ◽  
Author(s):  
N Osorio-Clavijo ◽  
O González-Martín ◽  
I E Papadakis ◽  
J Masegosa ◽  
L Hernández-García
Keyword(s):  
Power Law ◽  
High Energy ◽  
Spectral Slope ◽  
X Ray ◽  
Band Power ◽  
Neutral Material ◽  
Photon Index ◽  
Epoch Analysis ◽  
First Time ◽  
Reflection Component

ABSTRACT In this paper, we present a multi-epoch analysis of NGC 1052, a prototypical low-luminisity active galactic nucleus, using XMM–Newton, Suzaku and NuSTAR observations taken from 2001 to 2017. This is the first time that results from NuSTAR observations have been reported for NGC 1052. Regarding technical aspects, we found a wavelength-dependent calibration issue between simultaneous XMM–Newton and NuSTAR spectra, characterized by a change in the photon index of $\rm { \Gamma _{NuSTAR}- \Gamma _{XMM-Newton}=0.17\pm 0.04}$. We use ancillary Chandra data to decontaminate the nuclear spectrum from circumnuclear contributors. We find that two baseline models can fit the broad (0.5–50 keV) X-ray spectrum of the source. One consists of a power-law-like continuum that is absorbed by a uniform absorber, and is reflected by neutral material, and a separate power-law component in the soft band. The second model consists of a clumpy absorber. The reflection component is still present, but not the soft-band power law. Instead, absorption by a warm absorber is necessary to fit the spectra. This is the first time that a reflection component has been established in this object, thanks to high-energy data from NuSTAR. This component is constant in flux and shape, supporting the idea that it is produced away from the central source (probably in the torus). We find flux, spectral slope and absorption variations on time-scales of months to years. We also find that a patchy absorber can explain the behaviour of this source better, as it is ∼200 times more likely than the uniform absorber and yields smaller intrinsic variations.

scholarly journals The Soft X-ray Excesses Observed by ROSAT

1994 ◽  
Vol 159 ◽  
pp. 338-338
Author(s):  
R. Walter ◽  
H.H. Fink
Keyword(s):  
Power Law ◽  
Spectral Energy Distribution ◽  
Seyfert Galaxies ◽  
High Energy ◽  
Wide Distribution ◽  
Spectral Energy ◽  
Spectral Slope ◽  
X Ray ◽  
Object A ◽  
The Mean

The properties of the soft X-ray excesses of bright Seyfert 1 galaxies and Quasars are described using the observations obtained with the PSPC (0.1–2.4 keV) detector of the XRT telescope aboard ROSAT during the ROSAT all sky survey (RASS). The sample consists of 58 Seyfert 1 type AGN detected with more than 300 counts during the RASS and observed at least once with IUE.The soft X-ray photon indices of our sample members range from 1.6 to 3.4 in a wide distribution (< Γ > = 2.50, σ = 0.48). The width of the distribution is considerably larger than the mean statistical uncertainty on the individual spectral slopes (σ = 0.33). Excepting for IC 4329A and Mrk 766, the mean contribution of absorbing cold matter intrinsic to the Seyfert galaxies of our sample to the absorbing column density is less than 1020cm−2. In IC 4329A and Mrk 766 intrinsic absorbtion is observed at soft X-ray. Both sources are also strongly reddened by dust.An excess of soft X-ray flux is detected in 90% of the sources above the exptrapolation of the hard X-ray power law. It can be shown that the PSPC spectral slope is a measure of the strength of the soft X-ray excess. If the reddened sources are excluded, a correlation appears between the strength of the ultraviolet blue bump and the soft X-ray photon index (figure 1). The ratio of the ultraviolet to infrared fluxes and the ultraviolet spectral slope are also related to the strength of the blue bump. The observations are compatible with a model where most of the spectral variations arising among the sources studied are driven by the strength of the bump component, which varies by a factor of 100 from object to object. A bump model consisting of a power law with a high energy cutoff at 80 eV can fit most of the sources. In any case, the spectral energy distribution of the ultraviolet to soft X-ray bump is characterised by vFv(1375 Å) = (1–5) ∫ε > 150eVFεdε.

scholarly journals X-ray emission properties of BLAGN in the XMM-2dF Wide Angle Survey

2006 ◽  
Vol 2 (S238) ◽  
pp. 59-64
Author(s):  
S. Mateos ◽  
M. G. Watson ◽  
J. A. Tedds ◽  
F. J. Carrera ◽  
M. Page ◽  
...  
Keyword(s):  
Spectral Analysis ◽  
Statistical Analysis ◽  
Power Law ◽  
Column Density ◽  
Wide Angle ◽  
X Ray ◽  
Emission Properties ◽  
Photon Index ◽  
The Mean ◽  
X Ray Absorption

AbstractWe present the preliminary results of the X-ray spectral analysis of one of the largest samples of X-ray selected BLAGN assembled so far from the XMM-2dF Wide Angle Survey. The sample, with 641 spectroscopically identified BLAGN, provides a unique resource to carry out a statistical analysis of the emission properties of these objects over a broad range of X-ray luminosities and redshifts. The X-ray spectra of the majority of the objects were best fitted with a power law with a near constant mean spectral photon index. No obvious trend of this spectral parameter with X-ray luminosity or redshift was found.We measured the mean photon index of our objects to be ∼1.96 ± 0.05 with an intrinsic dispersion σ=0.22±0.03. X-ray absorption was detected in ∼8% of the sources, with no preferred luminosity or redshift and having typical values of the absorbing column density ≤1022cm−2.

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 NGC 300 ULX1: A new ULX pulsar in NGC 300

2018 ◽  
Vol 14 (S346) ◽  
pp. 242-246 ◽  
Author(s):  
Chandreyee Maitra ◽  
Stefania Carpano ◽  
Frank Haberl ◽  
Georgios Vasilopoulos
Keyword(s):  
Neutron Star ◽  
Power Law ◽  
Accretion Rate ◽  
Black Body ◽  
High Mass ◽  
X Ray ◽  
Body Model ◽  
X Ray Binaries ◽  
Intrinsic Luminosity

Abstract. NGC 300 ULX1 is the fourth to be discovered in the class of the ultra-luminous X-ray pulsars. Pulsations from NGC 300 ULX1 were discovered during simultaneous XMM-Newton / NuSTAR observations in Dec. 2016. The period decreased from 31.71 s to 31.54 s within a few days, with a spin-up rate of –5.56×10–7 s s–1, likely one of the largest ever observed from an accreting neutron star. Archival Swift and NICER observations revealed that the period decreased exponentially from ~45 s to ~17.5 s over 2.3 years. The pulses are highly modulated with a pulsed fraction strongly increasing with energy and reaching nearly 80% at energies above 10 keV. The X-ray spectrum is described by a power-law and a disk black-body model, leading to a 0.3–30 keV unabsorbed luminosity of 4.7×1039 erg s–1. The spectrum from an archival XMM-Newton observation of 2010 can be explained by the same model, however, with much higher absorption. This suggests, that the intrinsic luminosity did not change much since that epoch. NGC 300 ULX1 shares many properties with supergiant high mass X-ray binaries, however, at an extreme accretion rate.

scholarly journals X-ray Properties of 3C 111: Separation of Primary Nuclear Emission and Jet Continuum

Universe ◽  
2020 ◽  
Vol 6 (11) ◽  
pp. 219
Author(s):  
Elena Fedorova ◽  
B.I. Hnatyk ◽  
V.I. Zhdanov ◽  
A. Del Popolo
Keyword(s):  
Accretion Disk ◽  
Power Law ◽  
Line Emission ◽  
High Energy ◽  
Power Law Model ◽  
X Ray ◽  
Additional Information ◽  
Observational Dataset ◽  
Simple Power ◽  
Photon Index

3C111 is BLRG with signatures of both FSRQ and Sy1 in X-ray spectrum. The significant X-ray observational dataset was collected for it by INTEGRAL, XMM-Newton, SWIFT, Suzaku and others. The overall X-ray spectrum of 3C 111 shows signs of a peculiarity with the large value of the high-energy cut-off typical rather for RQ AGN, probably due to the jet contamination. Separating the jet counterpart in the X-ray spectrum of 3C 111 from the primary nuclear counterpart can answer the question is this nucleus truly peculiar or this is a fake “peculiarity” due to a significant jet contribution. In view of this question, our aim is to estimate separately the accretion disk/corona and non-thermal jet emission in the 3C 111 X-ray spectra within different observational periods. To separate the disk/corona and jet contributions in total continuum, we use the idea that radio and X-ray spectra of jet emission can be described by a simple power-law model with the same photon index. This additional information allows us to derive rather accurate values of these contributions. In order to test these results, we also consider relations between the nuclear continuum and the line emission.

scholarly journals Tidal disruption events seen in the XMM-Newton slew survey

2016 ◽  
Vol 12 (S324) ◽  
pp. 123-126
Author(s):  
Richard Saxton ◽  
S. Komossa ◽  
Andrew Read ◽  
Paulina Lira ◽  
Kate D. Alexander ◽  
...  
Keyword(s):  
Radio Emission ◽  
Real Time ◽  
Power Law ◽  
Early Phase ◽  
Classical Model ◽  
Thermal Processes ◽  
Tidal Disruption ◽  
X Ray ◽  
Hard Power ◽  
Sky Survey

AbstractXMM-Newton performs a survey of the sky in the 0.2-12 keV X-ray band while slewing between observation targets. The sensitivity in the soft X-ray band is comparable with that of the ROSAT all-sky survey, allowing bright transients to be identified in near real-time by a comparison of the flux in both surveys. Several of the soft X-ray flares are coincident with galaxy nuclei and five of these have been interpreted as candidate tidal disruption events (TDE). The first three discovered had a soft X-ray spectrum, consistent with the classical model of TDE, where radiation is released during the accretion phase by thermal processes. The remaining two have an additional hard, power-law component, which in only one case was accompanied by radio emission. Overall the flares decay with the classical index of t−5/3 but vary greatly in the early phase.

scholarly journals The Optical/Near-IR Colours of Red Quasars

2000 ◽  
Vol 17 (1) ◽  
pp. 56-71 ◽  
Author(s):  
Paul J. Francis ◽  
Matthew T. Whiting ◽  
Rachel L. Webster
Keyword(s):  
Power Law ◽  
High Redshift ◽  
Sloan Digital Sky Survey ◽  
Spectral Energy ◽  
Spectral Energy Distributions ◽  
Energy Distributions ◽  
Red Power ◽  
Near Ir ◽  
Sky Survey ◽  
Ir Photometry

AbstractWe present quasi-simultaneous multi-colour optical/near-IR photometry for 157 radio selected quasars, forming an unbiassed sub-sample of the Parkes Flat-Spectrum Sample. Data are also presented for 12 optically selected QSOs, drawn from the Large Bright QSO Survey. The spectral energy distributions of the radio- and optically-selected sources are quite different. The optically selected QSOs are all very similar: they have blue spectral energy distributions curving downwards at shorter wavelengths. Roughly 90% of the radio-selected quasars have roughly power-law spectral energy distributions, with slopes ranging from Fv∝v0 to Fv∝v−2. The remaining 10% have spectral energy distributions showing sharp peaks: these are radio galaxies and highly reddened quasars. Four radio sources were not detected down to magnitude limits of H ∼ 19·6. These are probably high redshift (z > 3) galaxies or quasars. We show that the colours of our red quasars lie close to the stellar locus in the optical: they will be hard to identify in surveys such as the Sloan Digital Sky Survey. If near-IR photometry is added, however, the red power-law sources can be clearly separated from the stellar locus: IR surveys such as 2MASS should be capable of finding these sources on the basis of their excess flux in the K-band.

scholarly journals Broad-band study of high-synchrotron-peaked BL Lac object 1ES 1218+304

2020 ◽  
Vol 496 (4) ◽  
pp. 5518-5527
Author(s):  
N Sahakyan
Keyword(s):  
Energy Distribution ◽  
Electron Energy ◽  
Power Law ◽  
Spectral Energy Distribution ◽  
Broad Band ◽  
Energy Distributions ◽  
X Ray ◽  
Bl Lac ◽  
Photon Index ◽  
Γ Ray

ABSTRACT The origin of the multiwavelength emission from the high-synchrotron-peaked BL Lac 1ES 1218+304 is studied using the data from SwiftUVOT/XRT, NuSTAR, and Fermi-LAT. A detailed temporal and spectral analysis of the data observed during 2008–2020 in the  γ-ray (&gt;100 MeV), X-ray (0.3–70 keV), and optical/UV bands is performed. The γ-ray spectrum is hard with a photon index of 1.71 ± 0.02 above 100 MeV. The SwiftUVOT/XRT data show a flux increase in the UV/optical and X-ray bands; the highest 0.3–3 keV X-ray flux was (1.13 ± 0.02) × 10−10 erg cm−2 s−1. In the 0.3–10 keV range, the averaged X-ray photon index is &gt;2.0 which softens to 2.56 ± 0.028 in the 3–50 keV band. However, in some periods, the X-ray photon index became extremely hard (&lt;1.8), indicating that the peak of the synchrotron component was above 1 keV, and so 1ES 1218+304 behaved like an extreme synchrotron BL Lac. The hardest X-ray photon index of 1ES 1218+304 was 1.60 ± 0.05 on MJD 58489. The time-averaged multiwavelength spectral energy distribution is modelled within a one-zone synchrotron self-Compton leptonic model using a broken power law and power law with an exponential cutoff electron energy distributions. The data are well explained when the electron energy distribution is $E_{\rm e}^{-2.1}$ extending up to γbr/cut ≃ (1.7 − 4.3) × 105, and the magnetic field is weak (B ∼ 1.5 × 10−2 G). By solving the kinetic equation for electron evolution in the emitting region, the obtained electron energy distributions are discussed considering particle injection, cooling, and escape.

scholarly journals X-ray Constraints on AGN Clustering

1989 ◽  
Vol 134 ◽  
pp. 492-493
Author(s):  
G. De Zotti ◽  
M. Persic ◽  
A. Franceschini ◽  
L. Danese ◽  
G.G.C. Palumbo ◽  
...  
Keyword(s):  
Space Distribution ◽  
Background Intensity ◽  
Additional Contribution ◽  
List Type ◽  
X Ray ◽  
Upper Limit ◽  
Angular Scale ◽  
Sky Survey ◽  
The Mean ◽  
X Ray Background

Studies of the HEAO–1 A2 all–sky survey data have established that the level of anisotropy of the extragalactic X–ray background (XRB) is relatively low: –The cell–to–cell XRB intensity variations can be entirely accounted for by Poisson fluctuations in the space distribution of known classes of sources; the 90% confidence upper limit to any additional contribution on a scale of 26 square degrees is 2.3% (Shafer and Fabian 1983).–No significant correlations of XRB intensity fluctuations appear to be present; the formal 90% confidence upper limit on the amplitude of autocorrelations, relative to the mean background intensity, for an angular scale of 3° is Γ(3°) ≤ 1.9 × 10−2 (Persic et al. 1988).

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