scholarly journals 3.10. X-ray constraints on accretion and starburst processes in galactic nuclei

1998 ◽  
Vol 184 ◽  
pp. 109-110
Author(s):  
A. Ptak ◽  
P. Serlemitsos ◽  
T. Yaqoob ◽  
R. Mushotzky ◽  
Y. Terashima ◽  
...  
Keyword(s):  
Power Law ◽  
Galactic Nuclei ◽  
Seyfert Galaxies ◽  
Soft Component ◽  
Short Term ◽  
Hard Component ◽  
X Ray ◽  
Ngc 6946 ◽  
Process Elements ◽  
Low Activity

Although the galaxies in our sample are heterogenous in their optical classifications (LLAGN: M51, NGC 3147, NGC 4258; LINER: NGC 3079, NGC 3310, NGC 3998, NGC 4579, NGC 4594; starburst: M82, NGC 253, NGC 3628, NGC 6946), they are fit well by a “canonical” spectrum with a hot, optically-thin thermal component with T ~ 8 × 106 K and an absorbed (NH ~ 1022 cm−2) power-law with an energy index α ~ 0.7–0.8. Both the “soft” component, most likely due to SN or superwind-heated ISM, and the “hard” power-law, most likely due to a micro-AGN and/or blackhole candidates, appear to be common in low-activity galaxies. If the soft component is associated with a superwind outflow, than ~ 10% of the X-ray emission is due to “swept-up” ISM rather than superwind emission. The abundance of Fe relative to α-process elements tends to be sub-solar, possibly due to dust-depletion and/or type-II SN enrichment. The lack of short-term variability in the hard component suggests that if it is due to an AGN, then the mode of accretion is probably fundamentally different from “normal” Seyfert galaxies.

scholarly journals Correlated X-ray and Millimetre Variability of the Blazar 3C273

1994 ◽  
Vol 159 ◽  
pp. 193-196 ◽  
Author(s):  
I M McHardy ◽  
I Papadakis ◽  
C M Leach ◽  
E I Robson ◽  
W Junor ◽  
...  
Keyword(s):  
Power Law ◽  
Soft Component ◽  
Hard Component ◽  
X Ray ◽  
Simple Extrapolation

We present the results of X-ray and millimetre monitoring of the blazar 3C273 at 1–2 day intervals over the period 12 December 1992 to 24 January 1993. No large flares are seen in this period but variations in both wavebands of ∼ 30% on few day timescales are apparent. The ROSAT PSPC X-ray spectrum consists of 2 power-law components with the harder component dominating above 0.5 keV. There is very little correlation between the variability of the soft and hard components. The soft component does not correlate with the millimetre variations, but the hard component correlates reasonably well and leads the millimetre variations by about 10 days. These results show that the hard X-ray component cannot be a simple extrapolation of the millimetre/IR synchrotron component but may be explained as a self-Compton component in a shocked jet.

scholarly journals Soft X-ray Spectra of Seyfert Galaxies

1989 ◽  
Vol 134 ◽  
pp. 173-174
Author(s):  
C. M. Urry ◽  
J. S. Kruper ◽  
C. R. Canizares
Keyword(s):  
Active Galactic Nuclei ◽  
Power Law ◽  
Galactic Nuclei ◽  
Seyfert Galaxies ◽  
Spectral Indices ◽  
X Ray

The first X-ray (2–10 keV) spectral surveys of active galactic nuclei (AGN) were remarkably uniform, with spectral indices narrowly distributed about α=0.65, independent of radio-emitting properties or X-ray luminosity (Mushotzky 1984). In the few AGN detected above 20 keV, this canonical power law extended to at least 50 keV (Rothschild et al. 1983, Pounds 1985, Worrall et al. 1980; Halpern 1982; Worrall and Marshall 1984). In practice these surveys were dominated by low luminosity Seyfert 1 galaxies.

scholarly journals Active Nuclei and Redshift Problems

1983 ◽  
Vol 6 ◽  
pp. 531-533
Author(s):  
Geoffrey Burbidge
Keyword(s):  
Galactic Nuclei ◽  
Seyfert Galaxies ◽  
Radio Sources ◽  
Powerful Radio ◽  
Radiation Mechanism ◽  
X Ray ◽  
Major Interest ◽  
Relativistic Particles

More than 20 years ago V. A. Ambartsumian proposed that much of the activity in galaxies was dominated and even generated by their nuclei. Subsequent observational work in radio, optical and x-ray frequencies has borne out his prophecy, and major interest has centered about the nature of the machine in the galactic nucleus. The major characteristic of this machine is that it releases energy rapidly and often spasmodically by processes which are not thermonuclear in origin.The original studies which led to the conclusion that nuclei were all important were observations of the powerful radio sources and Seyfert galaxies, and evidence for the ejection of gas from galaxies of many types. The realization that the synchrotron mechanism was the dominant radiation mechanism and the later studies of Compton radiation were fundamental in leading to the conclusion that large fluxes of relativistic particles must be generated in galactic nuclei.

scholarly journals Hardness Ratio in Evolving Low-Mass X-ray Binary Systems

1987 ◽  
Vol 125 ◽  
pp. 199-199
Author(s):  
J. Shaham ◽  
M. Tavani
Keyword(s):  
Neutron Star ◽  
Accretion Disk ◽  
Binary Systems ◽  
Spectral Component ◽  
Soft Component ◽  
Hard Component ◽  
X Ray ◽  
Low Mass ◽  
Additional Support ◽  
X Ray Binaries

Spectral observations of low-mass X-ray binaries (LMXBs) show that the soft component usually dominates over the hard one. These results provide additional support to an interpretation based on models of LMXBs in which the neutron star while, on the average, spinning up, is also experiencing a spinning down torque. Under these conditions, a fraction of the luminosity associated with the gravitational release of energy on the surface of the accreting neutron star may manifest itself as luminosity originating in the inner part of the accretion disk. It is probably possible to separate the two contributions; the stellar luminosity can be associated with the hard component of the spectrum and the disk luminosity, related to the exchange of energy due to the torque between the rapidly spinning neutron star and the accretion disk, can be associated with the soft spectral component.

scholarly journals Identification of AGN in the XMM-Newton X-ray survey of the SMC

2019 ◽  
Vol 622 ◽  
pp. A29 ◽  
Author(s):  
Chandreyee Maitra ◽  
Frank Haberl ◽  
Valentin D. Ivanov ◽  
Maria-Rosa L. Cioni ◽  
Jacco Th. van Loon
Keyword(s):  
Near Infrared ◽  
Spectral Characteristics ◽  
Selection Criterion ◽  
Galactic Nuclei ◽  
Seyfert Galaxies ◽  
Mid Infrared ◽  
X Ray ◽  
Stellar Density ◽  
Narrow Emission

Context. Finding active galactic nuclei (AGN) behind the Magellanic Clouds (MCs) is difficult because of the high stellar density in these fields. Although the first AGN behind the Small Magellanic Cloud (SMC) were reported in the 1980s, it is only recently that the number of AGN known behind the SMC has increased by several orders of magnitude. Aims. The mid-infrared colour selection technique has proven to be an efficient means of identifying AGN, especially obscured sources. The X-ray regime is complementary in this regard and we use XMM-Newton observations to support the identification of AGN behind the SMC. Methods. We present a catalogue of AGN behind the SMC by correlating an updated X-ray point-source catalogue from our XMM-Newton survey of the SMC with previously identified AGN from the literature as well as a list of candidates obtained from the ALLWISE mid-infrared colour-selection criterion. We studied the properties of the sample with respect to their redshifts, luminosities, and X-ray spectral characteristics. We also identified the near-infrared counterpart of the sources from the VISTA observations. Results. The redshift and luminosity distributions of the sample (where known) indicate that we detect sources ranging from nearby Seyfert galaxies to distant and obscured quasars. The X-ray hardness ratios are compatible with those typically expected for AGN, and the VISTA colours and variability are also consistent with AGN. A positive correlation was observed between the integrated X-ray flux (0.2–12 keV) and the ALLWISE and VISTA magnitudes. We further present a sample of new candidate AGN and candidates for obscured AGN. Together these make an interesting subset for further follow-up studies. An initial spectroscopic follow-up of 6 out of the 81 new candidates showed that all six sources are active galaxies, although two have narrow emission lines.

scholarly journals Physics of Relativistic Jets on Sub-Milliarcsecond Scales

1984 ◽  
Vol 110 ◽  
pp. 207-214
Author(s):  
Martin J. Rees
Keyword(s):  
Energy Production ◽  
Galactic Nuclei ◽  
Primary Energy ◽  
Relativistic Jets ◽  
Short Term ◽  
X Ray ◽  
Long Term Stability ◽  
Extended Sources ◽  
Vlbi Data

The observed superluminal components have (deprojected) lengths of ~ 1020 cm, and imply relativistic bulk motions on these scales. There are, however, persuasive reasons for attributing the primary energy production to scales 1014–1015 cm. Moreover, the initial bifurcation and collimation must also be imposed on these small scales if the long-term stability of the jet axis in extended sources is due to the gyroscopic effect of a spinning black hole (Rees 1978). The issues I shall address in this talk are: how the jet gets from ~ 1015cm to ~ 1019 cm; and what VLBI data can tell us about the properties of galactic nuclei on scales below ~ 1019 cm — scales where optical and X-ray studies provide some evidence, but where there is no short-term hope of achieving spatial resolution.

On the origin of power-law X-ray spectra of active galactic nuclei

1984 ◽  
Vol 287 ◽  
pp. 534 ◽  
Author(s):  
I. Schlosman ◽  
J. Shaham ◽  
G. Shaviv
Keyword(s):  
Active Galactic Nuclei ◽  
Power Law ◽  
Galactic Nuclei ◽  
X Ray

scholarly journals 11.12. X-ray emission from LINERs observed with ASCA

1998 ◽  
Vol 184 ◽  
pp. 479-480 ◽  
Author(s):  
Y. Terashima ◽  
H. Kunieda ◽  
P.J. Serlemitsos ◽  
A. Ptak
Keyword(s):  
Power Law ◽  
Seyfert Galaxies ◽  
X Ray ◽  
Photon Index

We present X-ray observations of LINERs with ASCA. We detected a hard point-like source of X-ray luminosity of 1040–1041 erg s−1 at the nucleus. Their hard X-ray continuum is well represented by power-law of photon index ~ 1.8. The X-ray to Hα luminosity ratio LX/LHα is quite similar to Seyfert galaxies and strongly support the presence of low luminosity AGNs.

scholarly journals X-Rays from Active Galactic Nuclei

1983 ◽  
Vol 6 ◽  
pp. 491-498 ◽  
Author(s):  
A.C. Fabian
Keyword(s):  
Active Galactic Nuclei ◽  
Galactic Nuclei ◽  
Seyfert Galaxies ◽  
X Rays ◽  
Bl Lac Objects ◽  
X Ray ◽  
Bl Lac

Recent X-ray observations of active galactic nuclei and Seyfert galaxies in particular are briefly reviewed. The application of the efficiency limit to rapidly varying luminous sources such as NGC 6814 is discussed. It is argued that the variability and probable MeV spectral turnover imply that most of the electrons which radiate the observed flux are only mildly relativistic. A possible link between the steep soft X-ray spectra and featureless optical continua of BL Lac objects is considered.

scholarly journals Cosmological Evolution of the Central Engine in High-Luminosity, High-Accretion Rate AGN

2014 ◽  
Vol 1 (1) ◽  
pp. 90-95
Author(s):  
Matteo Guainazzi
Keyword(s):  
Active Galactic Nuclei ◽  
Accretion Rate ◽  
Galactic Nuclei ◽  
Seyfert Galaxies ◽  
Cosmological Evolution ◽  
High Luminosity ◽  
X Ray ◽  
Central Engine ◽  
The Status ◽  
Multi Wavelength

In this paper I discuss the status of observational studies aiming at probing the cosmological evolution of the central engine in high-luminosity, high-accretion rate Active Galactic Nuclei (AGN). X-ray spectroscopic surveys, supported by extensive multi-wavelength coverage, indicate a remarkable invariance of the accretion disk plus corona system, and of their coupling up to redshifts z≈6. Furthermore, hard X-ray (<em>E</em> &gt;10 keV) surveys show that nearby Seyfert Galaxies share the same central engine notwithstanding their optical classication. These results suggest that the high-luminosity, high accretion rate quasar phase of AGN evolution is homogeneous over cosmological times.

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