scholarly journals Recurring obscuration in NGC 3783

2018 ◽  
Vol 619 ◽  
pp. A112 ◽  
Author(s):  
J. S. Kaastra ◽  
M. Mehdipour ◽  
E. Behar ◽  
S. Bianchi ◽  
G. Branduardi-Raymont ◽  
...  
Keyword(s):  
Column Density ◽  
Extreme Ultraviolet ◽  
Galactic Nuclei ◽  
Seyfert Galaxies ◽  
Continuum Emission ◽  
X Ray ◽  
Transient Nature ◽  
Hardness Ratio ◽  
Ultraviolet Photons ◽  
The Continuum

Context. Obscuration of the continuum emission from active galactic nuclei by streams of gas with relatively high velocity (>1000 km s−1) and column density (>3 × 1025 m−2) has been seen in a few Seyfert galaxies. This obscuration has a transient nature. In December 2016 we witnessed such an event in NGC 3783. Aims. The frequency and duration of these obscuration events is poorly known. Here we study archival data of NGC 3783 in order to constrain this duty cycle. Methods. We use archival Chandra/NuSTAR spectra taken in August 2016. We also study the hardness ratio of all Swift XRT spectra taken between 2008 and 2017. Results. In August 2016, NGC 3783 also showed evidence of obscuration. While the column density of the obscuring material is ten times lower than in December 2016, the opacity is still sufficient to block a significant fraction of the ionising X-ray and extreme ultraviolet photons. From the Swift hardness ratio behaviour we find several other epochs with obscuration. Obscuration with columns >1026 m−2 may take place about half of the time. Also, in archival X-ray data taken by the Advanced Satellite for Cosmology and Astrophysics (ASCA) in 1993 and 1996 we find evidence of obscuration. Conclusions. Obscuration of the ionising photons in NGC 3783 occurs more frequently than previously thought. This may not always have been recognised due to low-spectral-resolution observations, overly limited spectral bandwidth or confusion with underlying continuum variations.

scholarly journals The Origin of Continuum Emission in Active Galactic Nuclei

1994 ◽  
Vol 159 ◽  
pp. 5-16 ◽  
Author(s):  
Joel N. Bregman
Keyword(s):  
Accretion Disk ◽  
Near Infrared ◽  
Galactic Nuclei ◽  
Black Body ◽  
Continuum Emission ◽  
Radiation Mechanism ◽  
X Ray ◽  
Pair Plasma ◽  
Inverse Compton ◽  
The Continuum

The general understanding of the continuum emission from AGN has changed from the picture where nonthermal processes were responsible for all of the emission. The current body of observation indicates that there are two types of objects, one being the blazar class (or blazar component), where nearly all of the emission is nonthermal, due primarily to synchrotron and inverse Compton emission. Variability studies indicate that the emitting region decreases with size from the radio through the X-ray region, where the size of the X-ray region is of order a light hour. More than two dozen of these radio-loud AGNs have been detected at GeV energies (one source at TeV energies), for which the radiation mechanism may be inverse Compton mechanism.In the other class, the radio-quiet AGN (component), the emission is almost entirely thermal, with radiation from dust dominating the near infrared to submillimeter region. The optical to soft X-ray emission is often ascribed to black body emission from an opaque accretion disk, but variability studies may not be consistent with expectations. Another attractive model has free-free emission being responsible for the optical to soft X-ray emission. The highest frequencies at which these AGN are detected is the MeV range, and these data should help to determine if this emission is produced in a scattering atmosphere, such as that around an accretion disk, or by another model involving an opaque pair plasma.

scholarly journals FUV and optical spectrophotometry of X-ray selected Seyferts

1986 ◽  
Vol 119 ◽  
pp. 347-348
Author(s):  
J. T. Clarke ◽  
S. Bowyer ◽  
M. Grewing
Keyword(s):  
Seyfert Galaxies ◽  
Continuum Emission ◽  
Balmer Line ◽  
X Ray ◽  
Positive Correlation ◽  
Optical Spectrophotometry ◽  
Distinguishing Features ◽  
The Continuum

Nearly simultaneous FUV and optical spectrophotometry of X-ray selected Seyfert galaxies has revealed an average Ly α/H β ratio of 22, a positive correlation between the ratio Ly α/H β and the width of the lines, and additional Ly α emission in the wings of one source which is not matched by emission in the Balmer line wings. However, we find no distinguishing features in the continuum emission from these X-ray selected objects compared with other samples. If the correlation between Ly α/H β and the width of the lines is found to apply to larger samples of Seyferts, it may be that our objects appear Ly α bright because they are also broad-lined compared with other samples.

scholarly journals What controls the UV-to-X-ray continuum shape in quasars?

2021 ◽  
Author(s):  
John D Timlin ◽  
W N Brandt ◽  
Ari Laor
Keyword(s):  
Physical Mechanism ◽  
Extreme Ultraviolet ◽  
Spectral Shape ◽  
Continuum Emission ◽  
X Rays ◽  
Spectral Slope ◽  
High Quality ◽  
Broad Absorption ◽  
X Ray ◽  
The Continuum

Abstract We present an investigation of the interdependence of the optical-to-X-ray spectral slope (αox), the  He ii equivalent-width (EW), and the monochromatic luminosity at 2500 Å (L2500). The values of αox and  He ii EW are indicators of the strength/shape of the quasar ionizing continuum, from the ultraviolet (UV; 1500–2500 Å), through the extreme ultraviolet (EUV; 300–50 Å), to the  X-ray (2 keV) regime. For this investigation, we measure the  He ii EW of 206 radio-quiet quasars devoid of broad absorption lines that have high-quality spectral observations of the UV and 2 keV X-rays. The sample spans wide redshift (≈ 0.13–3.5) and luminosity (log(L2500) ≈ 29.2–32.5 erg s−1 Hz−1) ranges. We recover the well-known αox–L2500 and  He ii EW–L2500 anti-correlations, and we find a similarly strong correlation between αox and  He ii EW, and thus the overall spectral shape from the UV, through the EUV, to the  X-ray regime is largely set by luminosity. A significant αox– He ii EW correlation remains after removing the contribution of L2500 from each quantity, and thus the emission in the EUV and the X-rays are also directly tied. This set of relations is surprising, since the UV, EUV, and  X-ray emission are expected to be formed in three physically distinct regions. Our results indicate the presence of a redshift-independent physical mechanism that couples the continuum emission from these three different regions, and thus controls the overall continuum shape from the UV to the  X-ray regime.

X-ray probing of NGC 1275 nuclear region with Hitomi, Swift, and Suzaku

2018 ◽  
Vol 14 (S342) ◽  
pp. 118-121
Author(s):  
Yasushi Fukazawa
Keyword(s):  
Gamma Ray ◽  
Seyfert Galaxies ◽  
Continuum Emission ◽  
Line Center ◽  
Nuclear Region ◽  
X Ray ◽  
Line Region ◽  
Flux Increase ◽  
Ngc 1275 ◽  
The Continuum

AbstractNGC 1275 has been known as a ppint-like X-ray source with a continuum and a Fe-K line. Unlike radio and GeV/TeV gamma-ray emissions, origin of X-ray emission is not yet understood; is it a jet emission like blazars or an accretion corona emission like Seyfert galaxies. X-ray emission is important to determine the SED of jet emission to constrain jet parameters and also understand the relation between accretion and jet. Here we report a recent X-ray probing of NGC 1275 nuclear region with Hitomi/SXS, Swift/XRT, and Suzaku/XIS. Hitomi/SXS gave the first opportunity to measure a Fe-K line of AGNs with several eV resolution. The line center is consistent with the neutral iron emission, and the width is constrained to be 500-1600 km/s (FWHM). This ruled out the origin of broad line region and inner accretion disk. A low-covering-fraction molecular torus or a rotating molecular disk around pc scales, illuminated by accretion corona emission, is suggested as a possible origin. For the continuum emission, Suzaku/XIS monitor observations revealed that the X-ray flux has gradually increased as the GeV gamma-ray flux. Swift/XRT showed a several-days flux increase, associated with the GeV gamma-ray flare. These results on the continuum emission suggests a contribution of jet emission to the X-ray emission. Based on the combined results of Fe-K line and continuum, we discuss some scenarios for X-ray emitting region.

scholarly journals Emission Components in Seyfert Galaxies and Quasars

1994 ◽  
Vol 159 ◽  
pp. 203-212
Author(s):  
Thierry J.-L. Courvoisier
Keyword(s):  
Seyfert Galaxies ◽  
Continuum Emission ◽  
X Ray ◽  
Excess Emission ◽  
Bl Lac ◽  
The Relationship ◽  
The Continuum

The continuum emission components of Seyfert galaxies and quasars are reviewed with a particular emphasis on the correlations observed between these components. It is shown that the blue bump emission which is observed in Seyfert galaxies and quasars and not in BL Lac type objects is not hidden in the latter objects by a strong beaming of the jet emission. The shape of the blue bump is described and some consequences of these observations for the interpretation of this component are given. The relationship between the X-ray emission of quasars and the radio beaming properties of the object should be re-visited when the shape of the soft excess emission can be better established.

scholarly journals New Constraints on the Continuum Emission Mechanism of Active Galactic Nuclei: Intensive Monitoring of NGC 7469 in the X‐Ray and Ultraviolet

1998 ◽  
Vol 505 (2) ◽  
pp. 594-606 ◽  
Author(s):  
K. Nandra ◽  
J. Clavel ◽  
R. A. Edelson ◽  
I. M. George ◽  
M. A. Malkan ◽  
...  
Keyword(s):  
Active Galactic Nuclei ◽  
Galactic Nuclei ◽  
Continuum Emission ◽  
Emission Mechanism ◽  
X Ray ◽  
Intensive Monitoring ◽  
Ngc 7469 ◽  
The Continuum

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 Compton-Thick AGN in the NuSTAR ERA VII. A joint NuSTAR, Chandra, and XMM-Newton Analysis of Two Nearby, Heavily Obscured Sources

2021 ◽  
Vol 922 (2) ◽  
pp. 159
Author(s):  
A. Traina ◽  
S. Marchesi ◽  
C. Vignali ◽  
N. Torres-Albà ◽  
M. Ajello ◽  
...  
Keyword(s):  
Spectral Analysis ◽  
Energy Range ◽  
Active Galactic Nuclei ◽  
Column Density ◽  
Galactic Nuclei ◽  
Seyfert Galaxies ◽  
Line Of Sight ◽  
Broad Energy Range ◽  
Larger Sample ◽  
Broad Energy

Abstract We present the joint Chandra, XMM-Newton, and NuSTAR analysis of two nearby Seyfert galaxies, NGC 3081 and ESO 565-G019. These are the only two having Chandra data in a larger sample of 10 low-redshift (z ≤ 0.05), candidates Compton-thick (CT) Active Galactic Nuclei selected in the 15–150 keV band with Swift-BAT that were still lacking NuSTAR data. Our spectral analysis, performed using physically motivated models, provides an estimate of both the line-of-sight (l.o.s.) and average (N H,S ) column densities of the two torii. NGC 3081 has a Compton-thin l.o.s. column density N H,z = [0.58–0.62] × 1024 cm−2, but the N H,S , beyond the CT threshold (N H,S = [1.41–1.78] × 1024 cm−2), suggests a “patchy” scenario for the distribution of the circumnuclear matter. ESO 565-G019 has both CT l.o.s. and N H,S column densities (N H,z > 2.31 × 1024 cm−2 and N H,S > 2.57 × 1024 cm−2, respectively). The use of physically motivated models, coupled with the broad energy range covered by the data (0.6–70 keV and 0.6–40 keV, for NGC 3081 and ESO 565-G019, respectively) allows us to constrain the covering factor of the obscuring material, which is C TOR = [0.63–0.82] for NGC 3081, and C TOR = [0.39–0.65] for ESO 565-G019.

scholarly journals Evolution and State of the Local ISM

1996 ◽  
Vol 171 ◽  
pp. 442-442
Author(s):  
T. Schmutzler ◽  
D. Breitschwerdt
Keyword(s):  
Basic Feature ◽  
Emission Lines ◽  
Continuum Emission ◽  
Ionization Equilibrium ◽  
X Ray ◽  
Self Consistent ◽  
X Ray Background ◽  
Collisional Ionization ◽  
Consistent Approach ◽  
The Continuum

The most puzzling observations concerning the LISM (distance < 100 pc) can be explained by a fast adiabatically cooled gas in the cavity of an old superbubble. The ultrasoft X-ray background and contributions to the C- and M-bands are due to the continuum emission of delayed recombination [1]. In contrast to collisional ionization equilibrium (CIE) models, but consistent with recent observations [2], our model predicts a lack of emission lines and a low emissivity in the EUV range. In the figure below we compare the emissivities resulting from CIE at T = 106 K and those from our model at T = 4.2 × 104 K. The basic feature of our model is a thermally self-consistent approach of the time-dependent evolution.

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.

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