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  • 1
    Online Resource
    Online Resource
    Oxford University Press (OUP) ; 2022
    In:  Monthly Notices of the Royal Astronomical Society Vol. 516, No. 2 ( 2022-09-12), p. 1865-1880
    In: Monthly Notices of the Royal Astronomical Society, Oxford University Press (OUP), Vol. 516, No. 2 ( 2022-09-12), p. 1865-1880
    Abstract: We present the discovery of highly collimated radio jets spanning a total of 355 kpc around the nearby elliptical galaxy NGC 2663, and the possible first detection of recollimation on kiloparsec scales. The small distance to the galaxy (∼28.5 Mpc) allows us to resolve portions of the jets to examine their structure. We combine multiwavelength data: radio observations by the Murchison Widefield Array (MWA), the Australian Square Kilometre Array Pathfinder (ASKAP) and the Australia Telescope Compact Array (ATCA), and X-ray data from Chandra, Swift, and SRG/eROSITA. We present intensity, rotation measure, polarization, spectral index, and X-ray environment maps. Regions of the southern jet show simultaneous narrowing and brightening, which can be interpreted as a signature of the recollimation of the jet by external, environmental pressure, though it is also consistent with intermittent active galactic nuclei or complex internal jet structure. X-ray data suggest that the environment is extremely poor; if the jet is indeed recollimating, the large recollimation scale (40 kpc) is consistent with a slow jet in a low-density environment.
    Type of Medium: Online Resource
    ISSN: 0035-8711 , 1365-2966
    Language: English
    Publisher: Oxford University Press (OUP)
    Publication Date: 2022
    detail.hit.zdb_id: 2016084-7
    SSG: 16,12
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  • 2
    In: Monthly Notices of the Royal Astronomical Society, Oxford University Press (OUP), Vol. 484, No. 3 ( 2019-04-11), p. 4287-4297
    Type of Medium: Online Resource
    ISSN: 0035-8711 , 1365-2966
    Language: English
    Publisher: Oxford University Press (OUP)
    Publication Date: 2019
    detail.hit.zdb_id: 2016084-7
    SSG: 16,12
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  • 3
    Online Resource
    Online Resource
    Oxford University Press (OUP) ; 2019
    In:  Monthly Notices of the Royal Astronomical Society ( 2019-01-25)
    In: Monthly Notices of the Royal Astronomical Society, Oxford University Press (OUP), ( 2019-01-25)
    Type of Medium: Online Resource
    ISSN: 0035-8711 , 1365-2966
    Language: English
    Publisher: Oxford University Press (OUP)
    Publication Date: 2019
    detail.hit.zdb_id: 2016084-7
    SSG: 16,12
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  • 4
    Online Resource
    Online Resource
    Oxford University Press (OUP) ; 2019
    In:  Monthly Notices of the Royal Astronomical Society Vol. 489, No. 4 ( 2019-11-11), p. 5398-5412
    In: Monthly Notices of the Royal Astronomical Society, Oxford University Press (OUP), Vol. 489, No. 4 ( 2019-11-11), p. 5398-5412
    Abstract: A multi-epoch X-ray spectral and variability analysis is conducted for the narrow-line Seyfert 1 (NLS1) active galactic nucleus (AGN) Mrk 478. All available X-ray data from XMM–Newton and Suzaku satellites, spanning from 2001 to 2017, are modelled with a variety of physical models, including partial covering, soft Comptonization, and blurred reflection, to explain the observed spectral shape and variability over the 16 yr. All models are a similar statistical fit to the data sets, though the analysis of the variability between data sets favours the blurred reflection model. In particular, the variability can be attributed to changes in flux of the primary coronal emission. Different reflection models fit the data equally well, but differ in interpretation. The use of reflionx predicts a low disc ionization and power law dominated spectrum, while relxill predicts a highly ionized and blurred reflection dominated spectrum. A power law dominated spectrum might be more consistent with the normal X-ray-to-UV spectral shape (αox). Both blurred reflection models suggest a rapidly spinning black hole seen at a low inclination angle, and both require a sub-solar (∼0.5) abundance of iron. All physical models require a narrow emission feature at $6.7{\rm \, keV}$ likely attributable to Fe xxv emission, while no evidence for a narrow $6.4{\rm \, keV}$ line from neutral iron is detected.
    Type of Medium: Online Resource
    ISSN: 0035-8711 , 1365-2966
    Language: English
    Publisher: Oxford University Press (OUP)
    Publication Date: 2019
    detail.hit.zdb_id: 2016084-7
    SSG: 16,12
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  • 5
    Online Resource
    Online Resource
    Oxford University Press (OUP) ; 2018
    In:  Monthly Notices of the Royal Astronomical Society Vol. 475, No. 1 ( 2018-03-21), p. 128-138
    In: Monthly Notices of the Royal Astronomical Society, Oxford University Press (OUP), Vol. 475, No. 1 ( 2018-03-21), p. 128-138
    Type of Medium: Online Resource
    ISSN: 0035-8711 , 1365-2966
    Language: English
    Publisher: Oxford University Press (OUP)
    Publication Date: 2018
    detail.hit.zdb_id: 2016084-7
    SSG: 16,12
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  • 6
    In: Astronomy & Astrophysics, EDP Sciences, Vol. 669 ( 2023-01), p. A127-
    Abstract: Context. The space density of X-ray-luminous, blindly selected active galactic nuclei (AGN) traces the population of rapidly accreting super-massive black holes through cosmic time. It is encoded in the X-ray luminosity function, whose bright end remains poorly constrained in the first billion years after the Big Bang as X-ray surveys have thus far lacked the required cosmological volume. With the eROSITA Final Equatorial-Depth Survey (eFEDS), the largest contiguous and homogeneous X-ray survey to date, X-ray AGN population studies can now be extended to new regions of the luminosity–redshift space ( L 2 − 10 keV   〉  10 45  erg s −1 and z   〉  6). Aims. The current study aims at identifying luminous quasars at z   〉  5.7 among X-ray-selected sources in the eFEDS field in order to place a lower limit on black hole accretion well into the epoch of re-ionisation. A secondary goal is the characterisation of the physical properties of these extreme coronal emitters at high redshifts. Methods. Cross-matching eFEDS catalogue sources to optical counterparts from the DESI Legacy Imaging Surveys, we confirm the low significance detection with eROSITA of a previously known, optically faint z  = 6.56 quasar from the Subaru High-z Exploration of Low-luminosity Quasars (SHELLQs) survey. We obtained a pointed follow-up observation of the source with the Chandra X-ray telescope in order to confirm the low-significance eROSITA detection. Using new near-infrared spectroscopy, we derived the physical properties of the super-massive black hole. Finally, we used this detection to infer a lower limit on the black hole accretion density rate at z   〉  6. Results. The Chandra observation confirms the eFEDS source as the most distant blind X-ray detection to date. The derived X-ray luminosity is high with respect to the rest-frame optical emission of the quasar. With a narrow Mg II line, low derived black hole mass, and high Eddington ratio, as well as its steep photon index, the source shows properties that are similar to local narrow-line Seyfert 1 galaxies, which are thought to be powered by young super-massive black holes. In combination with a previous high-redshift quasar detection in the field, we show that quasars with L 2 − 10 keV   〉  10 45  erg s −1 dominate accretion onto super-massive black holes at z  ∼ 6.
    Type of Medium: Online Resource
    ISSN: 0004-6361 , 1432-0746
    RVK:
    RVK:
    Language: English
    Publisher: EDP Sciences
    Publication Date: 2023
    detail.hit.zdb_id: 1458466-9
    SSG: 16,12
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  • 7
    Online Resource
    Online Resource
    Oxford University Press (OUP) ; 2019
    In:  Monthly Notices of the Royal Astronomical Society Vol. 488, No. 4 ( 2019-10-01), p. 4831-4842
    In: Monthly Notices of the Royal Astronomical Society, Oxford University Press (OUP), Vol. 488, No. 4 ( 2019-10-01), p. 4831-4842
    Abstract: We have carried out a systematic analysis of the nearby (z = 0.0279) active galaxy Zw 229.015 using multi-epoch, multi-instrument, and deep pointed observations with XMM–Newton, Suzaku, Swift,and NuSTAR. Spectral and temporal variability are examined in detail on both the long (weeks-to-years) and short (hours) time-scales. A deep Suzaku observation of the source shows two distinct spectral states; a bright-soft state and a dim-hard state in which changes in the power-law component account for the differences. Partial covering, blurred reflection, and soft Comptonization models describe the X-ray spectra comparably well, but the smooth, rather featureless, spectrum may be favouring the soft Comptonization scenario. Moreover, independent of the spectral model, the observed spectral variability is ascribed to the changes in the power-law continuum only and do not require changes in the properties of the absorber or blurred reflector incorporated in the other scenarios. The multi-epoch observations between 2009 and 2018 can be described in similar fashion. This could be understood if the primary emission is originating at a large distance from a standard accretion disc or if the disc is optically thin and geometrically thick as recently proposed for Zw 229.015. Our investigation shows that Zw 229.015 behaves similar to sources like Akn 120 and Mrk 530 that exhibit a strong soft excess, but weak Compton hump and Fe Kα emission.
    Type of Medium: Online Resource
    ISSN: 0035-8711 , 1365-2966
    Language: English
    Publisher: Oxford University Press (OUP)
    Publication Date: 2019
    detail.hit.zdb_id: 2016084-7
    SSG: 16,12
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  • 8
    In: Astronomy & Astrophysics, EDP Sciences, Vol. 647 ( 2021-3), p. A6-
    Abstract: The ultra-soft narrow-line Seyfert 1 galaxy 1H 0707−495 is a well-known and highly variable active galactic nucleus (AGN), with a complex, steep X-ray spectrum, and has been studied extensively with XMM-Newton . 1H 0707−495 was observed with the extended ROentgen Survey with an Imaging Telescope Array (eROSITA) aboard the Spectrum-Roentgen-Gamma (SRG) mission on October 11, 2019, for about 60 000 s as one of the first calibration and pointed verification phase (CalPV) observations. The eROSITA light curves show significant variability in the form of a flux decrease by a factor of 58 with a 1 σ error confidence interval between 31 and 235. This variability is primarily in the soft band, and is much less extreme in the hard band. No strong ultraviolet variability has been detected in simultaneous XMM-Newton Optical Monitor observations. The UV emission is L UV ≈ 10 44  erg s −1 , close to the Eddington limit. 1H 0707−495 entered the lowest hard flux state seen in 20 yr of XMM-Newton observations. In the eROSITA All-Sky Survey (eRASS) observations taken in April 2020, the X-ray light curve is still more variable in the ultra-soft band, but with increased soft and hard band count rates more similar to previously observed flux states. A model including relativistic reflection and a variable partial covering absorber is able to fit the spectra and provides a possible explanation for the extreme light-curve behaviour. The absorber is probably ionised and therefore more transparent to soft X-rays. This leaks soft X-rays in varying amounts, leading to large-amplitude soft-X-ray variability.
    Type of Medium: Online Resource
    ISSN: 0004-6361 , 1432-0746
    RVK:
    RVK:
    Language: English
    Publisher: EDP Sciences
    Publication Date: 2021
    detail.hit.zdb_id: 1458466-9
    SSG: 16,12
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  • 9
    Online Resource
    Online Resource
    Oxford University Press (OUP) ; 2022
    In:  Monthly Notices of the Royal Astronomical Society Vol. 510, No. 3 ( 2022-01-17), p. 4370-4378
    In: Monthly Notices of the Royal Astronomical Society, Oxford University Press (OUP), Vol. 510, No. 3 ( 2022-01-17), p. 4370-4378
    Abstract: A sample of 22 narrow-line type 1 Seyfert (NLS1) and 47 broad-line type 1 Seyfert (BLS1) galaxies observed with Suzaku is used to examine the Fe K-band properties of each group. Three different models are used to examine the presence of: narrow neutral Fe K α line at $6.4{\rm \, keV}$ and ionized Fe xxv and Fe xxvi emission lines (model A); a broad emission feature at around $6{-}7{\rm \, keV}$ (model B); and an absorption edge at ${\sim}7.1{\rm \, keV}$ (model C). In all three models, the neutral Fe K α line is weaker (lower luminosity and equivalent width) in NLS1s than in BLS1s. Model (B) also finds a more significant broad component (larger equivalent width) in NLS1s than in BLS1s. The feature does not appear to be an artifact of steeper spectra in NLS1s, but rather an intrinsic property of these sources. From model (C), the optical depth of the absorption edge appears comparable between the two samples. When comparing the absorption with the emission line properties, NLS1s seem to exhibit a lower ratio of emission-to-absorption of iron than BLS1s, and have a lower value than expected based on the fluorescence yield. The observed differences may arise from different torus geometries (e.g. larger opening angle in NLS1s), and/or additional sources of Fe K emission and absorption in NLS1s beyond pure fluorescence (e.g. originating in the disc and broad-line region).
    Type of Medium: Online Resource
    ISSN: 0035-8711 , 1365-2966
    Language: English
    Publisher: Oxford University Press (OUP)
    Publication Date: 2022
    detail.hit.zdb_id: 2016084-7
    SSG: 16,12
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  • 10
    Online Resource
    Online Resource
    Oxford University Press (OUP) ; 2020
    In:  Monthly Notices of the Royal Astronomical Society Vol. 498, No. 4 ( 2020-10-01), p. 5207-5226
    In: Monthly Notices of the Royal Astronomical Society, Oxford University Press (OUP), Vol. 498, No. 4 ( 2020-10-01), p. 5207-5226
    Abstract: A sample of narrow-line Seyfert 1 (NLS1) and broad-line Seyfert 1 (BLS1) galaxies observed with Suzaku is presented. The final sample consists of 22 NLS1s and 47 BLS1s, for a total of 69 active galactic nuclei (AGNs) that are all at low redshift (z & lt; 0.5) and exhibit low host-galaxy column densities ( & lt;1022${\rm cm}^{-2}\,$). The average spectrum for each object is fit with a toy model to characterize important parameters, including the photon index, soft excess, Compton hump (or hard excess), narrow iron line strength, luminosity, and X-ray Eddington ratio (Lx/LEdd). We confirm previous findings that NLS1s have steeper power laws and higher X-ray Eddington ratios, but also find that NLS1 galaxies have stronger soft and hard excesses than their BLS1 counterparts. Studying the correlations between parameters shows that the soft and hard excesses are correlated for NLS1 galaxies, while no such correlation is observed for BLS1s. Performing a principal component analysis (PCA) on the measured X-ray parameters shows that while the X-ray Eddington ratio is the main source of variations within our sample (PC1), variations in the soft and hard excesses form the second principal component (PC2) and it is dominated by the NLS1s. The correlation between the soft and hard excesses in NLS1 galaxies may suggest a common origin for the two components, such as a blurred reflection model. The presented Suzaku sample of Seyfert 1 galaxies is a useful tool for the analysis of the X-ray properties of AGNs, and for the study of the soft and hard excesses observed in AGNs.
    Type of Medium: Online Resource
    ISSN: 0035-8711 , 1365-2966
    Language: English
    Publisher: Oxford University Press (OUP)
    Publication Date: 2020
    detail.hit.zdb_id: 2016084-7
    SSG: 16,12
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