X-ray spectral variability of seven LINER nuclei with<i>XMM-Newton</i>and<i>Chandra</i>data

Hernández-García, L.; González‐Martín, O.; Márquez, I.; Masegosa, J.

doi:10.1051/0004-6361/201321563

Cited by 51 publications

(63 citation statements)

References 87 publications

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“…Furthermore, the same anticorrelation is seen in our spectral fits when the absorbing column is allowed to vary as well as the photon index. The values of Γ found are between those found by Weaver et al (1999) and by Hernández-García et al (2013) Γ = 1.37 − 1.70 for similar models, though Hernández-García et al (2013) attribute the primary cause of spectral changes in NGC 1052 to variations in the absorbing column, not the photon index. As the source displays harder-when-brighter behaviour, if the spectral variations are caused by absorption variation alone this absorption must be negatively correlated with the luminosity of the system, as in e.g.…”

Section: Appendix A: Notes On Spectral Fitting Of Individual Palomar Agnsupporting

confidence: 68%

“…This saturation is once again seen in observations of both AGN and BHXRBs, using a small number of observations from large samples of sources (Yang et al 2015;Gu & Cao 2009;Hernández-García et al 2013). …”

Section: Introductionmentioning

confidence: 80%

“…Previous studies have looked for changes in the photon index with luminosity of individual LLAGN before (Younes et al 2011;Hernández-García et al 2013, but been unsuccessful; our ability to detect changes in the photon index more easily is likely due to the larger flux-ranges covered by our data. As the amplitude of the change in Γ is proportional to the change in the luminosity of the system, a large flux range is essential.…”

Section: Agn and Bhxrb State Analoguesmentioning

confidence: 95%

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Long-term X-ray spectral variability in AGN from the Palomar sample observed bySwift

Connolly

McHardy

Skipper

et al. 2016

Mon. Not. R. Astron. Soc.

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We present X-ray spectral variability of 24 local active galactic nuclei (AGN) from the Palomar sample of nearby galaxies, as observed mainly by Swift. From hardness ratio measurements, we find that 18 AGN with low accretion rates show hardening with increasing count rate, converse to the softer-when-brighter behaviour normally observed in AGN with higher accretion rates. Two AGN show softening with increasing count rate, two show more complex behaviour, and two do not show any simple relationship.Sufficient data were available for the spectra of 13 AGN to be summed in fluxbins. In 9 of these sources, correlated luminosity-dependent changes in the photon index (Γ) of a power-law component are found to be the main cause of hardness variability. For 6 objects, with a low accretion rate as a fraction of the Eddington rate (ṁ Edd ), Γ is anticorrelated withṁ Edd , i.e. 'harder-when-brighter' behaviour is observed. The 3 higher-ṁ Edd -rate objects show a positive correlation between Γ anḋ m Edd . This transition from harder-when-brighter at lowṁ Edd to softer-when-brighter at highṁ Edd can be explained by a change in the dominant source of seed-photons for X-ray emission from cyclo-synchrotron emission from the Comptonising corona itself to thermal seed-photons from the accretion disc. This transition is also seen in the 'hard state' of black hole X-ray binaries (BHXRBs). The results support the idea that LINERs are analogues of BHXRBs in the hard state and that Seyferts are analogues of BHXRBs in either the high-accretion-rate end of the hard state or in the hard-intermediate state.

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Section: Appendix A: Notes On Spectral Fitting Of Individual Palomar Agnsupporting

confidence: 68%

Section: Introductionmentioning

confidence: 80%

Section: Agn and Bhxrb State Analoguesmentioning

confidence: 95%

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Long-term X-ray spectral variability in AGN from the Palomar sample observed bySwift

Connolly

McHardy

Skipper

et al. 2016

Mon. Not. R. Astron. Soc.

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“…The radio core is known to be variable (see also Sect. 3.1) and NGC 3998 also shows variability in the ultraviolet (Maoz et al 2005) and X-ray (Younes et al 2012;Hernández-García et al 2013) regimes. At X-ray energies, NGC 3998 contains a nuclear source with L X (2-10 keV) ∼ 2.5 × 10 41 erg s −1 (Terashima et al 2000;Ptak et al 2004).…”

Section: Overview Of Ngc 3998mentioning

confidence: 93%

A rare example of low surface-brightness radio lobes in a gas-rich early-type galaxy: the story of NGC 3998

Frank

Morganti

Oosterloo

et al. 2016

A&A

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We study the nearby lenticular galaxy NGC 3998. This galaxy is known to host a low-power radio AGN with a kpc-size one-sided jet and a large, nearly polar H i disc. It is therefore a good system to study to understand the relation between the availability of cold-gas and the triggering of AGNs in galaxies. Our new WSRT data reveal two faint, S-shaped radio lobes extending out to ∼10 kpc from the galaxy centre. Remarkably, we find that the inner H i disc warps back towards the stellar mid-plane in a way that mirrors the warping of the radio lobes. We suggest that the polar H i disc was accreted through a minor merger, and that the torques causing it to warp in the inner regions are also responsible for feeding the AGN. The "S" shape of the radio lobes would then be due to the radio jets adapting to the changing angular momentum of the accreted gas. The extended radio jets are likely poorly collimated, which would explain their quick fading and, therefore, their rarity in galaxies similar to NGC 3998. The fuelling of the central super-massive black hole is likely occurring via "discrete events", suggested by the observed variability of the radio core and the extremely high core dominance, which we attribute to the formation and ejection of a new jet resulting from a recent fuelling event.

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“…This is the third in a series of papers aimed at studying the X-ray variability in different families of AGN. In Hernández-García et al (2013, this study was made for LINERs, while the study of Seyfert 1 and the comparison between different families of AGN will be presented in forthcoming papers. This paper is organized as follows.…”

Section: Introductionmentioning

confidence: 99%

X-ray spectral variability of Seyfert 2 galaxies

Hernández-García

Masegosa

González‐Martín³

et al. 2015

A&A

Self Cite

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Context. Variability across the electromagnetic spectrum is a property of active galactic nuclei (AGN) that can help constrain the physical properties of these galaxies. Nonetheless, the way in which the changes happen and whether they occur in the same way in every AGN are still open questions. Aims. This is the third in a series of papers with the aim of studying the X-ray variability of different families of AGN. The main purpose of this work is to investigate the variability pattern(s) in a sample of optically selected Seyfert 2 galaxies. Methods. We use the 26 Seyfert 2s in the Véron-Cetty and Véron catalog with data available from Chandra and/or XMM-Newton public archives at different epochs, with timescales ranging from a few hours to years. All the spectra of the same source were simultaneously fitted, and we let different parameters vary in the model. Whenever possible, short-term variations from the analysis of the light curves and/or long-term UV flux variations were studied. We divided the sample into Compton-thick and Compton-thin candidates to account for the degree of obscuration. When transitions between Compton-thick and thin were obtained for different observations of the same source, we classified it as a changing-look candidate. Results. Short-term variability at X-rays was studied in ten cases, but variations are not found. From the 25 analyzed sources, 11 show long-term variations. Eight (out of 11) are Compton-thin, one (out of 12) is Compton-thick, and the two changing-look candidates are also variable. The main driver for the X-ray changes is related to the nuclear power (nine cases), while variations at soft energies or related to absorbers at hard X-rays are less common, and in many cases these variations are accompanied by variations in the nuclear continuum. At UV frequencies, only NGC 5194 (out of six sources) is variable, but the changes are not related to the nucleus. We report two changing-look candidates, MARK 273 and NGC 7319. Conclusions. A constant reflection component located far away from the nucleus plus a variable nuclear continuum are able to explain most of our results. Within this scenario, the Compton-thick candidates are dominated by reflection, which suppresses their continuum, making them seem fainter, and they do not show variations (except MARK 3), while the Compton-thin and changing-look candidates do.

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X-ray spectral variability of seven LINER nuclei withXMM-NewtonandChandradata

Cited by 51 publications

References 87 publications

Long-term X-ray spectral variability in AGN from the Palomar sample observed bySwift

Long-term X-ray spectral variability in AGN from the Palomar sample observed bySwift

A rare example of low surface-brightness radio lobes in a gas-rich early-type galaxy: the story of NGC 3998

X-ray spectral variability of Seyfert 2 galaxies

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