Extreme X-Ray Variability in the Narrow-Line QSO PHL 1092

Abstract.We have compiled a list of 83 objects classified as Narrow-Line Seyfert 1 galaxies (NLS1s) or known to have a broad Balmer component narrower than 2 000 km s −1 . Of these, 19 turned out to have been spectroscopically misidentified in previous studies; only 64 of the selected objects are genuine NLS1s. We have spectroscopically observed 59 of them and tried to characterize their Narrow and Broad-Line Regions (NLR and BLR) by fitting the emission-lines with Gaussian and/or Lorentzian profiles. In most cases, the broad Balmer components are well fitted by a single Lorentzian profile, confirming previous claims that Lorentzian rather than Gaussian profiles are better suited to reproduce the shape of the NLS1s broad emission lines. This has consequences concerning their FWHMs and line ratios: when the broad Balmer components are fitted with a Lorentzian, most narrow line regions have line ratios typical of Seyfert 2s while, when a Gaussian profile is used for fitting the broad Balmer components, the line ratios are widely scattered in the usual diagnostic diagrams (Veilleux & Osterbrock 1987); moreover, the FWHM of the best fitting Lorentzian is systematically smaller than the FWHM of the Gaussian. We find that, in general, the [O III] lines have a relatively narrow Gaussian profile (∼200-500 km s −1 FWHM) with often, in addition, a second broad (∼500-1 800 km s −1 FWHM), blueshifted Gaussian component. We do not confirm that the [O III] lines are weak in NLS1s. As previously suggested, there is a continuous transition of all properties between NLS1s and classical Broad-Line Seyfert 1 Galaxies (BLS1s) and the limit of 2000 km s −1 used to separate the two species is arbitrary; R4570, the ratio of the Fe II to the Hβ fluxes, could be a physically more meaningful parameter to distinguish them.

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“…The X-ray flux has changed by a factor 13.1 in 10 years (Forster & Halpern 1996) and by a factor 4 in ∼3 × 10 4 s ( Ulrich et al 1999).…”

Section: Mark 705 (0923+12)mentioning

confidence: 99%

A spectrophotometric atlas of Narrow-Line Seyfert 1 galaxies

Véron-Cetty

Véron

Gonçalves³

2001

A&A

285

324

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“…125 Brandt, & Fink 1996 ;Forster & Halpern 1996 ;Laor et al 1997a). ASCA spectra from NLS1s have the advantage of a broader bandpass and better energy resolution than the ROSAT PSPC spectra.…”

Section: Introductionmentioning

confidence: 99%

A Comprehensive Spectral and Variability Study of Narrow‐Line Seyfert 1 Galaxies Observed by ASCA . II. Spectral Analysis and Correlations

Leighly

1999

ASTROPHYS J SUPPL S

315

197

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I present a comprehensive and uniform analysis of 25 ASCA observations from 23 narrow-line Seyfert 1 galaxies (NLS1s). The spectral analysis and correlations are presented in this paper ; the reduction and time series analysis are presented in the companion paper. A maximum likelihood analysis conÐrms that the hard X-ray photon index is signiÐcantly steeper at more than 90% conÐdence in this sample of NLS1s compared with a random sample of Seyfert galaxies with broad optical lines. Soft excess emission was detected in 17 of the 19 objects that had no signiÐcant absorption, a result that demonstrates that soft excesses appear considerably more frequently in NLS1s than in Seyfert 1 galaxies with broad optical lines. The strength of the soft excess, parameterized using a Ñux ratio obtained from the blackbody plus power-law model, has a wide range of values in these objects (a factor of 50). The photon index was found to be correlated with the Hb FWHM, despite the small range of the latter parameter ; however, neither parameter is correlated with the strength of the soft excess or ROSAT slope. Therefore, assuming that an excess of soft photons causes the steep photon index and narrow Hb FWHM, that excess may lie primarily in the unobservable EUV. The strength of the soft excess is correlated with the variability parameters, so that objects with strong soft excesses show higher amplitude variability ; this potentially important result is not easily explained. While a range of 2 orders of magnitude in luminosity is represented, the temperature of the soft excess is approximately consistent throughout the sample, in contrast with expectations of simple accretion disk models. The presence of ionized absorption was sought using a two-edge model. It was found that this component appears to be typically less common in NLS1s and some evidence was found that the typical ionization state is lower compared with broad-line Seyfert galaxies. This fact, plus evidence for a correlation between the presence of the warm absorber and signiÐcant optical polarization, may imply that the inner warm absorber is missing or is too highly ionized to be detected, and only the outer, dusty, less ionized warm absorber is present in many cases. The iron line equivalent width appears to be similar among narrow and broad-line Seyfert galaxies. This could mean that reprocessing occurs with similar geometry in both classes of objects ; however, the detection of ionized iron lines in a few objects, implying possibly altered Ñuorescence yields, and poor statistics, makes this conclusion tentative. Constraints on physical processes and models based on extreme values of orientation and accretion rate for NLS1s are examined in light of the observational results.

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“…Although X-ray variability has been observed in AGN for more than two decades, its origin is still poorly understood. Narrow-Line Seyfert 1 galaxies (NLS1) often display rapid, large amplitude X-ray variability as well as extreme long term changes (Forster & Halpern 1996;Boller et al 1997;Brandt et al 1999), and therefore they represent the ideal class for an X-ray temporal analysis. PKS 0558-504 (z = 0.137, m B = 14.97) is one of the few radio-loud NLS1.…”

Section: Introductionmentioning

confidence: 99%

XMM-Newton monitoring of X-ray variability in the quasar PKS 0558-504

Gliozzi

Brinkmann

O’Brien

et al. 2001

A&A

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Abstract. We present the temporal analysis of X-ray observations of the radio-loud Narrow-Line Seyfert 1 galaxy (NLS1) PKS 0558-504 obtained during the XMM-Newton Calibration and Performance Verification (Cal/PV) phase. The long term light curve is characterized by persistent variability with a clear tendency for the X-ray continuum to harden when the count rate increases. Another strong correlation on long time scales has been found between the variability in the hard band and the total flux. On shorter time scales the most relevant result is the presence of smooth modulations, with characteristic time of ∼2 hours observed in each individual observation. The short term spectral variability turns out to be rather complex but can be described by a well defined pattern in the hardness ratio-count rate plane.

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Extreme X-Ray Variability in the Narrow-Line QSO PHL 1092

Cited by 50 publications

References 36 publications

A spectrophotometric atlas of Narrow-Line Seyfert 1 galaxies

A spectrophotometric atlas of Narrow-Line Seyfert 1 galaxies

A Comprehensive Spectral and Variability Study of Narrow‐Line Seyfert 1 Galaxies Observed by ASCA . II. Spectral Analysis and Correlations

XMM-Newton monitoring of X-ray variability in the quasar PKS 0558-504

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