An increase in the X-ray absorption of NGC 4151

Barr, P.; White, N. E.; Sanford, P. W.; Ives, J. C.

doi:10.1093/mnras/181.1.43p

Cited by 44 publications

(21 citation statements)

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“…Within the available statistics we find no necessity for the inclusion of an iron absorption edge at ~ 7 keV, as detected by Ariel V and HEAO A-2, (Barr et al 1977 andHolt et al 1980 respectively). With only two PHA channels covering the 6-7 keV range it is quite conceivable that the 6.7 keV 'feature' is the net result of a fluorescence line and an absorption edge.…”

Section: 1ngc 4151supporting

confidence: 59%

Ariel-6 medium energy spectral observations of active galaxies

et al. 1981

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X-ray spectra of the BL Lac type object Mkn 421 and several Seyfert type 1 galaxies; IIIZw2, MCG8-11-11 and NGC 4151, have been obtained using the Leicester University instrument on board the Ariel-6 satellite. The Mkn 421 spectrum is best represented by two powerlaw components, the soft component having ~ ~ 3.4 whilst the hard flux has ~1.0.In MCGS-11-11 there is clear evidence for spectral variability between our observation in late 1979 and that of HEAO-1/A2 in 1977. The Ariel-6 spectrum of MCGS-11-11 can be fitted by a powerlaw of index ~ ~ 2.1 together with an iron line at ~ 6.2 keV with an equivalent width of ~ 1.6 keV. The first X-ray spectrum of IIIZw2 is also presented, fitting with a powerlaw we find an index of ~1.7.With the exception of NGC 4151 there is no evidence for a significant column of cool material along the line of sight. OBSERVATIONSThe X-ra~ observations were accomplished using the Ariel-6 satellite. The Leicester University instrument consists of four multi-layered xenon filled proportional counters with an effective area of ~300 cm 2 and a sensitive energy range of 1-50 keV. Each detector is sub-divided into two sections, the spectra from front and rear being recorded independantly over the 1-20 keV and 10-50 keV ranges respectively.Both of these energy ranges are further sub-divided into 16 logarithmically spaced channels.Mechanical collimators provide a ~ 3 ~ FWHM circular field of view pointing ~ 1 ~ from the satellite spin axis.

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Section: 1ngc 4151supporting

confidence: 59%

Ariel-6 medium energy spectral observations of active galaxies

et al. 1981

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“…Some quasars have appreciable fractions of their luminosities in this range; see Culhane (1978), Elvis et al (1978), Giacconi (1978), Marshall et al (1978), Sta'rk, Burnell, and Culhane (1978), Swanenberg et al (1978), Barr et al (1977), DiCocco et al (1977), and Gursky and Schwartz (1977). In Burbidge (1978) and many references therein, as well as Bahcall (1978).…”

Section: B Quasars As Observed Opticallymentioning

confidence: 99%

The emission lines of quasars and similar objects

1979

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Much of our information about quasars is derived from their emission-line spectra. The analysis of such spectra has become an intricate subject which differs considerably from traditional, low-density nebular astrophysics. This review is intended to explain our present understanding of the situation, including some aspects of galactic nuclei whose luminosities are more modest than quasars. Quasars line-emitting regions are probably photoionized (even if supplementary heating processes also occur). So fax, models have been constructed which include ionization and thermal equilibria, the transfer of resonance-line and related photons, and the likely effects of absorption and scattering by dust grains. From comparisons between emission-line intensities produced in these models and observed quasars spectra, it appears that certain densities and pressures and size scales occur in or around quasars. The relative abundances of elements are not very far from solar values, although it is suspected that heavy elements -carbon, nitrogen, and oxygen in particular -are moderately "overabundant" in quasars. The emission-line intensities also provide indirect information about quasars ultraviolet and soft-x-ray continua; there are hints that photons with energies between 20 and 300 eV -which are not directly observable -may even represent the peak of the luminous output of a typical quasar. Finally, some gas-dynamical questions, while extremely important, are very difficult to answer, because of a lack of observables. CONTENTS 715

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“…Previous spectra have also shown that NGC 4151 exhibits a low energy cut-off which, for a Seyfert galaxy, is atypical and large, with a corresponding absorbing column of cold gas in the range n~ ~ I0 zz -I0 x3 H atoms cm -2 (Barr et al, 1977;Mushotzky et al, 1978;Hall et al, 1981).…”

Section: Introductionmentioning

confidence: 96%

The soft X-ray spectrum of NGC 4151

Pounds

Warwick

Culhane³

et al. 1985

Space Sci Rev

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EXOSAT observations of the Seyfert galaxy NGC 4151 over the period July 1983 to April 1984 have revealed a decreasing flux in the 2 -10 keV band.In accord with previous measurements a power law spectrum attenuated with a simple column of cold gas does not provide a satisfactory spectral fit below N3 keV, where a lower relative opacity is required.Inclusion of additional low energy data from the EXOSAT telescopes allows the modelling of the absorbing column to be improved and reveals a second, separate, soft X-ray spectral component.

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An increase in the X-ray absorption of NGC 4151

Cited by 44 publications

References 0 publications

Ariel-6 medium energy spectral observations of active galaxies

Ariel-6 medium energy spectral observations of active galaxies

The emission lines of quasars and similar objects

The soft X-ray spectrum of NGC 4151

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