IUCAA Preprints

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Author: search.filters.author.Kembhavi, A.K.Subject: search.filters.subject.Quasars

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    On the origin of the featureless soft X-ray excess emission from the Seyfert 1 galaxy ESO 198–G24
    (IUCAA, 2015-02) Laha, Sibasish; Dewangan, Gulab Chand; Kembhavi, A.K.
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    The soft x-ray excess in quasars
    (2014-11-22) Kembhavi, A.K.; Fabian, A.C.
    A soft x-ray excess in the energy range of a few tenths of a ke V has been detected in some quasars , and there are indications in the x-ray data which point to the excess being a feature universal to all quasars. The poor energy resolution in the concerned energy band make it impossible at the present to observationally constrain the excess quantitatively. We show in this paper that the shape of the excess sensitively determines the surface density therefore allows an assessment of the nature of the excess
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    Properties of warm absorbers in active galaxies: a systematic stability curve analysis
    (2008-10-14) Chakravorty, Susmita; Kembhavi, A.K.
    Signatures of warm absorbers are seen in soft X-ray spectra of about half of all Seyfert1 galaxies observed and in some quasars and blazars. We use the thermal equilibrium curve to study the influence of the shape of the ionizing continuum, density and the chemical composition of the absorbing gas on the existence and nature of the warm absorbers. We describe circumstances in which a stable warm absorber can exist as a multiphase medium or one with continuous variation in pressure. In particular we find the following results: i) the warm absorber exists only if the spectral index of the X-ray power-law ionizing continuum α > 0.2 and has a multiphase nature if α ∼ 0.8, which interestingly is the spectral index formost of the observed Seyfert 1 galaxies; ii) thermal and ionization states of highly dense warm absorbers are sensitive to their density if the ionizing continuum is sufficiently soft, i.e. dominated by the ultraviolet iii) absorbing gas with super Solar metallicity is more likely to have a multiphase nature; iv) the nature of the warm absorber is significantly influenced by the absence of iron and associated elements which are produced in the later stages of star formation history in supernovae of type Ia.