Stability of warm absorbers in AGN

Ms. Susmita Chakravorty, IUCAA, Pune, India

Signatures of warm absorbers are seen in soft X-ray spectra of about half of all Seyfert1 galaxies observed. Using the thermal equilibrium curve we study the influence of the shape of the ionizing continuum and the chemical composition of the absorbing gas on the stability of warm absorbers. Interestingly we find that warm absorbers are more likely to exist as a multiphase system for ionizing continuum with X-ray spectral index of 0.8 which is typical of AGN. Moreover, if an ionizing continuum has a soft X-ray excess component, the stability of absorbing gas at 10^5 K is doubled. The 10^6 K phase of the absorber is found to be reinforced if the absorber has super Solar metallicity. These results indicate a consistent picture of warm absorbers to be gas in thermal equilibrium and having multiple phases in pressure equilibrium.