* Astronomy

Members Login
Post Info TOPIC: Quasar MR2251-178


L

Posts: 131433
Date:
MR 2251-178
Permalink  
 


Title: The puzzling X-ray continuum of the quasar MR 2251-178
Author: E. Nardini, J. N. Reeves, D. Porquet, V. Braito, N. Grosso, J. Gofford

We report on a comprehensive X-ray spectral analysis of the nearby radio-quiet quasar MR 2251-178, based on the long-look (~ 400 ks) XMM-Newton observation carried out in November 2011. As the properties of the multiphase warm absorber (thoroughly discussed in a recent, complementary work) hint at a steep photoionizing continuum, here we investigate into the nature of the intrinsic X-ray emission of MR 2251-178 by testing several physical models. The apparent 2-10 keV flatness as well as the subtle broadband curvature can be ascribed to partial covering of the X-ray source by a cold, clumpy absorption system with column densities ranging from a fraction to several x10^23 cm^-2. As opposed to more complex configurations, only one cloud is required along the line of sight in the presence of a soft X-ray excess, possibly arising as Comptonized disc emission in the accretion disc atmosphere. On statistical grounds, even reflection with standard efficiency off the surface of the inner disc cannot be ruled out, although this tentatively overpredicts the observed ~ 14-150 keV emission. It is thus possible that each of the examined physical processes is relevant to a certain degree, and hence only a combination of high-quality, simultaneous broadband spectral coverage and multi-epoch monitoring of X-ray spectral variability could help disentangling the different contributions. Yet, regardless of the model adopted, we infer for MR 2251-178 a bolometric luminosity of ~ 5-7 x 10^45 erg/s, implying that the central black hole is accreting at ~ 15-25 per cent of the Eddington limit.

Read more (220kb, PDF)



__________________


L

Posts: 131433
Date:
Quasar MR2251-178
Permalink  
 


Title: Chandra LETGS spectroscopy of the Quasar MR2251-178 and its warm absorber
Authors: J.M. Ramírez (1), S. Komossa (1), V. Burwitz (1), S. Mathur (2) ((1) Max-Planck-Institut für extraterrestriche Physik, Garching, Germany, (2) Department of Astronomy, Ohio State University, Columbus)

We present an analysis of our Chandra Low Energy Transmission Grating Spectrometer (LETGS) observation of the quasar MR2251-178. The warm absorber of MR2251-178 is well described by a hydrogen column density, N_H~2x10^21 cm^-2, and an ionisation parameter log(xi)~0.6. We find in the spectrum weak evidence for narrow absorption lines from Carbon and Nitrogen which indicate that the ionised material is in outflow. We note changes (in time) of the absorption structure in the band (0.6-1) keV (around the UTAs plus the OVII and OVIII K-edges) at different periods of the observation. We measure a (0.1-2) keV flux of 2.58x10^-11 ergs cm^-2 s^-1. This flux implies that the nuclear source of MR2251-178 is in a relatively low state. No significant variability is seen in the light curve. We find evidence for an extra cold material in the line of sight, and set an upper limit of N_H~1.2x10^20 cm^-2. The X-ray spectrum does not appear to show evidence for dusty material, though an upper limit in the neutral carbon and oxygen column densities can only be set to N_CI~2x10^19 cm^-2 and N_OI~9x10^19 cm^-2, respectively.

Read more (177kb, PDF)

__________________
Page 1 of 1  sorted by
Quick Reply

Please log in to post quick replies.



Create your own FREE Forum
Report Abuse
Powered by ActiveBoard