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Register a new userMrk 1014: An AGN Dominated ULIRG at X-rays
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In this paper we report on an XMM-Newton observation of the ultraluminous infrared QSO Mrk 1014. The X-ray observation reveals a power-law dominated (photon index of about 2.2) spectrum with a slight excess in the soft energy range. AGN and starburst emission models fit the soft excess emission equally well, however, the most plausible explanation is an AGN component as the starburst model parameter, temperature and luminosity, appear physically unrealistic. The mean luminosity of Mrk 1014 is about 2 times 10^44 erg s^-1. We have also observed excess emission at energies greater than 5 keV. This feature could be attributed to a broadened and redshifted iron complex, but deeper observations are required to constrain its origin. The light curve shows small scale variability over the 11 ks observation. There is no evidence of intrinsic absorption in Mrk 1014. The X-ray observations support the notion of an AGN dominated central engine. We establish the need for a longer observation to constrain more precisely the nature of the X-ray components.
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We present preliminary results on the variability properties of AGN above 20 keV in order to show the potential of the INTEGRAL IBIS/ISGRI and Swift/BAT instruments for hard X-ray timing analysis of AGN. The 15-50 keV light curves of 36 AGN observed by BAT during 5 years show significantly larger variations when the blazar population is considered (average normalized excess variance = 0.25) with respect to the Seyfert one (average normalized excess variance = 0.09). The hard X-ray luminosity is found to be anti-correlated to the variability amplitude in Seyfert galaxies and correlated to the black hole mass, confirming previous findings obtained with different AGN hard X-ray samples. We also present results on the Seyfert 1 galaxy IC 4329A, as an example of spectral variability study with INTEGRAL/ISGRI data. The position of the high-energy cut-off of this source is found to have varied during the INTEGRAL observations, pointing to a change of temperature of the Comptonising medium. For several bright Seyfert galaxies, a considerable amount of INTEGRAL data have already been accumulated and are publicly available, allowing detailed spectral variability studies at hard X-rays.
We present deep spectroscopic and imaging data of the host galaxies of Mrk 1014, IRAS 07598+6508, and Mrk 231. These objects form part of both the QSO and the ultraluminous infrared galaxy (ULIG) families, and may represent a transition stage in an evolutionary scenario. Our imaging shows that all three objects have highly perturbed hosts with tidal tails and destroyed disks, and appear to be in the final stages of major mergers. The host galaxies of the three objects have spectra typical of E+A galaxies, showing simultaneously features from an old and a young stellar component. We model spectra from different regions of the host galaxies using Bruzual & Charlot spectral synthesis models using two component models including an old underlying population and recent superposed starbursts. Our results indicate a strong connection between interactions and vigorous bursts of star formation in these objects. We propose that the starburst ages found are indicative of young ages for the QSO activity. The young starburst ages found are also consistent with the intermediate position of these objects in the far infrared color-color diagram. (abridged)
Variability at all observed wavelengths is a distinctive property of AGN. Hard X-rays provide us with a view of the innermost regions of AGN, mostly unbiased by absorption along the line of sight. Swift/BAT offers the unique opportunity to follow, on time scales of days to years and with a regular sampling, the 14-195 keV emission of the largest AGN sample available up to date for this kind of investigation. We study the amplitude of the variations, and their dependence on sub-class and on energy, for a sample of 110 radio quiet and radio loud AGN selected from the BAT 58-month survey. About 80% of the AGN in the sample are found to exhibit significant variability on months to years time scales, radio loud sources being the most variable. The amplitude of the variations and their energy dependence are incompatible with variability being driven at hard X-rays by changes of the absorption column density. In general, the variations in the 14-24 and 35-100 keV bands are well correlated, suggesting a common origin of the variability across the BAT energy band. However, radio quiet AGN display on average 10% larger variations at 14-24 keV than at 35-100 keV and a softer-when-brighter behavior for most of the Seyfert galaxies with detectable spectral variability on month time scale. In addition, sources with harder spectra are found to be more variable than softer ones. These properties are generally consistent with a variable power law continuum, in flux and shape, pivoting at energies >~ 50 keV, to which a constant reflection component is superposed. When the same time scales are considered, the timing properties of AGN at hard X-rays are comparable to those at lower energies, with at least some of the differences possibly ascribable to components contributing differently in the two energy domains (e.g., reflection, absorption).
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We investigate the polarization of Compton scattered X-rays from relativistic jets in active galactic nuclei using Monte Carlo simulations. We consider three scenarios: scattering of photons from an accretion disk, scattering of cosmic microwave background (CMB) photons, and synchrotron self-Comptonization (SSC) within the jet. For Comptonization of thermal disk photons or CMB photons the maximum linear polarization attained is slightly over 20% at viewing angles close to 90 degrees. The value decreases with the viewing inclination. For SSC, the maximum value may exceed 80%. The angle dependence is complicated, and it varies with the photon injection sites. Our study demonstrates that X-ray polarization, in addition to multi-wavelength spectra, can distinguish certain models for emission and particle acceleration in relativistic jets.
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