Constraints on Black Hole Spin in a Sample of Broad Iron Line AGN

We present a uniform X-ray spectral analysis of nine type-1 active galactic nuclei (AGN) that have been previously found to harbor relativistically broadened iron emission lines. We show that the need for relativistic effects in the spectrum is robust even when one includes continuum "reflection" from the accretion disk. We then proceed to model these relativistic effects in order to constrain the spin of the supermassive black holes in these AGN. Our principal assumption, supported by recent simulations of geometrically-thin accretion disks, is that no iron line emission (or any associated Xray reflection features) can originate from the disk within the innermost stable circular orbit. Under this assumption, which tends to lead to constraints in the form of lower limits on the spin parameter, we obtain non-trivial spin constraints on five AGN. The spin parameters of these sources range from moderate (a approximates 0.6) to high (a > 0.96). Our results allow, for the first time, an observational constraint on the spin distribution function of local supermassive black holes. Parameterizing this as a power-law in dimensionless spin parameter (f(a) varies as absolute value of (a) exp zeta), we present the probability distribution for zeta implied by our results. Our results suggest 90% and 95% confidence limits of zeta > -0.09 and zeta > -0.3 respectively

O VII and O VIII absorption by hot gas in the vicinity of the Galaxy

(abridged) We searched for evidence of soft X-ray absorption by hot gas in the vicinity of the Galaxy in a small sample of fifteen type I AGN observed with the high resolution X-ray gratings on board Chandra. We find that around half of the sight lines in our sample exhibit absorption due to local H- or He-like Oxygen (or both) at confidence levels ranging from >90% to >3sigma. Depending on the sight line, the absorption can be identified with hot gas in particular local structures, the Local Group (LG) or the putative local hot intergalactic medium (IGM). Several sight lines in our sample coincide with sight lines in a study of O VI absorption by local gas, so an assumption of collisional ionization equilibrium (CIE) allows us to constrain the temperature of the local hot gas. We show that some portion of the hot absorbing outflows apparently detected in the spectra of NGC 4051, PDS 456 and PG 1211+143 respectively could actually correspond to absorption by hot local gas since the outflow velocity from each of these AGN coincides with the respective cosmological recession velocity of the AGN.Comment: 8 pages. Modified discussion of Fe-K band absorption features in PDS 456 and PG 1211+14

XMM-Newton Archival Study of the ULX Population in Nearby Galaxies

We present the results of an archival XMM-Newton study of the bright X-ray point sources (L_X > 10^38 erg/s) in 32 nearby galaxies. From our list of approximately 100 point sources, we attempt to determine if there is a low-state counterpart to the Ultraluminous X-ray (ULX) population, searching for a soft-hard state dichotomy similar to that known for Galactic X-ray binaries and testing the specific predictions of the IMBH hypothesis. To this end, we searched for "low-state" objects, which we defined as objects within our sample which had a spectrum well fit by a simple absorbed power law, and "high-state" objects, which we defined as objects better fit by a combined blackbody and a power law. Assuming that ``low-state'' objects accrete at approximately 10% of the Eddington luminosity (Done & Gierlinski 2003) and that "high-state" objects accrete near the Eddington luminosity we further divided our sample of sources into low and high state ULX sources. We classify 16 sources as low-state ULXs and 26 objects as high-state ULXs. As in Galactic black hole systems, the spectral indices, Gamma, of the low-state objects, as well as the luminosities, tend to be lower than those of the high-state objects. The observed range of blackbody temperatures for the high state is 0.1-1 keV, with the most luminous systems tending toward the lowest temperatures. We therefore divide our high-state ULXs into candidate IMBHs (with blackbody temperatures of approximately 0.1 keV) and candidate stellar mass BHs (with blackbody temperatures of approximately 1.0 keV). A subset of the candidate stellar mass BHs have spectra that are well-fit by a Comptonization model, a property similar of Galactic BHs radiating in the "very-high" state near the Eddington limit.Comment: 54 pages, submitted to ApJ (March 2005), accepted (May 2006); changes to organization of pape

On the lack of X-ray iron line reverberation in MCG-6-30-15: Implications for the black hole mass and accretion disk structure

We use the method of Press, Rybicki & Hewitt (1992) to search for time lags and time leads between different energy bands of the RXTE data for MCG-6-30-15. We tailor our search in order to probe any reverberation signatures of the fluorescent iron Kalpha line that is thought to arise from the inner regions of the black hole accretion disk. In essence, an optimal reconstruction algorithm is applied to the continuum band (2-4keV) light curve which smoothes out noise and interpolates across the data gaps. The reconstructed continuum band light curve can then be folded through trial transfer functions in an attempt to find lags or leads between the continuum band and the iron line band (5-7keV). We find reduced fractional variability in the line band. The spectral analysis of Lee et al. (1999) reveals this to be due to a combination of an apparently constant iron line flux (at least on timescales of few x 10^4s), and flux correlated changes in the photon index. We also find no evidence for iron line reverberation and exclude reverberation delays in the range 0.5-50ksec. This extends the conclusions of Lee et al. and suggests that the iron line flux remains constant on timescales as short as 0.5ksec. The large black hole mass (>10^8Msun) naively suggested by the constancy of the iron line flux is rejected on other grounds. We suggest that the black hole in MCG-6-30-15 has a mass of M_BH~10^6-10^7Msun and that changes in the ionization state of the disk may produce the puzzling spectral variability. Finally, it is found that the 8-15keV band lags the 2-4keV band by 50-100s. This result is used to place constraints on the size and geometry of the Comptonizing medium responsible for the hard X-ray power-law in this AGN.Comment: 11 pages, 13 postscript figures. Accepted for publication in Ap

Irradiation of an Accretion Disc by a Jet: General Properties and Implications for Spin Measurements of Black Holes

X-ray irradiation of the accretion disc leads to strong reflection features, which are then broadened and distorted by relativistic effects. We present a detailed, general relativistic approach to model this irradiation for different geometries of the primary X-ray source. These geometries include the standard point source on the rotational axis as well as more jet-like sources, which are radially elongated and accelerating. Incorporating this code in the relline model for relativistic line emission, the line shape for any configuration can be predicted. We study how different irradiation geometries affect the determination of the spin of the black hole. Broad emission lines are produced only for compact irradiating sources situated close to the black hole. This is the only case where the black hole spin can be unambiguously determined. In all other cases the line shape is narrower, which could either be explained by a low spin or an elongated source. We conclude that for all those cases and independent of the quality of the data, no unique solution for the spin exists and therefore only a lower limit of the spin value can be given.Comment: accepted by MNRAS for publication; now proof corrected Versio

Iron Line Spectroscopy of NGC4593 with XMM-Newton: Where is the Black Hole Accretion Disk?

We present an analysis of the 2-10keV XMM-Newton/EPIC-pn spectrum of the Seyfert-1 galaxy NGC4593. Apart from the presence of two narrow emission lines corresponding to the Kalpha lines of cold and hydrogen-like iron, this spectrum possesses a power-law form to within 3-5%. There is a marked lack of spectral features from the relativistic regions of the black hole accretion disk. We show that the data are, however, consistent with the presence of a radiatively-efficient accretion disk extending right down to the radius of marginal stability if it possesses low iron abundance, an appropriately ionized surface, a very high inclination, or a very centrally concentrated emission pattern (as has been observed during the Deep Minimum State of the Seyfert galaxy MCG-6-30-15). Deeper observations of this source are required in order to validate or reject these models.Comment: 6 pages, 3 postscript figures. Accepted for publication in the Monthly Notices of the Royal Astronomical Societ

Relativistic Broadening of Iron Emission Lines in a Sample of AGN

We present a uniform X-ray spectral analysis of eight type-1 active galactic nuclei (AGN) that have been previously observed with relativistically broadened iron emission lines. Utilizing data from the XMM-Newton European Photon Imaging Camera (EPIC-pn) we carefully model the spectral continuum, taking complex intrinsic absorption and emission into account. We then proceed to model the broad Fe K feature in each source with two different accretion disk emission line codes, as well as a self-consistent, ionized accretion disk spectrum convolved with relativistic smearing from the inner disk. Comparing the results, we show that relativistic blurring of the disk emission is required to explain the spectrum in most sources, even when one models the full reflection spectrum from the photoionized disk.Comment: 50 pages (preprint format), 24 figures. Accepted by Ap

Decaying Raphia farinifera Palm Trees Provide a Source of Sodium for Wild Chimpanzees in the Budongo Forest, Uganda

For some years, chimpanzees have been observed eating the pith of decaying palm trees of Raphia farinifera in the Budongo Forest, Uganda. The reasons for doing this have until now been unknown. An analysis of the pith for mineral content showed high levels of sodium to be present in the samples. By contrast, lower levels were found in bark of other tree species, and also in leaf and fruit samples eaten by chimpanzees. The differences between the Raphia samples and the non-Raphia samples were highly significant (p<0.001). It is concluded that Raphia provides a rich and possibly essential source of sodium for the Budongo chimpanzees. Comparison of a chewed sample (wadge) of Raphia pith with a sample from the tree showed a clear reduction in sodium content in the chewed sample. Black and white colobus monkeys in Budongo Forest also feed on the pith of Raphia. At present, the survival of Raphia palms in Budongo Forest is threatened by the use of this tree by local tobacco farmers

Mineral Acquisition from Clay by Budongo Forest Chimpanzees

Chimpanzees of the Sonso community, Budongo Forest, Uganda were observed eating clay and drinking clay-water from waterholes. We show that clay, clay-rich water, and clay obtained with leaf sponges, provide a range of minerals in different concentrations. The presence of aluminium in the clay consumed indicates that it takes the form of kaolinite. We discuss the contribution of clay geophagy to the mineral intake of the Sonso chimpanzees and show that clay eaten using leaf sponges is particularly rich in minerals. We show that termite mound soil, also regularly consumed, is rich in minerals. We discuss the frequency of clay and termite soil geophagy in the context of the disappearance from Budongo Forest of a formerly rich source of minerals, the decaying pith of Raphia farinifera palms

Constraints on UV Absorption in the Intracluster Medium of Abell 1030

We present results from an extensive HST spectroscopic search for UV absorption lines in the spectrum of the quasar B2~1028+313, which is associated with the central dominant galaxy in the cluster Abell~1030 ($z=0.178$). This is one of the brightest known UV continuum sources located in a cluster, and therefore provides an ideal opportunity to obtain stringent constraints on the column densities of any cool absorbing gas that may be associated with the intracluster medium (ICM). Our HST spectra were obtained with the FOS and GHRS, and provide continuous coverage at rest-frame wavelengths from $\sim 975$ to 4060~\AA, thereby allowing the investigation of many different elements and ionization levels. We utilize a new technique that involves simultaneous fitting of large numbers of different transitions for each species, thereby yielding more robust constraints on column densities than can be obtained from a single transition. This method yields upper limits of $\lesssim 10^{11} - 10^{13}$ cm$^{-2}$ on the column densities of a wide range of molecular, atomic and ionized species that may be associated with the ICM. We also discuss a possible \Lya and C IV absorption system associated with the quasar. We discuss the implications of the upper limits on cool intracluster gas in the context of the physical properties of the ICM and its relationship to the quasar.Comment: Astrophysical Journal, in press, 19 pages, includes 5 PostScript figures. Latex format, uses aas2pp4.sty and epsfig.sty file