Search

We report Suzaku observations of the active, Compton-thick Circinus galaxy. Observations were obtained with both the X-ray Imaging spectrometer (XIS) and the Hard X-ray Detector (HXD). Below 10 keV, the nuclear spectrum is dominated by radiation reflected from cold dense gas of high column density, while above 13 keV the radiation is directly transmitted nuclear emission seen through a column density of $~ 4 x 10^{24} cm^-2. In the 0.2--10 keV band, the XIS spectrum is contaminated at 5% level by the brightest off-nuclear source in Circinus (CG X-1), but drops to 1% in the 5-10 keV and is negligible at higher energies. We find no significant evidence for variability in the hard (>12 keV) emission. The Circinus is marginally detected with the HXD/GSO in the 50--100 keV band at 2.5\sigma level. We model the 3-70 keV band XIS+PIN spectra with a four components: the Compton transmitted nuclear emission, the reflected nuclear emission, a soft power law (representing a combination of scattered nuclear emission, extended emission and contamination by sources in the galaxy below a few keV). The hard nuclear power-law is found to have a photon index Gamma_h ~= 1.6, very similar to the soft power-law. The high energy cut-off is E_C ~= 49 keV. These results agree with those from BeppoSax. An extrapolation of this model up to the GSO band shows good agreement with the GSO spectrum and supports our detection of the Circinus up to ~= 100keV., Comment: ApJ accepted

We report the results from our analysis of {\it Suzaku} XIS (0.5-10 keV) and HXD/PIN (15-40 keV) observations of five well-known local ULIRGs: {\em IRAS} F05189-2524, {\em IRAS} F08572+3915, Mrk 273, PKS 1345+12, and Arp 220. The XIS observations of F05189-2524 and Mrk 273 reveal strong iron lines consistent with Fe K$\alpha$ and changes in spectral shapes with respect to previous {\it Chandra} and {\it XMM-Newton} observations. Mrk 273 is also detected by the HXD/PIN at $\sim$1.8-$\sigma$. For F05189-2524, modeling of the data from the different epochs suggests that the change in spectral shape is likely due to the central source switching off, leaving behind a residual reflection spectrum, or an increase in the absorbing column. An increase in the covering fraction of the absorber can describe the spectral variations seen in Mrk 273, although a reduction in the intrinsic AGN luminosity cannot be formally ruled out. The {\it Suzaku} spectra of Mrk 273 are well fit by a ~94% covering fraction model with a column density of $\sim10^{24}$ cm$^{-2}$. The absorption-corrected log[$L_{\rm 2-10 keV}$ / $L_{\rm IR}$] ratio is consistent with those found in PG Quasars. The 0.5-10 keV spectrum of PKS 1345+12 and Arp 220 seem unchanged from previous observations and their hard X-ray emission is not convincingly detected by the HXD/PIN. The large column density derived from CO observations and the large equivalent width of an ionized Fe line in Arp 220 can be reconciled by an ionized reflection model. F08572+3915 is undetected in both the XIS and HXD/PIN, but the analysis of unpublished {\em Chandra} data provides a new measurement at low energies., Comment: 37 pages including 4 tables and 10 figures. Accepted for publication in ApJ. It is tentatively scheduled to appear in the January 20, 2009 issue of ApJ

We report on the detection of Fe Kalpha emission in F04103$-$2838, an ultraluminous infrared galaxy (ULIRG; log[L$_{\rm IR}$/L$_\odot$] $\ge$ 12) that is optically classified as a LINER. Previous {\it Chandra} observations suggested the presence of both a starburst and an AGN in this source. A deeper ($\sim$20 ksec) {\it XMM-Newton} spectrum reveals an Fe Kalpha line at rest frame energy $\sim$6.4 keV, consistent with cold neutral iron. The best-fit spectral model indicates the Fe Kalpha line has an equivalent width of $\sim$1.6 keV. The hard X-ray emission is dominated by a Compton-thick AGN with intrinsic 0.2--10 keV luminosity $\sim10^{44}$ ergs s$^{-1}$, while the soft X-ray emission is from $\sim$0.1 keV gas attributed to the starburst. The X-ray spectrum of this source bears a striking resemblance to that of the archetypal luminous infrared galaxy NGC 6240 despite differences in merger state and infrared properties., Comment: 23 pre-print pages including 5 figures and 1 table. Accepted by ApJ

We review the recent data on the knot HST-1 in the M87 jet in the context of typical blazar behavior. In particular we discuss the wide-band flare of 2005 which peaked at a factor of 50 to 80 times the intensity observed in 2000; the superluminal radio features; and the arguments that support the hypothesis that HST-1 was the source of the excess TeV emission found by H.E.S.S. in 2005. To the extent that M87 can be classified as a blazar, perhaps observed at a somewhat larger angle to the line of sight compared to most blazars, all of these blazar properties originate at a distance greater than 100 pc from the nucleus, and thus cannot be associated with the location of the 'launching of the jet'., Comment: 7 pages with embedded b/w figures. To be published in the proceedings of "Extragalactic Jets: Theory and Observation from Radio to Gamma Ray" ASP Conference Series, T. A. Rector and D. S. De Young (eds.)

SN 2000ft is detected in two independent Planetary Camera images (F547W and F814W) taken May 13, 2000, about two months before the predicted date of the explosion (July 19, 2000), based on the analysis of its radio light evolution by Alberdi and collaborators. The apparent optical magnitudes and red color of SN 2000ft indicate that it is observed through an extinction of at least A$_V$= 3.0 magnitudes. The extinction corrected lower limit to the absolute visual magnitude (M$_V$ $\leq -$ 18.0), identifies SN 2000ft as a luminous supernova in the optical, as other luminous radio supernovae before. SN 2000ft exploded in a region located at only 0.1 arcsec (i.e. 34 +/- 3 pc) west of a faint cluster (C24). No parent cluster is identified within the detection limits of the HST short exposures. The unambiguous detection of SN 2000ft in the visual shows that multi-epoch sub-arcsecond (FWHM less than 0.1 arcsec) optical imaging is also a valid tool that should be explored further to detect supernovae in the dusty (circum)nuclear regions of (U)LIRGs.

We report a spatially resolved, X-ray spectral analysis of NGC 4258 using archival {\it Chandra} and {\it XMM-Newton} observations. The {\it XMM-Newton} spectra of the nuclear region are well described by two power-law components, a soft (0.57 keV) thermal component, and an Fe K$\alpha$ line with EW = 40 $\pm$ 33 eV. The properties of the second, weaker power-law component are similar to those of an off-nuclear source $2.5\arcsec$ SW of the nucleus. The spectrum of the extended emission of the entire galaxy is well described by two thermal components (MEKAL) models with temperatures $\simeq 0.60$ and 0.22 keV. The {\it Chandra} and {\it XMM-Newton} spectra along the anomalous arms show that the absorbing column density to the SE anomalous arm is consistent with absorption by gas in our Galaxy, while the absorbing column to the NW anomalous arm is higher, indicating that the NW arm is partially on the far side of the galactic disk. The combined {\it Chandra} data clearly detect the X-ray emission from the hot spots at the end of the approximately N-S radio jets. By assuming the hot spots represent shocked thermal gas at the ends of the jets, we estimate shock powers of $\simeq 3 \times 10^{39} f^{-1/2}$ \ergps ($f $ is the filling factor), similar to the radiative power in the inner anomalous arms, consistent with the notion that the jets could be responsible for heating the gas in the anomalous arms., Comment: ApJ accepted; High resolution version can be found at http://www.astro.umd.edu/~yyang/AGNs/MS70759v2-1.pdf

We are conducting the first systematic 3D spectroscopic imaging survey to quantify the properties of the atomic gas (HI) in a distance-limited sample of 28 Seyfert galaxies and a sample of 28 inactive control galaxies with well-matched optical properties (the VHIKINGS survey). This study aims to address the role of the host galaxy in nuclear activity and confront outstanding controversies in optical/IR imaging surveys. Early results show possible relationships between Seyfert activity and HI extent, content and the prevalence of small, nearby gas-rich dwarf galaxies (M(HI)~10^7 Msun); results will be tested via rigorous comparison with control galaxies. Initial results from our optical followup study of 15 of our galaxies using the SAURON integral field unit on the WHT suggest a possible difference between Seyfert and inactive stellar and gaseous kinematics that support the conclusion that internal kinematics of galaxies are the key to nuclear activity., Comment: 6 pages to be published in the proceedings of "The Fate of Gas in Galaxies", held in Dwingeloo, July 2006

We present the results of a search for optical identifications of ultraluminous X-ray sources (ULXs) in M51 by using mosaic images taken with the Hubble Space Telescope Advanced Camera for Surveys in filters F435W (B), F555W (V), F814W (I), and F658N (Halpha). Our sample consisting of nine ULXs is defined by analyzing the three Chandra observations of M51 performed in 2000 June, 2001 June, and 2003 Aug. We found four ULXs have one or two candidates for counterparts, while two have multiple stars within their error circles. The other three have no candidate counterparts. Four ULXs are located near or in a star cluster, while others have no association with a cluster. These results indicate that the companion star, environment, and origin of ULXs are probably heterogeneous., Comment: 10 pages, 5 figures, accepted for publication in ApJ

In this paper, we focus on the limb-brightened, prolate spheroidal cavity of the radio galaxy Cygnus A, as revealed by the Chandra X-ray Observatory. We use the shock heated, thermal intracluster medium around the expanding cavity to infer the properties of the radio synchrotron-emitting gas inside the cavity. The gas along the N and S edges of the cavity is found to have an average temperature of 6.0 keV, which is hotter than the temperature (4.6 keV) of the adjacent intracluster gas. It is proposed that this hotter gas is intracluster gas shocked by the expanding cavity. The shock is thus inferred to be weak (Mach number 1.3, a value also inferred from the density jump at the cavity edge) and its velocity 1,460 km/s. The total kinetic power of the expansion is found to be 1.2 x 10^{46} erg/s, which is larger than both the total radio power and the power emitted by the entire intracluster medium in the 2 -- 10 keV band. It appears that most of the power of the jets in Cygnus A is currently going into heating the intracluster medium. From the derived pressure inside the cavity, there is no conclusive evidence for a component contributing pressure additional to the magnetic fields and relativistic particles responsible for the synchrotron radio emission. Further, the ratio of energy densities in positive to negative cosmic rays in Cygnus A is between 1 and 100 (the value in our Galaxy)., Comment: 5 pages, 3 figures, published in The Astrophysical Journal Letters 2006 Volume 644 Page 9. Replaces previous version with minor corrections to numerical factors

We present a model for the accretion flow around the supermassive black hole in the LINER nucleus of NGC 1097 which fits the optical to X-ray spectral energy distribution (SED). The X-ray segment of the SED is based on observations with the Chandra X-Ray Observatory, which are reported here for the first time. The inner part of the flow is modeled as a radiatively inefficient accretion flow (RIAF) and the outer part as a standard thin disk. The value of the transition radius (~225 Schwarzschild radii) between the RIAF and outer thin disk was obtained from our previous fitting of the double-peaked Balmer emission line profile, which originates in the thin disk. The black hole mass was inferred from measurements of the stellar velocity dispersion in the host galaxy. When these parameters are used in the accretion flow model, the SED can be successfully reproduced, which shows that the line profile model and the accretion flow model are consistent with each other. A small remaining excess in the near-UV is accounted by the contribution of an obscured starburst located within 9 pc from the nucleus, as we reported in an earlier paper. The radio flux is consistent with synchrotron emission of a relativistic jet modeled by means of the internal shock scenario. In an appendix we also analyze the Chandra X-ray observations of the ~1 kpc circumnuclear star-forming ring and of an ultraluminous compact X-ray source located outside the ring., Comment: 10 pages and 6 figures formatted with emulateapj, accepted for publication in ApJ

Having conducted a search for the 22 GHz water vapor line towards galaxies with nuclear activity, large nuclear column densities or high infrared luminosities, we present H_2O spectra for NGC2273, UGC5101 and NGC3393 with isotropic luminosities of 7, 1500, and 400 L_sun. The H_2O maser in UGC5101 is by far the most luminous yet found in an ultraluminous infrared galaxy. NGC3393 reveals the classic spectrum of a `disk maser', represented by three distinct groups of Doppler components. As in all other known cases except NGC4258, the rotation velocity of the putative masing disk is well below 1000 km/s. Based on the literature and archive data, X-ray absorbing column densities are compiled for the 64 galaxies with reported maser sources beyond the Magellanic Clouds. For NGC2782 and NGC5728, we present Chandra archive data that indicate the presence of an active galactic nucleus in both galaxies. The correlation between absorbing column and H_2O emission is analyzed. There is a striking difference between kilo- and megamasers with megamasers being associated with higher column densities. All kilomasers (L_H_2O < 10 L_sun) except NGC2273 and NGC5194 are Compton-thin, i.e. their absorbing columns are < 10^24 cm^-2. Among the H_2O megamasers, 50% arise from Compton-thick and 85% from heavily obscured (> 10^23 cm^-2) active galactic nuclei. These values are not larger but consistent with those from samples of Seyfert 2 galaxies not selected on the basis of maser emission. The similarity in column densities can be explained by small deviations in position between maser spots and nuclear X-ray source and a high degree of clumpiness in the circumnuclear interstellar medium., Comment: 16 pages, 7 figures, 5 tables. Accepted for publication in A&A

The X-ray intensity of knot HST-1, 0.85" from the nucleus of the radio galaxy M87, has increased by more than a factor of 50 during the last 5 years. The optical increase is similar and our more limited radio data indicate a commensurate activity. We give the primary results of our Chandra X-ray Observatory monitoring program and consider some of the implications of this extreme variability in a relativistic jet. We find that the data support a 'modest beaming synchrotron' model as indicated in our earlier papers. Based on this model, the decay of the X-ray lightcurve appears to be dominated by light travel time across the emitting region of HST-1, rather than synchrotron loss timescales., Comment: ApJ accepted, 7 pages, 4 figures

We present results from Chandra observations of 14 ultraluminous infrared galaxies (ULIRGs; log(L_IR/L_Sun) >= 12) with redshifts between 0.04 and 0.16. The goals of the observations were to investigate any correlation between infrared color or luminosity and the properties of the X-ray emission and to attempt to determine whether these objects are powered by starbursts or active galactic nuclei (AGNs). The sample contains approximately the same number of high and low luminosity objects and ``warm'' and ``cool'' ULIRGs. All 14 galaxies were detected by Chandra. Our analysis shows that the X-ray emission of the two Seyfert 1 galaxies in our sample are dominated by AGN. The remaining 12 sources are too faint for conventional spectral fitting to be applicable. Hardness ratios were used to estimate the spectral properties of these faint sources. The photon indices for our sample plus the Chandra-observed sample from Ptak et al.(2003) peak in the range of 1.0-1.5, consistent with expectations for X-ray binaries in a starburst, an absorbed AGN, or hot bremsstrahlung from a starburst or AGN. The values of photon index for the objects in our sample classified as Seyferts (type 1 or 2) are larger than 2, while those classified as HII regions or LINERs tend to be less than 2. The hard X-ray to far-infrared ratios for the 12 weak sources are similar to those of starbursts, but we cannot rule out the possibility of absorbed, possibly Compton-thick, AGNs in some of these objects. Two of these faint sources were found to have X-ray counterparts to their double optical and infrared nuclei., Comment: 40 pages, 5 tables, 14 figures, accepted by ApJ

We report evidence for a recent burst of star formation located within 9 pc of the active nucleus of NGC 1097. The observational signatures of the starburst include UV absorption lines and continuum emission from young stars observed in a small-aperture HST spectrum. The burst is a few times 10^6 yr old, has a mass of approximately 10^6 solar masses, an observed luminosity of 1.5 x 10^7 solar luminosities and is obscured by approximately 3 visual magnitudes. The importance of this finding is two-fold: (1) the proximity of the starburst to the active nucleus and thus possible association with it; (2) its obscuration by and apparent association with a dusty absorbing medium, while the broad emission lines appear unobscured, suggesting that the starburst could be embedded in a circumnuclear torus as predicted in the Unified Model of active galactic nuclei., Comment: 12 pages, 3 eps figures, accepted for publication in ApJ Letters

We reanalyze the deep Chandra observations of the M87 jet, first examined by Wilson & Yang (2002). By employing an analysis chain that includes image deconvolution, knots HST-1 and I are fully separated from adjacent emission. We find slight but significant variations in the spectral shape, with values of $\alpha_x$ ranging from $\sim 1.2-1.6$. We use VLA radio observations, as well as HST imaging and polarimetry data, to examine the jet's broad-band spectrum and inquire as to the nature of particle acceleration in the jet. As shown in previous papers, a simple continuous injection model for synchrotron-emitting knots, in which both the filling factor, $f_{acc}$, of regions within which particles are accelerated and the energy spectrum of the injected particles are constant, cannot account for the X-ray flux or spectrum. Instead, we propose that $f_{acc}$ is a function of position and energy and find that in the inner jet, $f_{acc} \propto E_\gamma^{-0.4 \pm 0.2} \propto E_e^{-0.2 \pm 0.1}$, and in knots A and B, $f_{acc} \propto E_\gamma^{-0.7 \pm 0.2} \propto E_e^{-0.35 \pm 0.1}$, where $E_\gamma$ is the emitted photon energy and and $E_e$ is the emitting electron energy. In this model, the index $p$ of the injected electron energy spectrum ($n(E_{e}) \propto E_{e}^{-p}$) is $p=2.2$ at all locations in the jet, as predicted by models of cosmic ray acceleration by ultrarelativistic shocks. There is a strong correlation between the peaks of X-ray emission and minima of optical percentage polarization, i.e., regions where the jet magnetic field is not ordered. We suggest that the X-ray peaks coincide with shock waves which accelerate the X-ray emitting electrons and cause changes in the direction of the magnetic field; the polarization is thus small because of beam averaging., Comment: Accepted for publication in ApJ; 21 pages, 9 figures, 2 tables; abstract shortened for astro-ph; Figures 1, 7 and 8 at reduced resolution

We present the completed results of a high resolution radio imaging survey of all (~200) low-luminosity active galactic nuclei (LLAGNs) and AGNs in the Palomar Spectroscopic Sample. The high incidences of pc-scale radio nuclei, with T(brightness) >=10^7 K, and sub-parsec jets argue for accreting black holes in >=50% of all LINERs and low-luminosity Seyferts; there is no evidence against all LLAGNs being mini-AGNs. The radio luminosity function (RLF) of Palomar Sample LLAGNs and AGNs extends three orders of magnitude below, and is continuous with, that of `classical' AGNs. We find marginal evidence for a low-power turnover in the RLF; nevertheless LLAGNs are responsible for a significant fraction of present day mass accretion. Adopting the jet model of Falcke & Biermann, we show that the accretion energy output in LLAGNs is dominated by the energy in the observed jets rather than the radiated bolometric luminosity. The Palomar LLAGNs and AGNs follow the same scaling between jet power and narrow line region (NLR) luminosity as the pc to kpc jets in powerful radio galaxies. Eddington ratios of <= 10^{-1} - 10^{-5} are implied in jet models of the radio emission. We find evidence that, in analogy to Galactic black hole candidates, LINERs are in a `low/hard' state (gas poor nuclei, low Eddington ratio, ability to launch collimated jets) while low-luminosity Seyferts are in a `high' state (gas rich nuclei, higher Eddington ratio, less likely to launch collimated jets). The jets are energetically more significant than supernovae in the LLAGN host galaxies, and are potentially able to deposit sufficient energy into the innermost parsecs to significantly slow the gas supply to the accretion disk., Comment: Results and content same as pervious submission; language and wording updated for clarity. To appear in A&A

LINER nuclei, which are present in many nearby galactic bulges, may be the manifestation of low-rate or low-radiative-efficiency accretion onto supermassive central black holes. However, it has been unclear whether the compact UV nuclear sources present in many LINERs are clusters of massive stars, rather than being directly related to the accretion process. We have used HST to monitor the UV variability of a sample of 17 galaxies with LINER nuclei and compact nuclear UV sources. Fifteen of the 17 galaxies were observed more than once, with two to five epochs per galaxy, spanning up to a year. We detect significant variability in most of the sample, with peak-to-peak amplitudes from a few percent to 50%. In most cases, correlated variations are seen in two independent bands (F250W and F330W). Comparison to previous UV measurements indicates, for many objects, long-term variations by factors of a few over decade timescales. Variability is detected in LINERs with and without detected compact radio cores, in LINERs that have broad H-alpha wings detected in their optical spectra (``LINER 1's''), and in those that do not (``LINER 2s''). This variability demonstrates the existence of a non-stellar component in the UV continuum of all types, and sets a lower limit to the luminosity of this component. We note a trend in the UV color (F250W/F330W) with spectral type - LINER 1s tend to be bluer than LINER 2s. This trend may indicate a link between the shape of the nonstellar continuum and the presence or the visibility of a broad-line region. In one target, the post-starburst galaxy NGC 4736, we detect variability in a previously noted UV source that is offset by 2.5" (60 pc in projection) from the nucleus. This may be the nearest example of a binary active nucleus, and of the process leading to black hole merging., Comment: accepted to ApJ

We report Chandra X-ray Observatory and 1.4 GHz Australian Long Baseline Array (LBA) observations of the radio galaxy PKS 2153--69 and its environment. The Chandra image reveals a roughly spherical halo of hot gas extending out to 30 kpc around PKS 2153--69. Two depressions in the surface brightness of the X-ray halo correspond to the large scale radio lobes, and interpreting these as cavities inflated with radio plasma we infer a jet power of 4x10^42 erg/s. Both radio lobes contain hot spots that are detected by Chandra. In addition, the southern hot spot is detected in the 1.4 GHz LBA observation, providing the highest linear resolution image of a radio lobe hot spot to date. The northern hot spot was not detected in the LBA observation. The radio to X-ray spectra of the hot spots are consistent with a simple power law emission model. The nucleus has an X-ray spectrum typical of a type 1 active galactic nucleus, and the LBA observation shows a one-sided nuclear jet on 0.1" scales. Approximately 10" northeast of the nucleus, X-ray emission is associated with an extra-nuclear cloud. The X-ray emission from the cloud can be divided into two regions, an unresolved western component associated with a knot of radio emission (in a low resolution map), and a spatially extended eastern component aligned with the pc-scale jet and associated with highly ionized optical line-emitting clouds. The X-ray spectrum of the eastern component is very soft (Gamma > 4.0 for a power law model or kT ~0.22 keV for a thermal plasma). The LBA observation did not detect compact radio emission from the extra-nuclear cloud. (Abstract truncated)., Comment: Accepted for publication in the Astrophysical Journal. It is tentatively scheduled for the ApJ 10 April 2005, v623 1 issue

Using the Green Bank Telescope, we have conducted a survey for 1.3 cm water maser emission toward the nuclei of nearby active galaxies, the most sensitive large survey for H2O masers to date. Among 145 galaxies observed, maser emission was newly detected in eleven sources and confirmed in one other. Our survey targeted nearby (v < 12,000 km/s, mainly type 2 AGNs north of declination -20 degrees, and includes a few additional sources as well. We find that more than a third of Seyfert 2 galaxies have strong maser emission, though the detection rate declines beyond v about 5000 km/s due to sensitivity limits. Two of the masers discovered during this survey are found in unexpected hosts: NGC 4151 (Seyfert 1.5) and NGC 2782 (starburst). We discuss the possible relations between the large X-ray column to NGC 4151 and a possible hidden AGN in NGC 2782 to the detected masers. Four of the masers discovered here, NGC 591, NGC 4388, NGC 5728 and NGC 6323, have high-velocity lines symmetrically spaced about the systemic velocity, a likely signature of molecular gas in a nuclear accretion disk. The maser source in NGC 6323, in particular, reveals the classic spectrum of a "disk maser" represented by three distinct groups of Doppler components. Future single-dish and VLBI observations of these four galaxies could provide a measurement of the distance to each galaxy, and of the Hubble constant, independent of standard candle calibrations., Comment: published in ApJ Letters

We present the completed results of a high resolution radio imaging survey of all (around 200) low-luminosity active galactic nuclei (LLAGNs) in the Palomar spectroscopic Sample of all (around 470) nearby bright northern galaxies. The high incidence of pc-scale radio nuclei, with implied brightness temperatures of the order of 10E7 K, and sub-parsec jets argue for accreting black holes in 50% of all LLAGNs; there is no evidence against all LLAGNs being mini-AGNs.The detected parsec-scale radio nuclei are preferentially found in massive ellipticals and in type 1 nuclei (i.e. nuclei with broad Halpha emission). The radio luminosity function (RLF) of Palomar Sample LLAGNs extends three orders of magnitude below, and is continuous with, that of "classical" AGNs.We find marginal evidence for a low-power turnover in the RLF; nevertheless LLAGNs are responsible for a significant fraction of accretion in the local universe. The accretion energy output in LLAGNs is dominated by the energy in the observed jets rather than the radiated bolometric luminosity. The Palomar LLAGNs follow the same scaling between jet power and narrow line region (NLR) luminosity as the parsec to kilo-parsec jets in powerful radio galaxies. Low accretion rates (of 10E-2 to 10E-6 of the Eddington rate) are impliedin both advection- and jet-type models, with evidence for increasing "radio-loudness" with decreasing Eddington fraction. The jets are energetically more significant than supernovae in the LLAGN host galaxies, and are potentially able to dump sufficient energy into the innermost parsecs to significantly slow the accretion inflow. Detailed results can be found in Nagar et al. (2002a) and Nagar et al. (2004, to appear in Astronomy & Astrophysics)., Comment: 4 pages. 5 figures. Proceedings of the 7th European VLBI Network Symposium held in Toledo, Spain on October 12-15, 2004. Editors: R. Bachiller, F. Colomer, J.-F. Desmurs, P. de Vicente (Observatorio Astronomico Nacional), p. 51-54. Needs evn2004.cls

We present the results of UV spectroscopy of AGNs with double-peaked Balmer emission lines. In 2/3 of the objects, the far-UV resonance lines are strong, with single-peaked profiles resembling those of Seyfert galaxies. The Mg II line is the only UV line with a double-peaked profile. In the remaining objects, the far-UV resonance lines are relatively weak but still single-peaked. The latter group also displays prominent UV absorption lines, indicative of a low-ionization absorber. We interpret the difference in the profiles of the emission lines as resulting from two different regions: a dense, low-ionization accretion disk (the predominant source of the Balmer and Mg II lines), and a lower density, higher-ionization wind (the predominant source of the far-UV resonance lines). These results suggest a way of connecting the double-peaked emitters with the greater AGN population: in double-peaked emitters the accretion rate onto the black hole is low, making the wind feeble and allowing the lines from the underlying disk to shine through. This scenario also implies that in the majority of AGNs, the wind is the source of the broad emission lines., Comment: To appear in "The Interplay among Black Holes, Stars and ISM in Galactic Nuclei," IAU Coll. 222, eds. Storchi Bergmann, Ho, and Schmitt

For the past 10 years there has been an active debate over whether fast shocks play an important role in ionizing emission line regions in Seyfert galaxies. To investigate this claim, we have studied the Seyfert 2 galaxy Mkn 78, using HST UV/optical images and spectroscopy. Since Mkn 78 provides the archetypal jet-driven bipolar velocity field, if shocks are important anywhere they should be important in this object. Having mapped the emission line fluxes and velocity field, we first compare the ionization conditions to standard photoionization and shock models. We find coherent variations of ionization consistent with photoionization model sequences which combine optically thick and thin gas, but are inconsistent with either autoionizing shock models or photoionization models of just optically thick gas. Furthermore, we find absolutely no link between the ionization of the gas and its kinematic state, while we do find a simple decline of ionization degree with radius. We feel this object provides the strongest case to date against the importance of shock related ionization in Seyferts., Comment: 4 pages, 1 figure, to appear in the proceedings of IAU Symposium 222 "The Interplay among Black Holes, Stars and ISM in Galactic Nuclei", T. Storchi Bergmann, L.C. Ho & H.R. Schmitt, eds

We compare recent HST observations of Seyfert and quasar NLRs and find that type-2 AGNs follow a relation consistent with that expected for a distribution of gas ionized by a central source R(NLR,2) \propto L^{0.32 +/- 0.05}, while type-1 objects are fit with a steeper slope of 0.55 +/- 0.05. The latter is comparable to the scaling found for the BLR size with continuum luminosity (slope: 0.5-0.7). Therefore, we investigate what we can learn about the BLR size if the NLR size is only determined by the AGN luminosity. We find that NLR and BLR size are related linearly following R(BLR) \propto R(NLR,1)^{0.88 +/- 0.1}. This relation can be used to estimate BH masses., Comment: 2 pages, 1 figure, to appear in the proceedings of "The Interplay among Black Holes, Stars and ISM in Galactic Nuclei", IAU 222, eds. Th. Storchi Bergmann, L.C. Ho, and H.R. Schmitt

We report EVN, MERLIN and VLBA observations at 18 cm, 6 cm and 3.6 cm of the Seyfert galaxies NGC 7674, NGC 5506, NGC 2110 and Mrk 1210 to study their structure and proper motions on pc scales and to add some constraints on the many possible causes of the radio-quietness of Seyferts. The component configurations in NGC 7674 and NGC 2110 are simple, linear structures, whereas the configurations in NGC 5506 and Mrk 1210 have multiple components with no clear axis of symmetry. We suggest that NGC 7674 is a low-luminosity compact symmetric object. Comparing the images at different epochs, we find a proper motion in NGC 7674 of (0.92+-0.07) c between the two central components separated by 282 pc and, in NGC 5506, we find a 3 sigma upper limit of 0.50 c for the components separated by 3.8 pc. Our results confirm and extend earlier work showing that the outward motion of radio components in Seyfert galaxies is non-relativistic on pc scales. We briefly discuss whether this non-relativistic motion is intrinsic to the jet-formation process or results from deceleration of an initially relativistic jet by interaction with the pc or sub-pc scale interstellar medium. We combined our sample with a list compiled from the literature of VLBI observations made of Seyfert galaxies, and found that most Seyfert nuclei have at least one flat-spectrum component on the VLBI scale, which was not seen in the spectral indices measured at arcsec resolution. We found also that the bimodal alignment of pc and kpc radio structures displayed by radio galaxies and quasars is not displayed by this sample of Seyferts, which shows a uniform distribution of misalignment between 0 deg and 90 deg. The frequent misalignment could result from jet precession or from deflection of the jet by interaction with gas in the interstellar medium., Comment: 21 pages, 12 figures, accepted by A&A

We report sub-arcsecond resolution X-ray imaging spectroscopy of the low luminosity active galactic nucleus of NGC 4258 and its immediate surroundings with the Chandra X-ray Observatory. NGC 4258 was observed four times, with the first two observations separated by one month, followed over a year later by two consecutive observations. The spectrum of the nucleus is well described by a heavily absorbed, hard X-ray power law of variable luminosity, plus a constant, thermal soft X-ray component. We do not detect an iron K alpha emission line with the upper limit to the equivalent width of a narrow, neutral iron line ranging between 94 and 887 eV (90% confidence) for the different observations. During the second observation on 2000-04-17, two narrow absorption features are seen with >99.5% confidence at ~6.4 keV and ~6.9 keV, which we identify as resonant absorption lines of Fe XVIII - Fe XIX K alpha and Fe XXVI K alpha, respectively. In addition, the 6.9 keV absorption line is probably variable on a timescale of ~6000 sec. The absorption lines are analyzed through a curve of growth analysis, which allows the relationship between ionic column and kinematic temperature or velocity dispersion to be obtained for the observed equivalent widths. We discuss the properties of the absorbing gas for both photo and collisionally ionized models. Given that the maser disk is viewed at an inclination i = 82 degrees, the gas responsible for the 6.9 keV absorption line may be in an inner disk, a disk-wind boundary layer or be thermal gas entrained at the base of the jet. The gas which gives rise to the photoelectric absorption may be the same as that which causes the 6.4 keV Fe K alpha absorption provided that the gas has a bulk velocity dispersion of a few thousand km/s. (Abstract abridged)., Comment: To appear in The Astrophysical Journal v601 n1 Jan 20 2004. 24 pages, 6 figures

This paper presents the results of a high resolution radio imaging survey of 83 of the 118 ultraluminous infrared galaxies (ULIRGs) in the IRAS 1 Jy ULIRG sample. We have observed these ULIRGs at 15GHz with the Very Large Array (VLA). We find that ~75% of Seyferts (both type 1 and 2) and LINERs have radio nuclei which are compact at our 150mas resolution. The detection rate of HII nuclei is significantly lower (32%); the detections among these are preferentially HII + LINER/Seyfert composite nuclei. Among ULIRGs with multiple optical or near-IR nuclei our observations detected only one (or no) nucleus; in these the radio detection is typically towards the brightest near-IR nucleus. The compactness of the radio sources, the higher detection rates in AGN-type nuclei than HII nuclei, the preferential detection of nuclei with unresolved point sources in the near-IR, the low soft X-ray to nuclear radio luminosity ratio (arguing against thermal emission powering the radio nuclei), and the lack of correlation between radio power and Halpha luminosity, all support an origin of the detected radio nuclei in AGN related activity. This result is especially interesting for LINER ULIRGs for which signatures of AGNs have often been ambiguous in other wavebands. Such a high incidence of AGN would provide, for the first time, a large sample in which to study the interplay between AGN, starbursts, and galaxy mergers., Comment: To appear in A&A. 8 pages

We report on X-ray emission from the Seyfert 2 galaxy NGC4388 observed with the Chandra X-ray Observatory. A hard X-ray peak is found at the position of the active nucleus suggested by optical and radio observations. Extended soft X-ray emission correlates well with the ionization cone found in optical line emission. A large soft X-ray extension is found up to 16 kpc to the north of the galaxy. Photoionized gas with low ionization parameters (xi<3) appears to be the likely explanation of this emission. The same ionized gas clouds could be responsible for the optical [OIII] emission. Fe K line emission from cold material is found to be extended by a few kpc., Comment: 12 pages, one colour figure included, MNRAS in press

We present the results of two Chandra observations (separated by 1 year) of the population of X-ray sources in the spiral galaxy M51 (NGC 5194 and NGC 5195). 113 X-ray sources have been detected in an 8'.4x8'.4 region. Nine and 28 sources have luminosities exceeding 10^39 erg/s (ULXs) and 10^38 erg/s in the 0.5-8 keV band, respectively, assuming they are associated with M51. The number of ULXs is much higher than found in most normal spiral and elliptical galaxies. Most of the X-ray sources and all seven of the ULXs in NGC 5194 are located in, or close to, a spiral arm, suggesting a connection with recent star formation. The cumulative luminosity function of the X-ray sources in NGC 5194 with Lx>10^38 erg/s is well described by a power law N(>Lx) \propto Lx^-\alpha with \alpha=0.91. The X-ray spectra of most of the detected sources are consistent with a power law with a photon index between 1 and 2, with a few sources showing harder or softer spectra. The spectra of most ULXs are consistent with both a power law and a multicolor disk blackbody (MCD) model, while a power law model is preferable to a MCD model in two ULXs. A drastic spectral variability and emission lines in ULXs are also presented. The masses of the compact objects and mass accretion rates in ULXs and other X-ray sources are not well constrained by these observations. If we adopt a MCD interpretation, their MCD parameters imply that most of the X-ray sources are stellar mass (~5-10 M_solar) black holes accreting near or above the Eddington rate.(abridged), Comment: 35 pages, accepted for publication in the Astrophysical Journal

We present an analysis of the compact X-ray source population in the Seyfert~2 galaxy NGC 1068, imaged with Chandra. We find a total of 84 compact sources, of which 66 are projected onto the galactic disk of NGC 1068. Spectra of the brightest sources have been modeled with both multi-color disk blackbody and power-law models. The power-law model provides the better description of the spectrum for most of these sources. Five sources have 0.4-8 keV intrinsic luminosities greater than 10^{39} erg/s, assuming that their emission is isotropic and that they are associated with NGC 1068. We refer to these sources as Intermediate Luminosity X-ray Objects (IXOs). If these five sources are X-ray binaries accreting with luminosities that are both sub-Eddington and isotropic, then the implied source masses are >7 solar masses, and so they are inferred to be black holes. The brightest source has a much harder spectrum (Gamma = 0.9\pm0.1) than that found in Galactic black hole candidates and other IXOs. It also shows large-amplitude variability on both short-term and long-term timescales. The ratio of the number of sources with luminosities greater than 2.1 x 10^{38} erg/s in the 0.4-8 keV band to the rate of massive star formation is the same, to within a factor of two, for NGC 1068, the Antennae, NGC 5194 (the main galaxy in M51), and the Circinus galaxy. This suggests that the rate of production of X-ray binaries per massive star is approximately the same for galaxies with currently active star formation, including ``starbursts''., Comment: 33 pages, 10 figures. To appear in The Astrophysical Journal, v591 n1, July 1, 2003 issue

We present Chandra X-ray monitoring of the M87 jet in 2002, which shows that the intensity of HST-1, an optical knot 0.8" from the core, increased by a factor of two in 116 days and a factor of four in 2 yrs. There was also a significant flux decrease over two months, with suggestive evidence for a softening of the spectrum. From this variability behavior, we argue that the bulk of the X-ray emission of HST-1 comes from synchrotron emission. None of the other conceivable emission processes can match the range of observed characteristics. By estimating synchrotron model parameters for various bulk relativistic velocities, we demonstrate that a model with a Doppler factor, delta, in the range 2 to 5 fits our preliminary estimates of light travel time and synchrotron loss timescales., Comment: 4 pages with 3 embedded figures; 1 of which is color but prints ok in b/w. Accepted for publication in the ApJL

We present single-dish monitoring of the spectra of 13 extragalactic water megamasers taken over a period of 9 years and a single epoch of sensitive spectra for 7 others. Our data include the first K-band science observations taken with the new 100 m Green Bank Telescope (GBT). In the context of a circumnuclear, molecular disk model, our results suggest that either (a) the maser lines seen are systemic features subject to a much smaller acceleration than present in NGC 4258, presumably because the gas is farther from the nuclear black hole, or (b) we are detecting ``satellite'' lines for which the acceleration is in the plane of the sky. We also report a search for water vapor masers towards the nuclei of 58 highly inclined, nearby galaxies., Comment: accepted by ApJS

This paper is a brief review of the processes responsible for X-ray emission from radio jets, lobes and hot spots. Possible photons in inverse Compton scattering models include the radio synchrotron radiation itself (i.e. synchrotron self-Compton [SSC] emission), the cosmic microwave background (CMB), the galaxy starlight and radiation from the active nucleus. SSC emission has been detected from a number of hot spots. Scattering of the CMB is expected to dominate for jets (and possibly hot spots) undergoing bulk relativistic motion close to the direction towards the observer. Scattering of infrared radiation from the AGN should be observable from radio lobes, especially if they are close to the active nucleus. Synchrotron radiation is detected in some sources, most notably the jet of M87. I briefly discuss why different hot spots emit X-rays by different emission mechanisms and the nature of the synchrotron spectra., Comment: To be published in the proceedings of the Bologna conference ``The Physics of Relativistic Jets in the Chandra and XMM Era'', New Astronomy Review

We use Chandra, HST and VLA observations of M87 to investigate the physics of X-ray emission from AGN jets. We find that X-ray hotspots in the M87 jet occur primarily in regions with hard optical-to-X-ray spectra and lower than average polarization. Particle injection appears to be required both continuously in the jet sheath as well as locally at X-ray hotspots., Comment: 4 pages, 2 figures, submitted to "The Physics of Relativistic Jets in the CHANDRA and XMM Era", Bologna 2002

Results from Chandra studies of the intracluster medium around M87 and Cygnus A are summarized., Comment: Conference proceeding from ``Active Galactic Nuclei: from Central Engine to Host'', 4 pages, 2 figures

Water vapor emission at 22 GHz is reported from the nucleus of the LINER galaxy Mrk 1419 (NGC 2960). Single-dish spectra of the maser source show properties that are similar to those seen in NGC 4258, namely (1) a cluster of systemic H2O features, (2) two additional H2O clusters, one red- and one blue-shifted by about 475 km/s, (3) a likely acceleration of the systemic features, and (4) no detectable velocity drifts in the red- and blue-shifted features. Interpreting the data in terms of the paradigm established for NGC 4258, i.e. assuming the presence of an edge-on Keplerian circumnuclear annulus with the systemic emission arising from the near side of its inner edge, the following parameters are derived: Rotational velocity: 330-600 km/s; radius: 0.13-0.43 pc; binding mass: about 10 million solar masses. With the galaxy being approximately ten times farther away than NGC 4258, a comparison of linear and angular scales (the latter via Very Long Baseline Interferometry) may provide an accurate geometric distance to Mrk 1419 that could be used to calibrate the cosmic distance scale., Comment: 4 pages, 5 Postscript figures, A&A Letters

The results of Chandra snapshot observations of 11 LINERs (Low-Ionization Nuclear Emission-line Regions), three low-luminosity Seyfert galaxies, and one HII-LINER transition object are presented. Our sample consists of all the objects with a flat or inverted spectrum compact radio core in the VLA survey of 48 low-luminosity AGNs (LLAGNs) by Nagar et al. (2000). An X-ray nucleus is detected in all galaxies except one and their X-ray luminosities are in the range 5x10^38 to 8x10^41 erg/s. The X-ray spectra are generally steeper than expected from thermal bremsstrahlung emission from an advection-dominated accretion flow (ADAF). The X-ray to Halpha luminosity ratios for 11 out of 14 objects are in good agreement with the value characteristic of LLAGNs and more luminous AGNs, and indicate that their optical emission lines are predominantly powered by a LLAGN. For three objects, this ratio is less than expected. Comparing with properties in other wavelengths, we find that these three galaxies are most likely to be heavily obscured AGN. We use the ratio RX = \nu L\nu (5 GHz)/LX, where LX is the luminosity in the 2-10 keV band, as a measure of radio loudness. In contrast to the usual definition of radio loudness (RO = L\nu(5 GHz)/L\nu(B)), RX can be used for heavily obscured (NH >~ 10^23 cm^-2, AV>50 mag) nuclei. Further, with the high spatial resolution of Chandra, the nuclear X-ray emission of LLAGNs is often easier to measure than the nuclear optical emission. We investigate the values of RX for LLAGNs, luminous Seyfert galaxies, quasars and radio galaxies and confirm the suggestion that a large fraction of LLAGNs are radio loud., Comment: 15 pages, accepted for publication in ApJ

(abbreviated): This paper presents the results of a high resolution radio imaging survey of all known (96) low-luminosity active galactic nuclei (LLAGNs) at D<19Mpc. We find that almost half of all LINERs and low-luminosity Seyferts have flat-spectrum radio cores when observed at 150mas resolution. Higher (2mas) resolution observations of a flux-limited subsample have provided a 100% (16 of 16) detection rate of pc-scale radio cores, with implied brightness temperatures > 10^8 K. The five LLAGNs with the highest core radio fluxes also have pc-scale `jets.' Compact radio cores are almost exclusively found in massive ellipticals and in type1 nuclei. The core radio power is correlated with the nuclear optical `broad' Halpha luminosity, the nuclear optical `narrow' emission line luminosity and width, and with the galaxy luminosity. In these correlations LLAGNs fall close to the low-luminosity extrapolations of more powerful AGNs. About half of all LLAGNs with multiple epoch data show significant inter-year radio variability. Investigation of a sample of ~150 nearby bright galaxies, most of them LLAGNs, shows that the nuclear (<150mas size) radio power is strongly correlated with both the black hole mass and the galaxy bulge luminosity; linear regression fits to all ~150 galaxies give: log P(2cm) = 1.31 log M_blackhole + 8.77 and log P(2cm) = 1.89 log L_B(bulge) - 0.17. Low accretion rates are implied in both advection- and jet-type models. In brief, all evidence points towards the presence of accreting massive black holes in a large fraction, perhaps all, of LLAGNs., Comment: to appear in A&A

We have observed the narrow-line regions (NLRs) of the seven brightest radio-quiet PG (or BQS) quasars (z < 0.5) with the Wide Field and Planetary Camera 2 on board the Hubble Space Telescope (HST). Linear-ramp filters were used to image the [OIII] lambda 5007 line emission with 0.0455-0.1 arcsec pixel resolution. We find that the NLRs are very compact with typical extents of 2-4 arcsec. Two quasars show compact filamentary structures similar to Seyfert NLRs. They may be related to radio outflows. Most interestingly, when including a sample of Seyfert galaxies observed with HST, we tentatively find that the size of the NLR is proportional to the square root of the [OIII] luminosity. This is comparable to the scaling found for the size of the broad-line region with continuum luminosity, which has been interpreted in terms of a constant photoionization parameter. The relation determined here connects the NLR of radio-quiet quasars and Seyferts over three orders of magnitude in [OIII] luminosity., Comment: 6 pages, 4 figures, accepted for publication in ApJ Letters

The results of Chandra snapshot observations of 11 LINERs (Low-Ionization Nuclear Emission-line Regions), three low-luminosity Seyfert galaxies, and one HII-LINER transition object are presented. Our sample consists of all the objects with a flat or inverted spectrum compact radio core in the VLA survey of 48 low-luminosity AGN (LLAGN) by Nagar et al. (2000). An X-ray nucleus is detected in all galaxies except one and their X-ray luminosities are in the range 5x10^38 to 8x10^41 ergs s^-1. The X-ray to Halpha luminosity ratios for 11 out of 14 objects are in good agreement with the value characteristic of LLAGNs and more luminous AGNs, and indicate that their optical emission lines are predominantly powered by a LLAGN. For three objects, this ratio is less than expected. Comparing with multi-wavelength results, we find that these three galaxies are most likely to be heavily obscured AGN. We compare the radio to X-ray luminosity ratio of LLAGNs with those of more-luminous AGNs, and confirm the suggestion that a large fraction of LLAGNs are radio loud., Comment: 4 pages, To appear in the proceedings of the workshop "X-ray spectroscopy of AGN with Chandra and XMM-Newton", Eds., Th. Boller, S. Komossa, S. Kahn, and H. Kunieda

We present two high-resolution Chandra X-ray observations of supernova (SN) 1994I which show, for the first time, that the interaction of the blast wave from a Type Ic SN with its surrounding circumstellar material (CSM) can give rise to soft X-ray emission. Given a 0.3-2 keV band X-ray luminosity of L_x ~ 1 x 10^{37} ergs/s between six and seven years after the outburst of SN 1994I, and assuming the X-ray emission arises from the shock-heated CSM, we derive a pre-SN mass-loss rate of \dot{M} ~ 1 x 10^{-5} M_sun/yr (v_w/10 km/s). Combining the results with earlier ROSAT observations, we construct the X-ray lightcurve of SN 1994I. A best-fit X-ray rate of decline of L_x \propto t^{-s} with index s~1 and a CSM density profile of rho_csm \propto r^{-1.9\pm0.1} are inferred, consistent with what is expected for a constant mass-loss rate and constant wind velocity profile for the SN progenitor (rho_csm \propto r^{-2})., Comment: 5 pages, 3 figures, accepted for publication in the Astrophysical Journal Letters

We present the results of Chandra observations of off-nuclear X-ray sources in the spiral galaxy M51 (NGC 5194). 113 X-ray sources have been detected in the field of view and 84 among them project within the disk of NGC 5194. Six and twenty eight sources have luminosities exceeding 1x10^39 ergs s^-1 and 1x10^38 ergs s^-1 in the 0.5-8 keV band, respectively. The number of luminous sources is much higher than normal spiral and elliptical galaxies and similar to galaxies experiencing starburst activity. X-ray spectra of most of the detected sources are consistent with a power law with a photon index between 1 and 2, while one source has an extremely hard spectrum and two sources have soft spectra. The spectra of three ultraluminous sources are consistent with both a power law and a multicolor disk blackbody (MCD) model, while a power law model is preferable to a MCD model in two objects. One luminous object which shows a remarkable spectrum, including emission lines, is also found and discussed., Comment: 4 pages, to appear in the Proceedings of the Symposium on ``New Visions of the Universe in the XMM-Newton and Chandra Era'', 26-30 November 2001, ESTEC, The Netherlands

We report sub-arcsecond X-ray imaging spectroscopy of M87 and the core of the Virgo cluster with the Chandra X-ray Observatory. The X-ray morphology shows structure on arcsecond (~100 pc) to ten arcminute (~50 kpc) scales, the most prominent feature being an "arc" running from the east, across the central region of M87 and off to the southwest. A ridge in the radio map, ending in an "ear"-shaped structure, follows the arc to the east. Depressions in the X-ray surface brightness correspond to the inner radio lobes and there is no evidence of shock-heated gas surrounding them. There are also at least two approximately circular (centered near the nucleus) "edges" in the X-ray brightness distribution, the radii of which are slightly larger than the nuclear distances of the inner radio lobes and intermediate radio ridges, respectively. We speculate that these discontinuities may be spherical pulses or "fronts" driven by the same jet activity as is responsible for the radio structure; such pulses are found in recent numerical simulations. All these results provide good evidence that the nuclear activity affects the intra-cluster medium. We present a temperature map of the intra-cluster medium, and obtain the temperature, pressure and cooling time as a function of nuclear distance for the arcs and the ambient intra-cluster medium. We show that the gas in the arcs is cooler than, and probably over-pressured with respect to, the ambient intra-cluster medium. The metal abundances of the cooler gas in the arc are somewhat enhanced relative to the ambient intra-cluster medium, favoring a ``buoyant plume'' origin for the X-ray arc, in which ambient gas near the nucleus is entrained by buoyant radio plasma and carried to larger nuclear distances. (Abstract truncated)., Comment: Accepted for publication in The Astrophysical Journal; 22 pages, 8 figures. Text and figures were improved during the refereeing process. For a high resolution version, see http://www.astro.umd.edu/~ayoung/papers/

We report Chandra imaging-spectroscopy and RXTE spectroscopy of the nearby, powerful radio galaxy Cygnus A. Various aspects of the results are discussed, including the X-ray properties of the nucleus, the radio hot spots, the cluster of galaxies, the prolate cavity in the ICM inflated by the radio jets and ``bands'' of thermal gas which encircle the cavity in its equatorial plane. The hard X-ray emission of the nucleus extends to 100 keV and originates from an unresolved source absorbed by a large column density (N$_{\rm H}$ $\simeq$ 2 $\times$ 10$^{23}$ cm$^{-2}$) of gas. The soft ($<$ 2 keV) nuclear emission exhibits a bi-polar structure which extends $\simeq$ 2 kpc from the nucleus and is strongly correlated with both optical continuum and emission-line morphologies. It is suggested that this nebulosity is photoionized by the nucleus and that the extended X-rays are electron-scattered nuclear radiation. All four radio hot spots are detected in X-rays, with the emission resulting from synchrotron self-Compton radiation in an approximately equipartition field. The temperature of the X-ray emitting intracluster gas drops from $\simeq 8$ keV more than 100 kpc from the center to $\simeq 5$ keV some 80 kpc from the center, with the coolest gas immediately adjacent to the radio galaxy. There is a metallicity gradient in the X-ray emitting gas, with the highest metallicities ($\sim$ solar) found close to the center, decreasing to $\sim 0.3$ solar in the outer parts. (Abstract truncated)., Comment: 9 pages, 12 figures, to be published in ``New Visions of the Universe in the XMM-Newton and Chandra Era'', Ed. F. Jansen (in press) (2002) (European Space Agency ESA SP-488)

Chandra X-ray observations of the giant elliptical galaxy M87 resolve the thermal state of the hot interstellar medium into the accretion (Bondi) radius of its central 3 10^9 Msun black hole. We measure the X-ray gas temperature and density profiles and calculate the Bondi accretion rate, Mdot_Bondi \sim 0.1 Msun/yr. The X-ray luminosity of the active nucleus of M87 observed with Chandra is L_{x, 0.5-7 \keV} \sim 7 \times 10^{40}erg/s. This value is much less than the predicted nuclear luminosity, L_{Bondi} \sim 5 \times 10^{44} erg/s, for accretion at the Bondi rate with a canonical accretion radiative efficiency of 10%. If the black hole in M87 accretes at this rate it must do so at a much lower radiative efficiency than the canonical value. The multiwavelength spectrum of the nucleus is consistent with that predicted by an advection-dominated flow. However, as is likely, the X-ray nucleus is dominated by jet emission then the properties of flow must be modified, possibly by outflows. We show that the overall energetics of the system are just consistent with the predicted Bondi nuclear power. This suggests that either most of the accretion energy is released in the relativistic jet or that the central engine of M87 undergoes on-off activity cycles. We show that, at present, the energy dumped into the ISM by the jet may reduce the accretion rate onto the black hole by a factor \propto (v_j/c_s)^{-2}, where v_j is the jet velocity and c_s the ISM sound speed, and that this is sufficient to account for the low nuclear luminosity., Comment: emulateapj.sty, revised version, accepted by ApJ

There is now strong evidence that many low-luminosity AGNs (LLAGNs) contain accreting massive black holes and that the nuclear radio emission is dominated by parsec-scale jets launched by these black holes. Here, we present preliminary results on the 1.4 GHz to 667 GHz spectral shape of a well-defined sample of 16 LLAGNs. The LLAGNs have a falling spectrum at high GHz frequencies. Several also show a low-frequency turnover with a peak in the 1-20 GHz range. The results provide further support for jet dominance of the core radio emission. The LLAGNs show intriguing similarities with gigahertz-peaked spectrum (GPS) sources., Comment: 6 pages, to appear in ASP Conference series, 2002, Vol. 258

Using the HST STIS spectrograph we have obtained a grid of [O III] and H-beta emission-line spectra at 0"05x0"19 and 60 km/s (FWHM) resolution that covers much of the NLR of NGC 1068. We find emitting knots that have blueshifted radial velocities up to 3200 km/s relative to galaxy systemic, are 70-150 pc NE of the nucleus and up to 40 pc from the radio jet, emit several percent of the NLR line flux but no significant continuum, span velocity extents of up to 1250 km/s but a small fraction of the sky seen from the nucleus, coincide with a region of enhanced IR coronal-line emission, and have ionized masses $\sim$200 Msun/ne4 (ne4=10^4 cm^{-3}). We argue that the blueshifted knots are ablata from disintegrating molecular clouds that are being photoionized by the AGN, and are being accelerated readiatively by the AGN or mechanically by the radio jet. In their kinematic properties, the knots resemble the associated absorbers seen projected on the UV continua of some AGN. Between 2"5-4"5 from the nucleus, emission is redshifted relative to systemic, a pattern that we interpret as gas in the galaxy disk being pushed away from us by the NE radio lobe., Comment: 13 pages LaTeX w/ convenient embedded EPS figs, scheduled for ApJ April 1/02

We report X-ray imaging - spectroscopy of the jet of M87 at sub arc second resolution with the Chandra X-ray Observatory. The galaxy nucleus and all the knots seen at radio and optical wavelengths, as far from the nucleus as knot C, are detected in the X-ray observations. There is a strong trend for the ratio of X-ray to radio, or optical, flux to decline with increasing distance from the nucleus. At least three knots are displaced from their radio/optical counterparts, being tens of pc closer to the nucleus at X-ray than at radio or optical wavelengths. The X-ray spectra of the nucleus and knots are well described by power laws absorbed by cold gas, with only the unresolved nucleus exhibiting intrinsic absorption. In view of the similar spectra of the nucleus and jet knots, and the high X-ray flux of the knots closest to the nucleus, we suggest that the X-ray emission coincident with the nucleus may actually originate from the pc - or sub-pc - scale jet rather than the accretion disk. Arguments are given that the X-ray emission process is unlikely to be inverse Compton scattering. Instead, we favor synchrotron radiation. Plotted as $\nu$S$_{\rm \nu}$, the spectra of the knots generally peak in or just above the optical - near infrared band. However, the overall spectra of at least three knots cannot be described by simple models in which the spectral index monotonically increases with frequency, as would result from synchrotron losses or a high energy cut-off to the injected electron spectrum. Instead, these spectra must turn down just above the optical band and then flatten in the X-ray band. (Abstract truncated), Comment: To be published in the Astrophysical Journal, v568 n1, March 20, 2002 issue. Revised discussion of inverse Compton scattering 1/30/2002

We report Chandra ACIS and quasi-simultaneous RXTE observations of the nearby, powerful radio galaxy Cygnus A, with the present paper focusing on the properties of the active nucleus. In the Chandra observation, the hard (> a few keV) X-ray emission is spatially unresolved with a size \approxlt 1 arcsec (1.5 kpc, H_0 = 50 km s^-1 Mpc^-1) and coincides with the radio and near infrared nuclei. In contrast, the soft (< 2 keV) emission exhibits a bi-polar nebulosity that aligns with the optical bi-polar continuum and emission-line structures and approximately with the radio jet. In particular, the soft X-ray emission corresponds very well with the [O III] \lambda 5007 and H\alpha + [N II] \lambda\lambda 6548, 6583 nebulosity imaged with HST. At the location of the nucleus there is only weak soft X-ray emission, an effect that may be intrinsic or result from a dust lane that crosses the nucleus perpendicular to the source axis. The spectra of the various X-ray components have been obtained by simultaneous fits to the 6 detectors. The compact nucleus is detected to 100 keV and is well described by a heavily absorbed power law spectrum with \Gamma_h = 1.52^{+0.12}_{-0.12} (similar to other narrow line radio galaxies) and equivalent hydrogen column N_H (nuc) = 2.0^{+0.1}_{-0.2} \times 10^{23} cm^-2. (Abstract truncated)., Comment: To be published in the Astrophysical Journal, v564 January 1, 2002 issue; 34 pages, 11 figures (1 color)

We present simultaneous, sub-arcsecond (<=50pc) resolution 5 GHz, 8.4 GHz, and 15 GHz VLA observations of a well-defined sample of sixteen low-luminosity active galactic nuclei (LLAGNs). The radio emission in most of these nuclei does not show the rising spectrum (0.2 <= s <= 1.3, L_nu propto nu^{s}) expected from thermal electrons in an advection dominated accretion flow (ADAF) with or without weak to moderately-strong outflows. Rather, the flat radio spectra are indicative of either synchrotron self-absorbed emission from jets, convection-dominated accretion flows (CDAFs) with L >= 10^{-5} L_Edd, or ADAFs with strong (p >= 0.6) outflows. The jet interpretation is favored by three factors: a) the detection of pc-scale radio extensions, morphologically reminiscent of jets, in the five nuclei with the highest peak radio flux-density; b) the domination of parsec-scale jet radio emission over unresolved `core' emission in the three best-studied nuclei; and c) the lack of any clear correlation between radio spectral shape and black hole mass as would be expected from the dependence of the radio turnover frequency on black hole mass in ADAF and CDAF models. A jet domination of nuclear radio emission implies significantly lower accretion rates in ADAF-type models than earlier estimated from core radio luminosities., Comment: To appear in Astrophysical Journal Letters, October 1, 2000

The results from a recent Chandra ACIS-S study of the cluster surrounding Cygnus A are presented. We have deprojected the X-ray spectra taken from various elliptical shells in order to derive the run of temperature, density, pressure, and abundance for the ICM as a function of radius. We confirm a drop in temperature of the X-ray emitting gas from $\sim 8$ keV more than $\sim 2^{\prime}$ from the center to $\simeq 5$ keV some $30^{\prime\prime}$ from the center, with the coolest gas immediately adjacent to the radio galaxy. ``Belts'' of slightly cooler ($\simeq 4$ keV) X-ray emitting gas run around the minor dimension of the cavity created by the radio source. We find a metallicity gradient in the X-ray emitting gas, with the highest metallicities ($\sim$ solar) in the inner annuli, decreasing to $\sim 0.3$ solar in the outer parts. The total mass within 500 kpc is found to be (2.0--2.8) $\times 10^{14} M_{\odot}$ and approximately 3.5--5% of the mass is X-ray emitting gas [ABRIDGED]., Comment: 27 pages, 13 figures (2 color). To appear in The Astrophysical Journal, v565 n1 Jan 20, 2002 issue