======================================================================== G C N E W S * Newsflash * - The Newsletter for Galactic Center Research - gcnews@aoc.nrao.edu http://www.aoc.nrao.edu/~gcnews ======================================================================== Vol. 27, No. 5 Aug 9, 2007 Recently submitted papers: -------------------------- 1) Measuring the kinetic power of AGN in the radio mode (Merloni et al., MNRAS) 2) A Study of Stellar Photometric Variability Within the Central 4 pc of the Galactic Center with Infrared Image Subtraction (Peeples et al., Acta Astron.) 3) Apoastron Shift Constraints on Dark Matter Distribution at the Galactic Center (Zakharov et al., Phys.Rev.D) 4) Stellar Relaxation Processes Near the Galactic Massive Black Hole (Alexander, 2007 STScI Symp.) ------------------------------------------------------------------------ Email : am@mpe.mpg.de Title : Measuring the kinetic power of AGN in the radio mode Author(s): Andrea Merloni^1,2 \& Sebastian Heinz^3 Institute: (1) Max-Planck-Institut fuer Astrophysik, Karl-Schwarzschild-Strasse 1, D-85741, Garching, Germany (2) Max-Planck-Institut fuer Extraterrestrische Physik, Giessenbachstr., D-85741, Garching, Germany (3) Astronomy Department, University of Wisconsin-Madison, Madison, WI 53706 Paper : MNRAS, July 2007, in press EPrint : arXiv:0707.3356v1 Abstract: We have studied the relationship among nuclear radio and X-ray power, Bondi rate and the kinetic luminosity of sub-Eddington active galactic nuclear (AGN) jets, as estimated from the pdV work done to inflate the cavities and bubbles observed in the hot X-ray emitting atmospheres of their host galaxies and clusters. Besides the recently discovered correlation between jet kinetic and Bondi power, we show that a clear correlation exists also between Eddington-scaled kinetic power and bolometric luminosity, given by: \log (L_kin/L_Edd) = (0.49+/-0.07) \log (L_ bol/L_Edd) - (0.78+/-0.36). The measured slope suggests that these objects are in a radiatively inefficient accretion mode, and has been used to put stringent constraints on the properties of the accretion flow. Interestingly, we found no statistically significant correlations between Bondi power and bolometric AGN luminosity, apart from that induced by their common dependence on L_kin, thus confirming the idea that most of the accretion power emerges from these systems in kinetic form. We have then analyzed the relation between kinetic power and radio core luminosity. Combining the measures of jet power with estimators of the un-beamed radio flux of the jet cores as, for example, the so-called 'fundamental plane' of active black holes, we are able to determine, in a statistical sense, both the probability distribution of the mean jets Lorentz factor, that peaks at \Gamma_m 7, and the intrinsic relationship between kinetic and radio core luminosity (and thus the jet radiative efficiency), that we estimate as: \log L_ kin=(0.81 +/- 0.11)\log L_R + 11.9^+4.1_-4.4, in good agreement with theoretical predictions of synchrotron jet models. With the aid of these findings, quantitative assessments of kinetic feedback from supermassive black holes in the radio mode (i.e. at low dimensionless accretion rates) will be possible based on accurate determinations of the central engine properties alone, such as mass, radio core and/or X-ray luminosity. As an example, we suggest that Sgr A^* may follow the same correlations of radio mode AGN, based on its observed radiative output as well as on estimates of the accretion rate both at the Bondi radius and in the inner flow. If this is the case, the supermassive black hole in the Galactic center is the source of 5 * 10^38 ergs s^-1 of mechanical power, equivalent to about 1.5 supernovae every 10^5 years. ------------------------------------------------------------------------ Email : molly@astronomy.ohio-state.edu Title : A Study of Stellar Photometric Variability Within the Central 4 pc of the Galactic Center with Infrared Image Subtraction Author(s): Molly S. Peeples, K. Z. Stanek, D. L. DePoy Institute: (1) Ohio State University Paper : Acta Astron., 57 (2007) 73 EPrint : astro-ph/0703769 Abstract: We present a catalog of 110 variable stars within 1' of Sgr A* based on image subtraction of near-infrared (H and K) photometry. Our images were obtained over 133 nights from 2000-2002 in H-band and over 134 nights from 2001-2002 in K-band; the typical FWHM is 1.4''. We match the catalog to other near-infrared, X-ray, and radio (i.e., maser) data, and we discuss some of the more interesting objects. The catalog includes 14 periodic sources, several known long-period variables and three new LPV candidates. We associate IRS 10* with OH, SiO, and H2O masers and a bright X-ray point source; this analysis suggests IRS 10* is an AGB star with an accreting companion. Among the approximately 90 newly discovered sources are a probable cataclysmic variable, a potential edge-on contact 84 day period eclipsing binary, and a possible 41 day period pulsating variable. ------------------------------------------------------------------------ Email : nucita@le.infn.it Title : Apoastron Shift Constraints on Dark Matter Distribution at the Galactic Center Author(s): A.F. Zakharov A.A. Nucita F. De Paolis G. Ingrosso Paper : Phys.Rev.D, 2007, in press Abstract: The existence of dark matter (DM) at scales of few pc down to 10^-5 pc around the centers of galaxies and in particular in the Galactic Center region has been considered in the literature. Under the assumption that such a DM clump, principally constituted by non-baryonic matter (like WIMPs) does exist at the center of our galaxy, the study of the gamma -ray emission from the Galactic Center region allows us to constrain both the mass and the size of this DM sphere. Further constraints on the DM distribution parameters may be derived by observations of bright infrared stars around the Galactic Center. Hall and Gondolo \citehallgondolo used estimates of the enclosed mass obtained in various ways and tabulated by Ghez et al. (2003, 2005). Moreover, if a DM cusp does exist around the Galactic Center it could modify the trajectories of stars moving around it in a sensible way depending on the DM mass distribution. Here, we discuss the constraints that can be obtained with the orbit analysis of stars (as S2 and S16) moving inside the DM concentration with present and next generations of large telescopes. In particular, consideration of the S2 star apoastron shift may allow improving limits on the DM mass and size. ------------------------------------------------------------------------ Email : tal.alexander@weizmann.ac.il Title : Stellar Relaxation Processes Near the Galactic Massive Black Hole Author(s): Tal Alexander Paper : Invited talk. To appear in "2007 STScI spring symposium: Black Holes", eds, M. Livio & A. M. Koekemoer, Cambridge University Press, in press. EPrint : astro-ph/0708.0688 Web : http://xxx.lanl.gov/abs/0708.0688 Abstract: The massive black hole (MBH) in the Galactic Center and the stars around it form a unique stellar dynamics laboratory for studying how relaxation processes affect the distribution of stars and compact remnants and lead to close interactions between them and the MBH. Recent theoretical studies suggest that processes beyond "minimal" two-body relaxation may operate and even dominate relaxation and its consequences in the Galactic Center. I describe loss-cone refilling by massive perturbers, strong mass segregation and resonant relaxation; review observational evidence that these processes play a role in the Galactic Center and discuss some cosmic implications for the rates of gravitational wave emission events from compact remnants inspiraling into MBHs, and the coalescence timescales of binary MBHs. ------------------------------------------------------------------------ (Older versions of the Newsflash can be found at the gcnews web-page) ======================================================================== Edited by Sera Markoff, Loránt Sjouwerman, Joseph Lazio, Cornelia Lang, Rainer Schödel, Masaaki Sakano, Feng Yuan - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - For Abstract submission please follow the instructions which are at http://www.aoc.nrao.edu/~gcnews/home/submission.shtml ========================================================================