======================================================================== G C N E W S * Newsflash * - The Newsletter for Galactic Center Research - gcnews@aoc.nrao.edu http://www.aoc.nrao.edu/~gcnews ======================================================================== Vol. 26, No. 3 Feb 15, 2007 ######################################################################## # # # NEWS: the Bad-Honneff GC06 proceedings are on the web at # # http://www.iop.org/EJ/toc/1742-6596/54/1 # # # # Santa Fe Physics and Astrophysics of Supermassive Black-Holes talks # # http://qso.lanl.gov/meetings/meet2006/participate.html # # # # Prague IAU symposium 238 video's on the Galactic center & BH's # # http://www.astronomy2006.com/symposia-archive.php?symposium=238 # # # # (all links are avalable through GCNEWS's conferences page) # # # ######################################################################## Recently submitted papers: -------------------------- 1) A Possible Link Between the Galactic Center HESS Source and Sgr A* (Ballantyne et al., ApJL) 2) Properties of the Radio-Emitting Gas Around SgrA* (Loeb & Waxman, JCAP) 3) A symbiotic scenario for the rapid formation of supermassive black holes (Richter & Viollier, JCAP) 4) The Cosmic Ray Distribution in Sagittarius B (Crocker et al., ) ------------------------------------------------------------------------ Email : drb@physics.arizona.edu Title : A Possible Link Between the Galactic Center HESS Source and Sgr A* Author(s): D. R. Ballantyne(1), Fulvio Melia(1,2,3), Siming Liu(4), and Roland M. Crocker(5) Institute: (1) Department of Physics, The University of Arizona, Tucson (2) Steward Observatory, The University of Arizona, Tucson (3) Sir Thomas Lyle Fellow and Miegunyah Fellow. (4) Theoretical Division, Los Alamos National Laboratory, Los Alamos (5) School of Chemistry and Physics, The University of Adelaide, Adelaide, Australia Paper : ApJ Letters, in press EPrint : astro-ph/0701709 Abstract: Recently, HESS and other air Cerenkov telescopes have detected a source of TeV gamma -rays coincident with the Galactic center. It is not yet clear whether the gamma -rays are produced via leptonic or hadronic processes, so it is important to consider possible acceleration sites for the charged particles which produce the gamma -rays. One exciting possibility for the origin of these particles is the central black hole, Sgr A*, where the turbulent magnetic fields close to the event horizon can accelerate protons to TeV energies. Using a realistic model of the density distribution in a 6 pc*6 pc*6 pc cube at the Galactic center, we here calculate the trajectories followed by these TeV protons as they gyrate through the turbulent medium surrounding Sgr A*. Diffusing out from the black hole, the protons produce TeV gamma -rays via \pi^0 decay following a collision with a proton in the surrounding medium. After following over 222,000 such trajectories, we find that the circumnuclear ring around Sgr A* can reproduce the observed 0.1-100 TeV HESS spectrum and flux if the protons are injected into this medium with an effective power-law index 0.75, significantly harder than the observed photon index of 2.25. The total energy in the steady-state 1-40 TeV proton population surrounding Sgr A* is inferred to be 2* 10^47 ergs. Only 31% of the emitted 1-100 TeV protons encounter the circumnuclear torus, leaving a large flux of protons that diffuse outward to contribute to the Galactic ridge emission observed by HESS on scales of > 1^o. ------------------------------------------------------------------------ Email : loeb@cfa.harvard.edu Title : Properties of the Radio-Emitting Gas Around SgrA* Author(s): Abraham Loeb^1,2 \& Eli Waxman^3 Institute: (1) Astronomy Department, Harvard University, Cambridge, MA 02138, USA (2) Einstein Minerva center, Weizmann Institute of Science, Rehovot, Israel (3) Physics Faculty, Weizmann Institute of Science, Rehovot, Israel Paper : JCAP, Jan 2007, submitted; astro-ph/0702043 EPrint : astro-ph/0702043 Abstract: We show that the radial profiles of the temperature and density of the electrons as well as the magnetic field strength around the massive black hole at the Galactic center, Sgr A*, may be constrained directly from existing radio data without any need to make prior assumptions about the dynamics of the emitting gas. The observed spectrum and wavelength-dependent angular size of Sgr A* indicate that the synchrotron emission originates from an optically-thick plasma of quasi-thermal electrons. We find that the electron temperature rises above the virial temperature within tens of Schwarzschild radii from the black hole, suggesting that the emitting plasma may be outflowing. Constraints on the electron density profile are derived from polarization measurements. Our best-fit results differ from expectations based on existing theoretical models. However, these models cannot be ruled out as of yet due to uncertainties in the source size measurements. Our constraints could tighten considerably with future improvements in the size determination and simultaneous polarization measurements at multiple wavelengths. ------------------------------------------------------------------------ Email : max.c.richter@gmail.com Title : A symbiotic scenario for the rapid formation of supermassive black holes Author(s): M.C. Richter, G.B. Tupper and R.D. Viollier Institute: Centre for Theoretical Physics and Astrophysics, Department of Physics, University of Cape Town, South Africa Paper : JCAP, 2006, in press EPrint : astro-ph/0611552 Abstract: The most massive black holes, lurking at the centers of large galaxies, must have formed less than a billion years after the big bang, as they are visible today in the form of bright quasars at redshift larger than six. Their early appearance is mysterious, because the radiation pressure, generated by infalling ionized matter, inhibits the rapid growth of these black holes from stellar-mass black holes. It is shown that the supermassive black holes may form timeously through the accretion of predominantly degenerate sterile neutrino dark matter onto stellar-mass black holes. Our symbiotic scenario relies on the formation of, first, supermassive degenerate sterile neutrino balls through gravitational cooling and, then, stellar-mass black holes through supernova explosions of massive stars at the center of the neutrino balls. The observed lower and upper limits of the supermassive black holes are explained by the corresponding mass limits of the preformed neutrino balls. ------------------------------------------------------------------------ Email : roland.crocker@adelaide.edu.au Title : The Cosmic Ray Distribution in Sagittarius B Author(s): Roland M. Crocker^1, David Jones^1,2, Raymond J. Protheroe^1, Jurgen Ott^2,6, Ron Ekers^2,7, Fulvio Melia^3,8, Todor Stanev^4, and Anne Green^5 Institute: (1) ^1 School of Physics and Chemistry, University of Adelaide, 5005, Australia, (2) ^2 Australia Telescope National Facility, Marsfield,, 2122, Australia, (3) ^3Physics Department and Steward Observatory, ,The University of Arizona, Tucson, AZ 85721, (4) ^4Bartol Research Institute,, The University of Delaware, Newark, DE 19716-2593, (5) ^5School of Physics,, University of Sydney,, 2006, Australia, (6) ^6Bolton Fellow (7) ^7Federation Fellow (8) ^8Sir Thomas Lyle Fellow and Miegunyah Fellow EPrint : astro-ph/0702045 Abstract: The HESS instrument has observed a diffuse flux of TeV gamma -rays from a large solid angle around the Galactic center (GC). This emission is correlated with the distribution of gas in the region suggesting that the gamma -rays originate in collisions between cosmic ray hadrons (CRHs) and ambient matter. Of particular interest, HESS has detected gamma -rays from the Sagittarius (Sgr) B Molecular Cloud Complex. Prompted by the suggestion of a hadronic origin for the gamma rays, we have examined archival 330 and 74 MHz Very Large Array radio data and 843 MHz Sydney University Molonglo Sky Survey data covering Sgr B, looking for synchrotron emission from secondary electrons and positrons (expected to be created in the same interactions that supply the observed gamma rays). Intriguingly, we have uncovered non-thermal emission, but at a level exceeding expectation. Adding to the overall picture, recent observations by the Atacama Pathfinder Experiment telescope show that the cosmic ray ionization rate is ten times greater in the Sgr B2 region of Sgr B than the local value. Lastly, Sgr B2 is also a very bright X-ray source. We examine scenarios for the spectra of CRHs and/or primary electrons that would reconcile all these different data. We determine that (i) a hard ( E^-2.2), high-energy (> TeV) population CRHs is unavoidably required by the HESS gamma -ray data and (ii) the remaining broad-band, non-thermal phenomenology is explained either by a rather steep ( E^-2.9) spectrum of primary electrons or a ( E^-2.7) population of CRHs. No single, power-law population of either leptons or hadrons can explain the totality of broadband, non-thermal Sgr B phenomenology. ------------------------------------------------------------------------ (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, Robin Herrnstein - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - For Abstract submission please follow the instructions which are at http://www.aoc.nrao.edu/~gcnews/home/submission.shtml ========================================================================