Black Hole Astrophysics with Radio and Grav. Wave Observations - NRAO, Charlottesville VA, Nov 7-8 2008 Fred Lo--NRAO ============= - VLA, VLBA, ALMA Joan Centrella & Tuck Stebbins--this workshop ============================================= - EM and GW astronomy complementary - MBHs key sources for both; synergies between EM and GW observations - produce whitepaper - EM and GW can work collaboratively or complementarily - GWs and EM - GWs see compact objects; radio sees gas - GWs: no images, precise parameter distances; all sky - radio: great resolution, resolve geometry, highly detailed images, small field of view (PTA all sky) - science questions - hierarchical merger scenarios: low masses (seeds), spins, kicks - emergence from dark ages - galactic nuclei: EMRIs, tidal disruptions - EM counterparts - Fred: many heavy quasars (10^9) at z = 6.42, very luminous; Alma will see many objects at high zs, perhaps weighted to higher masses - Jim Condon: with surveys (NVSS), in continuum, we already see far quasars, but don't know which they are; see smaller BHs in nearby 200 Mpc Jim Ulvestad--VLBA instrumentation and binary BHs ================================================= - VLBA instrumentation - www.vlba.nrao.edu, world's only dedicated imaging VLBA - available year round - 90 cm--3 mm; sensitivity limited by data rate (bandwidth) - resolution in mid band = 0.8 mas, a few pc at z = 0.5, < 0.1 pc at Virgo - can distinguish motions and changes on 0.1 resolution elements: 0.02 pc at z = 1, can't see BH orbital motion very far - for nearby kicked BHs, may see movement across year (but need gas around MBH to make it a radio source) - 60 uJy in 0.8 mas corresponds to an equivalent T = 1e6 K: need nonthermal radiation from near black holes, possibly thermal from X-ray--emitting accretion flows - converse: any radio detection must be clue to BH presence - VLBA resolution typically 1e3-1e4 Schwarzschild radii. Exception: M87 has 3e9 Msun BH, diameter = 10uas - 0402+379 radio BBH - Pollack et al 2004 - 200 Mpc, in Caltech-Jodrell flat-spectrum sample - steep spectra found in two hotspots; separated by 7 pc - V(lobes) = 0.2c; delta V(C1,2) < 0.1c - Global VLBI: H absorption lines blue- and red-shifted 700 and 370 from systemic (determined from galaxy redshift); implies total binary M > 1.4e8 Msun - radio surveys of BBHs - CLASS survey: start from catalog, select flat spectra, look for lenses with VLA - flat spectra: optically thick/self-absorbed emission, selects for nuclei - VIPS: similar survey from CRATES sources, multifrequency follow up with VLBA: 15 BH candidates, preliminary indication is that none is binary - 0/1100; CJF had 1/300 - 1800hr campaign could follow up 10x candidates - ?/9000 - overall, see mostly 1e8-1e9 BHs Tuck Stebbins--LISA science and concept ======================================= - nice picture BBH, waves, LISA: ask Tuck for it - nice mission architecture figures, too - GW highlights - extreme conditions, signals directly from objects, read source dynamics - high-precision measurements with simple interpretations (no systematics?) - most powerful events in Universe - phenomena not directly observable in other ways - MY TALK: discuss uncertainties on EMRI rates - understanding formation and growth of MBHs - large stellar mass black holes or seed MBHs - spin discriminates growth by accretion, mergers, and may observe effects of gravitational recoil - MY TALK: effect of gas on waveforms? Luciano's model - can we have coalescences with one active AGN? Binary interactions tend to clear away gas - MY TALK: just Keplerian formula for MBH frequency in terms of typical masses, AU - what are EM counterpart signals? - pre-merger variability, disturbance of accretion rings, reestablishing accretion - how do you get 1e-22 strain? ucycle/sqrt(Hz) measurement over Gm with 1u light - MY TALK: opportunities to do mock data challenges Joseph Lazio--SKA ================= - key science: strong-field gravity with pulsars and black holes - aside: gas reveals galaxy mergers even when not clear in optical - Comerford et al.: emerging multiwavelength evidence for dual AGN nuclei - relativistic binaries (only BNS known) probe equivalence principle, strong gravity; post-Keplerian parameters in PSR J0737-3039 (Kramer et al.) - pulsar timing array as GW detector; current efforts just above predicted MBHB background - 3C 66B excluded - Galactic pulsar census, find 1% interesting - rapidly spinning millisecond - ultra-relativistic binaries - ultra-stable millisecond (for PTA) - SKA as part of multimessenger suite probing gravity (Chandra, GLAST, LIGO, LISA) - sensitivity: 12000 m2/K; survey speed: 6e7 deg2 m4 K-2; field of view 1 deg; angular resolution 15 mas - INTERESTING QUESTION: how would we organize LISA data analysis the same way that correlators are? - how to build a GW accelerator? A grape-like system? use some kind of waveform compression? - Massimo's question: MBH localization with LISA only possible with SKA? Massimo Dotti--electromagnetic signatures from MBH mergers ========================================================== - Torques in galactic mergers can bring gas to the center, creating disk. - MBH coalescence X-ray afterglow, several years after merger (Milosavljevic 2005?) - disk flows in to fill binary gap - observable in to z~3 at GLAST/Edge sensitivities - in dry merger, recoiling MBHs drag inner part of its own accretion disk (Loeb 2007) - dry merger, recoiling MBHs interact gravitationally with IGM, enhancing bremsstrahlung emission Jim Braatz--measure AGN accretion disks and BHs with masers =========================================================== - 22 GHz H20 transition produces brightest radio line observed - excited at 1e8-1e10 cm-3, 400K: conditions common throughout Milky way - beamed megamasers detected toward AGNs - give access to accretion disk and BH physics - time evolution of orbiting elements gives central mass - see ugc 3789, ngc 4258: model accretion disk in three dimensions - can map individual maser elements to sub-resolution VLBA positions - measure distances to galaxies - with High Sensitivity Array: - measure masses of tens of SMBH, given distance - absolute masses of few SMBH - H0 to a few percent - SKA a few times better Jim Ulvestad--low-luminosity AGNs ================================= - cannot see-low mass binary AGNs very far, even with VLBA - many Markarian galaxies have double optical nuclei - FOR MY TALK? Arp 99: merging galaxies make many supernovae within a few pc of nucleus, visible in radio (Neff et al. 2004) - EVLA will have some capability of surveying globular clusters in galaxy for IMBHs: if they're radiating because they have gas or shredding stars First day summary ================= - LISA: 1e4-1e7 Msun at high z; pulsar: 1e8-1e9 at low z; radio: high mass at high z, low mass at low z - so: what low-mass radio observations at near z will help observations at high z? Example: demonstrate Eddington accretion - no demonstrated oddities in nuclei that point to past mergers - dramatic increase in collecting area only with SKA (but pathfinder SKA by 2020, a few EVLAs) - targeted observations or survey speed? - surveys of variability: prefer wide/shallow or narrow/deep? - Allen telescope array Questions ========= - Does enhancement of SNe after mergers provide many binaries for tidal-stripping formation of EMRIs? Or is this taken into consideration already in statistics? - What are assumptions about discs for counterparts? - Status of last parsec problem - Figure of sensitivity for future radio instruments? Joan Wrobel--low-mass AGN in the local universe =============================================== - BHs grow by accretion (markers are AGNs) and mergers (as GWs, for M > 1e5 Msun) - So what do we know about AGNs from low-mass AGNs? - Spheres of influence are small, can't resolve it, so look optically for broad-line AGN - Eddington ratios ~ 0.4, radio quiet (accretion emits mainly in X rays; radio loud are jets; radio quiet may be outflows or corona of accretion disk) Avery Broderick--imaging BH horizons ==================================== - BH should create a dark silhouette, 10M wide, in front of background; scale is 55 uas for Sgr A* - in reality, we should image accretion disk... - how do accretion flows work? - how do jet forms, and depend on BH parameters? - can use hot spots as test particles to study GR - a way to relate the different EM and GW populations - can get uas resolution at sub-mm wavelength; Doeleman et al. 2008 - Sgr A*: 4.5e6 Msun, 8 kpc, 1e-8 Ledd, highly variable - Questions: - Is emission a radiatively inefficient accretion flow (RIAF) or a magnetically arrested disk (MAD)? - Does MHD do a good job? - What happens to 1e-6 Msun/yr that's available? - If there was no horizon, the infalling material would have to deposit energy, which would be visible - Model of accretion disk crescent can already be compared with images [AEB, Fish, Doeleman, Loeb (2008)] - Follow time-evolving dynamics of hot spots, get spin - M87: 4.5e9 Msun, 16 Mpc, 1e-6 Ledd - What is the structure of its jets? - Together, Sgr A* and M87 provide a means to qualitative compare representatives of the GW and EM black-hole samples Three meetings: NRAO, STScI (Mar 30-Apr 1), NOAO... X-ray crowd at GSFC