Friday Talks

Doug Finkbeiner - the Fermi Bubbles

Discovered bubbles
  • many explanations... e- e+, protons, agn, sf
  • "evidence for" but not "discovery of" a jet

9:30-9:50 am Mateusz Ruszkowski (USA): The Fermi Bubbles: Gamma-ray, Microwave, and Polarization Signatures of Leptonic AGN Jets (15 + 5 minutes)

Using simulation to fit to the fermi bubble
  • "double jet" much better fit than single

9:50-10:10 am Brian Lacki (USA): Sturm und Drang: The Turbulent, Magnetic Tempest in the Galactic Center (15 + 5 minutes)

Pressure balance
  • equipartition in MW
  • 100x in CMZ
  • 1000x in M82, 1e6x in Arp 220 + yet still equipartition
  • turbulence dissipates in a flow-crossing time + turbulent plasma drives b-field toward equipart
  • Q Steve: What is your outer scale? Most of molecular gas at radii of 100pc...
  • A: radii go outward... thickness of disk in 3D turbulence sets your upper scale.

11:15-11:40 am Timothy Linden (USA): Dark Matter in the Galactic Center (20 + 5 minutes)

Dark matter cross-section
  • significant only as a nonthermal energy source
  • dark matter is the source of electrons in the nonthermal filaments (Linden 2011)
  • Q Gillessen: Does NFW fit Fermi?
  • A: Yes, but requires adiabatic contraction and almost doesn't fit
  • Q: Baganoff: What is the dark matter energy injection?
  • A: 10^36 erg/s over 1 degree in 1-10 GeV electrons
  • Q: Wardle: predict sharp spectral cutoff below 100 GHz.
  • A: MHD makes filament, dark matter feeds electrons into it. Need to find sharp turnover
  • Q Farhad: Only a few nonthermal filaments have X-ray counterparts. Maybe a result of interaction.
  • A: Filaments will be hardest where they are dimmest

11:40-12:00 pm Chris Gordon (UK): Dark Matter and Pulsar Model Constraints from Galactic Center Fermi-LAT Gamma Ray Observations (15 + 5 minutes)

12:20-12:40 pm Miwa Goto (Germany): The cosmic-ray ionization rate in the Central parsec of the Galaxy - how we could deal with 10^4 discrepancy? (15 + 5 minutes)

CR rate 1.6e-15 near Sgr A*
  • disk CR rate: ~1x10-17
  • Uncertainties in extrapolated CR spectrum
  • Chemistry may be way off

2:00-2:20 pm Andrew Lehmann (Australia): The Galactic Centre molecular cloud G0.13-0.13: a laboratory for understanding cosmic-ray electron acceleration and

Clouds fluoresce in 6.4 keV Fe K-alpha line
  • electrons from either SN or arc
  • electron losses very fast at low energies + only high energies can penetrate the cloud + Arc electrons higher energy, penetrate further
  • Q: how do electrons escape? field line diffusion? wandering?
  • A: Unknown
  • Q: B-field?
  • A: Turbulent, so diffusion holds

2:20-2:40 pm Chuck Hailey (USA): First Results from the NuSTAR "Mini-Survey" of the Galactic Center Region (15 + 5 minutes)

  • cannonball: not detected, swamped
  • x-ray filament
  • "GeV results for the PWN in the CMZ"
  • Sgr A-E a magnetic flux tube? + Where do you get 50 TeV electrons?
  • HESS TeV source: everything >40 keV is from a pwn + INTEGRAL source was an artifact

3:30-3:55 pm Shep Doeleman (USA): Science with the Event Horizon Telescope (20 + 5 minutes)

  • pierce the scattering screen
  • intrinsic size larger than scattering

3:55-4:15 pm Geoff Bower (USA): The Galactic Center Pulsar, SGR 1745-29 (15 + 5 minutes)

  • Limit of 20% on pointlike contribution to Sgr A* emission

Diffuse X-rays in the CMZ / NIR comparison

"GCDX"
  • 7x10^7 K gas.
  • gas can freely escape
  • extinction-corrected stellar number density map
  • awesome extinction-polarization maps + Hatano et al2013

Discussion

Farhad: Morphology in inner 1.5" "Missing Pulsar" problem. Dispersion Measure problem: hard to see pulsars

5:00-5:25 pm Mitch Begelman (USA): Symposium Summary (25 minutes)

  • "Maybe the solar system is in the Galactic center..."
  • Galactic "Center": dynamical
  • CMZ: Characterized by physical conditions - amount of molecular gas and extreme conditions
  • CMZ vs starbursts: 10-100x lower pressure, 10^-4 gamma rays
  • CMZ disagrees with "sacred" KS law (or Krumholz-McKee law)
  • Supsersonic turbulence accepted in the CMZ... not in Mitch's circles
  • intermittent SF: turbulent, cloud-cloud collisions
  • turbulent clouds are transient
  • starbursts = global conditions, local: cloud collisions
  • pressure gradient in the CMZ -> wind
  • could wind-strength be the trigger? + put threshold at 10x tidal limit + wind luminosity required = L_w = 10 (c_s^2 sigma^3 / G) T_100 sigma_150^3 erg/s + bimodal: feedback drives further SF
  • CND - CMZ connection...
  • Central nuclear cluster: formed from binaries? + tidal limit on SF + tidal compression -> tiny jeans mass
  • G2 + Mitch thinks it contains a star + high eccentricity means hard to form close-in + plausible star with 50km/s 10^-7 msun/yr

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