22 research outputs found
Spectrum of two component flows around a super-massive black hole: an application to M87
We calculate the spectra of two-component accretion flows around black holes
of various masses, from quasars to nano-quasars. Specifically, we fit the
observational data of M87 very satisfactorily using our model and find that the
spectrum may be well fitted by a sub-Keplerian component alone, and there is
little need of any Keplerian component. The non-thermal distribution of
electrons produced by their acceleration across the standing shock in the
sub-Keplerian component is enough to produce the observed flat spectrum through
the synchrotron radiation.Comment: 12 pages, 2 figures and 1 table. Accepted in Astrophysical Journal
Lette
Constraining spins of supermassive black holes from TeV variability. II. fully general relativistic calculations
The fast variability of energetic TeV photons from the center of M87 has been
detected, offering a new clue to estimate spins of supermassive black holes
(SMBHs). We extend the study of Wang et al. (2008) by including all of general
relativistic effects. We numerically solve the full set of relativistic
hydrodynamical equations of the radiatively inefficient accretion flows (RIAFs)
and then obtain the radiation fields around the black hole. The optical depth
of the radiation fields to TeV photons due to pair productions are calculated
in the Kerr metric. We find that the optical depth strongly depends on: (1)
accretion rates as \tautev\propto \dot{M}^{2.5-5.0}; (2) black hole spins;
and (3) location of the TeV source. Jointly considering the optical depth and
the spectral energy distribution radiated from the RIAFs, the strong
degeneration of the spin with the other free parameters in the RIAF model can
be largely relaxed. We apply the present model to M87, wherein the RIAFs are
expected to be at work, and find that the minimum specific angular momentum of
the hole is . The present methodology is applicable to M87-like
sources with future detection of TeV emissions to constrain the spins of SMBHs.Comment: 12 pages, 11 figures. Minor typos corrected. published version in Ap
Direct time radio variability induced by non-axisymmetric standing accretion shock instability: implications for M87
We show for the first time the direct time variable radio images in the
context of shocked accretion flows around a black hole under the general
relativistic treatment of both hydrodynamics and radiation transfer. Time
variability around a black hole can be induced by the non-axisymmetric standing
accretion shock instability (namely Black Hole SASI). Since the spiral arm
shock waves generate the density and temperature waves at the post shock
region, they cause time variability in the black hole vicinity. Based on our
dynamical simulations, we discuss a possibility of detection for the time
variable radio images of M87 by the future space telescope VSOP2/ASTRO-G
satellite. The most luminous part of the images is predicted to be near 15
Schwarzschild radii for some snapshots. We show that our results are consistent
with existing observational data such as timeaveraged radio spectra, VLBA
images and variability timescale for M87. We also discuss observations of M87
with millimeter and sub-millimeter interferometers.Comment: 17 pages, 5 figures, Accepted to publication for Ap
Cosmic Ray Generation by Quasar Remnants: Constraints and Implications
The quasar remnant cores of nearby giant elliptical galaxies NGC 4486 (M87),
NGC 1399, NGC 4649 and NGC 4472 are the sites of supermassive (greater than one
billion solar masses) black holes. These objects are investigated as to the
viability of the conjecture that they could harbor compact dynamos capable of
generating the highest energy cosmic rays. For an accretion process involving
an equipartition magnetic field near the event horizons of the underlying
putative spun-up black holes, the energy achievable in accelerating protons
could well be greater or equal than 100 EeV for all these when only considering
the drag induced by curvature radiation. Estimates of the SED (spectral energy
distribution) of ambient core photons lead to the conclusion that the energy
losses arising from photo-pion production in proton collisions with these
target photons are relatively small for all but M87. For M87, the ambient
photon field is likely to be a limiting factor. Accretion rates on the order of
one solar mass per year, comparable to the Bondi rates and to the stellar mass
loss rates, are associated with (greater than 100 EeV) cosmic ray generation in
the other (electromagnetically dark) galactic core sites. If these sites are
found to be sources of such cosmic rays, it would suggest the presence of a
global inflow of interstellar gas all the way into the center of the host
galaxy.Comment: 11 pages Latex, no figures, uses mn and amssymb style files, accepted
for publication in MNRA
Soil nitrogen status as a regulator of carbon substrate flows through microbial communities with elevated CO2
To assess how microbial processing of organic C inputs to forest soils may be influenced by elevated CO2 and altered N dynamics, we followed the fate of 13C-labeled substrates in soils from the Duke Free Air Carbon Enrichment site where differences in soil N status have been imposed by 7 years of N amendments. Heterotrophic respiration and δ13C of respired CO2-C and phospholipid fatty acids (PLFA) were measured to track activities of microbial groups and estimate a relative measure of substrate use efficiency (PLFA-based SUE). Results indicate an increased proportion of fungal and actinomycete activity in elevated CO2 soils, which varied with substrate. The negative effect of N on vanillin phenolic-C incorporation into actinomycete PLFA suggests legacies of fertilization can mitigate increased C flow into actinomycetes with elevated CO2. Further, the fourfold increase in PLFA-based SUE for vanillin phenolic-C in elevated CO2 soils that received N suggests future enhanced N limitation in elevated CO2 soils may promote enhanced respiratory loss relative to incorporation of some C-substrates into microbial biomass. These short-term incubations did not reveal greater loss of soil organic carbon via respiration or shifts in SUE with elevated CO2. However, observed relative increases in activity of actinomycetes and fungi with elevated CO2 and mitigation of this effect on actinomycetes with N amendments suggests that elevated CO2 and predicted N limitation may alter the fate of slow-turnover soil organic matter (SOM) in two competing ways. Investigations need to focus on how these microorganisms may increase slow-turnover substrate use while possibly enhancing the prevalence of microbial cell wall structures that can serve as precursors of stabilized SOM