192,912 research outputs found
The long-term optical behavior of MRK421
All data available in B band for the BL Lac object MRK421 from 22
publications are used to construct a historical light curve, dating back to
1900. It is found that the light curve is very complicated and consists of a
set of outbursts with very large duration. The brightness of MRK421 varies from
11.6 magnitude to more than 16 magnitude. Analyses with Jurkevich method of
computing period of cyclic phenomena reveal in the light curve two kinds of
behaviors. The first one is non-periodic with rapid, violent variations in
intensity on time scales of hours to days. The second one is periodic with a
possible period of years. Another possible period of years is not very significant. We have tested the robustness of the
Jurkevich method. The period of about one year found in the light curves of
MRK421 and of other objects is a spurious period due to the method and the
observing window. We try to explain the period of years under the
thermal instability of a slim accretion disk around a massive black hole of
mass of .Comment: Tex, 14 pages, 5 Postscript figures. Accepted for publication in A&A
Supplement Serie
X-shaped radio galaxies as observational evidence for the interaction of supermassive binary black holes and accretion disk at pc scale
A supermassive black hole binary may form during galaxy mergering. we
investigate the interaction of the supermassive binary black holes (SMBBHs) and
an accretion disk and show that the detected X-shaped structure in some FRII
radio galaxies may be due to the interaction-realignment of inclined binary and
accretion disk occurred within the pc scale of the galaxy center. We compare in
detail the model and observations and show that the configuration is consistent
very well with the observations of X-shaped radio sources. X-shaped radio
feature form only in FRII radio sources due to the strong interaction between
the binary and a standard disk, while the absence of X-shaped FRI radio
galaxies is due to that the interaction between the binary and the radiatively
inefficient accretion flow in FRI radio sources is negligible. It is suggested
that the binary would keep misaligned with the outer disk for most of the life
time of FRII radio galaxies and the orientation of jet in most FRII radio
galaxies distributes randomly, while the jets in most FRI radio galaxies is
expected to be vertical to the accretion disk and thus the major axis of host
galaxy. We discuss the relationship of X-shaped and double-double radio
galaxies (DDRGs). The model is applied in paticular to two X-shaped radio
sources 4C+01.30 and 3C293 and one DDRG source J0116-473 and show that the
SMBBHs in the three objects have black hole mass ratios .Comment: 35 pages, no figure, no table. Accepted for publication in MNRA
Enhanced off-center stellar tidal disruptions by supermassive black holes in merging galaxies
Off-center stellar tidal disruption flares have been suggested to be a
powerful probe of recoiling supermassive black holes (SMBHs) out of galactic
centers due to anisotropic gravitational wave radiations. However, off-center
tidal flares can also be produced by SMBHs in merging galaxies. In this paper,
we computed the tidal flare rates by dual SMBHs in two merging galaxies before
the SMBHs become self-gravitationally bounded. We employ an analytical model to
calculate the tidal loss-cone feeding rates for both SMBHs, taking into account
two-body relaxation of stars, tidal perturbations by the companion galaxy, and
chaotic stellar orbits in triaxial gravitational potential. We show that for
typical SMBHs with mass 10^7 M_\sun, the loss-cone feeding rates are enhanced
by mergers up to \Gamma ~ 10^{-2} yr^{-1}, about two order of magnitude higher
than those by single SMBHs in isolated galaxies and about four orders of
magnitude higher than those by recoiling SMBHs. The enhancements are mainly due
to tidal perturbations by the companion galaxy. We suggest that off-center
tidal flares are overwhelmed by those from merging galaxies, making the
identification of recoiling SMBHs challenging. Based on the calculated rates,
we estimate the relative contributions of tidal flare events by single, binary,
and dual SMBH systems during cosmic time. Our calculations show that the
off-center tidal disruption flares by un-bound SMBHs in merging galaxies
contribute a fraction comparable to that by single SMBHs in isolated galaxies.
We conclude that off-center tidal disruptions are powerful tracers of the
merging history of galaxies and SMBHs.Comment: 17 pages, 8 figures; Typos are corrected to match the published
version in Ap
Mass estimate of the Swift J 164449.3+573451 supermassive black hole based on the 3:2 QPO resonance hypothesis
A dormant Swift source J 164449.3+573451 (Sw 164449+57)recently experienced a
powerful outburst, caused most probably by a tidal disruption of a star by the
super-massive black hole at the center of the source. During the outburst, a
quasi periodic oscillation (QPO) was detected in the observed X-ray flux from
Sw 164449+57. We show that if the observed QPO belongs to a "3:2 twin peak QPO"
(with the second frequency not observed), the mass of the black hole in Sw
164449+57 is rather low, M ~ 10^5 M_sun, and the source belongs to a class of
intermediate mass black holes. The low mass of the source has been pointed out
previously by several authors.Comment: Accepted by Astronomy and Astrophysic
Critical point of QCD from lattice simulations in the canonical ensemble
A canonical ensemble algorithm is employed to study the phase diagram of QCD using lattice simulations. We lock in the desired quark number sector
using an exact Fourier transform of the fermion determinant. We scan the phase
space below and look for an S-shape structure in the chemical potential,
which signals the coexistence phase of a first order phase transition in finite
volume. Applying Maxwell construction, we determine the boundaries of the
coexistence phase at three temperatures and extrapolate them to locate the
critical point. Using an improved gauge action and improved Wilson fermions on
lattices with a spatial extent of 1.8 \fm and quark masses close to that of
the strange, we find the critical point at and baryon
chemical potential .Comment: 5 pages, 7 figures, references added, published versio
- …