190 research outputs found
Institutional Strategy And Multinationals’ Entry Mode Choice
The ability of Multinational Corporations (MNCs) using different entry mode choices to strategically influence their environments has become an important concern in international business research. We adopt the concept of institutional strategy to explain patterns of MNCs’action that are directed toward managing the various institutional pressures. The institutional strategies vary with different multinational entry mode choices used by MNCs.
This study proposes that the MNCs using different entry mode choice adopt different institutional strategies to respond two primary institutional pressures---internal (parent) and external (host country). In order to provide a constructive alternative explanation for multinationals’ entry mode choice in institutional perspectives, further empirical research and literature review is required
Evidence for Photoionization Driven Broad Absorption Line Variability
We present a qualitative analysis of the variability of quasar broad
absorption lines using the large multi-epoch spectroscopic dataset of the Sloan
Digital Sky Survey Data Release 10. We confirm that variations of absorption
lines are highly coordinated among different components of the same ion or the
same absorption component of different ions for C IV, Si IV and N V.
Furthermore, we show that the equivalent widths of the lines decrease or
increase statistically when the continuum brightens or dims. This is further
supported by the synchronized variations of emission and absorption line
equivalent width, when the well established intrinsic Baldwin effect for
emission lines is taken into account. We find that the emergence of an
absorption component is usually accompanying with dimming of the continuum
while the disappearance of an absorption line component with brightening of the
continuum. This suggests that the emergence or disappearance of a C IV
absorption component is only the extreme case, when the ionic column density is
very sensitive to continuum variations or the continuum variability amplitude
is larger. These results support the idea that absorption line variability is
driven mainly by changes in the gas ionization in response to continuum
variations, that the line-absorbing gas is highly ionized, and in some extreme
cases, too highly ionized to be detected in UV absorption lines. Due to
uncertainties in the spectroscopic flux calibration, we cannot quantify the
fraction of quasars with asynchronized continuum and absorption line
variations.Comment: 41 pages, 15 figures, accepted to Ap
Long Term Spectral Evolution of Tidal Disruption Candidates Selected by Strong Coronal Lines
We present results of follow-up optical spectroscopic observations of seven
rare, extreme coronal line emitting galaxies reported by Wang et al. (2012)
with Multi-Mirror Telescope (MMT). Large variations in coronal lines are found
in four objects, making them strong candidates of tidal disruption events
(TDE). For the four TDE candidates, all the coronal lines with ionization
status higher than [Fe VII] disappear within 5-9 years. The [Fe VII] faded by a
factor of about five in one object (J0952+2143) within 4 years, whereas emerged
in other two without them previously. A strong increment in the [O III] flux is
observed, shifting the line ratios towards the loci of active galactic nucleus
on the BPT diagrams. Surprisingly, we detect a non-canonical [O III]5007/[O
III]4959 2 in two objects, indicating a large column density of O and
thus probably optical thick gas. This also requires a very large ionization
parameter and relatively soft ionizing spectral energy distribution (e.g.
blackbody with K). Our observations can be explained as
echoing of a strong ultraviolet to soft X-ray flare caused by tidal disruption
events, on molecular clouds in the inner parsecs of the galactic nuclei.
Re-analyzing the SDSS spectra reveals double-peaked or strongly blue-shouldered
broad lines in three of the objects, which disappeared in the MMT spectra in
two objects, and faded by a factor of ten in 8 years in the remaining object
with a decrease in both the line width and centroid offset. We interpret these
broad lines as arising from decelerating biconical outflows. Our results
demonstrate that the signatures of echoing can persist for as long as ten
years, and can be used to probe the gas environment in the quiescent galactic
nuclei.Comment: 30 Pages, 10 Figures, 2 Tables, Accepted for Publication in Ap
Long Fading Mid-Infrared Emission in Transient Coronal Line Emitters: Dust Echo of Tidal Disruption Flare
The sporadic accretion following the tidal disruption of a star by a
super-massive black hole (TDE) leads to a bright UV and soft X-ray flare in the
galactic nucleus. The gas and dust surrounding the black hole responses to such
a flare with an echo in emission lines and infrared emission. In this paper, we
report the detection of long fading mid-IR emission lasting up to 14 years
after the flare in four TDE candidates with transient coronal lines using the
WISE public data release. We estimate that the reprocessed mid-IR luminosities
are in the range between and erg~s
and dust temperature in the range of 570-800K when WISE first detected these
sources three to five years after the flare. Both luminosity and dust
temperature decreases with time. We interpret the mid-IR emission as the
infrared echo of the tidal disruption flare. We estimate the UV luminosity at
the peak flare to be 1 to 30 times erg s and for warm dust
masses to be in the range of 0.05-1.3 Msun within a few parsecs. Our results
suggest that the mid-infrared echo is a general signature of TDE in the
gas-rich environment
Mid-infrared variability of changing-look AGN
It is known that some active galactic nuclei (AGNs) transited from type 1 to
type 2 or vice versa. There are two explanations for the so-called changing
look AGNs: one is the dramatic change of the obscuration along the
line-of-sight, the other is the variation of accretion rate. In this paper, we
report the detection of large amplitude variations in the mid-infrared
luminosity during the transitions in 10 changing look AGNs using WISE and newly
released NEOWISE-R data. The mid-infrared light curves of 10 objects echoes the
variability in the optical band with a time lag expected for dust reprocessing.
The large variability amplitude is inconsistent with the scenario of varying
obscuration, rather supports the scheme of dramatic change in the accretion
rate.Comment: Published by ApjL, 7 pages, 3 figures, 2 table
Discovery of An Active Intermediate-Mass Black Hole Candidate in the Barred Bulgeless Galaxy NGC 3319
We report the discovery of an active intermediate-mass black hole (IMBH)
candidate in the center of nearby barred bulgeless galaxy . The
point X-ray source revealed by archival Chandra and XMM-Newton observations is
spatially coincident with the optical and UV galactic nuclei from Hubble Space
Telescope observations. The spectral energy distribution derived from the
unresolved X-ray and UV-optical flux is comparable with active galactic nuclei
(AGNs) rather than ultra-luminous X-ray sources, although its bolometric
luminosity is only . Assuming an Eddington
ratio range between 0.001 and 1, the black hole mass (M_\rm{BH}) will be
located at , placing it in the so-called
IMBH regime and could be the one of the lowest reported so far. Estimates from
other approaches (e.g., fundamental plane, X-ray variability) also suggest
M_\rm{BH}\lesssim10^5~M_{\odot}.Similar to other BHs in bulgeless galaxies,
the discovered IMBH resides in a nuclear star cluster with mass of
. The detection of such a low-mass BH offers us an
ideal chance to study the formation and early growth of SMBH seeds, which may
result from the bar-driven inflow in late-type galaxies with a prominent bar
such as .Comment: ApJ accepted, 2 tables, 6 figure
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