236 research outputs found
A self-lensing supermassive binary black hole at radio frequencies: the story of Spikey continues
The quasar J1918+4937 was recently suggested to harbour a
milliparsec-separation binary supermassive black hole (SMBH), based upon
modeling the narrow spike in its high-cadence Kepler optical light curve. Known
binary SMBHs are extremely rare, and the tight constraints on the physical and
geometric parameters of this object are unique. The high-resolution radio
images of J1918+4937 obtained with very long baseline interferometry (VLBI)
indicate a rich one-sided jet structure extending to 80 milliarcseconds. Here
we analyse simultaneously-made sensitive 1.7- and 5-GHz archive VLBI images as
well as snapshot 8.4/8.7-GHz VLBI images of J1918+4937, and show that the
appearance of the wiggled jet is consistent with the binary scenario. We
develop a jet structural model that handles eccentric orbits. By applying this
model to the measured VLBI component positions, we constrain the inclination of
the radio jet, as well as the spin angle of the jet emitter SMBH. We find the
jet morphological model is consistent with the optical and radio data, and that
the secondary SMBH is most likely the jetted one in the system. Furthermore,
the decade-long 15-GHz radio flux density monitoring data available for
J1918+4937 are compatible with a gradual overall decrease in the the total flux
density caused by a slow secular change of the jet inclination due to the
spin-orbit precession. J1918+4937 could be an efficient high-energy neutrino
source if the horizon of the secondary SMBH is rapidly rotating.Comment: 12 pages, 5 figures, 4 tables, accepted for publication in MNRA
Slowly rotating BoseâEinstein condensate compared with the rotation curves of 12 dwarf galaxies
Context. The high plateaus of the rotation curves of spiral galaxies suggest either that there is a dark component or that the Newtonian gravity requires modifications on galactic scales to explain the observations. We assemble a database of 12 dwarf galaxies, for which optical (R-band) and near-infrared (3.6âÎŒm) surface brightness density together with spectroscopic rotation curve data are available, in order to test the slowly rotating BoseâEinstein condensate (BEC) dark matter model.
Aims. We aim to establish the angular velocity range compatible with observations, bounded from above by the requirement of finite-size halos, to check the model fits with the dataset, and the universality of the BEC halo parameter â.
Methods. We constructed the spatial luminosity density of the stellar component of the dwarf galaxies based on their 3.6âÎŒm and R-band surface brightness profiles, assuming an axisymmetric baryonic mass distribution with arbitrary axis ratio. We built up the gaseous component of the mass by employing an inside-truncated disk model. We fitted a baryonic plus dark matter combined model, parametrized by the M/L ratios of the baryonic components and parameters of the slowly rotating BEC (the central density Ïc, size of the BEC halo â in the static limit, angular velocity Ï) to the rotation curve data.
Results. The 3.6âÎŒm surface brightness of six galaxies indicates the presence of a bulge and a disk component. The shape of the 3.6âÎŒm and R-band spatial mass density profiles being similar is consistent with the stellar mass of the galaxies emerging wavelength-independent. The slowly rotating BEC model fits the rotation curve of 11 galaxies out of 12 within the 1Ï significance level, with the average of â as 7.51 kpc and standard deviation of 2.96 kpc. This represents an improvement over the static BEC model fits, also discussed. For the 11 best-fitting galaxies the angular velocities allowing for a finite-size slowly rotating BEC halo are less then 2.2â
Ăâ
10â16 sâ1.For a scattering length of the BEC particle of aâââ106 fm, as allowed by terrestrial laboratory experiments, the mass of the BEC particle is slightly better constrained than in the static case as mâââ[1.26â
Ăâ
10â17â
Ă·â
3.08â
Ăâ
10â17] (eV câ2)
Dogs recognize dog and human emotions
The perception of emotional expressions allows animals to evaluate the social intentions and motivations of each other. This usually takes place within species; however, in the case of domestic dogs, it might be advantageous to recognize the emotions of humans as well as other dogs. In this sense, the combination of visual and auditory cues to categorize others' emotions facilitates the information processing and indicates high-level cognitive representations. Using a cross-modal preferential looking paradigm, we presented dogs with either human or dog faces with different emotional valences (happy/playful versus angry/aggressive) paired with a single vocalization from the same individual with either a positive or negative valence or Brownian noise. Dogs looked significantly longer at the face whose expression was congruent to the valence of vocalization, for both conspecifics and heterospecifics, an ability previously known only in humans. These results demonstrate that dogs can extract and integrate bimodal sensory emotional information, and discriminate between positive and negative emotions from both humans and dogs
Cosmic neutrinos from temporarily gamma-suppressed blazars
Despite the uncovered association of a high-energy neutrino with the apparent
flaring state of blazar TXS 0506+056 in 2017, the mechanisms leading to
astrophysical particle acceleration and neutrino production are still
uncertain. Recent studies found that when transparent to -rays,
-flaring blazars do not have the opacity for protons to produce
neutrinos. Here we present observational evidence for an alternative
explanation, in which -ray emission is suppressed during efficient
neutrino production. A large proton and target photon density help produce
neutrinos while temporarily suppress the observable -emission due to a
large opacity. We show that the Fermi-LAT -flux of
blazar PKS 1502+106 was at a local minimum when IceCube recorded the coincident
high-energy neutrino IC-190730A. Using data from the OVRO 40-meter Telescope,
we find that radio emission from PKS 1502+106 at the time period of the
coincident neutrino IC-190730A was in a high state, in contrast to earlier time
periods when radio and fluxes are correlated for both low and high
states. This points to an active outflow that is -suppressed at the
time of neutrino production. We find similar local -suppression in
other blazars, including in MAGIC's TeV flux of TXS\,0506+056 and Fermi-LAT's
flux of blazar PKS B1424-418 at the time of coincident IceCube neutrino
detections. Using temporary -suppression, neutrino-blazar coincidence
searches could be substantially more sensitive than previously assumed,
enabling the identification of the origin of IceCube's diffuse neutrino flux
possibly with already existing data.Comment: 8 pages, 3 figures, accepted to ApJ Letter
Multiple AGN in the crowded field of the compact group SDSSJ0959+1259
We present a multi-wavelength study of a newly discovered compact group (CG),
SDSS J0959+1259, based data from XMM-Newton, SDSS and the Calar Alto optical
imager BUSCA. With a maximum velocity offset of 500 km s, a mean
redshift of 0.035, and a mean spatial extension of 480 kpc, this CG is
exceptional in having the highest concentration of nuclear activity in the
local Universe, established with a sensitivity limit L10
erg s in 2--10 keV band and R-band magnitude . The group is
composed of two type-2 Seyferts, one type-1 Seyfert, two LINERs and three star
forming galaxies. Given the high X-ray luminosity of LINERs which reaches erg s, it is likely that they are also accretion driven,
bringing the number of active nuclei in this group to to 5 out of 8 (AGN
fraction of 60\%). The distorted shape of one member of the CG suggests that
strong interactions are taking place among its galaxies through tidal forces.
Therefore, this system represents a case study for physical mechanisms that
trigger nuclear activity and star formation in CGs.Comment: 8 pages, 4 figures and 4 tables. Accepted for publication in MNRA
Precession-induced Variability in AGN Jets and OJ 287
The combined study of the flaring of Active Galactic Nuclei (AGN) at radio
wavelengths and pc-scale jet kinematics with Very Long Baseline Interferometry
(VLBI) has led to the view that i) the observed flares are associated with
ejections of synchrotron blobs from the core, and ii) most of the flaring would
follow a one-to-one correlation with the component ejection. Recent results
have provided mounting evidence that the quasi-regular component injections
into the relativistic jet may not be the only cause of the flux variability. We
propose that AGN flux variability and jet morphology changes can both be of
deterministic nature, i.e. having a geometric/kinetic origin linked to the
time-variable Doppler beaming of the jet emission as its direction changes due
to precession (and nutation). The physics of the underlying jet leads to
shocks, instabilities, or to ejections of plasmoids. The appearance
(morphology, flux, etc.) of the jet can, however, be strongly affected and
modulated by precession. We demonstrate this modulating power of precession for
OJ 287. For the first time, we show that the spectral state of the Spectral
Energy Distribution (SED) can be directly related to the jet's precession
phase. We model the SED evolution and reproduce the precession parameters.
Further, we apply our precession model to eleven prominent AGN. We show that
for OJ 287 precession seems to dominate the long-term variability () of the AGN flux, SED spectral state, and jet morphology, while
stochastic processes affect the variability on short timescales ().Comment: 48 pages, 26 figures, 14 tables; published in the Astrophysical
Journa
Dark Matter as a Non-Relativistic Bose-Einstein Condensate with Massive Gravitons
We confront a non-relativistic Bose-Einstein Condensate (BEC) model of light bosons interacting gravitationally either through a Newtonian or a Yukawa potential with the observed rotational curves of 12 dwarf galaxies. The baryonic component is modeled as an axisymmetric exponential disk and its characteristics are derived from the surface luminosity profile of the galaxies. The purely baryonic fit is unsatisfactory, hence a dark matter component is clearly needed. The rotational curves of five galaxies could be explained with high confidence level by the BEC model. For these galaxies, we derive: (i) upper limits for the allowed graviton mass; and (ii) constraints on a velocity-type and a density-type quantity characterizing the BEC, both being expressed in terms of the BEC particle mass, scattering length and chemical potential. The upper limit for the graviton mass is of the order of 10(-26) eV/c(2), three orders of magnitude stronger than the limit derived from recent gravitational wave detections
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