27 research outputs found
Accretion-modified Stars in Accretion Disks of Active Galactic Nuclei: the Low-luminosity Cases and an Application to Sgr A\!^{*}
In this paper, we investigate the astrophysical processes of stellar-mass
black holes (sMBHs) embedded in advection-dominated accretion flows (ADAFs) of
supermassive black holes (SMBHs) in low-luminosity active galactic nuclei
(AGNs). The sMBH is undergoing Bondi accretion at a rate lower than the SMBH.
Outflows from the sMBH-ADAF dynamically interact with their surroundings and
form a cavity inside the SMBH-ADAF, thereby quenching the accretion onto the
SMBH. Rejuvenation of the Bondi accretion is rapidly done by turbulence. These
processes give rise to quasi-periodic episodes of sMBH activities and create
flickerings from relativistic jets developed by the Blandford-Znajek mechanism
if the sMBH is maximally rotating. Accumulating successive sMBH-outflows
trigger viscous instability of the SMBH-ADAF, leading to a flare following a
series of flickerings. Recently, the similarity of near-infrared flare's orbits
has been found by GRAVITY/VLTI astrometric observations of Sgr A\!^{*}: their
loci during the last 4-years consist of a ring in agreement with the
well-determined SMBH mass. We apply the present model to Sgr A\!^{*}, which
shows quasi-periodic flickerings. A SMBHH of is preferred
orbiting around the central SMBH of Sgr A\!^{*} from fitting radio to X-ray
continuum. Such an extreme mass ratio inspiraling (EMRI) provides an excellent
laboratory for LISA, Taiji and Tianqin detection of mHz gravitational waves
with strains of , as well as their polarization.Comment: 16 pages, 3 figures, accepted by ApJ
Star Formation in Self-gravitating Disks in Active Galactic Nuclei. III. Efficient Production of Iron and Infrared Spectral Energy Distributions
Strong iron lines are a common feature of the optical spectra of active
galactic nuclei (AGNs) and quasars from to the local Universe, and
[Fe/Mg] ratios do not show cosmic evolution. During active episodes, accretion
disks surrounding supermassive black holes (SMBHs) inevitably form stars in the
self-gravitating part and these stars accrete with high accretion rates. In
this paper, we investigate the population evolution of accretion-modified stars
(AMSs) to produce irons and magnesium in AGNs. The AMSs as a new type of stars
are allowed to have any metallicity but without significant loss from stellar
winds since the winds are choked by the dense medium of the disks and return to
the core stars. Mass functions of the AMS population show a pile-up or cutoff
pile-up shape in top-heavy or top-dominant forms if the stellar winds are
strong, consistent with the narrow range of supernovae (SN) explosions driven
by the known pair-instability. This provides an efficient way to produce
metals. Meanwhile, SN explosions support an inflated disk as a dusty torus.
Furthermore, the evolving top-heavy initial mass functions (IMFs) lead to
bright luminosity in infrared bands in dusty regions. This contributes a new
component in infrared bands which is independent of the emissions from the
central part of accretion disks, appearing as a long-term trending of the NIR
continuum compared to optical variations. Moreover, the model can be further
tested through reverberation mapping of emission lines, including LIGO/LISA
detections of gravitational waves and signatures from spatially resolved
observations of GRAVITY+/VLTI.Comment: 35 pages, 22 figure
Supermassive black holes with high accretion rates in active galactic nuclei. XIII. Ultraviolet time lag of Hβ emission in Mrk 142
Funding: We acknowledge the support of the Natural Sciences and Engineering Research Council of Canada (NSERC), Discovery Grant RGPIN/04157. V.C.K. acknowledges the support of the Ontario Graduate Scholarships. C.H. acknowledges support from the National Science Foundation of China (12122305). The research of V.C.K. was partially supported by the New Technologies for Canadian Observatories, an NSERC CREATE program.We performed a rigorous reverberation-mapping analysis of the broad-line region (BLR) in a highly accreting (L/LEdd = 0.74–3.4) active galactic nucleus, Markarian 142 (Mrk 142), for the first time using concurrent observations of the inner accretion disk and the BLR to determine a time lag for the Hβ λ4861 emission relative to the ultraviolet (UV) continuum variations. We used continuum data taken with the Niel Gehrels Swift Observatory in the UVW2 band, and the Las Cumbres Observatory, Dan Zowada Memorial Observatory, and Liverpool Telescope in the g band, as part of the broader Mrk 142 multi-wavelength monitoring campaign in 2019. We obtained new spectroscopic observations covering the Hβ broad emission line in the optical from the Gemini North Telescope and the Lijiang 2.4-meter Telescope for a total of 102 epochs (over a period of eight months) contemporaneous to the continuum data. Our primary result states a UV-to-Hβ time lag of 8.68+0.75−0.72 days in Mrk 142 obtained from light-curve analysis with a Python-based Running Optimal Average algorithm. We placed our new measurements for Mrk 142 on the optical and UV radius-luminosity relations for NGC 5548 to understand the nature of the continuum driver. The positions of Mrk 142 on the scaling relations suggest that UV is closer to the “true” driving continuum than the optical. Furthermore, we obtain log(M•/M⊙) = 6.32 ± 0.29 assuming UV as the primary driving continuum.Publisher PDFPeer reviewe
Supermassive Black Holes with High Accretion Rates in Active Galactic Nuclei. XIII. Ultraviolet Time Lag of H Emission in Mrk 142
We performed a rigorous reverberation-mapping analysis of the broad-line
region (BLR) in a highly accreting () active
galactic nucleus, Markarian 142 (Mrk 142), for the first time using concurrent
observations of the inner accretion disk and the BLR to determine a time lag
for the 4861 emission relative to the ultraviolet
(UV) continuum variations. We used continuum data taken with the Niel Gehrels
Swift Observatory in the UVW2 band, and the Las Cumbres Observatory, Dan Zowada
Memorial Observatory, and Liverpool Telescope in the g band, as part of the
broader Mrk 142 multi-wavelength monitoring campaign in 2019. We obtained new
spectroscopic observations covering the broad emission line in the
optical from the Gemini North Telescope and the Lijiang 2.4-meter Telescope for
a total of 102 epochs (over a period of eight months) contemporaneous to the
continuum data. Our primary result states a UV-to- time lag of
days in Mrk 142 obtained from light-curve analysis with
a Python-based Running Optimal Average algorithm. We placed our new
measurements for Mrk 142 on the optical and UV radius-luminosity relations for
NGC 5548 to understand the nature of the continuum driver. The positions of Mrk
142 on the scaling relations suggest that UV is closer to the "true" driving
continuum than the optical. Furthermore, we obtain assuming UV as the primary driving continuum.Comment: 35 pages, 12 figures, 11 tables, accepted for publication in Ap
A Two Micron Coherent Differential Absorption Lidar Development
A pulsed, 2-micron coherent Differential Absorption Lidar (DIAL)/Integrated Path Differential Absorption (IPDA) transceiver, developed under the Laser Risk Reduction Program (LRRP) at NASA, is integrated into a fully functional lidar instrument. This instrument measures atmospheric CO2 profiles (by DIAL) from a ground platform. It allows the investigators to pursue subsequent in science-driven deployments, and provides a unique tool for Active Sensing of CO2 Emissions over Night, Days, and Seasons (ASCENDS) validation that was strongly advocated in the recent ASCENDS Workshop. Keywords: Differential Absorption Lidar, Near Infrared Laser
Cosmology intertwined: A review of the particle physics, astrophysics, and cosmology associated with the cosmological tensions and anomalies
The standard Cold Dark Matter (CDM) cosmological model provides a good description of a wide range of astrophysical and cosmological data. However, there are a few big open questions that make the standard model look like an approximation to a more realistic scenario yet to be found. In this paper, we list a few important goals that need to be addressed in the next decade, taking into account the current discordances between the different cosmological probes, such as the disagreement in the value of the Hubble constant H0, the σ8–S8 tension, and other less statistically significant anomalies. While these discordances can still be in part the result of systematic errors, their persistence after several years of accurate analysis strongly hints at cracks in the standard cosmological scenario and the necessity for new physics or generalisations beyond the standard model. In this paper, we focus on the 5.0 σ tension between the Planck CMB estimate of the Hubble constant H0 and the SH0ES collaboration measurements. After showing the H0 evaluations made from different teams using different methods and geometric calibrations, we list a few interesting new physics models that could alleviate this tension and discuss how the next decade’s experiments will be crucial. Moreover, we focus on the tension of the Planck CMB data with weak lensing measurements and redshift surveys, about the value of the matter energy density m, and the amplitude or rate of the growth of structure (σ8, f σ8). We list a few interesting models proposed for alleviating this tension, and we discuss the importance of trying to fit a full array of data with a single model and not just one parameter at a time. Additionally, we present a wide range of other less discussed anomalies at a statistical significance level lower than the H0–S8 tensions which may also constitute hints towards new physics, and we discuss possible generic theoretical approaches that can collectively explain the non-standard nature of these signals. Finally, we give an overview of upgraded experiments and next-generation space missions and facilities on Earth that will be of crucial importance to address all these open questions
The impact and effectiveness of faculty development program in fostering the faculty’s knowledge, skills, and professional competence: A systematic review and meta-analysis
Background: Faculty vitality is the main ingredient to enhance professional education and competence. Enriching the faculty vitality in key domains of teaching, assessing, research, professionalism, and administration is perceived to improve educational environment significantly and enhances the academic performance of learners. Faculty development program (FDP) has been considered as a stand-alone educational pedagogy in fostering knowledge and professional skills of faculty. However, few studies have provided objective reports about the impact of such programs in a healthcare system. Methods: This research was conducted by selecting data sources of PubMed-Medline, Wiley online library, Cochrane library, Taylor & Francis Online, CINAHL, Springer link, Proquest, ISI Web of knowledge, ScienceDirect, EJS, EBSCO, Blackwell, Emerald and ABI Inform. This search followed a step-wise approach defined by the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA). A total of 37 studies that explored the impact of FDPs on medical and allied health faculty’s professional development were selected. Results: This meta-analysis reported a mean effect size of 0.73 that reflects a significant and positive impact of FDPs in enhancing faculty’s knowledge and professional competence (z-statistics of 4.46 significant at p-value < 0.05) using the random effects model and forest plot. Conclusion: This article reiterates the incorporation of FDPs in all healthcare institutions for improving the academic performance of faculty with resultant enrichment of learners’ knowledge and skills. Keywords: Faculty, Medical and allied health faculty, Faculty development program, Healthcare institutions, Personal developmen