We present the results of simultaneous multifrequency imaging observations at 22, 43, 86, and 129 GHz of OJ 287. We used the Korean Very Long Baseline Interferometry Network as part of the ...Interferometric Monitoring of Gamma-ray Bright active galactic nuclei (iMOGABA). The iMOGABA observations were performed during 31 epochs from 2013 January 16 to 2016 December 28. We also used 15 GHz OVRO and 225 GHz SMA flux density data. We analyzed four flux enhancements in the light curves. The estimated timescales of three flux enhancements were similar with timescales of ∼50 days at two frequencies. A fourth flux enhancement had a variability timescale approximately twice as long. We found that 225 GHz enhancements led the 15 GHz enhancements by a range of 7-30 days in the time delay analysis. We found the fractional variability did not change with frequency between 43 and 86 GHz. We could reliably measure the turnover frequency, , of the core of the source in three epochs. This was measured to be in a range from 27 to 50 GHz and a flux density at the turnover frequency, , ranging from 3 to 6 Jy. The derived SSA magnetic fields, , are in a range from 0.157 0.104 to 0.255 0.146 mG. We estimated the equipartition magnetic field strengths to be in a range from 0.95 0.15 to 1.93 0.30 mG. The equipartition magnetic field strengths are up to a factor of 10 higher than the values of . We conclude that the downstream jet may be more particle energy dominated.
The Photon Ring in M87 Broderick, Avery E.; Pesce, Dominic W.; Gold, Roman ...
The Astrophysical journal,
08/2022, Letnik:
935, Številka:
1
Journal Article
Recenzirano
Odprti dostop
Abstract
We report measurements of the gravitationally lensed secondary image—the first in an infinite series of so-called “photon rings”—around the supermassive black hole M87* via simultaneous ...modeling and imaging of the 2017 Event Horizon Telescope (EHT) observations. The inferred ring size remains constant across the seven days of the 2017 EHT observing campaign and is consistent with theoretical expectations, providing clear evidence that such measurements probe spacetime and a striking confirmation of the models underlying the first set of EHT results. The residual diffuse emission evolves on timescales comparable to one week. We are able to detect with high significance a southwestern extension consistent with that expected from the base of a jet that is rapidly rotating in the clockwise direction. This result adds further support to the identification of the jet in M87* with a black hole spin-driven outflow, launched via the Blandford–Znajek process. We present three revised estimates for the mass of M87* based on identifying the modeled thin ring component with the bright ringlike features seen in simulated images, one of which is only weakly sensitive to the astrophysics of the emission region. All three estimates agree with each other and previously reported values. Our strongest mass constraint combines information from both the ring and the diffuse emission region, which together imply a mass-to-distance ratio of
4.20
−
0.06
+
0.12
μ
as
and a corresponding black hole mass of (7.13 ± 0.39) × 10
9
M
⊙
, where the error on the latter is now dominated by the systematic uncertainty arising from the uncertain distance to M87*.
A Study of the Radio Spectrum of Mrk 421 Lee, Jee Won; Lee, Sang-Sung; Hodgson, Jeffrey ...
The Astrophysical journal,
04/2024, Letnik:
964, Številka:
2
Journal Article
Recenzirano
Odprti dostop
Abstract We present the results of a spectral analysis using simultaneous multifrequency (22, 43, 86, and 129 GHz) very long baseline interferometry (VLBI) observations of the Korean VLBI Network on ...BL Lac object, Markarian 421. The data we used were obtained from 2013 January to 2018 June. The light curves showed several flux enhancements with global decreases. To separate the variable and quiescent components in the multifrequency light curves for milliarcsecond-scale emission regions, we assumed that the quiescent radiation comes from the emission regions radiating constant optically thin synchrotron emissions (i.e., a minimum flux density with an optically thin spectral index). The quiescent spectrum determined from the multifrequency light curves was subtracted from the total CLEAN flux density, yielding a variable component in the flux that produces the time-dependent spectrum. We found that the observed spectra were flat at 22–43 GHz, and relatively steep at 43–86 GHz, whereas the quiescent-corrected spectra are sometimes quite different from the observed spectra (e.g., sometimes inverted at 22–43 GHz). The quiescent-corrected spectral indices were much more variable than the observed spectral indices. This spectral investigation implies that the quiescent-spectrum correction can significantly affect the multifrequency spectral index of variable compact radio sources such as blazars. Therefore, the synchrotron self-absorption B-field strength ( B SSA ) can be significantly affected because B SSA is proportional to the fifth power of turnover frequency.
Hepatitis C virus (HCV) is a major cause of liver cirrhosis and hepatocellular carcinoma. Here we report that infection of hepatic cells by HCV stimulates nuclear factor kappa B (NFκB)‐dependent ...production of thymic stromal lymphopoietin (TSLP). Hepatocyte‐derived TSLP in turn conditions dendritic cells (DCs) to drive T‐helper (Th)17 differentiation. The TSLP secreted by HCV‐infected hepatoma cells is capable of activating human monocyte‐derived DCs by up‐regulating the expression of CD40, CD86, CCL17, CCL22, and CCL20 which are activating markers of DCs. In addition, the production of key cytokines for Th17 differentiation, transforming growth factor beta (TGF‐β), interleukin (IL)‐6, and IL‐21, is enhanced by human monocytes upon coculture with HCV‐infected cells. Importantly, the blockade of TSLP using neutralizing antibody prevented the activation and maturation of DCs as well as the production of Th17 differentiation cytokines. DC conditioning by TSLP secreted from HCV‐infected cells activated naïve CD4+ T lymphocytes, resulting in Th17 differentiation. Furthermore, we can detect substantial levels of hepatocyte TSLP in fibrotic liver tissue from chronic HCV patients. Thus, blockade of TSLP released by HCV‐infected hepatocytes may suppress the induction/maintenance of hepatic Th17 responses and halt the progression of chronic liver disease to fibrosis and liver failure. Conclusion: Hepatocyte‐derived TSLP conditions DCs to drive Th17 differentiation. Treatment of TSLP neutralizing antibody in HCV‐infected hepatocyte/DC coculture abrogates DC conditioning and thereby inhibits Th17 differentiation. (HEPATOLOGY 2013)
Context. Very long baseline interferometry (VLBI) observations at 86 GHz (wavelength, λ = 3 mm) reach a resolution of about 50 μas, probing the collimation and acceleration regions of relativistic ...outflows in active galactic nuclei (AGN). The physical conditions in these regions can be studied by performing 86 GHz VLBI surveys of representative samples of compact extragalactic radio sources. Aims. To extend the statistical studies of compact extragalactic jets, a large global 86 GHz VLBI survey of 162 compact radio sources was conducted in 2010–2011 using the Global Millimeter VLBI Array (GMVA). Methods. The survey observations were made in a snapshot mode, with up to five scans per target spread over a range of hour angles in order to optimize the visibility coverage. The survey data attained a typical baseline sensitivity of 0.1 Jy and a typical image sensitivity of 5 mJy beam−1, providing successful detections and images for all of the survey targets. For 138 objects, the survey provides the first ever VLBI images made at 86 GHz. Gaussian model fitting of the visibility data was applied to represent the structure of the observed sources and to estimate the flux densities and sizes of distinct emitting regions (components) in their jets. These estimates were used for calculating the brightness temperature (Tb) at the jet base (core) and in one or more moving regions (jet components) downstream from the core. These model-fit-based estimates of Tb were compared to the estimates of brightness temperature limits made directly from the visibility data, demonstrating a good agreement between the two methods. Results. The apparent brightness temperature estimates for the jet cores in our sample range from 2.5 × 109 K to 1.3 × 1012 K, with the mean value of 1.8 × 1011 K. The apparent brightness temperature estimates for the inner jet components in our sample range from 7.0 × 107 K to 4.0 × 1011 K. A simple population model with a single intrinsic value of brightness temperature, T0, is applied to reproduce the observed distribution. It yields T0 = (3.77−0.14+0.10) × 1011 K T 0 = ( 3 . 77 − 0.14 + 0.10 ) × 10 11 K $ T_{\mathrm{0}} = (3.77^{+0.10}_{-0.14}) \times 10^{11} {\rm K} $ for the jet cores, implying that the inverse Compton losses dominate the emission. In the nearest jet components, T0 = (1.42−0.19+0.16) × 1011 K T 0 = ( 1 . 42 − 0.19 + 0.16 ) × 10 11 K $ T_{\mathrm{0}} = (1.42^{+0.16}_{-0.19}) \times 10^{11} {\rm K} $ is found, which is slightly higher than the equipartition limit of ∼5 × 1010 K expected for these jet regions. For objects with sufficient structural detail detected, the adiabatic energy losses are shown to dominate the observed changes of brightness temperature along the jet.
Chlorogenic acid is a polyphenol compound, derived from several fruit and plants. The aim of this study was to assess the in vitro antifungal activity of chlorogenic acid and its mode of action. The ...results indicate that chlorogenic acid exhibits antifungal activities against certain pathogenic fungi in an energy-independent manner, without any hemolytic effect on human erythrocytes. To elucidate the antifungal mode of action of chlorogenic acid, flow cytometry analysis by using DiBAC
(3) and changes in membrane dynamics using 1,6-diphenyl-1,3,5-hexatriene (DPH) were performed with
. The results suggest that chlorogenic acid may exert antifungal activity by disrupting the structure of the cell membrane. It is demonstrated that chlorogenic acid is a valid lead compound for the development of bioactive alternatives for treatment of fungal infections.
PKS 1510-089 is a bright and active γ-ray source that showed strong and complex γ-ray flares in mid-2015 during which the Major Atmospheric Gamma Imaging Cerenkov telescopes detected variable very ...high energy (photon energies >100 GeV) emission. We present long-term multifrequency radio, optical, and γ-ray light curves of PKS 1510-089 from 2013 to 2018, and results of an analysis of the jet kinematics and linear polarization using 43 GHz Very Long Baseline Array data observed between late 2015 and mid-2017. We find that a strong radio flare trails the γ-ray flares in 2015, showing an optically thick spectrum at the beginning and becoming optically thin over time. Two laterally separated knots of emission are observed to emerge from the radio core nearly simultaneously during the γ-ray flares. We detect an edge-brightened linear polarization near the core in the active jet state in 2016, similar to the quiescent jet state in 2008-2013. These observations indicate that the γ-ray flares may originate from compression of the knots by a standing shock in the core and the jet might consist of multiple complex layers showing time-dependent behavior, rather than of a simple structure of a fast jet spine and a slow jet sheath.
We study the kinematics of the M87 jet using the first-year data of the KVN and VERA Array (KaVA) large program, which has densely monitored the jet at 22 and 43 GHz since 2016. We find that the ...apparent jet speeds generally increase from 0.3c at 0.5 mas from the jet base to 2.7c at 20 mas, indicating that the jet is accelerated from subluminal to superluminal speeds on these scales. We perform a complementary jet kinematic analysis by using archival Very Long Baseline Array monitoring data observed in 2005-2009 at 1.7 GHz and find that the jet is moving at relativistic speeds up to 5.8c at distances of 200-410 mas. We combine the two kinematic results and find that the jet is gradually accelerated over a broad distance range that coincides with the jet collimation zone, implying that conversion of Poynting flux to kinetic energy flux takes place. If the jet emission consists of a single streamline, the observed trend of jet acceleration (Γ ∝ z0.16 0.01) is relatively slow compared to models of a highly magnetized jet. This indicates that Poynting flux conversion through the differential collimation of poloidal magnetic fields may be less efficient than expected. However, we find a nonnegligible dispersion in the observed speeds for a given jet distance, making it difficult to describe the jet velocity field with a single power-law acceleration function. We discuss the possibility that the jet emission consists of multiple streamlines following different acceleration profiles, resulting in jet velocity stratification.
Abstract
We present results from the first 22 GHz space very long baseline interferometric (VLBI) imaging observations of M87 by RadioAstron. As a part of the Nearby AGN Key Science Program, the ...source was observed in 2014 February at 22 GHz with 21 ground stations, reaching projected (
u
,
v
) spacings up to ∼11 G
λ
. The imaging experiment was complemented by snapshot RadioAstron data of M87 obtained during 2013–2016 from the AGN Survey Key Science Program. Their longest baselines extend up to ∼25 G
λ
. For all of these measurements, fringes are detected only up to ∼2.8 Earth diameter or ∼3 G
λ
baseline lengths, resulting in a new image with angular resolution of ∼150
μ
as or ∼20 Schwarzschild radii spatial resolution. The new image not only shows edge-brightened jet and counterjet structures down to submilliarcsecond scales but also clearly resolves the VLBI core region. While the overall size of the core is comparable to those reported in the literature, the ground-space fringe detection and slightly superresolved RadioAstron image suggest the presence of substructures in the nucleus, whose minimum brightness temperature exceeds
T
B
,
min
∼
10
12
K. It is challenging to explain the origin of this record-high
T
B
,
min
value for M87 by pure Doppler boosting effect with a simple conical jet geometry and known jet speed. Therefore, this can be evidence for more extreme Doppler boosting due to a blazar-like small jet viewing angle or highly efficient particle acceleration processes occurring already at the base of the outflow.
ABSTRACT Jets of compact radio sources are highly relativistic and Doppler boosted, making studies of their intrinsic properties difficult. Observed brightness temperatures can be used to study the ...intrinsic physical properties of relativistic jets, and constrain models of jet formation in the inner jet region. We aim to observationally test such inner jet models. The very long baseline interferometry (VLBI) cores of compact radio sources are optically thick at a given frequency. The distance of the core from the central engine is inversely proportional to the frequency. Under the equipartition condition between the magnetic field energy and particle energy densities, the absolute distance of the VLBI core can be predicted. We compiled the brightness temperatures of VLBI cores at various radio frequencies of 2, 8, 15, and 86 GHz. We derive the brightness temperature on sub-parsec scales in the rest frame of the compact radio sources. We find that the brightness temperature increases with increasing distance from the central engine, indicating that the intrinsic jet speed (the Lorentz factor) increases along the jet. This implies that the jets are accelerated in the (sub-)parsec regions from the central engine.
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