We present a census of sub-pc scale properties of the very long baseline interferometry (VLBI) cores in a complete sample of local Seyfert galaxies. Out of 23 sources with a Very Large Array (VLA) ...detection, 17 are detected also with VLBI at 1.7 GHz and/or 5 GHz, with an average monochromatic radio luminosity logP
5 GHz/W Hz−1 = 19.4. Radio cores are of heterogeneous nature, the majority of them showing elongated structures or accompanied by extra components, broad ranges of brightness temperatures (105-1010 K) and spectral indices (from steep to highly inverted). Interestingly, the detection rate (26 per cent) of water maser emission is considerably higher than that found in previous surveys (∼10 per cent), suggesting that distance biases could significantly affect our knowledge of the actual occurrence of this phenomenon. The VLBI observational properties of type 1 and type 2 nuclei are similar except for the T
B, which is on average higher in type 1. These results suggest that both thermal and non-thermal emission are common in low-luminosity active galactic nuclei, with a prevalence of free-free processes among type 2 cores, likely associated with molecular gas. Though limited by the low-number statistics, we find no significant correlation between the VLBI radio luminosity and the nuclear X-ray luminosity; the latter appears to be more connected to the tens of pc scale VLA radio emission, rather than to the sub-pc scales, particularly in the most X-ray luminous sources. The X-ray radio loudness parameter R
X ≡ L (6 cm)/L(2-10 keV) is on average very low (〈log R
X〉 = −4.8), with comparatively higher R
X found for sources with the largest black hole masses and the lowest Eddington ratios, although the radio power does not appear to depend on the accretion rate.
In this Letter, we report on dual-frequency European VLBI Network observations of the faintest and least luminous radio cores in Seyfert nuclei, going to sub-millijansky flux densities and radio ...luminosities around 10{sup 19} W Hz{sup -1}. We detect radio emission from the nuclear region of four galaxies (NGC 4051, NGC 4388, NGC 4501, and NGC 5033), while one (NGC 5273) is undetected at the level of approx100 muJy. The detected compact nuclei have rather different radio properties: spectral indices range from steep (alpha>0.7) to slightly inverted (alpha = -0.1), brightness temperatures vary from T{sub B} = 10{sup 5} K to larger than 10{sup 7} K, and cores are either extended or unresolved, in one case accompanied by lobe-like features (NGC 4051). In this sense, diverse underlying physical mechanisms can be at work in these objects: jet-base or outflow solutions are the most natural explanations in several cases; in the case of the undetected NGC 5273 nucleus, the presence of an advection-dominated accretion flow is consistent with the radio luminosity upper limit.
We investigated the detailed inner jet structure of M87 using Very Long Baseline Array data at 2, 5, 8.4, 15, 23.8, 43, and 86 GHz, especially focusing on the multi-frequency properties of the radio ...core at the jet base. First, we measured the size of the core region transverse to the jet axis, defined as W sub(c), at each frequency nu, and found a relation between W sub(c) and nu: W sub(c)(nu) alpha nu super(-0.71 + or - 0.05). Then, by combining W sub(c)(nu) and the frequency dependence of the core position r sub(c)(nu), which was obtained in our previous study, we constructed a collimation profile of the innermost jet W sub(c)(r) down to ~10 Schwarzschild radii (R sub(s)) from the central black hole. We found that W sub(c)(r) smoothly connects with the width profile of the outer edge-brightened, parabolic jet and then follows a similar radial dependence down to several tens of R sub(s). Closer to the black hole, the measured radial profile suggests a possible change in the jet collimation shape from the outer parabolic one, where the jet shape tends to become more radially oriented. This result could be related to a magnetic collimation process or/and interactions with surrounding materials at the jet base. The present results shed light on the importance of higher-sensitivity/resolution imaging studies of M87 at 86, 43, and 22 GHz; these studies should be examined more rigorously.
ABSTRACT We report on results from new high-sensitivity, high-resolution 86 GHz (3.5 mm) observations of the jet base in the nearby radio galaxy M87, obtained by the Very Long Baseline Array in ...conjunction with the Green Bank Telescope. The resulting image has a dynamic range exceeding 1500 to 1, the highest ever achieved for this jet at this frequency, resolving and imaging a detailed jet formation/collimation structure down to ∼10 Schwarzschild radii ( ). The obtained 86 GHz image clearly confirms some important jet features known at lower frequencies, i.e., a jet base with a wide opening angle, a limb-brightened intensity profile, a parabola-shape collimation profile and a counter jet. The limb-brightened structure is already well developed at mas ( , projected) from the core, where the corresponding apparent opening angle becomes as wide as ∼100°. The subsequent jet collimation near the black hole evolves in a complicated manner; there is a "constricted" structure at tens of from the core, where the jet cross section is locally shrinking. We suggest that external pressure support from the inner part of the radiatively inefficient accretion flow may be dynamically important in shaping/confining the footprint of the magnetized jet. We also present the first 86 GHz polarimetric experiment using very long baseline interferometry for this source, where a highly polarized (∼20%) feature is detected near the jet base, indicating the presence of a well-ordered magnetic field. As a by-product, we additionally report a 43/86 GHz polarimetric result for our calibrator 3C 273, suggesting an extreme rotation measure near the core.
We investigated the detailed radio structure of the jet of 1H 0323+342 using high-resolution multifrequency Very Long Baseline Array observations. This source is known as the nearest γ-ray emitting ...radio-loud narrow-line Seyfert 1 (NLS1) galaxy. We discovered that the morphology of the inner jet is well characterized by a parabolic shape, indicating that the jet is continuously collimated near the jet base. On the other hand, we found that the jet expands more rapidly at larger scales, resulting in a conical shape. The location of the "collimation break" is coincident with a bright quasi-stationary feature at 7 mas from core (corresponding to a deprojected distance on the order of ∼100 pc), where the jet width locally contracts together with highly polarized signals, suggesting a recollimation shock. We found that the collimation region is coincident with the region where the jet speed gradually accelerates, suggesting a coexistence of the jet acceleration and collimation zone, ending up with the recollimation shock, which could be a potential site of high-energy γ-ray flares detected by the Fermi-LAT. Remarkably, these observational features of the 1H 0323+342 jet are overall very similar to those of the nearby radio galaxy M87 and HST-1 as well as some blazars, suggesting that a common jet formation mechanism might be at work. Based on the similarity of the jet profile of the two sources, we also briefly discuss the mass of the central black hole of 1H 0323+342, which is also still highly controversial in this source and NLS1s in general.
Parabolic Jets from the Spinning Black Hole in M87 Nakamura, Masanori; Asada, Keiichi; Hada, Kazuhiro ...
Astrophysical journal/The Astrophysical journal,
12/2018, Letnik:
868, Številka:
2
Journal Article
Recenzirano
Odprti dostop
The M87 jet is extensively examined by utilizing general relativistic magnetohydrodynamic (GRMHD) simulations, as well as the steady axisymmetric force-free electrodynamic (FFE) solution. ...Quasi-steady funnel jets are obtained in GRMHD simulations up to the scale of ∼100 gravitational radii (rg) for various black hole (BH) spins. As is known, the funnel edge is approximately determined by the following equipartitions: (i) the magnetic and rest-mass energy densities and (ii) the gas and magnetic pressures. Our numerical results give an additional factor that they follow the outermost parabolic streamline of the FFE solution, which is anchored to the event horizon on the equatorial plane. We also show that the matter-dominated, nonrelativistic corona/wind plays a dynamical role in shaping the funnel jet into the parabolic geometry. We confirm a quantitative overlap between the outermost parabolic streamline of the FFE jet and the edge of the jet sheath in very long baseline interferometry (VLBI) observations at ∼(101-105)rg, suggesting that the M87 jet is likely powered by the spinning BH. Our GRMHD simulations also indicate a lateral stratification of the bulk acceleration (i.e., the spine-sheath structure), as well as an emergence of knotty superluminal features. The spin characterizes the location of the jet stagnation surface inside the funnel. We suggest that the limb-brightened feature could be associated with the nature of the BH-driven jet, if the Doppler beaming is a dominant factor. Our findings can be examined with (sub)millimeter VLBI observations, giving a clue for the origin of the M87 jet.
Abstract
We monitored the position of the close-by (about 370 Mpc) gamma-ray burst GRB 190829A, which originated from a massive star collapse, through very long baseline interferometry (VLBI) ...observations with the European VLBI Network and the Very Long Baseline Array, carrying out a total of nine observations between 9 and 117 days after the gamma-ray burst at 5 and 15 GHz, with a typical resolution of a few milliarcseconds. From a state-of-the art analysis of these data, we obtained valuable limits on the source size and expansion rate. The limits are in agreement with the size evolution entailed by a detailed modeling of the multiwavelength light curves with a forward-plus-reverse shock model, which agrees with the observations across almost 18 orders of magnitude in frequency (including the HESS data at TeV photon energies) and more than 4 orders of magnitude in time. Thanks to the multiwavelength, high-cadence coverage of the afterglow, inherent degeneracies in the afterglow model are broken to a large extent, allowing us to capture some unique physical insights; we find a low prompt emission efficiency of ≲10
−3
, a low fraction of relativistic electrons in the forward shock downstream
χ
e
< 13% (90% credible level), and a rapid decay of the magnetic field in the reverse shock downstream after the shock crossing. While our model assumes an on-axis jet, our VLBI astrometry is not sufficiently tight as to exclude any off-axis viewing angle, but we can exclude the line of sight to have been more than ∼2° away from the border of the gamma-ray-producing region based on compactness arguments.
Abstract
We report multiepoch very long baseline interferometric observations of the compact radio lobe in the radio galaxy 3C 84 (NGC 1275) during 2016–2020. The image sequence of 3C 84 reveals that ...the hotspot in the radio lobe showed the 1 year long frustration in 2017 within a compact region of about 0.07 pc, suggesting a strong collision between the jet and a compact dense cloud with an estimated average density of about (4–6) × 10
5
cm
−3
. Although the hotspot and the radio lobe began to move south again after its breakout, the radio lobe showed a morphological transition from an FR II- to FR I-class radio lobe and its radio flux became fainter. This is the first detection of the dynamical feedback from the cloud to the jet where the cloud located on the jet axis significantly interferes with the jet propagation and evolution at the central 1 pc region in the active galactic nucleus.
Abstract
The linear polarization images of the jet in the giant elliptical galaxy M87 have previously been observed with Very Long Baseline Array at 7 mm. They exhibit a complex polarization ...structure surrounding the optically thick and compact subparsec-scale core. However, given the low level of linear polarization in the core, it is required to verify that this complex structure does not originate from residual instrumental polarization signals in the data. We have performed a new analysis of the same data sets observed in four epochs by using the Generalized Polarization CALibration pipeline (GPCAL). This novel instrumental polarization calibration pipeline overcomes the limitations of LPCAL, a conventional calibration tool used in the previous M87 studies. The resulting images show a compact linear polarization structure with its peak nearly coincident with the total intensity peak, which is significantly different from the results of previous studies. The core linear polarization is characterized as fractional polarization of ∼0.2%–0.6% and polarization angles of ∼66°–92°, showing moderate variability. We demonstrate that, based on tests with synthetic data sets, LPCAL using calibrators having complex polarization structures cannot achieve sufficient calibration accuracy to obtain the true polarization image of M87 due to a breakdown of the “similarity approximation.” We find that GPCAL obtains more accurate D-terms than LPCAL by using observed closure traces of calibrators that are insensitive to both antenna gain and polarization leakage corruptions. This study suggests that polarization imaging of very weakly polarized sources has become possible with the advanced instrumental polarization calibration techniques.
In this paper, we describe the first multi-frequency synthesis observations of blazar 0059+581 made with the Radioastron spaceground interferometer in conjunction with the Korean VLBI Network (KVN), ...Medicina and Torun ground telescopes. We conducted these observations to assess the spaceground interferometer multi-frequency mode capability for the first time.
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