Apparent Transverse Velocity Research Articles

Mildly relativistic motion in the radio-quiet quasar PG 1351+640

ABSTRACT Measuring the proper motion of the emission component in radio-quiet quasars (RQQs) could help to distinguish between the origins of the radio emission and to understand whether the jet production mechanism is the same in radio-loud quasars and RQQs. PG 1351+640 is one of the few RQQs suitable for proper motion studies: it has two compact components on milli-arcsec scales, a flat-spectrum core and a steep-spectrum jet; both components are ≳2 mJy at 5 GHz and are well suited for Very Long Baseline Array (VLBA) observations. We compare recent VLBA observations with that made seventeen years ago and find no significant change in the core-jet separation between 2005 and 2015 (a proper motion of 0.003 mas yr−1). However, the core-jet separation increased significantly between 2015 and 2022, inferring a jet proper motion velocity of 0.063 mas yr−1, which corresponds to an apparent transverse velocity of $0.37\, c$ . The result suggests that the jet of the RQQ PG 1351+640 is mildly relativistic and oriented at a relatively small viewing angle.

Flare-induced Sunquake Signatures in the Ultraviolet as Observed by the Atmospheric Imaging Assembly

Abstract Sunquakes (SQs) have been routinely observed in the solar photosphere, but it is only recently that signatures of these events have been detected in the chromosphere. We investigate whether signatures of SQs are common in ultraviolet (UV) continua that sample the solar plasma several hundred km above where SQs are typically detected. We analyze observations from the Solar Dynamics Observatory’s Atmospheric Imaging Assembly (SDO/AIA) 1600 and 1700 Å passbands, for SQ signatures induced by the flares of Solar Cycle 24. We base our analysis on the 62 SQs detected in the recent statistical study presented by Sharykin & Kosovichev. We find that 9 out of 62 SQ candidates produced a response that is clearly detected in running-difference images from the AIA 1600 and 1700 Å channels. A binary frequency filter with a width of 2 mHz, centered on 6 mHz, was applied to the data. The first signature of each SQ was detected at distances between 5.2 and 25.7 Mm from the associated flare ribbon. Time–distance and regression analysis allowed us to calculate the apparent transverse velocities of the SQs in the UV data sets and found maximum velocities as high as 41 km s−1, 87 Mm away from the SQ source. Our analysis shows that flare-induced SQ signatures can be detected in the SDO/AIA 1600 and 1700 Å passbands, hinting at their presence in the lower chromosphere. There was no apparent correlation between GOES flare classification and the appearance of the SQ at these heights.

Scintillation Can Explain the Spectral Structure of the Bright Radio Burst from SGR 1935+2154

Abstract The discovery of a fast radio burst (FRB) associated with a magnetar in the Milky Way by the Canadian Hydrogen Intensity Mapping Experiment FRB collaboration (CHIME/FRB) and the Survey for Transient Astronomical Radio Emission 2 has provided an unprecedented opportunity to refine FRB emission models. The burst discovered by CHIME/FRB shows two components with different spectra. We explore interstellar scintillation as the origin for this variation in spectral structure. Modeling a weak scattering screen in the supernova remnant associated with the magnetar, we find that a superluminal apparent transverse velocity of the emission region of >9.5c is needed to explain the spectral variation. Alternatively, the two components could have originated from independent emission regions >8.3 × 104 km apart. These scenarios may arise in “far-away” models where the emission originates from well beyond the magnetosphere of the magnetar (for example, through a synchrotron maser mechanism set up by an ultrarelativistic radiative shock), but not in “close-in” models of emission from within the magnetosphere. If further radio observations of the magnetar confirm scintillation as the source of the observed variation in spectral structure, this scattering model thus constrains the location of the emission region.

Classical spectral sum rules and “half-naked” electron effects in radiation from relativistic electrons in external field

Two properties of the radiation emitted by a relativistic electron in an external field, in the classical approximation, are presented in details: 1) spectral sum rules and their relationship with the sum rules for oscillator strengths in atomic physics. Filtered sum rules can be used to remove infrared or ultraviolet divergences. 2) “half-naked electron” effects like the Landau-Pomeranchuk-Migdal and Ternovskij-Shul'ga-Fomin effects. These properties are best understood when introducing the apparent transverse velocity.

The Chromospheric Response to the Sunquake Generated by the X9.3 Flare of NOAA 12673

Abstract Active region NOAA 12673 was extremely volatile in 2017 September, producing many solar flares, including the largest of solar cycle 24, an X9.3 flare of 2017 September 06. It has been reported that this flare produced a number of sunquakes along the flare ribbon. We have used cotemporal and cospatial Helioseismic and Magnetic Imager (HMI) line of sight (LOS) and Swedish 1 m Solar Telescope (SST) observations to show evidence of the chromospheric response to these sunquakes. Analysis of the Ca ii 8542 Å line profiles of the wavefronts revealed that the crests produced a strong blue asymmetry, whereas the troughs produced at most a very slight red asymmetry. We used the combined HMI, SST data sets to create time–distance diagrams and derive the apparent transverse velocity and acceleration of the response. These velocities ranged from 4.5 to 29.5 km s−1 with a constant acceleration of 8.6 × 10−3 km s−2. We employed NICOLE inversions, in addition to the center-of-gravity method to derive LOS velocities ranging from 2.4 km s−1–3.2 km s−1. Both techniques show that the crests are created by upflows. We believe that this is the first chromospheric signature of a flare induced sunquake.

Photon Doppler velocimetry measurements of transverse surface velocities.

The goal of this work was to develop a technique for making transverse surface velocity measures utilizing Photon Doppler Velocimetry (PDV). Such a task is achieved by transmitting light and collecting Doppler-shifted light at an angle relative to the normal axis, where measured velocities are representative of a component of the transverse velocity. Because surface characteristics have an intrinsic effect on light scatter, different surface preparations were explored to direct reflectivity, including diffusion by means of sandpapering, or increasing retroreflectivity by coating with microspheres, milling v-cuts, and electrochemically etching grooves. Testing of these surface preparations was performed using an experiment featuring a 30 mm diameter aluminum disk rotating at 6000 or 6600 RPM. A single PDV collimator was positioned along the rotational axis of the disk at various angles, resolving the apparent transverse velocity. To characterize surface preparations, light return and velocities were recorded as a function of probe angle ranging from 0° to 51° from the surface normal for each preparation. Polished and electrochemically etched surfaces did not provide enough reflected light to resolve a beat frequency; however, sandpapered surfaces, retroreflective microspheres, and milled v-cuts provided adequate reflected light for incidence angles up to 51°. Applications of the surface preparations were then studied in gas gun experiments. Retroreflective microspheres were studied in a planar impact experiment, and milled v-cuts were studied in an oblique impact experiment. A normal and transverse profile of particle velocity was resolved in the oblique impact experiment.

Radio evidence for AGN activity: relativistic jets as tracers of SMBHs

AbstractAlthough the radio emission from most quasars appears to be associated with star forming activity in the host galaxy, about ten percent of optically selected quasars have very luminous relativistic jets apparently powered by a SMBH which is located at the base of the jet. When these jets are pointed close to the line of sight their apparent luminosity is enhanced by Doppler boosting and appears highly variable. High resolution radio interferometry shows directly the outflow of relativistic plasma jets from the SMBH. Apparent transverse velocities in these so-called “blazars” are typically about 7c but reach as much as 50c indicating true velocities within one percent of the speed of light. The jets appear to be collimated and accelerated in regions as much as a hundred parsecs downstream from the SMBH. Measurements made with Earth to space interferometers indicate apparent brightness temperatures of ~ 1014K or more. This is well in excess of the limits imposed by inverse Compton cooling. The modest Doppler factors deduced from the observed ejection speeds appear to be inadequate to explain the high observed brightness temperatures in terms of relativistic boosting.

The Exact Velocity in Low-redshift Stationary Radio Sources from its Apparent Longitudinal and Transverse Velocity

The Exact Velocity in Low-redshift Stationary Radio Sources from its Apparent Longitudinal and Transverse Velocity

Radio structure of the blazar 1156 + 295 with sub-pc resolution

1156+295 is a flat-spectrum quasar which is loud at radio and gamma-ray. Previous observations of the source revealed a radio morphology on pc to kpc scales consistent with a helical jet model. In our present research, this source was observed with the VLBA at 86, 43 and 15 GHz on four epochs from 10 May 2003 to 13 March 2005 aiming at studying the structure of the innermost jet in order to understand the relation between the helical structure and the astrophysical processes in the central engine. A core-jet structure with six jet components is identified. The apparent transverse velocities of the six jet components derived from proper motion measurements are in the range between 3.6 c and 11.6 c. The overall jet shape shows oscillatory morphology with multiple curvatures on pc scales which might be indicative of a helical pattern. Models of helical jet are discussed on the basis of both Kelvin-Helmholtz (K-H) instability and jet precession. The K-H instability model shows better agreement with the observed data. The overall radio structure on the scale from sub-pc to kpc appears to be fitted with a hydrodynamic model with the fundamental helical mode in Kelvin-Helmholtz (K-H) instability. This helical mode with an initial characteristic wavelength of 0.2 pc is excited at the base of the jet on the scale of 0.005 pc (or 1000R_s, the typical size of the broad line region for a super massive black hole of $4.3\times10^8M_{\odot}$). A presessing jet model can also fit the observed jet structure on the scale between 10 pc and 300 pc. However, additional astrophysical processes may be required for the presessing jet model in order to explain the bendings on the inner jet structure (1 to 10 pc) and re-collimation of the large scale jet outflow (>300 pc).

Superluminal apparent motions in distant radio sources

We derive the prediction of the standard model of superluminal radio sources for the apparent transverse velocity of a radio source located at redshift z. The apparent velocity of the source is reduced by a factor of 1+z compared to that of a similar nearby source. The cause of this reduction is recession of the distant source due to the expansion of the universe. The apparent velocity of a source can be estimated from its redshift and proper motion using the values of the Hubble constant and the mean densities of different energy components in the universe. We derive an expression for the velocity valid for the currently favored cosmological model: a flat universe with a nonzero cosmological constant.

Do the Mildly Superluminal VLBI Knots Exclude Ultrarelativistic Blazar Jets?

We compute the effective values of apparent transverse velocity and flux boosting factors for the VLBI radio knots of blazar jets by integrating over the angular distributions of these quantities across the widths of jets with finite opening angles but constant velocities. For high bulk Lorentz factors (Γ > 10), variations across the jet can be quite large if the opening angle, ω, is even a few degrees on subparsec scales. The resulting apparent speeds are often much lower than those obtained from the usual analyses that ignore the finite jet opening angles. We can thus reconcile the usually observed subluminal or mildly superluminal speeds with the very high (20) Γ factors, required by the inverse Compton origin and rapid variability of TeV fluxes, as well as by intraday radio variability. Thus it is possible to associate the VLBI radio knots directly with shocks in the ultrarelativistic main jet flow, without invoking very rapid jet deceleration on parsec scales or extremely unlikely viewing angles.

Sub‐Milliarcsecond Imaging of Quasars and Active Galactic Nuclei. III. Kinematics of Parsec‐scale Radio Jets

We report the results of a 15 GHz (2 cm) multi-epoch VLBA program, begun in 1994 to study the outflow in radio jets ejected from quasars and active galaxies. The observed flow of 208 distinct features measured in 110 quasars, active galaxies, and BL Lac objects shows highly collimated relativistic motion with apparent transverse velocities typically between zero and about 15c, with a tail extending up to about 34c. Within individual jets, different features appear to move with a similar characteristic velocity which may represent an underlying continuous jet flow, but we also see some stationary and even apparently inward moving features which co-exist with the main features. Comparison of our observations with published data at other wavelengths suggests that there is a systematic decrease in apparent velocity with increasing wavelength, probably because the observations at different wavelengths sample different parts of the jet structure. The observed distribution of linear velocities is not consistent with any simple ballistic model. Either there is a rather broad range of Lorentz factors, a significant difference between the velocity of the bulk relativistic flow and the pattern speed of underlying shocks, or a combination of these options. Assuming a ballistic flow, comparison of observed apparent velocities and Doppler factors computed from the time scale of flux density variations is consistent with a steep power law distribution of intrinsic Lorentz factors, an isotropic distribution of orientations of the parent population, and intrinsic brightness temperatures about an order of magnitude below the canonical inverse Compton limit. It appears that the parent population of radio jets is not dominated by highly relativistic flows (abridged).

Multifrequency interferometer and radio continuum monitoring observations of CTA 102

This paper represents the work of several years of observation of CTA 102 with both single dish telescopes and interferometric arrays, covering wavelengths from 1.2 cm to 1.3 mm. The resolution of the maps covers an order of magnitude from 0.5 mas to 50 μ as. The images presented demonstrate the rapid structural changes in this source. These rapid structural changes correlates with the outbursts seen in the total flux, turnover frequency and in the spectral index. We have calculated the Brightness Temperatures of the components ( T B ) directly from the determined component sizes and also using the logarithmic variability amplitudes and timescales to calculate the $T_{\mathrm{B}}$s. Both the methods yielded measurements of source frame T B s no higher than ~a $\rm few\times 10^{12}$ K. We find that the observed average proper motion is ~$0.4 \pm 0.07$ mas/yr, which corresponds to an apparent transverse velocity of $11 \pm 2$ c.

A Gamma‐Ray Flare of Quasar CTA 26

During the first 3 years of the Compton Gamma Ray Observatory mission, the blazar CTA 26 was observed 10 times by EGRET and not significantly detected. We report an observation in 1995 when CTA 26 flared to a peak γ-ray flux of (4.9 ± 1.5) × 10-6 cm-2 s-1 (E > 100 MeV), the third brightest of all EGRET blazars. Following the γ-ray flare, extensive VLBA and single-dish radio observations were obtained. We find two components of a milliarcsecond jet moving with apparent transverse velocities of 12 ± 1 h-1 c, and 5 ± 2 h-1 c (H0 = 100 h km s-1 Mpc-1, q0 = 0.1). The position angle of VLBI components appears to change with time. The slowest VLBI component's motion is consistent with ejection at the time of the 1995 γ-ray flare. A weak radio flare is also seen in Metsahovi millimeter radio monitoring data, peaking within weeks of the γ-ray flare.

The Compact Core-Jet Region of the Superluminal Quasar 3C 216

Abstract Space very long baseline interferometry (VLBI) observations of the quasar 3C 216 with the VLBI Space Observatory Programme (VSOP) reveal that the parsec scale structure of the source can be well described by compact jet models developed for interpreting the core region of radio-loud active galactic nuclei (AGN). The measured brightness temperature of TB = 7.9 × 1011 K is comparable to the inverse Compton limit, from which we determine a lower limit of δ ∼ 3 for the Doppler-boosting factor. The apparent transverse velocity of the superluminal component is βapp = (3.0±0.2) h−1, assuming a constant velocity, but deceleration of the jet material cannot be excluded from our data. A combination of the above values indicates that the viewing angle of the core-jet to the line-of-sight is less than 19°, and the jet Lorentz-factor exceeds 2.4. The observed small size of the source is probably caused by both an interaction with the interstellar medium and a projection effect.

Multiple-Epoch Monitoring of the Lobe-dominated Superluminal Quasar 3C 245

We report confirmation of superluminal motion in the nucleus of the lobe-dominated quasar 3C 245, based on three new 10.7 GHz epochs and a consistent reanalysis of older 10.7 GHz data; the total time spanned is a decade. In the inner 2 mas, we have tracked two components that have consistent motions in a position angle of 2900 3000, well fitted with constant apparent transverse velocities of flapp = (2.4 t 0.1) h-^{1 }and = (3.1 + 1.7) h ^{1 }(H_{0 }= 100 h km S-^{1 }Mpc <SUP>1</SUP>, q_{0 }= 0.5). We also present a new 8.4 GHz VLBI observation with superior short-baseline (u, v)-coverage that has yielded the best highresolution image to date of a faint, steep-spectrum extension of the one-sided jet, reaching out to &gt;40 mas from the VLBI core and having a brightness peak at 25 mas. We relate our findings to other properties of 3C 245 and interpret them in the context of relativistic beaming models and unification scenarios. We conclude that 3C 245 is in many ways a prototypical transition object between core- and lobe-dominated quasars.

The Radio Outburst from GRO J1655-40

Strong variable radio emission from the bright transient X-ray source GRO J1655-40 (X-ray Nova Scorpii 1994) has been detected at 843 MHz with the Molonglo Observatory Synthesis Telescope (MOST). As the hard X-ray intensity from the 1994 August outburst declined the radio output increased rapidly, reaching a peak of nearly 8 Jy some 12 days after the first X-ray peak. VLBI images obtained at this time showed two main components separating with an apparent transverse velocity &gt; c. The evolution of the radio spectrum suggests that the time delay between X-ray and radio emissions is due, at least in part, to opacity effects associated with this expansion.

Optical mapping reveals that repolarization spreads anisotropically and is guided by fiber orientation in guinea pig hearts.

Guinea pig hearts were stained with a voltage-sensitive dye and imaged on a photodiode array to record fluorescent action potentials (APs) from 124 sites. Activation and repolarization patterns were recorded from the epicardium during stimulation at different loci and correlated with the underlying fiber architecture. Endocardial APs were recorded by inserting a light guide into the ventricular cavity or by dissecting out the ventricular free wall to expose the endocardium. In hearts paced on the right atrium to simulate sinus rhythm, activation emerged synchronously over a large area of the ventricular epicardium and spread laterally in 5 to 7 ms. The apparent longitudinal and transverse velocities were 2.66 +/- 0.11 and 1.65 +/- 0.09 m/s (n = 12). In contrast, repolarization began near the apex on the endocardium and spread transmurally in 6 +/- 1.3 ms (n = 12) and then anisotropically along the epicardium in 25 to 30 ms with apparent maximum (0.53 +/- 0.11 m/s) and minimum (0.31 +/- 0.10 m/s) repolarization velocities that aligned with the longitudinal and transverse axes of epicardial fibers. When paced on the epicardium, activation of intact hearts (n = 12) and perfused sheets (n = 8) was anisotropic, with longitudinal (0.85 +/- 0.05 m/s) and transverse (0.44 +/- 0.04 m/s) conduction velocities that aligned with the epicardial fiber orientation. When activation was initiated at different sites on the epicardium, repolarization always began near the apex and exhibited patterns similar to those obtained under right atrial pacing, but with slower longitudinal (0.41 +/- 0.09 m/s) and transverse (0.23 +/- 0.07 m/s) repolarization velocities (n = 18). In sheets stretched parallel to the longitudinal axis of surface fibers, AP durations (APDs) increased as a function of fiber length, from the length at zero developed tension to 120% of the length at maximum developed tension (Lmax). Spatial distributions of APDs did not change during stretches along the rising phase of the length-tension curve. In sheets stretched to 50% of Lmax, APDs were shorter and more homogeneous on the endocardium (mean APD, 188 ms; delta APD, 195-186 = 9 ms) than on the epicardium (mean APD, 204 ms; delta APD, 212-186 = 26 ms; n = 8). In guinea pig hearts, activation is rapid; therefore, repolarization depends primarily on intrinsic spatial heterogeneities of APDs. Consequently, repolarization begins at endocardial cells with the shortest APDs and spreads transmurally and then anisotropically on the surface according to the epicardial cell orientation.

Superluminal Motion in the Large, Strongly Lobe-dominated Quasar 3C 47

Dual-epoch 10.7 GHz VLBI observations of the large, lobe-dominated quasar 3C 47 reveal a component moving with an apparent transverse velocity of (3.7<SUP>+0.9</SUP><SUB>-0.7</SUB>) h<SUP>-1</SUP>c (with H<SUB>0</SUB> = 100 h km s<SUP>-1</SUP> Mpc<SUP>-1</SUP>, q<SUB>0</SUB> = 0.5). 3C 47 is the most strongly lobe-dominated superluminal found to date, and it has the largest projected linear extent in our complete, low-frequency selected sample. Its moderately large superluminal motion is difficult to understand in the light of simple relativistic beaming models and popular unification hypotheses.

Erratum: VLBI, MERLIN and VLA observations of the blazar 1156 + 295: a bending relativistic jet

We present VLBI maps at 18, 6, 2.8 and 1.35 cm of the blazar 1156+295 which show a jet emerging from the core along position angle (PA)∼200 and bending to larger PA further out. Maps at 6 cm from 1987 May and 1988 November show different structure, indicating the probable movement from the core of a component with a very high apparent transverse velocity. The 2.8- and 1.35-cm maps are consistent with this hypothesis. We also present MERLIN and VLA total intensity and polarization maps at 18, 6 and 2 cm which show a 2-arcsec jet emerging from the core in PA - 190. We show how a bending relativistic jet can also explain the variability seen in this source.