Triple Radio Source Research Articles

Resolving the Collimation Zone of an Intermediate-mass Protostellar Jet

We report new VLA and e-MERLIN high-resolution and -sensitivity images of the triple radio continuum source in the Serpens star-forming region. These observations allowed us to perform a deep multifrequency, multiepoch study by exploring the innermost regions (≲100 au) of an intermediate-mass young stellar object for the first time, with a physical resolution of ∼15 au. The kinematic analysis of knots recently ejected by the protostar indicates that the jet is undergoing episodic variations in velocity. In addition, our multifrequency images reveal striking characteristics, e.g., a highly collimated ionized stream that would be launched at a radial distance of ∼0.4 au from the protostar and a narrow (∼28 au wide) ionized cavity that would be excited by the interaction of a wide-angle component with the surrounding toroid of infalling material. In light of these results, we propose the scenario in which both a highly collimated jet and a wide-angle wind coexist as the most plausible to explain our observations, either launched by the X-wind or X-plus-disk-wind mechanism.

A Catalog of Very Large Array Sky Survey Epoch 1 Quick Look Components, Sources, and Host Identifications

Abstract We announce here the public availability of a catalog of ν ∼ 3 GHz Quick Look observations from the first epoch of the Very Large Array Sky Survey. The catalog consists of three distinct and linkable tables, namely (a) the detected radio components, (b) the host identifications with total source properties for single-component, and close double/triple radio sources (angular separations of <10″), and (c) the Quick Look image metadata. Given the Quick Look images are limited in quality, we include data reliability flagging to improve the scientific usability of this catalog. Using our recommended quality flags, this catalog contains 1.7 × 106 unique radio components with S 3 GHz ≳ 1 mJy beam−1, and 6.2 × 105 host IDs (including 20,000 close-double and triple radio sources) reliably detected across the entire sky at δ > −40°. The catalog and an associated User Guide have been produced as part of the Canadian Initiative for Radio Astronomy Data Analysis, and are available at https://cirada.ca/catalogues.

GMRT observations of the protostellar jet associated with IRAS 16547-4247

We report continuum GMRT observations aimed to explore the behavior of the jet associated with IRAS 16547-4247 at very low frequencies (325 MHz and 610 MHz). The obtained maps reveal an elongated morphology in the SE-NW direction. In addition, the 610 MHz map shows three knots associated to the elongated morphology that seems to correspond to the triple radio source identified as the jet seen at higher frequencies. However, at 325 MHz, although an elongated morphology is also observed, only two knots appear in the map. By comparing our knot positions at both frequencies with a precessing jet model used in a previous work, we find that the knots fall closely to the wiggling path and, hence, they likely represent shocks of the material of the precessing jet with the medium. Only the nature of the southernmost knot detected at 325 MHz remains unclear. Besides, we found that the whole emission of the lobes is non-thermal down to very low frequencies and that the possible associated emission mechanisms work differently in in both lobes, causing the discrepancies between observed frequencies. To explain these discrepancies we investigate mechanisms such as synchrotron radiative losses in a magnetic field of about 0.5 mG in the shocks and find this possibility unlikely to occur. Alternatively, we invoke interaction with an inhomogeneous medium as the most probable scenario.

INVESTIGATING PARTICLE ACCELERATION IN PROTOSTELLAR JETS: THE TRIPLE RADIO CONTINUUM SOURCE IN SERPENS

ABSTRACT While most protostellar jets present free–free emission at radio wavelengths, synchrotron emission has also been proposed to be present in a handful of these objects. The presence of nonthermal emission has been inferred by negative spectral indices at centimeter wavelengths. In one case (the HH 80-81 jet arising from a massive protostar), its synchrotron nature was confirmed by the detection of linearly polarized radio emission. One of the main consequences of these results is that synchrotron emission implies the presence of relativistic particles among the nonrelativistic material of these jets. Therefore, an acceleration mechanism should be taking place. The most probable scenario is that particles are accelerated when the jets strongly impact against the dense envelope surrounding the protostar. Here we present an analysis of radio observations obtained with the Very Large Array of the triple radio source in the Serpens star-forming region. This object is known to be a radio jet arising from an intermediate-mass protostar. It is also one of the first protostellar jets where the presence of nonthermal emission was proposed. We analyze the dynamics of the jet and the nature of the emission and discuss these issues in the context of the physical parameters of the jet and the particle acceleration phenomenon.

Radio interferometric observations of two core-dominated triple radio sources atz > 3

Aims. We selected two radio quasars (J1036+1326 and J1353+5725) based on their 1.4-GHz radio structure, which is dominated by a bright central core and a pair of weaker and nearly symmetric lobes at ~10" angular separation. They are optically identified in the Sloan Digital Sky Survey (SDSS) at spectroscopic redshifts z>3. We investigate the possibility that their core-dominated triple morphology can be a sign of restarted radio activity in these quasars, involving a significant repositioning of the radio jet axis. Methods. We present the results of high-resolution radio imaging observations of J1036+1326 and J1353+5725, performed with the European Very Long Baseline Interferometry (VLBI) Network (EVN) at 1.6 GHz. These data are supplemented by archive observations from the Very Large Array (VLA).We study the large- and small-scale radio structures and the brightness temperatures, then estimate relativistic beaming parameters. Results. We show that the central emission region of these two high-redshift, core-dominated triple sources is compact but resolved at ~10 milli-arcsecond resolution. We find that it is not necessary to invoke large misalignment between the VLBI jet and the large-scale radio structure to explain the observed properties of the sources.

THE COLLIMATED JET SOURCE IN IRAS 16547-4247: TIME VARIATION, POSSIBLE PRECESSION, AND UPPER LIMITS TO THE PROPER MOTIONS ALONG THE JET AXIS

The triple radio source detected in association with the luminous infrared source IRAS 16547-4247 has previously been studied with high angular resolution and high sensitivity with the Very Large Array at 3.6 cm wavelength. In this paper, we present new 3.6 cm observations taken 2.68 years after the first epoch that allow a search for variability and proper motions, as well as the detection of additional faint sources in the region. We do not detect proper motions along the axis of the outflow in the outer lobes of this source at a 4σ upper limit of ∼160 km s−1. This suggests that these lobes are probably working surfaces where the jet is interacting with a denser medium. However, the brightest components of the lobes show evidence of precession, at a rate of 008 yr−1 clockwise in the plane of the sky. It may be possible to understand the distribution of almost all the identified sources as the result of ejecta from a precessing jet. The core of the thermal jet shows significant variations in flux density and morphology. We compare this source with other jets in low- and high-mass young stars and suggest that the latter can be understood as a scaled-up version of the former.

Gamma-ray emission from massive young stellar objects

Context.Massive stars form in dense and massive molecular cores. The exact formation mechanism is unclear, but it is possible that some massive stars are formed by processes similar to those that produce the low-mass stars, with accretion/ejection phenomena occurring at some point of the evolution of the protostar. This picture seems to be supported by the detection of a collimated stellar wind emanating from the massive protostar IRAS 16547-4247. A triple radio source is associated with the protostar: a compact core and two radio lobes. The emission of the southern lobe is clearly non-thermal. Such emission is interpreted as synchrotron radiation produced by relativistic electrons locally accelerated at the termination point of a thermal jet. Since the ambient medium is determined by the properties of the molecular cloud in which the whole system is embedded, we can expect high densities of particles and infrared photons. Because of the confirmed presence of relativistic electrons, inverse Compton and relativistic Bremsstrahlung interactions are unavoidable.

Signatures of restarted activity in core-dominated, triple radio sources selected from the FIRST survey

Signatures of the re-occurrence of activity in radio-loud AGNs, indicated either by the so-called double-double or X-shaped structures, have been observed in a number of radio sources. All such objects known to date have linear sizes of the order of a megaparsec. A number of the sources that are appreciably more compact than this, but that exhibit hints of a past phase of activity, were found in the VLA FIRST survey. Their structures show symmetric relic lobes straddling relatively bright, unresolved cores. Observations of the cores of 15 such structures with MERLIN at 5 GHz have shown that four of them are doubles or core-jets on the subarcsecond scale. Misalignments of between the axis of the inner structure and the line connecting the fitted maxima of the arcminute-scale relic lobes are clearly visible in three of the four sources. From these results, we can infer that a rapid repositioning of the central engine in each of these three radio sources is the most plausible interpretation of the observed morphology and that a merger is most likely the original cause of such a repositioning. In the case of TXS 1033+026, the optical image extracted from the SDSS archives clearly suggests that two objects separated by only 2.7 kpc (projected onto the sky plane) are indeed merging. The inner parts of TXS 0818+214 and TXS 1312+563 could be interpreted as double-lobed, and consequently, these sources could be of the double-double type; but further multifrequency observations are necessary to provide support for such an interpretation.

In Search of Circumstellar Disks around Young Massive Stars

We present 7 mm, 1.3 cm and 3.6 cm continuum observations made with the Very Large Array toward a sample of ten luminous IRAS sources that are believed to be regions of massive star formation. We detect compact 7 mm emission in four of these objects: IRAS 18089-1732(1), IRAS 18182-1433, IRAS 18264-1152 and IRAS 18308-0841 and for the first time find that these IRAS sources are associated with double or triple radio sources separated by a few arcseconds. We discuss the characteristics of these sources based mostly on their spectral indices and find that their nature is diverse. Some features indicate that the 7 mm emission is dominated by dust from disks or envelopes. Toward other components the 7 mm emission appears to be dominated by free-free radiation, both from ionized outflows or from optically thick H II regions. Furthermore, there is evidence of synchrotron contamination in some of these sources. Finally, we found that the sources associated with ionized outflows, or thermal jets are correlated with CH$_3$OH masers. The precise determination of the nature of these objects requires additional multifrequency observations at high angular resolution. The 3.6 cm continuum observations also revealed seven UCHII regions in the vicinity of the sources IRAS 18089-1732(1) and two more in the source IRAS 18182-1433. We show that the small photoionized nebulae of these UCHII regions are produced by early B-type stars.

High Angular Resolution Observations of the Collimated Jet Source Associated with a Massive Protostar in IRAS 16547−4247

A triple radio source recently detected in association with the luminous infrared source IRAS 16547-4247 has been studied with high angular resolution and high sensitivity with the Very Large Array at 3.6 and 2 cm. Our observations confirm the interpretation that the central object is a thermal radio jet, while the two outer lobes are most probably heavily obscured HH objects. The thermal radio jet is resolved angularly for the first time and found to align closely with the outer lobes. The opening angle of the thermal jet is estimated to be ~25°, confirming that collimated outflows can also be present in massive protostars. The proper motions of the outer lobes should be measurable over timescales of a few years. Several fainter sources detected in the region are most probably associated with other stars in a young cluster.

A Collimated Stellar Wind Emanating from a Massive Protostar

We report multi-wavelength observations towards IRAS 16547-4247, a luminous infrared source with a bolometric luminosity of 6.2 × 104 L ⊙. Dust continuum observations at 1.2-mm indicate that this object is associated with a dust cloud with a size of about 0.4 pc in diameter and a mass of about 1.3 × 103 M ⊙. Radio continuum observations show the presence of a triple radio source consisting of a compact central object and two outer lobes, separated by about 0.3 pc, symmetrically located from the central source. Molecular hydrogen line observations show a chain of knots that trace a collimated flow extending over 1.5 pc. We suggest that IRAS 16547-4247 corresponds to a dense massive core which hosts near its central region a high-mass star in an early stage of evolution. This massive YSO is undergoing the ejection of a collimated stellar wind which drives the H2 flow. The radio emission from the lobes arises in shocks resulting from the interaction of the collimated wind with the surrounding medium. We conclude that the thermal jets found in the formation of low-mass stars are also produced in high-mass stars.

A Triple Radio Continuum Source Associated with IRAS 16547–4247: A Collimated Stellar Wind Emanating from a Massive Protostar

We report the discovery, made using the Australia Telescope Compact Array, of a triple radio source toward IRAS 16547-4247, a luminous infrared source with a bolometric luminosity of 6.2 × 104 L☉. The radio source shows an almost linear structure consisting of a compact central object and two outer lobes separated by about 20'', located symmetrically to the central source. The radio emission from the lobes has spectral indices of -0.61 and -0.33, characteristic of nonthermal emission. The emission from the central object has a spectral index of 0.49, consistent with free-free emission from a thermal jet. Also reported are 1.2 mm continuum and molecular line observations made with the Swedish ESO Submillimeter Telescope. The 1.2 mm observations show that the dust emission arises from a region of 33'' × 25'' (FWHM) with a total flux of 16.4 Jy, implying a mass of 1.3 × 103 M☉. The line observations indicate that IRAS 16547-4247 is associated with a molecular core with a FWHM deconvolved angular size of 27'' (diameter of 0.38 pc at the distance of 2.9 kpc), a molecular hydrogen density of 5.2 × 105 cm-3, and a mass of 9.0 × 102 M☉. We propose that this dense massive core hosts a high-mass star in an early stage of evolution in which it is undergoing the ejection of a collimated stellar wind. The radio emission from the lobes arises in shocks resulting from the interaction of this collimated wind with the surrounding medium. Our observations indicate that the jets found in the formation of low-mass stars are also produced in high-mass stars, with IRAS 16547-4247 being the most luminous young stellar object presently known to host a jet.

Multi–frequency analysis of the two CSS quasars 3C 43 & 3C 298

We present and discuss observations made with MERLIN and VLBI at 1.7 and 5 GHz of the two CSS quasars 3C 43 and 3C 298. They show quite dierent morphologies, the former being a very distorted triple radio source, the latter a small FRII type object. Relativistic eects and structural distortions are discussed. Source ages are evaluated to be of the order of 10 5 years, therefore 3C 43 and 3C 298 can be considered fairly young radio sources. Some inference is also derived on the properties of the medium surrounding the radio emitting regions in these sub-galactic objects, whose density could be as low as 10 3 cm 3 .

The Narrow‐Line Region in the Seyfert 2 Galaxy NGC 3393

The narrow-line region (NLR) of the Seyfert 2 galaxy NGC 3393 is dominated by a symmetric structure which appears as S-shaped arms in Hubble Space Telescope (HST) images. These arms, which occupy the central few arcseconds of the nucleus, border a linear, triple-lobed radio source. We use HST imaging and spectra, ground-based optical images, long-slit spectra, Fabry-Perot imaging spectroscopy, and VLA radio data to perform a detailed investigation of the kinematics and ionization of the line-emitting gas in NGC 3393 and of its relationship with the relativistic gas responsible for the radio emission. The excitation map [O III] λ5007/(Hα + [N II] λλ6548, 6584) shows a biconical structure, consistent with the anisotropic nuclear ionizing radiation expected in the unified scheme. Extrapolation to ionizing frequencies of our upper limit to the 2100 A flux of the nuclear source provides a factor ≥3 × 104 too few ionizing photons to account for the recombination line emission, which also suggests that the nuclear ionizing source radiates anisotropically. However, the kinetic energy of the outflow is sufficient to power the line emission via photoionizing shocks, and a tentative detection of extended UV emission is consistent with this model. Furthermore, the broad component of the emission lines has a similar orientation and spatial extent as the triple radio source. Nevertheless, other tests are inconsistent with the photoionizing shock model—there is no correlation between local velocity dispersion, surface brightness, and excitation, and the gaseous abundances of [Ca II], Al II], and Mg II are much lower than expected if these species have been liberated into the gas phase through grain destruction by shocks. We conclude that the radio lobes appear to have created denser regions of gas on their leading edges, thus forming the S-shaped arms, but that the ionization is most likely due to photoionization by an obscured central source.

Modelling the 10-image lensed system B1933+503

A gravitational lens model is presented for the newly discovered 10-image system B1933+503. The underlying object, revealed by modelling, is a triple radio source on the scale of a couple of hundred mas that is well-aligned along the line of sight with a foreground and somewhat flattened lensing galaxy, the orientation and location of which match those of an observed galaxy, known to be at a redshift of 0.755. Uncertainties in the modelling are obtained by a Monte Carlo exercise. Observational tests of the lens model an proposed, and the time delays between various pairs of images are determined, as the core of the source is known to be significantly variable. Future observations of the lens hold the key to using B1933+503 to constrain Hubble's constant. Despite the absence of a source redshift, the utility of the system as a probe of the structure of the lens galaxy is unparalleled as it provides a surfeit of easily identifiable constraints for modelling the system.

The Serpens Radio Jet: evidence of precession of nutation

Previous VLA observations of the triple radio continuum source in Serpens showed that it has very unusual and extraordinary characteristics. While this source is associated with a star forming region, its outer components exhibit a combination of thermal and nonthermal spectra and large proper motions, Furthermore, the NW lobe has knotty and extended emission connecting the central source with the bright outer knot. Here, we present results of new VLA radio continuum high-angular resolution observations of this Radio Jet. Combining these observations with those obtained previously, we find that: a) one of the knots along the main body of the radio jet (knot G) exhibits proper motions similar to those observed in the outer NW and SE components, and the time variable knot A; b) the outer knots are moving away from the central source in slightly different directions; and c) the orientation of the central source seems to change with time. These results are consistent with a central precessing source that undergoes periodic ejection of material.

The triple radio continuum source in Serpens - The birth of a Herbig-Haro system?

view Abstract Citations (127) References (26) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Triple Radio Continuum Source in Serpens: The Birth of a Herbig-Haro System? Curiel, S. ; Rodriguez, L. F. ; Moran, J. M. ; Canto, J. Abstract Results are presented of a multifrequency, multiconfiguration study of the continuum emission from the triple radio continuum source in Serpens, observed with Very Large Array of the NRAO, which was carried out to investigate the spectral indices of the multiple components in Serpens in detail, to study the morphological characteristics of this radio source, and to resolve the angular structure of its components. In addition, the position of the H2O maser, known to be near this radio source was measured using the same instrument. On the basis of these observations, the triple radio continuum source in Serpens is identified as a young radio jet, with a dynamical age of only about 60 years, emanating from the central component. This radio jet exhibits a one-sided morphology that is very similar to that observed in optical Herbig-Haro jets, suggesting that jets associated with young stellar objects are intrinsically unipolar within the dynamical ages of the main jets. It is proposed that the Serpens radio jet could be a proto-Herbig-Haro system in an early stage of evolution. Publication: The Astrophysical Journal Pub Date: September 1993 DOI: 10.1086/173155 Bibcode: 1993ApJ...415..191C Keywords: Continuous Radiation; Herbig-Haro Objects; Interstellar Matter; Radio Jets (Astronomy); Star Formation; Pre-Main Sequence Stars; Stellar Evolution; Very Large Array (Vla); Astrophysics; RADIO CONTINUUM: INTERSTELLAR; ISM: JETS AND OUTFLOWS; STARS: FORMATION; STARS: PRE--MAIN-SEQUENCE full text sources ADS | data products SIMBAD (28)

The radio counterpart of the hard X-ray source GRS 1758-258

GRS 1758-258 and 1E 1740.7-2942 are two persistent hard X-ray sources in a region of about 100 deg 2 around the Galactic center. The Galactic center annihilator, 1E 1740.7-2942, has recently been found to be associated with a compact radio source from which a double radio jet emanates.In this Letter we report the results of a deep 6 cm VLA mapping of the field around the GRS 1758-258 X-ray position. Our observations reveal, as in 1E 1740.7-2942, the presence of another triple radio source, whose central component is time variable and falls inside the error circle (10″ of radius) of ROSAT

The triple radio continuum source in Serpens - Its interaction with the ambient molecular gas

VLA D observations of the NH 3 (1, 1) and NH 3 (2, 2) lines toward the triple radio continuum source in the Serpens region are presented. A nonthermal radio spectrum for the outer components of this triple radio source was suggested in 1989 by Rodriguez et al (1980, ApJ, 191). These spectral ammonia line observations were made in the VLA 4IF mode. A sensitivity of 4 mJy per channel of 48.8 kHz of resolution (∼0.6 km/s) was reached. A perturbation of the molecular gas near the triple radio continuum source is found in terms of heating and broadening of the ammonia lines

Diffusive shock acceleration in the lobes of the Serpens triple radio source

view Abstract Citations (23) References (26) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Diffusive Shock Acceleration in the Lobes of the Serpens Triple Radio Source Crusius-Watzel, Andre R. Abstract Recent observations of the triple radio source in the Serpens star formation region have shown large proper motions of the lobes. Their radio spectral index is characteristic of nonthermal emission. The possibility that this is synchrotron radiation from relativistic electrons is investigated. Particle acceleration can occur at the bow shock (bullet and jet model) or at the jet termination shock. The rates for ion-neutral damping and for the self-excitation of magnetic field fluctuations are compared. High levels of MHD turbulence and/or high Alfvenic Mach numbers are required to produce a power-law energy spectrum of electrons up to Lorentz factors of 1000. Diffusive shock acceleration of particles is then very efficient. Publication: The Astrophysical Journal Pub Date: October 1990 DOI: 10.1086/185824 Bibcode: 1990ApJ...361L..49C Keywords: H Ii Regions; Molecular Clouds; Particle Acceleration; Radio Sources (Astronomy); Shock Wave Propagation; Energy Spectra; Interstellar Magnetic Fields; Magnetohydrodynamic Turbulence; Polarized Electromagnetic Radiation; Synchrotron Radiation; Astrophysics; COSMIC RAYS: GENERAL; NEBULAE: GENERAL; PARTICLE ACCELERATION; RADIO SOURCES: GENERAL; SHOCK WAVES; STARS: PRE--MAIN-SEQUENCE full text sources ADS | data products SIMBAD (2)