Sub-milliarcsecond imaging of a bright flare and ejection event in the extragalactic jet 3C 111

Context. Flares in radio-loud active galactic nuclei are thought to be associated with the injection of fresh plasma into the compact jet base. Such flares are usually strongest and appear earlier at shorter radio wavelengths. Hence, very long baseline interferometry (VLBI) at millimeter(mm)-wavelengths is the best-suited technique for studying the earliest structural changes of compact jets associated with emission flares. Aims. We study the morphological changes of the parsec-scale jet in the nearby (z = 0.049) γ-ray bright radio galaxy 3C 111 following a flare that developed into a major radio outburst in 2007. Methods. We analyse three successive observations of 3C 111 at 86 GHz with the Global mm-VLBI Array (GMVA) between 2007 and 2008 which yield a very high angular resolution of ∼45 μas. In addition, we make use of single-dish radio flux density measurements from the F-GAMMA and POLAMI programmes, archival single-dish and VLBI data. Results. We resolve the flare into multiple plasma components with a distinct morphology resembling a bend in an otherwise remarkably straight jet. The flare-associated features move with apparent velocities of ∼4.0c to ∼4.5c and can be traced also at lower frequencies in later epochs. Near the base of the jet, we find two bright features with high brightness temperatures up to ∼1011 K, which we associate with the core and a stationary feature in the jet. Conclusions. The flare led to multiple new jet components indicative of a dynamic modulation during the ejection. We interpret the bend-like feature as a direct result of the outburst which makes it possible to trace the transverse structure of the jet. In this scenario, the components follow different paths in the jet stream consistent with expectations for a spine-sheath structure, which is not seen during intermediate levels of activity. The possibility of coordinated multiwavelength observations during a future bright radio flare in 3C 111 makes this source an excellent target for probing the radio-γ-ray connection.

Apparent superluminal core expansion and limb brightening in the candidate neutrino blazar TXS 0506+056

Context. IceCube has reported a very-high-energy neutrino (IceCube-170922A) in a region containing the blazar TXS 0506+056. Correlated gamma-ray activity has led to the first high-probability association of a high-energy neutrino with an extragalactic source. This blazar has been found to be in a radio outburst during the neutrino event. Aims. Our goal is to probe the sub-milliarcsecond properties of the radio jet right after the neutrino detection and during the further evolution of the radio outburst. Methods. We performed target of opportunity observations at 43 GHz frequency using very long baseline interferometry imaging, corresponding to 7 mm in wavelength, with the Very Long Baseline Array two and eight months after the neutrino event. Results. We produced two images of the radio jet of TXS 0506+056 at 43 GHz with angular resolutions of (0.2 × 1.1) mas and (0.2 × 0.5) mas, respectively. The source shows a compact, high brightness temperature core, albeit not approaching the equipartition limit and a bright and originally very collimated inner jet. Beyond approximately 0.5 mas from the millimeter-VLBI core, the jet loses this tight collimation and expands rapidly. During the months after the neutrino event associated with this source, the overall flux density is rising. This flux density increase happens solely within the core. Notably, the core expands in size with apparent superluminal velocity during these six months so that the brightness temperature drops by a factor of three despite the strong flux density increase. Conclusions. The radio jet of TXS 0506+056 shows strong signs of deceleration and/or a spine-sheath structure within the inner 1 mas, corresponding to about 70–140 pc in deprojected distance, from the millimeter-VLBI core. This structure is consistent with theoretical models that attribute the neutrino and gamma-ray production in TXS 0506+056 to interactions of electrons and protons in the highly relativistic jet spine with external photons originating from a slower moving jet region. Proton loading due to jet-star interactions in the inner host galaxy is suggested as the possible cause of deceleration.

Radio outburst from a massive (proto)star

Context. Recent observations of the massive young stellar object S255 NIRS 3 have revealed a large increase in both methanol maser flux density and IR emission, which have been interpreted as the result of an accretion outburst, possibly due to instabilities in a circumstellar disk. This indicates that this type of accretion event could be common in young/forming early-type stars and in their lower mass siblings, and supports the idea that accretion onto the star may occur in a non-continuous way. Aims. As accretion and ejection are believed to be tightly associated phenomena, we wanted to confirm the accretion interpretation of the outburst in S255 NIRS 3 by detecting the corresponding burst of the associated thermal jet. Methods. We monitored the radio continuum emission from S255 NIRS 3 at four bands using the Karl G. Jansky Very Large Array. The millimetre continuum emission was also observed with both the Northern Extended Millimeter Array of IRAM and the Atacama Large Millimeter/Submillimeter Array. Results. We have detected an exponential increase in the radio flux density from 6 to 45 GHz starting right after July 10, 2016, namely ~13 months after the estimated onset of the IR outburst. This is the first ever detection of a radio burst associated with an IR accretion outburst from a young stellar object. The flux density at all observed centimetre bands can be reproduced with a simple expanding jet model. At millimetre wavelengths we infer a marginal flux increase with respect to the literature values and we show this is due to free–free emission from the radio jet. Conclusions. Our model fits indicate a significant increase in the jet opening angle and ionized mass loss rate with time. For the first time, we can estimate the ionization fraction in the jet and conclude that this must be low (<14%), lending strong support to the idea that the neutral component is dominant in thermal jets. Our findings strongly suggest that recurrent accretion + ejection episodes may be the main route to the formation of massive stars.

LOCATION OF THE γ-RAY FLARING EMISSION IN THE PARSEC-SCALE JET OF THE BL LAC OBJECT AO 0235+164

We locate the γ-ray and lower frequency emission in flares of the BL Lac object AO 0235+164 at ≳12 pc in the jet of the source from the central engine. We employ time-dependent multi-spectral-range flux and linear polarization monitoring observations, as well as ultra-high resolution (~0.15 milliarcsecond) imaging of the jet structure at λ = 7 mm . The time coincidence in the end of 2008 of the propagation of the brightest superluminal feature detected in AO 0235+164 (Qs) with an extreme multi-spectral-range (γ-ray to radio) outburst, and an extremely high optical and 7 mm (for Qs) polarization degree provides strong evidence supporting that all these events are related. This is confirmed at high significance by probability arguments and Monte-Carlo simulations. These simulations show the unambiguous correlation of the γ-ray flaring state in the end of 2008 with those in the optical, millimeter, and radio regime, as well as the connection of a prominent X-ray flare in October 2008, and of a series of optical linear polarization peaks, with the set of events in the end of 2008. The observations are interpreted as the propagation of an extended moving perturbation through a re-collimation structure at the end of the jet's acceleration and collimation zone.

Evidence for shock-shock interaction in the jet of CTA 102

We have found evidence for interaction between a standing and a traveling shock in the jet of the blazar CTA 102. Our result is based in the study of the spectral evolution of the turnover frequency-turnover flux density (νm, Sm) plane. The radio/mm light curves were taken during a major radio outburst in April 2006.

Early Japanese contributions to space weather research (1945–1960)

Major contributions by Japanese scientists in the period of 1945 to 1960 are reviewed. This was the period when the foundation of the space weather research was laid by ground-based observations and theoretical research. Important contributions were made on such subjects as equatorial ionosphere in quiet times, tidal wind system in the ionosphere, formation of the F2 layer, VLF propagation above the ionosphere, and precursory phenomena (type IV radio outburst and polar cap absorption) to storms. At the IGY (1957, 1958), research efforts were intensified and new programs in space and Antarctica were initiated. Japanese scientists in this discipline held a tight network for communication and collaboration that has been kept to this day.

Microquasars: A Galactic-Extragalactic Connection?

Microquasars are Galactic X-ray binaries which show radio emission from relativistic outflows. Here we argue that the origins of radio emission from microquasars and compact extragalactic radio sources are similar. In particular, both can be explained qualitatively by a model in which shocks are propagating in the relativistic jets. The microquasar GRO J1655–40 is used to illustrate that the spectral evolution of its 1994 radio outburst can be explained by the growth phase of the generalised-shock model, similar to the case of the quasar 3C 273.