Strong Radio Outbursts Research Articles

Meteor shower modeling: Past and future Draconid outbursts

This work presents numerical simulations of meteoroid streams released by comet 21P/Giacobini-Zinner over the period 1850–2030. The initial methodology, based on Vaubaillon et al. (2005), has been updated and modified to account for the evolution of the comet's dust production along its orbit. The peak time, intensity, and duration of the shower were assessed using simulated activity profiles that are calibrated to match observations of historic Draconid outbursts. The characteristics of all the main apparitions of the shower are reproduced, with a peak time accuracy of half an hour and an intensity estimate correct to within a factor of 2 (visual showers) or 3 (radio outbursts). Our model also revealed the existence of a previously unreported strong radio outburst on October 9, 1999, that has since been confirmed by archival radar measurements. The first results of the model, presented in Egal et al. (2018), provided one of the best predictions of the recent 2018 outburst. Three future radio outbursts are predicted in the next decade, in 2019, 2025 and 2029. The strongest activity is expected in 2025 when the Earth encounters the young 2012 trail. Because of the dynamical uncertainties associated with comet 21P's orbital evolution between the 1959 and 1965 apparitions, observations of the 2019 radio outburst would be particularly helpful to improve the confidence of subsequent forecasts.

EVERY BCG WITH A STRONG RADIO AGN HAS AN X-RAY COOL CORE: IS THE COOL CORE-NONCOOL CORE DICHOTOMY TOO SIMPLE?

Radio AGN feedback in X-ray cool cores has been proposed as a crucial ingredient in the evolution of baryonic structures. However, it has long been known that strong radio AGN also exist in "noncool core" clusters, which brings up the question whether an X-ray cool core is always required for radio feedback. In this work, we present a systematic analysis of BCGs and strong radio AGN in 152 groups and clusters from the Chandra archive. All 69 BCGs with radio AGN more luminous than 2x10^23 W Hz^-1 at 1.4 GHz are found to have X-ray cool cores. The BCG cool cores can be divided into two classes, the large-cool-core (LCC) class and the corona class. Small coronae, easily overlooked at z>0.1, can trigger strong heating episodes in groups and clusters, long before large cool cores are formed. Strong radio outbursts triggered by coronae may destroy embryonic large cool cores and thus provide another mechanism to prevent formation of large cool cores. However, it is unclear whether coronae are decoupled from the radio feedback cycles as they have to be largely immune to strong radio outbursts. Our sample study also shows the absence of groups with a luminous cool core while hosting a strong radio AGN, which is not observed in clusters. This points to a greater impact of radio heating on low-mass systems than clusters. As examples of the corona class, we also present detailed analyses of a BCG corona associated with a strong radio AGN (ESO 137-006 in A3627) and one of the faintest coronae known (NGC 4709 in the Centaurus cluster). Our results suggest that the traditional cool core / noncool core dichotomy is too simple. A better alternative is the cool core distribution function, with the enclosed X-ray luminosity or gas mass.

VLBI Observations of the Most Radio-Loud, Narrow-Line Quasar SDSS J094857.3 + 002225

Abstract We observed the narrow-line quasar SDSS J094857.3$+$002225, which is known to have the highest radio loudness in the narrow-line Seyfert 1 galaxies (NLS1s), at 1.7–15.4 GHz with the Very Long Baseline Array (VLBA). This is the first very-long-baseline interferometry (VLBI) investigation of a radio-loud NLS1. We independently discovered (1) very high brightness temperatures from its compactness in a VLBA image and (2) flux variation among the VLBA observation and our other observations with the VLBA and the Very Large Array (VLA). A Doppler factor larger than 2.7–5.5 was required to meet an intrinsic limit of brightness temperature in the rest frame. This is evidence for highly relativistic nonthermal jets in an NLS1. We suggest that the Doppler factor is one of the most important parameters in the determination of the radio loudness of NLS1s. The accretion disk of SDSS J094857.3$+$002225 is probably in a very high state, rather than the high/soft state, by analogy with X-ray binaries with strong radio outbursts and superluminal jets, such as GRS 1915$+$105.

Simultaneous Multiwavelength Observations of Sagittarius A*

We observed Sgr A* using the Very Large Array (VLA) and the Giant Metrewave Radio Telescope (GMRT) at multiple centimeter and millimeter wavelengths on 2003 June 17. The measured flux densities of Sgr A*, together with those obtained from the Submillimeter Array (SMA) and the Keck II 10 m telescope on the same date, are used to construct a simultaneous spectrum of Sgr A* from 90 cm to 3.8 mu m. The simultaneous spectrum shows a spectral break at about 3.6 cm, a possible signature of synchrotron self-absorption of the strong radio outburst that occurred near epoch 2003 July 17. At 90 cm, the flux density of Sgr A* is 0.22 +/- 0.06 Jy, suggesting a sharp decrease in flux density at wavelengths longer than 47 cm. The spectrum at long cm wavelengths appears to be consistent with free-free absorption by a screen of ionized gas with a cutoff similar to 100 cm. This cutoff wavelength appears to be three times longer than that of similar to 30 cm suggested by Davies, Walsh, & Booth based on observations in 1974 and 1975. Our analysis suggests that the flux densities of Sgr A* at wavelengths longer than 30 cm could be attenuated and modulated by stellar winds from massive stars close to Sgr A*.

Broad-band Radio Spectra Variability of 550 AGN in 1997-2001

AbstractResults are presented of long-term monitoring at the radio telescope RATAN–600 and a model interpretation of instantaneous 1–22 GHz spectra at six frequencies for a sample of 550 compact extragalactic radio sources. The sources are selected from the Preston et al. (1985) VLBI survey and are located in the declination range from −30° to +43°. Dependence of the index of variability on frequency is analysed for different subsamples. Factors of flux density variations range from 1 to 15. A typical behaviour of spectra evolution during strong radio outbursts in various objects is recognised suggesting a common physical nature of the variability. Invoking VLBI observations in spectra–structure analysis, we find that usually more than 70% of the total emission is coming from the mas scale at frequencies higher than 5 GHz. The observed variability can be explained in the model with a relativistic jet of parsec scale in the longitudinal magnetic field or in the shock-in-jet model.

Development of a two-sided relativistic jet in Cygnus X-3

We present multi-epoch radio maps of the microquasar Cygnus X-3 obtained with the Very Large Array (VLA). The observations were carried out as a Target-of-Opportunity (ToO) project triggered by a series of strong (>5 Jy) radio outbursts in September 2000. We find that Cygnus X-3 was well resolved and clearly elongated in the North-South direction at the VLA resolution in the weeks after the triggering events. In particular, the VLA map from our final epoch of observation perfectly shows the development of a two-sided radio jet extending over ~0.05 pc scales. We interpret both the proper motion and the brightness asymmetry between the jet components in the framework of special relativity effects. Assuming a distance of 10 kpc, the true jet velocity that we derive is close to with a large angle with the line of sight. The possible connection between the VLA bipolar jets and the elongated one-sided structures observed at milli-arcsecond angular scales is also discussed.

Strong Radio Outbursts in Six Active Galactic Nuclei in 1997-1998

The beginnings of strong radio flares in six AGNs were detected and their evolution was studied using 1–22 GHz five epoch instantaneous spectral observations in 1997–1998. The phenomena started at the highest frequency and moved to the lower frequency in a regular fashion. Such behavior of the flares in AGNs can be explained by synchrotron emission from a compact relativistic jet implying different physical models which are discussed. For different types of AGNs the same behavior of flares is revealed, in favor of the same basic physical model for BL Lacs and quasars. A birth of new VLBI components in compact jets associated with these outbursts is predicted.

High-Energy Gamma and Radio Variability of Blazars in the Model of Non-Stationary Jets

A model has been developed for impulsive VLBI jet formation and gamma ray outbursts of Blazars. Propagation of newly expelled matter in the old channel of a jet is calculated supposing that the main driving force is the electromagnetic field. The new outflowing matter overtakes the old matter and forms double, fast or slow magnetosonic shock fronts. In the region of the fronts, the number of particles and their energy increase continuously with propagation time from the central object (Romanova and Lovelace, 1995). Accelerated electrons and positrons in the front interact with a diffuse field of UV photons (inverse Compton scattering), with the magnetic field (synchrotron radiation), and with synchrotron photons (SSC processes), thus creating radiation in a very wide range of bands. The self-consistent relativistic equations for the number of particles, the momentum, energy, and magnetic flux in the front are derived and solved numerically (Lovelace and Romanova, 1995). The time-dependent apparent luminosities in the radio to gamma ray bands are calculated taking into account the Doppler boost of the photons. The model predicts a short outburst of radiation in gamma rays (weeks or so) connected with Compton processes, a sharp (less than a day) outburst in the X-rays with a smooth decrease of the luminosity connected with SSC processes, and synchrotron radiation changing from infrared to radio bands (Fig. 1A). The lepton distribution function was taken as fl = K1/γ2 in the main energy containing range, γ1 ≤ γ ≤ γ2, steeper distribution fl = K2/γ3 for γ2 ≤ γ ≤ γ3, and even steeper for γ ≥ γ3. For γ < γ1, fl is assumed negligible as a result of synchrotron self-absorption. The lowest frequency f(syn1), determined by self-absorption, corresponds initially to the infrared band, and later - to the radio band. From Fig.1B, one can see that radio at 3 mm may start to appear after 2 weeks after outburst. But its maximum may correspond to much later times (months), because f(syn1) decreases slowly with time. The appearance of the new VLBI component in QSO 0528+134, which approximately coincides with the strong gamma-ray flash and with the beginning of the strong mm radio outburst (Krichbaum, et al. 1995; Pohl, et al. 1995), supports the proposed model.Both authors were supported in part by NSF grant AST-9320068. MMR is grateful to RFBR and Organizers of the Symposium for the partial support.

Correlation between X-ray intensity and radio outbursts of Cygnus X-3

view Abstract Citations (46) References (53) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Correlation between X-Ray Intensity and Radio Outbursts of Cygnus X-3 Watanabe, Hiroaki ; Kitamoto, Shunji ; Miyamoto, Sigenori ; Fielder, R. L. ; Waltman, E. B. ; Johnston, K. J. ; Ghigo, F. D. Abstract The relationship between the X-ray flux (1-20 keV) and the radio flux density (S and X bands) of Cygnus X-3 is investigated during a 4.5 yr interval, spanning 1987 March-1991 September. This period included seven strong radio outbursts with flux densities greater than 5 Jy at S band. All radio flares with maximum flux density greater than 0.5 Jy, including the seven strong radio outbursts, occurred when the 1-6 keV X-ray flux, averaged within 5 days before and after the peak of the radio flare, was greater than 0.37 counts/s/sq cm, which was corrected for the 4.8 hr intensity modulation. These X-ray fluxes correspond to a high state with a luminosity of roughly 1038 ergs/s at 8.5 kpc, implying that a very high accretion rate induces the radio flares. However, no simultaneous increase of X-rays during the radio outburst was detected. This fact suggests that the direct cause of the radio outbursts is some other process, during the high accretion rate, such as a gradual storage and a sudden release of energy by a twisting magnetic field in the accretion process. Population distributions of the mean X-ray flux (1-6 keV) and the X-ray softness ratio (1-6 keV/6-20 keV) was also studied, and they indicated the existence of two distinct states, i.e., high (soft) and low (hard) states. This fact suggests a bimodal behavior of the accretion disk. Publication: The Astrophysical Journal Pub Date: September 1994 DOI: 10.1086/174649 Bibcode: 1994ApJ...433..350W Keywords: Radio Astronomy; Radio Bursts; Radio Stars; Spaceborne Astronomy; Stellar Luminosity; Stellar Mass Accretion; X Ray Astronomy; X Ray Stars; Correlation; Flux Density; Ginga Satellite; Light Curve; Luminous Intensity; Astronomy; RADIO CONTINUUM: STARS; STARS: INDIVIDUAL CONSTELLATION NAME: CYGNUS X-3; X-RAYS: STARS full text sources ADS | data products SIMBAD (3)

On the radio variability of V410 Tauri

The radio flux density of the star V410 Tauri has been monitored at 6 and 2 cm wavelengths at monthly intervals over a one-year period with the VLA. In contrast to earlier observations, the radio emission was typically at the level of roughly 1 mJy with flat or negative spectral indices. No large radio 'flare' events were detected. However, a periodicity analysis of the quiescent data shows statistically significant evidence for a modulation of the radio emission, with a period of 0.933 days, or one-half the optical period reported by Vrba, et al. (1988). If the modulation is real, it would imply that (1) the radio emission is produced either in localized zones on two opposite hemispheres of the star, or in a single, presumably high-latitude, structure that remains visible for an entire rotation period; (2) this zone or zones must be comparable to the stellar radius in size; (3) the energy spectrum of the radiating electrons is stable over long times (greater than 1 yr) but the absolute intensity level in the quiescent state may vary by factors of a few; and (4) the emission solid angle varies with viewing angle of the emission zone. It is suggested that gyrosynchrotron radiation from closed-loop magnetic structures may be responsible for the quasisteady low-level radio emission reported here. A geometric model for the radio emission structure may explain qualitatively the modulation of the radio emission. By analogy with the premain-sequence star DoAr 21, this same physical mechanism may produce both the 'quiescent' and 'flaring' radio emission. The monitoring results suggest that strong radio outbursts, such as were previously observed for V410 Tau, are relatively rare.

Mark III very long baseline interferometry positions of eight stellar systems and astrometric comparisons

Accurate positions of eight stellar systems are derived from Mark III VLBI observations conducted with multistation arrays. These radio positions are referred to the VLBI extragalactic reference frame of equinox and equator J2000.0. The estimated precision of the best position is 2 mas and was obtained during a relatively strong radio outburst of the RS CVn stellar system HR 5110. This precision is appropriate to link the future HIPPARCOS optical reference frame to the extragalactic VLBI frame. Typically, the astrometric precision is ≡0arcsec.01 and is essentially limited by the signal-to-noise ratio of the VLBI data. Comparisons of the authors' VLBI positions to VLA and optical FK4-based positions of these stars are presented in the J2000.0 system. The agreement between the VLBI and optical positions is satisfactory (0arcsec.05 on average) and interpreted as demonstrating that the preliminary optical FK5 frame defined by Fricke (1982) is aligned with the VLBI extragalactic reference frame at that level.

A radio jet associated with the symbiotic star CH Cygni

We present observations that show that the symbiotic star CH Cygni recently underwent a strong radio outburst that produced a radio-emitting thermal jet. The jet is two-sided and is expanding lengthwise at an observed rate (end to end) of 1 arcsec/year, corresponding to a transverse velocity of 1100 km∙s−1 in each direction. The electron density on January 22, 1985 exceeded 2 × 106 cm−3, and the mass of the (ionized) gas exceeded [Formula: see text]. The emergence of the jet coincided with a decline in the visual luminosity of [Formula: see text].The data are consistent with a jet produced by supercritical accretion in a binary containing a red giant and a [Formula: see text] white dwarf. The discovery of a jet in such a system provides confirming evidence of the role played by accretion in determining the optical and radio properties of this system. It is also the first expanding jet found to be associated with an evolved stellar object.

A radio outburst and jet from the symbiotic star CH Cyg

CH Cyg is an M7 III star that is known to undergo periods of brightening in the blue-violet continuum at irregular intervals of a few years1–3. During the active phase, the spectrum also exhibits strong Balmer emission and emission lines from He I, Fe II and various forbidden transitions, giving it the appearance of a symbiotic star. As part of a monitoring programme on symbiotic stars, observations with the National Radio Astronomy Observatory Very Large Array (VLA) have been made on CH Cyg over the past year at intervals of a few months. During the period April 1984 to May 1985 this monitoring revealed a strong radio outburst coincident with the production of a multi-component jet, and a comparison of high-resolution maps at two epochs separated by 75 days shows that the jet is expanding at a rate of 1.1 arc s yr−1. The onset of the radio outburst coincides in time with a remarkable decline in the visual brightness of the star. The luminosity of the star during the optically active state and the energetics of the mass loss suggest that the outburst is the result of accretion at, or near, the Eddington limit onto the surface of a white dwarf.

Detection of a sub-milliarcsecond radio component in the RS CVn system HR 1099

The RS CVn system HR 1099 was observed with a five station VLBI array at a frequency of 8.4 GHz during a strong radio outburst of approximately 400 mJy. The data are consistent with a circular Gaussian source of 0.8 + or - 0.12 milli-arcsec (FWHM), corresponding to a linear size of 4 + or - 0.6 x 10 to the 11th cm. This is comparable to the distance between the surfaces of the two stars, or to 75 percent of the diameter of the chromospherically active K star. Extrapolation of published photometric data shows that the starspot formation of HR 1099 was facing toward the observers at the times of observations. The high equivalent brightness temperature, approximately 10 billion K, is consistent with gyrosynchrotron emission from a power-law energy distribution of electrons in a magnetic field of strength about 30 gauss.

Discovery of strong radio flaring from HR 1099

view Abstract Citations (109) References (25) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Discovery of a strong radio flaring from HR 1099. Feldman, P. A. ; Taylor, A. R. ; Gregory, P. C. ; Seaquist, E. R. ; Balonek, T. J. ; Cohen, N. L. Abstract A remarkable series of strong radio outbursts was discovered from the RS CVn binary HR 1099 (=V711 Tau) starting on 20 February 1978. The flux density at 10.5 GHz was monitored for nine days at the Algonquin Radio Observatory and whenever possible at 15.5 and 7.9 GHz at Haystack Observatory. These data show, for the first time, detailed temporal development of several RS CVn radio flares. The mechanism of radio emission is almost certainly nonthermal gyrosynchrotron radiation in a volume whose characteristic dimension is several times larger than the stellar size(s) but comparable with the binary star separation. Publication: The Astronomical Journal Pub Date: December 1978 DOI: 10.1086/112346 Bibcode: 1978AJ.....83.1471F Keywords: Binary Stars; Radiant Flux Density; Radio Bursts; Radio Stars; Stellar Radiation; Microwave Emission; Nonthermal Radiation; Radio Astronomy; Synchrotron Radiation; Tables (Data); Astrophysics; Radio Bursts:RS CVn Binaries full text sources ADS | data products SIMBAD (3)

An unusually strong radio outburst in Algol - VLBI observations

For 8 hours during a strong radio flare on Jan. 15, 16, 1975, the close binary system Beta Persei (Algol) was observed with a three-station VLBI array operating at 7850 MHz. The size of the radio source was estimated to have been about 1.7 milliarcsec (0.05 AU), based on a model of a uniformly bright disk. The corresponding brightness temperature was nearly 10 billion K, indicating that the emission was probably nonthermal. There was no evidence for expansion of the source; the upper limit on the rate of any expansion was 100 km/s. The position of the Algol radio source with respect to an extragalactic reference frame was also determined from these observations with an uncertainty of about 0.1 arcsec in each coordinate.

An unusually strong radio outburst in Algol : flux density spectral and polarization observations.

We have monitored the largest radio outburst to date from the binary $beta$ Per (Algol). The observations, made at frequencies of 1400, 2695, 6000, and 8085 MHz, mark the first time a non-X-ray radio binary has been observed at flux densities exceeding 1 Jy. The outburst probably consisted of two Algol-type flares. The radio spectrum remained essentially constant throughout the outburst, and no polarization was detected. (AIP)

Streaming of solar particles between Sun and Earth

It has long been known that the physical state of the Earth’s upper atmosphere is closely related to solar activity-the growth and decay of sunspots, the corona, uprushing prominences and bright chromospheric flares. In particular, transient radiative and corpuscular emissions associated with solar flares produce the most outstanding electromagnetic disturbances in the environment of the Earth. It is generally believed that geomagnetic storms are caused by the impact of solar plasma clouds with the geomagnetic field(l). Associated aurora1 and ionospheric effects are the direct consequence of disturbances induced in the upper atmosphere. The evidence of continual agitation of the geomagnetic field in the polar regions suggests a constant stream of incoming particles even during geomagnetically quiet periods. This accords with certain observations of the motion of comet tailP, for which the name solar wind or streaming plasma has been proposed in contrast to the storm-producing plasma cloud(3). The accumulated evidence of recent years indicates that the Sun emits not only lowenergy plasmas but also, on occasions, very-high-energy particles, known as solar cosmic raysc4). Since 1942, eight events showing an unusual increase in cosmic ray intensity have been found in ground-based observations. They were associated with intense solar flares, and the particles arrived at the Earth within very short time-delay, indicating that the energy exceeded the relativistic range. Several small but distinct solar cosmic ray events have also been identified since the International Geophysical Year (1957-8) strengthened considerably the precise world network of neutron monitors. An arrival of sub-relativistic-energy particles is not detectable at ground level, but this information is now available from recently developed rocket and balloon measurements and indirectly by ionospheric observations. These particles emitted from a solar flare impinge onto the ionosphere in the polar-cap regions, thereby producing enhanced ionization and a particular type of aurora1 glow. Thus, the events are known as polar-cap blackouts(5-7), polar-cap absorptionPlO) and polar-glow auroraeol). Direct measurements by balloon(12) and by satellites (13) .have revealed that the energy spectrum of these solar particles is considerably broad, ranging from 1 to 1000 MeV. Statistical studies have shown that such events are much more numerous than was ever suspectedo4), and also that they are closely related to the particular type of solar flares associated with strong radio outbursts of continuum radiationul in particular, comprehensive measurements by recent space probes and satellites. Thus, it is now evident that an enormous number of particles with a considerable wide-energy spectrum is streaming out from the Sun. Since solar particles detected in the environment of

THE EVOLUTION OF GALAXIES, II

It is generally assumed that galaxies evolve and that their present appearance is determined by their evolutionary history (see Paper I1). Underlying most of the recent work on the evolution of galaxies is the tacit assumption that the evolutionary time scale of galaxies is of the same order as the age of the universe. This assumption leads to the conclusion that the evolution of galaxies, at least during the last few 109 years, has been a slow and gradual affair. Recent investigations of strong extragalactic radio sources indicate that this conclusion may not be correct. The energies involved in strong radio outbursts are so high that they might well be capable of exerting a profound influence on the subsequent evolution of those galaxies in which they occur. This suggests that one should at least consider the possibility that the evolutionary history of galaxies is affected both by catastrophic events and by gradual changes. Among the 20 or 30 nearest intrinsically bright galaxies there are at least two2»8 (NGC 5128 = Centaurus A, a peculiar ellir> tical, and NGC 3034 = M 82, an irregular or edge-on spiral) in which a violent explosion must have taken place within the astronomically speaking recent past. The available data seem to suggest that explosive events in galaxies are perhaps infrequent, but certainly not exceedingly rare. This raises the interesting question whether optical evidence might indicate that a galaxy was formerly a radio source. In the case of elliptical galaxies this possibility appears remote because the explosion presumably will affect only the invisible interstellar gas and not the stars. In the case of spiral and irregular galaxies the situation appears more promising because a violent explosion will affect both the dynamics and the distribution of the interstellar gas, which in turn determines the distribution of the OB stars which outline the spiral arms. The aftereffects of a violent explosion on the spiral arms of a galaxy might remain discernible during a few periods of rotation. Spiral arms contribute but little to the total light of Sb