Radio Observations of the 20 January 2005 X-class Flare

We present a multi-frequency and multi-instrument study of the 20 January 2005 event. We focus mainly on the complex radio signatures and their association with the active phenomena taking place: flares, CMEs, particle acceleration, and magnetic restructuring. As a variety of energetic-particle accelerators and sources of radio bursts are present, in the flare – ejecta combination, we investigate their relative importance in the progress of this event. The dynamic spectra of ARTEMIS-IV – Wind/Waves – HiRAS, with 2000 MHz – 20 kHz frequency coverage, were used to track the evolution of the event from the low corona to the interplanetary space; these were supplemented with SXR, HXR, and γ-ray recordings. The observations were compared with the expected radio signatures and energetic-particle populations envisaged by the Standard Flare – CME model and the reconnection outflow termination shock model. A proper combination of these mechanisms seems to provide an adequate model for the interpretation of the observational data.     

A statistical study of Galactic SNRs using the PMN survey

The Parkes–MIT–NRAO (PMN) radio survey has been used to generate a quasi all-sky study of Galactic Supernova Remnants (SNRs) at a common frequency of 4.85 GHz (λ=6 cm). We present flux densities estimated for the sample of 110 Southern Galactic SNRs (up to δ=−65°) observed with the Parkes 64-m radio telescope and an additional sample of 54 from the Northern PMN (up to δ=+64°) survey undertaken with the Green Bank 43-m (20 SNRs) and 91-m (34 SNRs) radio telescopes. Out of this total sample of 164 selected SNRs (representing 71% of the currently 231 known SNRs in the Green catalogue) we consider 138 to provide reliable estimates of flux density and surface brightness distribution. This sub-sample represents those SNRs which fall within carefully chosen selection criteria which minimises the effects of the known problems in establishing reliable fluxes from the PMN survey data. Our selection criteria are based on a judicious restriction of source angular size and telescope beam together with careful evaluation of fluxes on a case by case basis. Direct comparison of our new fluxes with independent literature values gives excellent overall agreement. This gives confidence in the newly derived PMN fluxes when the selection criteria are respected. We find a sharp drop off in the flux densities for Galactic SNRs beyond 4 Jy and then a fairly flat distribution from 5 to 9 Jy, a slight decline and a further flat distribution from 9 to 20 Jy though the numbers of SNR in each Jy bin are low. We also re-visit the contentious Σ–D (radio surface brightness–SNRs diameter) relation to determine a new power law index for a sub-sample of shell type SNRs which yields β=−2.2±0.6. This new evaluation of the Σ–D relation, applied to the restricted sample, provides new distance estimates and their Galactic scale height distribution. We find a peak in the SNR distribution between 7–11 kpc with most restricted to ±100 pc Galactic scale height.     

Relationship of great soft X-ray flares with other solar activity phenomena

We present study of relationship of GSXR flares with Hα flares, hard X-ray (HXR) bursts, microwave (MW) bursts at 15.4 GHz, type II/IV radio bursts, coronal mass ejections (CMEs), protons flares (>10 MeV) and ground level enhancement (GLE) events we find that about 85.7%, 93%, 97%, 69%, 60%, 11.1%, 79%, 46%, and 23%% GSXR flares are related/associated with observed Hα flares, HXR bursts, MW bursts at 15.4 GHz, type II radio bursts, type IV radio bursts, GLE events, CMEs, halo CMEs, and proton flares (>10 MeV), respectively. In the paper we have studied the onset time delay of GSXR flares with Hα flares, HXR, and MW bursts which shows the during majority GSXR flares SXR emissions start before the Hα, HXR and MW emissions, respectively while during 15–20% of GSXR flares the SXR emissions start after the onset of Hα, HXT and MW emissions, respectively indicating two types of solar flares. The, onset time interval between SXR emissions and type II radio bursts, type IV radio bursts, GLE events CMEs, halo CMEs, and protons flares are 1–15 min, 1–20 min, 21–30 min, 21–40 min, 21–40 min, and 1–4 hrs, respectively. Following the majority results we are of the view that the present investigations support solar flares models which suggest flare triggering first in the corona and then move to chromospheres/ photosphere to starts emissions in other wavelengths. The result of the present work is largely consistent with “big flare syndrome” proposed by Kahler (1982).     

Are There Radio-quiet Solar Flares?

Some 15% of solar flares having a soft X-ray flux above GOES class C5 are reported to lack coherent radio emission in the 100 – 4000 MHz range (type I – V and decimetric emissions). A detailed study of 29 such events reveals that 22 (76%) of them occurred at a radial distance of more than 800″ from the disk center, indicating that radio waves from the limb may be completely absorbed in some flares. The remaining seven events have statistically significant trends to be weak in GOES class and to have a softer non-thermal X-ray spectrum. All of the non-limb flares that were radio-quiet above 100 MHz were accompanied by metric type III emission below 100 MHz. Out of 201 hard X-ray flares, there was no flare except near the limb (R>800″) without coherent radio emission in the entire meter and decimeter range. We suggest that flares above GOES class C5 generally emit coherent radio waves when observed radially above the source.     

The Geminga fraction

Radio-quiet γ-ray pulsars like Geminga may account for a number of the unidentified EGRET sources in the Galaxy. The number of Geminga-like pulsars is very sensitive to the geometry of both the γ-ray and radio beams. Recent studies of the shape and polarization of pulse profiles of young radio pulsars have provided evidence that their radio emission originates in wide cone beams at altitudes that are a significant fraction (1–10%) of their light cylinder radius. Such wide radio emission beams will be visible at a much larger range of observer angles than the narrow core components thought to originate at lower altitude. Using 3D geometrical modeling that includes relativistic effects from pulsar rotation, we study the visibility of such radio cone beams as well as that of the γ-ray beams predicted by slot gap and outer gap models. From the results of this study, one can obtain revised predictions for the fraction of Geminga-like, radio quiet pulsars present in the γ-ray pulsar population.      

Orientation of extragalactic radio sources relative to the elliptical galaxies associated with them

The relative orientations of the optical and radio axes of radio galaxies are analyzed using data for 271 objects. It is found that the radio axes correlate with the minor axes of the optical galaxies for more elongated radio galaxies (K > 2.5, where K is the ratio of the lengths of the major and minor axes of the radio image) and for radio galaxies of the class FRII, whereas for less elongated radio galaxies (K < 2.5) and radio galaxies of the class FRI the radio axes correlate with the major axes of the optical galaxy. In both cases the correlation turns out to be more significant when the radio galaxies are classified in terms of their elongation than when they are classified in terms of the Fanaroff-Riley criterion. The classification in terms of elongation of the radio image can therefore be of interest for understanding overall problems associated with the mechanism of formation and evolution of radio galaxies. A theoretical foundation for such a classification may be the alternative mechanism of formation of radio galaxies from relativistic plasma ejected from the central part of the optical galaxy and moving in its large-scale, dipole magnetic field. Translated from Astrofizika, Vol. 42, No. 3, pp. 365–371, July–September, 1999.     

Finding Faint Intermediate-Mass Black Holes in the Radio Band

We discuss the prospects for detecting faint intermediate-mass black holes, such as those predicted to exist in the cores of globular clusters and dwarf spheroidal galaxies. We briefly summarize the difficulties of stellar dynamical searches, then show that recently discovered relations between black hole mass, X-ray luminosity and radio luminosity imply that in most cases, these black holes should be more easily detected in the radio than in the X-rays. Finally, we show upper limits from some radio observations of globular clusters, and discuss the possibility that the radio source in the core of the Ursa Minor dwarf spheroidal galaxy might be a ∼10,000–100,000 M⊙ black hole.     

Radio-to-TeV γ-ray emission from PSR B1259–63

We discuss the implications of the recent X-ray and TeV γ-ray observations of the PSR B1259–63 system (a young rotation powered pulsar orbiting a Be star) for the theoretical models of interaction of pulsar and stellar winds. We show that previously considered models have problems to account for the observed behaviour of the system. We develop a model in which the broad band emission from the binary system is produced in result of collisions of GeV–TeV energy protons accelerated by the pulsar wind and interacting with the stellar disk. In this model the high energy γ-rays are produced in the decays of secondary neutral pions, while radio and X-ray emission are synchrotron and inverse Compton emission produced by low-energy (≤100 MeV) electrons from the decays of secondary charged π ^± mesons. This model can explain not only the observed energy spectra, but also the correlations between TeV, X-ray and radio emission components.      

Galaxy evolution from a microJansky radio survey

A strong evolution of galaxies is observed for 0<z<1, as evidenced by an increase of almost an order of magnitude in the galaxy star-formation rate density. However, it is known that dust obscuration has affected our understanding of galaxy evolution over this significant fraction of the age of the Universe. In order to study galaxy evolution free from dust induced biases, an ultra deep radio survey – the Phoenix Deep Survey – was initiated. With a detection limit of 60μJy, this homogeneous survey, complemented with multiwavelength (photometric and spectroscopic) observations, is being used to build a consistent picture of galaxy evolution. The ultra-deep radio source counts are presented, and interpreted using luminosity function evolutionary models. The discovery of extremely dusty galaxies from this survey, along with the clustering properties of the sub-mJy radio population, are also discussed. This revised version was published online in July 2006 with corrections to the Cover Date.     

The Dynamics of Radio Galaxies and Double–Double Radio Galaxies

Relativistic and magnetized plasma ejected by radio loud AGNs through jets form the diffuse lobes of radio galaxies. The radiating particles (electron/electron–positron) in lobes emit in radio via the synchrotron process and X-ray via inverse-Compton scattering of cosmic microwave background photons. The thermal environment around radio galaxies emits X-rays via the thermal bremsstrahlung process. By combining information from these processes we can measure physical conditions in and around the radio lobes and thus study the dynamics of radio galaxies, including double–double radio galaxies.     

A Hidden Radio Halo in the Galaxy Cluster A 1682?

High sensitivity observations of radio halos in galaxy clusters at frequencies ν ≤ 330 MHz are still relatively rare, and very little is known compared to the classical 1.4 GHz images. The few radio halos imaged down to 150–240 MHz show a considerable spread in size, morphology and spectral properties. All clusters belonging to the GMRT Radio Halo Survey with detected or candidate cluster-scale diffuse emission have been imaged at 325 MHz with the GMRT. Few of them were also observed with the GMRT at 240 MHz and 150 MHz. For A 1682, imaging is particularly challenging due to the presence of strong and extended radio galaxies at the center. Our data analysis suggests that thew radio galaxies are superposed to very low surface brightness radio emission extended on the cluster scale, which we present here.     

Origin of the Submillimeter Radio Emission During the Time-Extended Phase of a Solar Flare

Solar flares observed in the 200 – 400 GHz radio domain may exhibit a slowly varying and time-extended component which follows a short (few minutes) impulsive phase and can last for a few tens of minutes to more than one hour. The few examples discussed in the literature indicate that such long-lasting submillimeter emission is most likely thermal bremsstrahlung. We present a detailed analysis of the time-extended phase of the 27 October 2003 (M6.7) flare, combining 1 – 345 GHz total-flux radio measurements with X-ray, EUV, and Hα observations. We find that the time-extended radio emission is, as expected, radiated by thermal bremsstrahlung. Up to 230 GHz, it is entirely produced in the corona by hot and cool materials at 7 – 16 MK and 1 – 3 MK, respectively. At 345 GHz, there is an additional contribution from chromospheric material at a few 10⁴ K. These results, which may also apply to other millimeter–submillimeter radio events, are not consistent with the expectations from standard semiempirical models of the chromosphere and transition region during flares, which predict observable radio emission from the chromosphere at all frequencies where the corona is transparent.     

RATAN-600 7.6-cm deep sky strip surveys at the declination of the SS433 source during the 1980–1999 period. Data reduction and the catalog of radio sources in the right-ascension interval 7h ≤ R.A. < 17h

We use two independent methods to reduce the data of the surveys made with RATAN-600 radio telescope at 7.6 cm in 1988–1999 at the declination of the SS433 source. We also reprocess the data of the “Cold” survey (1980–1981). The resulting RCR (RATAN COLD REFINED) catalog contains the right ascensions and fluxes of objects identified with those of the NVSS catalog in the right-ascension interval 7 ^h ≤ R.A. < 17 ^h . We obtain the spectra of the radio sources and determine their spectral indices at 3.94 and 0.5 GHz. The spectra are based on the data from all known catalogs available from the CATS, Vizier, and NED databases, and the flux estimates inferred from the maps of the VLSS and GB6 surveys. For 245 of the 550 objects of the RCR catalog the fluxes are known at two frequencies only: 3.94 GHz (RCR) and 1.4 GHz (NVSS). These are mostly sources with fluxes smaller than 30mJy. About 65% of these sources have flat or inverse spectra (α > −0.5). We analyze the reliability of the results obtained for the entire list of objects and construct the histograms of the spectral indices and fluxes of the sources. Our main conclusion is that all 10–15 mJy objects found in the considered right-ascension interval were already included in the decimeter-wave catalogs.     

Discovery of a Giant Radio Halo in a Massive Merging Cluster at z?=?0.443

We have discovered a giant radio halo in the massive merging cluster MACSJ0417.5-1154. This cluster, at a redshift of 0.443, is one of the most X-ray luminous galaxy cluster in the MAssive Cluster Survey (MACS) with an X-ray luminosity in the 0.1–2.4 keV band of 2.9×10⁴⁵ erg s^− 1. Recent observations from GMRT at 230 and 610 MHz have revealed a radio halo of ∼ 1.2 × 0.3 Mpc² in extent. This halo is elongated along the North-West, similar to the morphology of the X-ray emission from Chandra. The 1400 MHz radio luminosity (L _r) of the halo is ∼2 × 10²⁵ W Hz^− 1, in good agreement with the value expected from the L _x − L _r correlation for cluster halos.     

Microwave observations of compact radio sources during solar eclipses on RT-22

Based on the observations of solar eclipses performed on the RT-22 radio telescope at CrAO in the wavelength range 2.0–3.5 cm, we consider the fine spatial structure of the microwave emission from the quiet Sun. We have established that the positions of compact radio sources with a typical size of about 7″.0 and coronal bright points coincide. The mean radio flux exceeds the level of the quiet Sun by 0.28 sfu. The brightness temperatures increase with wavelength and lie within the range 0.3–2.7 MK. Evidence for a nonthermal nature of the emission from compact radio sources has been obtained.     

The Radio Recombination Line Intensities Of Atoms And Ions: Helium,Carbon And Oxygen

The radio recombination line intensities of heavy elements of helium, carbon and oxygen are calculated with accounting for dielectronic recombination. Dielectronic recombination rates are determined accurate to the second order of a perturbation theory and the rates are described as function of principal quantum number for helium-like atom or ion. Balance equations are solved for the departure coefficients from LTE b_n. The collision and spontaneous transition rates are accounted for the balance equations, in which non-equilibrium distribution source is dielectronic recombination. Non-equilibrium amplification coefficients are found as functions of a medium temperature, density and ion charge z = 1–3 for radio recombination lines. Optical depths are calculated for the heavy element low-frequency lines with the numbers 300 > n > 1200. For the chosen electronic temperatures and densities T_e = 0.8× 10⁴–10× 10⁴ K, N_e = 0.05–0.1 cm⁻³ the line optical depth is determined by the values τ_L∼ 0.1× 10⁻⁴–100× 10⁻⁴. Calculated for free-free transition rates, the optical depth is given by using the value τ_ff∼ 10⁻²τ_L.     

Quasiperiodic oscillations in the active solar regionsfrom the data of nobeyama radioheliograph

The use of integral characteristics of radio spots showed that in addition to the known 3–5-min oscillations, the above-spot regions of sunspots exhibit quasiperiodic oscillations of intensity, perimeter, sectional area, and area of the surface of the above-spot source radio image with periods in the ranges of 25–80, 90–110, 120–140, and 160–210 min. These periods are observed for all spots studied using the different characteristics of a radio source, which does not contradict the interpretation of these low-frequency oscillations as natural oscillations of spots near a certain position of stable equilibrium.     

Further VLA observations of hydrogen deficient stars

VLA observations at 6 cm have been obtained for three hydrogen-deficient objects υ Sgr, V 348 Sgr, and A bell 58. A bell 58 was also observed at 2 cm. Only upper limits to the flux density could be set for these sources. A new radio source at 6 cm was found in the field of υ Sgr. The upper limit for 6 cm flux density of V348 Sgr sets an upper limit to its reddening asE(B–V) ≤ 0.65. The hydrogen deficient planetary nebula A 58 shows much lower radio flux than expected from the infrared-radio flux density relationship of planetary nebulae. National Radio Astronomy Observatory’s Very Large Array is operated by Associated Universities Inc. under contract with National Science Foundation, USA.     

Galaxy Evolution in the Reddest Possible Filter

We describe an observational programme aimed at understanding the radio emission from distant, rapidly evolving galaxy populations. These observations were carried out at 1.4 and 8.5 GHz with the VLA, centred on the Hubble Deep Field, obtaining limiting flux densities of 40 and 8 μJy respectively. The differential count of the radio sources is marginally sub-Euclidean to the completeness limits(γ = − 2.4 ± 0.1) and fluctuation analysis suggests nearly 60 sources per arcmin² at the 1 μJy level. Using high-resolution 1.4 GHz observations obtained with MERLIN, we resolve all radio sources detected in the VLA complete sample and measure a median angular size for the microjansky radio population of 1-2". This clue, coupled with the steep spectral index of the 1.4 GHz selected sample, suggests diffuse synchrotron radiation in z ∼ 1 galactic discs. The wide-field HST and ground-based optical exposures show that the radio sources are identified primarily with disc systems composed of irregulars, peculiars, interacting/merging galaxies and a few isolated field spirals. Only 20% of the radio sources can be attributed to AGN – the majority are probably associated with starburst activity. The available redshifts range from 0.1 to 3, with a mean of about 0.8. We are plrobably witnessing a major episode of starburst activity in these luminous (L > L _*) systems, occasionallyaccompanied by an embedded AGN.About 20% of the radio sources remain unidentified to I = 26-28 inthe HDF and flanking fields. Several of these objectshave extremely red counterparts. We suggestthat these are high-redshift dusty protogalaxies. This revised version was published online in July 2006 with corrections to the Cover Date.     

A Fundamental Plane of Black Hole Activity: Pushing Forward the Unification Scheme

We examine the disc-jet connection in stellar mass and supermassive black holes by investigating the properties of their compact emission in the hard X-ray and radio bands. We compile a sample of ∼100 active galactic nuclei with measured mass, 5 GHz core emission, and 2–10 keV luminosity, together with eight galactic black holes with a total of ∼50 simultaneous observations in the radio and X-ray bands. Using this sample, we study the correlations between the radio (L_R) and the X-ray (L_X) luminosity and the black hole mass (M). We find that the radio luminosity is correlated with both M and L_X, at a highly significant level. We show how this result can be used to extend the standard unification by orientation scheme to encompass unification by mass and accretion rate.