Annual cycles in the interstellar scintillation time-scales of PKS B1519–273 and PKS B1622–253

We have used the University of Tasmania's 30-m radio telescope at Ceduna in South Australia to regularly monitor the flux density of a number of southern blazars. We report the detection of an annual cycle in the variability time-scale of the centimetre radio emission of PKS B1622−253. Observations of PKS B1519−273 over a period of nearly 2 yr confirm the presence of an annual cycle in the variability time-scale in that source. These observations prove that interstellar scintillation is the principal cause of inter-day variability at radio wavelengths in these sources. The best-fitting annual cycle model for both sources implies a high degree of anisotropy in the scattering screen and that it has a large velocity offset with respect to the local standard of rest. This is consistent with a greater screen distance for these 'slow' intra-day variability (IDV) sources than for rapid scintillators such as PKS B0405−385 or J1819+3845.     

Substructures in lens galaxies: PG1115+080 and B1555+375, two fold configurations

We study the anomalous flux ratio which is observed in some four-image lens systems, where the source lies close to a fold caustic. In this case two of the images are close to the critical curve and their flux ratio should be equal to unity, instead in several cases the observed value differs significantly. The most plausible solution is to invoke the presence of substructures, as for instance predicted by the Cold Dark Matter scenario, located near the two images. In particular, we analyze the two fold lens systems PG1115+080 and B1555+375, for which there are not yet satisfactory models which explain the observed anomalous flux ratios. We add to a smooth lens model, which reproduces well the positions of the images but not the anomalous fluxes, one or two substructures described as singular isothermal spheres. For PG1115+080 we consider a smooth model with the influence of the group of galaxies described by a SIS and a substructure with mass ∼10⁵ M _⊙ as well as a smooth model with an external shear and one substructure with mass ∼10⁸ M _⊙. For B1555+375 either a strong external shear or two substructures with mass ∼10⁷ M _⊙ reproduce the data quite well.     

On the Multiplicity of the O-Star Cyg OB2 #8a and its Contribution to the γ-ray Source 3EG J2033+4118

We present the results of an intensive spectroscopic campaign in the optical waveband revealing that Cyg OB2 #8A is an O6+O5.5 binary system with a period of about 21.9 days. Cyg OB2 #8A is a bright X-ray source, as well as a non-thermal radio emitter. We discuss the binarity of this star in the framework of a campaign devoted to the study of non-thermal emitters, from the radio waveband to γ-rays. In this context, we attribute the non-thermal radio emission from this star to a population of relativistic electrons, accelerated by the shock of the wind-wind collision. These relativistic electrons could also be responsible for a putative γ-ray emission through inverse Compton scattering of photospheric UV photons, thus contributing to the yet unidentified EGRET source 3EG J2033+4118. Based partly on data Obtained at the Observatoire de Haute-Provence, France.     

The radio source Z0254+43: z = 4.067

In January 2005 spectral observations of the radio source Z0254+43 were made on the BTA at the Special Astrophysical Observatory (SAO) of the Russian Academy of Sciences (RAN) and its red shift was found to be z=4.057. The BVRI magnitudes were found to be 22.68, 21.19, 19.94, and 19.23, respectively. Photometric observations in December 2005 on the Zeiss-1000 at the SAO revealed no significant variation in the optical emission from this object over that year. We can discuss its variability on an hourly time scale with some caution. The variability of the flux from Z0254+43 was observed from 1990–2005 on the RATAN-600 over a wide range of frequencies. It turns out that the amplitude of the variability is minimal at a frequency of ∼8 GHz. A model for the variability has been constructed which yields an estimate of ∼28° for the orientation of the jet of Z0254+43 to the line of sight. The luminosity of Z0254+43 in the optical range is ∼2·10²⁶ W/Hz and in the radio frequency range, ∼2·1027 W/Hz. __________ Translated from Astrofizika, Vol. 49, No. 2, pp. 209–220 (May 2006).     

Solar wind velocity and normalized scintillation index from single-station IPS observations

The recently refurbished Ooty Radio Telescope in southern India was used in a two-month campaign of interplanetary scintillation (IPS) observations in collaboration with the Cambridge IPS array in England during April–May 1992. The unique feature of this campaign was that, for the first time, scintillation enhancements were predicted in real time by observing solar events on 7–8 May, 1992 and then detected at both Ooty and Cambridge. Also, for the first time, high spatial resolution ( 100 sources sr^–1) solar wind all-sky velocity maps were obtained at Ooty. Good consistency is found between the IPS observations from both observatories andin-situ shocks detected at Earth by IMP-8.Yohkoh soft X-ray images were used to infer the generation of a coronal mass ejection on 7 May, 1992.     

Statistical Tests of the Unification Scheme for High Luminosity Double Radio Sources

We have carried out some statistical tests of relativistic beaming and radio source orientation scenarios using the core dominance parameter Rand linear size D of a recent sample of double-lobed quasars and radio galaxies as orientation indicators. Our results show that the maximum Doppler boosting occurs within a cone angle of ∼ 13^°corresponding to an optimum Lorentz factor of ∼ 5. On the average, quasar cores appear to be boosted by a factor of ∼ 10 relative to those of radio galaxies. In general, we found that quasars lie at closer angles to the line of sight than radio galaxies with median values of 28^° and 51^°respectively, implying a relative foreshortening factor of ∼ 2. These results are consistent with the simple relativistic beaming and orientation-based unification hypotheses in which quasars are the beamed counterparts of powerful radio galaxies which form the isotropic parent population. The results show a strong evidence that orientation of source axis with respect to the line of sight is a crucial parameter in the classification schemes for radio sources. This revised version was published online in July 2006 with corrections to the Cover Date.     

MANGALA VALLES, MARS: ASSESSMENT OF EARLY STAGES OF FLOODING AND DOWNSTREAM FLOOD EVOLUTION

The Mangala Valles system is an ∼ ∼900 km fluvially carved channel system located southwest of the Tharsis rise and is unique among the martian outflow channels in that it heads at a linear fracture within the crust as opposed to a collapsed region of chaos as is the case with the circum-Chryse channels. Mangala Valles is confined within a broad, north–south trending depression, and begins as a single valley measuring up to 350 km wide that extends northward from a Memnonia Fossae graben, across the southern highlands toward the northern lowlands. Approximately 600 km downstream, this single valley branches into multiple channels, which ultimately lose their expression at the dichotomy boundary. Previous investigations of Mangala Vallis suggested that many of the units mapped interior to the valley were depositional, related to flooding, and that a minimum of two distinct periods of flooding separated by tens to hundreds of millions of years were required to explain the observed geology. We use infrared and visible images from the THermal EMission Imaging System (THEMIS), and topographic data from the Mars Orbiting Laser Altimeter (MOLA), to investigate the nature of the units mapped within Mangala Vallis. We find that the geomorphology of the units, as well as their topographic and geographic distribution, are consistent with most of them originating from a single assemblage of volcanic flow deposits, once continuous with volcanic flows to the south of the Memnonia Fossae source graben. These flows resurfaced the broad, north–south trending depression into which Mangala Vallis formed prior to any fluvial activity. Later flooding scoured and eroded this volcanic assemblage north of the Mangala source graben, resulting in the present distribution of the units within Mangala Vallis. Additionally, our observations suggest that a single period of catastrophic flooding, rather than multiple periods separated by tens to hundreds of millions of years, is consistent with and can plausibly explain the interior geology of Mangala Vallis. Further, we present a new scenario for the source and delivery of water to the Mangala source graben that models flow of groundwater through a sub-cryosphere aquifer and up a fracture that cracks the cryosphere and taps this aquifer. The results of our model indicate that the source graben, locally enlarged to a trough near the head region of Mangala, would have required less than several days to fill up prior to any spill-over of water to the north. Through estimates of the volume of material missing from Mangala (13,000–20,000 km³), and calculation of mean discharge rates through the channel system (∼ ∼5 × 10⁶ m³ s⁻¹), we estimate that the total duration of fluvial activity through the Mangala Valles was 1–3 months.     

Synchrotron self-Compton models of high brightness temperature radio sources

We re-examine the maximum brightness temperature that a synchrotron source can sustain by adapting standard synchrotron theory to an electron distribution that exhibits a deficit at low energy. The absence of low energy electrons reduces the absorption of synchrotron photons, allowing the source to reach a higher brightness temperature without the onset of catastrophic cooling. We find that a temperature of ∼10¹⁴ K is possible at GHz frequencies. In addition, a high degree of intrinsic circular polarisation is produced. We compute the stationary, synchrotron and self-Compton spectrum arising from the continuous injection of such a distribution (modelled as a double power-law) balanced by radiative losses and escape, and compare it with the simultaneously observed multi-wavelength spectrum of the BL Lac object S5 0716+714. This framework may provide an explanation of other high brightness-temperature sources without the need for mechanisms such as coherent emission or proton synchrotron radiation.     

Coherent Synchrotron Radiation of Gamma-Ray Bursts

By now there is no doubt that the gamma-ray bursts (GRB) have a cosmological origin. This allows to regard GRB as the most powerful known energy sources, ε∼ 10⁵⁴ erg (with a total number of gamma quanta N_γ∼ 10⁶⁰). A plausible mechanism of coherent synchrotron radiation (CSR) of relativistic electrons driven by a local magnetic field is studied in this paper. We consider relativistic electrons arising in the Compton scattering of a GRB in directions close to that of the ray from the source to a ground-based observer. The synchrotron pulses from Compton electrons located at different points on the line between the GRB source and the observer arrive at the observation point simultaneously. This simultaneity ensures the coherence of the detected radiation. Both molecular clouds in the host galaxy of the GRB and our own Galaxy, as well as the Earth atmosphere are assumed to be scatterers of the GRB radiation. Signals of each scatterer reach the Earth surface, and can be detected at radio wavelengths. We estimate the characteristics of this radiation. The comparison of GRB data with the corresponding information on CSR pulses offers a way to determine some global characteristics of the medium between the Earth and the GRB source.     

High-Dispersion Spectroscopy of the Sodium (NA) Emission within the Inner Coma of C/1995 O1 (Hale-Bopp)

Very-high spectral resolution observations of the neutral Na emission have enabled measurements of the velocity dispersions of the Na atoms within ∼40,000 km of the opto center of Hale-Bopp. Asymmetric Na D line profiles imply both an in situ or core Na source and a secondary Na source at locations within the inner coma. The core velocity distribution had a FWHM of 2 km s^-1. The extended source FWHM increased with distance from the nucleus (up to ∼6 km s^-1, but appeared smaller in the more dusty regions (∼2.5–3.0 km s^-1) of the inner coma. The D₂/D₁ line strength ratio was consistent with an optically thin inner coma. Within 5,000 km of the opto center the continuum spatial intensity profiles decreased as ∼r^-1 while the Na D emission decreased at less than r^-1. This revised version was published online in July 2006 with corrections to the Cover Date.     

Constraints on unstable heavy neutrinos from cosmology

Cosmological scenarios with massive unstable neutrinos are discussed. Restrictions on the mass and the lifetime of the unstable neutrino are derived from (a) age and mass density of the universe and (b) the growth of primordial fluctuations. It will not be possible to accommodate unstable neutrinos with masses above ∼ 1 ke V in standard cosmology unless they have exceedingly small lifetime: Τ <5 × 10⁸ s.     

Hard X-ray emission from the SNR G337.2+0.1

We report hard X-ray emission of the non-thermal supernova remnant G337.2+0.1. The source presents centrally filled and diffuse X-ray emission. A spectral study confirms that the column density of the central part of the object is about N _H∼5.9(±1.5)×10²² cm⁻² and its X-ray spectrum is well represented by a single power-law with a photon index Γ=0.96±0.56. Detailed spectral analysis indicates that the outer region is highly absorbed and quite softer than the inner region. Characteristics already observed in other well-known X-ray plerions. Based on the gathered information, we confirm the SNR nature of G337.2+0.1, and suggest that the central region of the source is a pulsar wind nebula (PWN), originated by an energetic though yet undetected pulsar.     

Preparing For Hyperseed MAC: An Observing Campaign To Monitor The Entry Of The Genesis Sample Return Capsule

The imminent return of the Genesis Sample Return Capsule (SRC) from the Earth’s L1 point on September 8, 2004, represents the first opportunity since the Apollo era to study the atmospheric entry of a meter-sized body at or above the Earth’s escape speed. Until now, reentry heating models are based on only one successful reentry with an instrumented vehicle at higher than escape speed, the 22 May 1965 NASA “FIRE 2” experiment. In preparation of an instrumented airborne and ground-based observing campaign, we examined the expected bolide radiation for the reentry of the Genesis SRC. We find that the expected emission spectrum consists mostly of blackbody emission from the SRC surface (T∼ ∼2630 K@peak heating), slightly skewed in shape because of a range of surface temperatures. At high enough spectral resolution, shock emission from nitrogen and oxygen atoms, as well as the first positive and first negative bands of N₂⁺, will stand out above this continuum. Carbon atom lines and the 389-nm CN band emission may also be detected, as well as the mid-IR 4.6-μm CO band. The ablation rate can be studied from the signature of trace sodium in the heat shield material, calibrated by the total amount of matter lost from the recovered shield. A pristine collection of the heat shield would also permit the sampling of products of ablation.     

A massive, dusty toroid with large grains in the pre-planetary nebula IRAS22036+5306

Using the Submillimeter Array (SMA), we have obtained high angular-resolution (∼1″) interferometric maps of the submillimeter (0.88 mm) continuum and CO J=3–2 line from IRAS 22036+5306 (I 22036), a bipolar pre-planetary nebula (PPN) with knotty jets discovered in our HST SNAPshot survey of young PPNe. In addition, we have obtained supporting lower-resolution (∼10″) 2.6 mm continuum and CO, ¹³CO J=1–0 observations with the Owens Valley Radio Observatory (OVRO) interferometer. We find an unresolved source of submillimeter (and millimeter-wave) continuum emission in I 22036, implying a very substantial mass (0.02–0.04M _⊙) of large (i.e., radius ≳1 mm), cold (≲50 K) dust grains associated with I 22036’s toroidal waist. The CO J=3–2 observations show the presence of a very fast (∼220 km s⁻¹), highly collimated, massive (0.03M _⊙) bipolar outflow with a very large scalar momentum (about 10³⁹ g cm s⁻¹), and the characteristic spatio-kinematic structure of bow-shocks at the tips of this outflow. The fast outflow in I 22036, as in most PPNe, cannot be driven by radiation pressure. The large mass of the torus suggests that it has most likely resulted from common-envelope evolution in a binary, however it remains to be seen whether or not the time-scales required for the growth of grains to millimeter sizes in the torus are commensurate with such a formation scenario. The presence of the torus should facilitate the formation of the accretion disk needed to launch the jet. We also find that the ¹³C/¹²C ratio in I 22036 is very high (0.16), close to the maximum value achieved in equilibrium CNO-nucleosynthesis (0.33). The combination of the high circumstellar mass (i.e., in the torus and an extended dust shell inferred from ISO far-infrared spectra) and the high ¹³C/¹²C ratio in I 22036 provides strong support for this object having evolved from a massive (≳4M _⊙) progenitor in which hot-bottom-burning has occurred.     

Gamma-Ray Line Observations of the 2000 July 14 Flare and SEP Impact on the Earth

The HXS and GRS detectors on Yohkoh observed the 14 July 2000, X5.7 flare, beginning at ∼ 10:20 UT, ∼ 4 min before the peak in soft X-rays. The hard X-rays and γ-rays peaked ∼ 3 min later at ∼ 10:27 UT. Solar γ-ray emission lasted until ∼ 10:40 UT. Impact of high-energy ions at the Sun is revealed by the γ-ray lines from neutron capture, annihilation radiation and de-excitation that are visible above the bremsstrahlung continuum. From measurement of these lines we find that the flare-averaged spectrum of accelerated protons is consistent with a power law ge10 MeV with index 3.14±0.15 and flux 1.1×10³² protons MeV⁻¹ at 10 MeV. We estimate that there were ∼1.5×10³⁰ erg in accelerated ions if the power law extended without a break down to 1 MeV; this is about 1% of the energy in electrons > 20 keV from measurements of the hard X-rays. We find no evidence for spectral hardening in the hard X-rays that has been suggested as a predictor for the occurrence of solar energetic particle (SEP) events. This was the third largest proton event above 10 MeV since 1976. The GRS and HXS also observed γ-ray lines and continuum produced by the impact of SEP on the Earth's atmosphere beginning about 13 UT on 14 July. These measurements show that the SEP spectrum softened considerably over the next 24 hours. We compare these measurements with proton measurements in space.     

Disks Around Post-Main Sequence Binaries

We propose that at least two stars on or near the AGB have long-lived orbiting disks: HD 44179, the central star in the Red Rectangle, and BM Gem, a carbon-rich star with an oxygen-rich circumstellar envelope. The CO emission from both of these disks has a spike with a width near ∼2 km s⁻¹, indicating disk radii of ∼10¹⁶ cm. The dust in such disks is therefore quite cold (near T ∼ 50 K for the Red Rectangle) and may emit primarily at submillimeter wavelengths. The disks around stars where there is also substantial mass loss may not be easily observable; there could be many as yet undiscovered disks around AGB stars This revised version was published online in September 2006 with corrections to the Cover Date.     

Cooling of magnetars with internal layer heating

We model thermal evolution of magnetars with a phenomenological heat source in a spherical internal layer and compare the results with observations of persistent thermal radiation from magnetars. We show that the heat source should be located in the outer magnetar’s crust, at densities ρ≲5×10¹¹ g cm⁻³, and the heating rate should be ∼10²⁰ erg cm⁻³ s⁻¹. Heating deeper layers is extremely inefficient because the thermal energy is mainly radiated away by neutrinos and does not warm up the surface to the magnetar’s level. This deep heating requires too much energy; it is inconsistent with the energy budget of neutron stars.      

1.3 mm Plateau de Bure Observations of IRC+10216

The Plateau de Bure millimeter-wave interferometer has been used at 1.3 mm wavelength to observe the prototype carbon-star IRC+10216 in the continuum and in the v = 1, J = 13 − 11 transition of SiS at 234.8 GHz. The 3 mm continuum and the v = (0, 2⁰, 2), J = 1 − 0 HCN transition were simultaneously observed. The source of vibrationally excited SiS appears resolved, and a source size of ∼ 0.4″ or 7 10¹⁴cm (10 stellar radii) is derived, in agreement with a crude model of line formation. This revised version was published online in September 2006 with corrections to the Cover Date.     

On the supernova remnants produced by pulsars

We conclude that pulsar-driven supernova remnants (SNRs) are extremely rare objects. Indeed an analysis of the known sample of plerions suggests a very low birthrate ∼ 1 in 240 years. Long-lived and bright plerions like the Crab nebula are likely to be produced only when the pulsar has an initial period ∼ 10–20 milliseconds and a field ∼ 10¹² G. Such pulsars inside rapidly expanding shell remnants should also produce detectable plerions. The extreme rarity of SNRs with such hybrid morphology leads us to conclude that these pulsars must have been born with an initial period larger than ∼ 35–70 milliseconds. Joint Astronomy Program, Department of Physics, Indian Institute of Science, Bangalore 560012.