Soft gamma-ray bursts from the superluminal source GRS 1915+105?

The power required to eject relativistic plasma clouds in the hard X-ray transient GRS 1915+105 is at least 100 times the luminosity of the soft-ray bursts (SGRs) that were observed by BATSE from the same region of the sky in the year 1992. We show that there are spatial, time, and spectral coincidences between GRS 1915+105 and the SGRs observed by BATSE which suggest that they are one and the same source. However, the position of the SGRs is rather uncertain and until better positions are obtained, the question on the association of GRS 1915+105 with the SGRs must remain open.     

Chemistry in grain aggregates: a source of complex molecules?

The aggregation of grains in dense protostellar clouds brings together materials such as silicates, carbons, polycyclic aromatic hydrocarbons and ices to form porous structures with high internal volume. Some physical and chemical properties of these aggregate grains are discussed in the context of the role that they may play in the formation of complex organic and organometallic compounds. One characteristic of such grains that is unique outside planetary systems is the availability of all elements and a number of their common compounds in a composite solid. In dark clouds, the chemistry inside aggregate grains will be driven by cosmic ray heating and sputtering. This occurs in an environment where the products of such reactions can be retained within the dust particle. Hot atom chemistry and secondary reactions are facilitated by the re-entrant nature of such aggregated structures, leading to the possible formation of complex organic compounds. In particular, the sputtering of Si, Mg and Fe from silicate dust is discussed, and it is shown that a variety of organometallic compounds could be expected in ices within aggregate grains. The optical depth for ultraviolet light within aggregates is large, so that materials inside such grains will be effectively shielded from ambient radiation. However, the incorporation of luminifors such as those grain components responsible for the extended red emission converts ultraviolet to visible and near-infrared radiation, and might moderate photochemistry within aggregates. It is suggested that the chemical environment within aggregates may be conducive to the formation and retention of complex molecules such as amino acids, peptides and a variety of organometallic compounds.     

IGR J16318-4848: An X-ray source in a dense envelope?

We analyze in detail the ASCA observations of the hard X-ray source IGR J16318-4848, which was recently discovered by the INTEGRAL observatory (Courvoisier et al. 2003). The source has an anomalously hard spectrum in the energy range 0.5–10 keV and is virtually undetectable below 4 keV because of strong photoabsorption (n _H L>4×10²³ cm^?2). The Kα line of neutral or weakly ionized iron with an equivalent width of ～2.5 keV dominates in the energy range 4–10 keV. There is also evidence for the presence of a second line at energy ～7 keV. Our analysis of archival observational data for the infrared counterpart of IGR J16318-4848 that was discovered by Foschini et al. (2003) revealed the source in the wavelength range 1–15 µm. Available data suggest that the object can be an X-ray binary system surrounded by a dense envelope. The source may be a high-mass X-ray binary similar to GX 301-2. We believe that IGR J16318-4848 can be the first representative of a hitherto unknown population of strongly absorbed Galactic X-ray sources that could not be detected by previous X-ray observatories.     

A Seyfert-like nucleus concealed in BL Lacertae?

We present a series of new spectroscopic observations of BL Lacertae. The observations were obtained over a period of 30 months and sample the violent continuum flare of 1997 June–August. The equivalent width of the recently discovered broad H α line varies approximately inversely with the optical continuum flux, implying that the broad-line-emitting gas does not respond significantly to large variations in the beamed synchrotron continuum which dominates the spectrum at optical wavelengths. The simplest and most plausible interpretation of this result is that the broad-line region in BL Lacertae is 'unaware' of the synchrotron beam and is photoionized by another source, a likely candidate being a hot accretion disc. Alternatively, similar behaviour would be observed if the broad-line region is indeed photoionized by the synchrotron beam but is predominantly matter-bounded so that it absorbs only a small fraction of the incident ionizing photon flux.     

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.     

FBS 0137+400: A Mass-Losing AGB Carbon Mira?

The absolute K-band magnitude determined for the object FBS 0137+400 is typical for Asymptotic Giant Branch (AGB) carbon stars. The large J - K color index as well as large amplitude variability (K > 0.4) and the presence of H in the emission indicate also that this star is a mass-losing long-period Carbon Mira variable with thick circumstellar shell. The IRAS LRS spectrum indicates the presence of a dust shell surrounding this object. Monitoring of the K-band magnitude is necessary for the determination of the pulsation period of FBS 0137+400.     

A beam of particles in ultrahigh-energy cosmic rays?

Three particles with energies of 36, 35, and 58 EeV arrived from one sky region were recorded by two EAS arrays during a day. The events are assumed to have been produced by the beam of particles that resulted from the interaction of cosmic rays with a relativistic shock front.     

Is the ‘superhot’ hard x-ray component in solar flares consistent with a thermal source?

It has been shown by Brown and Emslie (1988) that any optically thin thermal bremsstrahlung source must emit an energy spectrumL () (keV s^–1 keV^–1) which has the property that higher derivatives alternate in sign, i.e., (–) ^j L(^j)() > 0 for allj. In this short note, we apply this test to the superhot component discussed by Linet al. (1981) in order to determine whether a strictly thermal interpretation of this component is valid. We find that all statistically significant higher derivatives do indeed have the correct sign; this strengthens the identification of this component as due to a thermal source.Presidential Young Investigator.     

Where are the binary source gravitational microlensing events? II

Despite the same multiplicity of lenses and sources, the frequency of detection of binary source events is relatively very low compared with that of binary lens events. Dominik pointed out that the rarity of binary source events is caused mainly by the large difference in amplification between the component stars. In this paper, we determine that the fraction of events with similar source star amplifications is as large as ∼8 per cent, and thus show that the very low detection rate for binary source events cannot be explained by this effect alone. By carrying out realistic simulations of binary source events, we find that a significant number of binary source events are additionally missed from detection for various other reasons. First, if the flux ratio between the component stars is very large, the light curve of the bright star is hardly affected by the light from the faint star. Secondly, if the separation is too small, the binary source stars behave like a single star, making it difficult to separate the binary source event from a single source event. Finally, although the probability of detecting binary source events increases as the source separation increases, some fraction of binary source events will still be missed because the light curves of these events will mimic those of single source events with longer time-scales and larger values of the impact parameter.     

Could circinus X-1 be a gamma ray source?

The eccentric orbit binary model which has been developed by Haynes, Lerche and Murdin (1979) for the radio-emitting X-ray source Circinus X-1 is used to calculate the inverse Compton -ray flux. Burst-like behaviour is predicted in association with the formation near orbital periastron of a luminosity-driven, radially expanding shock front.     

Particle beams as a source of noise storm depression?

The February 5, 1986 flare-related radio continuum depression is studied, compared with other noise storm depression events and discussed in the framework of current type I storm models. The influence of flare plasma flow or shocks and of superthermal electrons on noise storm radiation is considered. The presence of fast drifting emission features just before and during the decrease of the intensity, the association between the depression onset and the microwave burst maximum, the simultaneous appearance of the intensity minimum over a broad spectral range as well as preflare evidence of an interconnection of the flare site and the noise storm source are arguments for a preference of the role of beams of superthermal electrons. We distinguish abrupt and slow depressions (Figure 5). The abrupt depressions are in agreement with Melrose's (1980) predictions. Slow depressions can only be understood by invoking the diffusion of super-thermal electrons through the magnetic field carrying the storm source.     

A magnetic core in the Sun? The solar rotator

The previously found solar distortion rotating rigidly and wave-like on the surface with a 12 day period is interpreted as the shape of the gravitational potential induced by the solar core distorted by an internal magnetic field and rotating rigidly with this period. The distortion does not have a symmetry axis and the necessary magnetic field is not compatible with the axial symmetry required of a quasi-static field locked in the rotating core. It is concluded that if the solar distortion is due to such a process the core is oscillating with a very long period, a toroidal oscillation with a period of the order of years.This research was supported in part by the National Science Foundation.     

A γ Doradus candidate in eclipsing binary BD And?

The BVR photometric light curves of the eclipsing binary BD And were obtained in 2008 and 2009. We estimated the mass ratio of the system as 0.97 and the photometric solutions were derived. The results show that BD And is a detached binary system, whose components have a little temperature difference of about 40 K. By analyzing photometric available light minimum times, we also derived an update ephemeris and found for the first time a possible periodic oscillation with an amplitude of 0.011 days and a period of 9.6 years. The results indicate that the periodic oscillation could be caused by a third component physically attached to the eclipsing binary. After removing the light variations due to the eclipses and proximity effects, the light-curve distortions are further explained by the pulsation of the primary component with a dominant period of ∼1 day. In accordance with the position of the primary component on the Hertzsprung–Russell diagram and its pulsation period, the primary component of BD And could be an excellent γ Doradus candidate. It is rarely phenomenon that a component of the eclipsing binary system is a γ Doradus variable.     

The plausible source(s) of 26Al in the early solar system: A massive star or the X‐wind irradiation scenario?

Abstract— A quantitative analysis is presented for the irradiation contributions of the short‐lived nuclides, specifically ²⁶Al, by the X‐wind scenario in the early solar system. The analysis is based on the comprehensive numerical simulations of the scenario that involves thermal processing of protoCAIs during the decades long X‐wind cycle. It would be difficult to explain the canonical value of ²⁶Al/²⁷Al in Ca‐Al‐rich inclusions on the basis of its inferred irradiation yields. Hence, the bulk inventory of ²⁶Al in the early solar system was not produced by the X‐wind scenario. We suggest the predominant occurrence of gradual flares compared to impulsive flares in the early solar system as in the case of the modern solar flares. One tenth of the bulk ²⁶Al was only produced by irradiation in case the entire solar inventory of ¹⁰Be was produced by local irradiation. The bulk ²⁶Al inventory along with ⁶⁰Fe was probably synthesized by a massive star. We present a qualitative model of the astrophysical settings for the formation of the solar system on the basis of a survey of the presently active star forming regions. We hypothesize that the formation of the solar system could have occurred almost contemporaneously with the formation of the massive star within a single stellar cluster. As the massive star eventually exploded as supernova Ib/c subsequent to Wolf‐Rayet stages, the short‐lived nuclides were probably injected into the solar proto‐planetary disc. The dynamically evolving stellar cluster eventually dispersed within the initial ?10 million years prior to the major planetary formation episodes.     

Auroral recombination of N and O: A possible source for emission in the γ and δ bands of NO

Radiative recombination of N and O provides a significant source for auroral emission in the γ and δ bands of NO with selective population of vibrational levels in the A²Σ⁺ and C²Π states. This mechanism may account for emissions detected near 2150 Å. Models are derived for the auroral ionosphere and include estimates for the concentrations of N and NO. The concentration of NO is estimated to have a value of about 10⁸ cm^?1 near 140 km in an IBC III aurora. The corresponding density for N is about 5 × 10⁷cm^?3 and the concentration ratio $\text{NO}{}^{\mathrm{+}}\text{O}{}_2{}^{\mathrm{+}}$ has a value of about 5.5.     

Heavy ion formation in Titan's ionosphere: Magnetospheric introduction of free oxygen and a source of Titan's aerosols?

Discovery by Cassini's plasma instrument of heavy positive and negative ions within Titan's upper atmosphere and ionosphere has advanced our understanding of ion neutral chemistry within Titan's upper atmosphere, primarily composed of molecular nitrogen, with ~2.5% methane. The external energy flux transforms Titan's upper atmosphere and ionosphere into a medium rich in complex hydrocarbons, nitriles and haze particles extending from the surface to 1200 km altitudes. The energy sources are solar UV, solar X-rays, Saturn's magnetospheric ions and electrons, solar wind and shocked magnetosheath ions and electrons, galactic cosmic rays (GCR) and the ablation of incident meteoritic dust from Enceladus’ E-ring and interplanetary medium. Here it is proposed that the heavy atmospheric ions detected in situ by Cassini for heights >950 km, are the likely seed particles for aerosols detected by the Huygens probe for altitudes <100 km. These seed particles may be in the form of polycyclic aromatic hydrocarbons (PAH) containing both carbon and hydrogen atoms C_nH_x. There could also be hollow shells of carbon atoms, such as C₆₀, called fullerenes which contain no hydrogen. The fullerenes may compose a significant fraction of the seed particles with PAHs contributing the rest. As shown by Cassini, the upper atmosphere is bombarded by magnetospheric plasma composed of protons, H₂⁺ and water group ions. The latter provide keV oxygen, hydroxyl and water ions to Titan's upper atmosphere and can become trapped within the fullerene molecules and ions. Pickup keV N₂⁺, N⁺ and CH₄⁺ can also be implanted inside of fullerenes. Attachment of oxygen ions to PAH molecules is uncertain, but following thermalization O+ can interact with abundant CH₄ contributing to the CO and CO₂ observed in Titan's atmosphere. If an exogenic keV O+ ion is implanted into the haze particles, it could become free oxygen within those aerosols that eventually fall onto Titan's surface. The process of freeing oxygen within aerosols could be driven by cosmic ray interactions with aerosols at all heights. This process could drive pre-biotic chemistry within the descending aerosols. Cosmic ray interactions with grains at the surface, including water frost depositing on grains from cryovolcanism, would further add to abundance of trapped free oxygen. Pre-biotic chemistry could arise within surface microcosms of the composite organic-ice grains, in part driven by free oxygen in the presence of organics and any heat sources, thereby raising the astrobiological potential for microscopic equivalents of Darwin's “warm ponds” on Titan.     

E+A星系的研究进展

E+A星系的光谱具有很强的巴耳末吸收线,缺乏与恒星形成相关的发射线,将典型的椭圆星系(E)和A型恒星的光谱进行线性组合就能够拟合出这类星系的光谱.它们的颜色、形态、星族年龄等参数介于典型的早型和晚型星系之间.E+A星系近期经历了星暴活动,在星系演化进程中,它们处于晚型到早型的过渡阶段,可能在演变过程中扮演着重要角色.介...     

Could giant impacts cripple core dynamos of small terrestrial planets?

Large impacts not only create giant basins on terrestrial planets but also heat their interior by shock waves. We investigate the impacts that have created the largest basins existing on the planets: Utopia on Mars, Caloris on Mercury, Aitken on Moon, all formed at ∼4 Ga. We determine the impact-induced temperature increases in the interior of a planet using the “foundering” shock heating model of Watters et al. (Watters, W.A., Zuber, M.T., Hager, B.H. [2009]. J. Geophys. Res. 114, E02001. doi:10.1029/2007JE002964). The post-impact thermal evolution of the planet is investigated using 2D axi-symmetric convection in a spherical shell of temperature-dependent viscosity and thermal conductivity, and pressure-dependent thermal expansion. The impact heating creates a superheated giant plume in the upper mantle which ascends rapidly and develops a strong convection in the mantle of the sub-impact hemisphere. The upwelling of the plume rapidly sweeps up the impact-heated base of the mantle away from the core-mantle boundary and replaces it with the colder surrounding material, thus reducing the effects of the impact-heated base of the mantle on the heat flux out of core. However, direct shock heating of the core stratifies the core, suppresses the pre-existing thermal convection, and cripples a pre-existing thermally-driven core dynamo. It takes about 17, 4, and 5 Myr for the stratified cores of Mars, Mercury, and Moon to exhaust impact heat and resume global convection, possibly regenerating core dynamos.     

A family of well behaved charge analogues of?a?well behaved neutral solution in?general relativity

A family of charge analogues of a neutral solution with g ₄₄=(1+Cr ²)⁶ has been obtained by using a specific electric intensity, which involves a parameter K. Both neutral and charged solutions are analysed physically subject to the surface density 2×10¹⁴ gm/cm³ (neutron star). The neutral solution is well behaved for 0.0<Ca ²≤0.10477 while its charge analogues are well behaved for a wide range of a parameter K (0≤K≤72) i.e. pressure, density, pressure-density ratio, velocity of sound is monotonically decreasing and the electric intensity is monotonically increasing in nature for the given range of the parameter K. The maximum mass and radius occupied by the neutral solution are 3.4126M _Θ and 18.9227 km for Ca ²=0.10447 respectively. While the red shift at centre Z ₀=0.9686 and red shift at the surface Z _a =0.4612. For the charged solution, the maximum mass and radius are 5.6111M _Θ and 17.2992 km respectively for K=3.0130 and Ca ²=0.2500, with the red shift Z ₀=3.0113 and Z _a =1.0538.