Interaction of the supernova remnant HB3 with the ambient interstellar gas

The well-known shell supernova remnant (SNR) HB3 is part of a feature-rich star-forming region together with the nebulae W3, W4, and W5. We study the HI structure around this SNR using five RATAN-600 drift curves obtained at a wavelength of 21 cm with an angular resolution of 2′ in one coordinate over the radial-velocity range ?183 to +60 km s^?1 in a wider region of the sky and with a higher sensitivity than in previous works by other authors. The spatial-kinematic distribution of HI features around the SNR clearly shows two concentric expanding shells of gas that surround the SNR and coincide with it in all three coordinates (α, δ, and V). The outer shell has a radius of 133 pc, a thickness of 24 pc, and an expansion velocity of 48 km s^?1. The mass of the gas in it is ≈2.3 × 10⁵M_⊙. For the inner shell, these parameters are 78 pc, 36 pc, 24 km s^{? 1}, and 0.9 × 10⁵M_⊙, respectively. The inner shell is immediately adjacent to the SNR. Assuming that the outer shell was produced by the stellar wind and the inner shell arose from the shock wave of the SNR proper, we estimated the age of the outer shell, ≈1.7 × 10⁶ yr, and the mechanical luminosity of the stellar wind, 1.5 × 10³⁸ erg s^?1. The inner shell has an age of ≈10⁶ yr and corresponds to a total supernova explosion energy of ≈10⁵² erg.     

H I distribution in the region of the supernova remnant G78.2+2.1

Based on RATAN-600 21-cm line observations with an angular resolution of 2.4′ over a wide range of radial velocities, we analyze the neutral-hydrogen distribution in the region of the SNR G78.2+2.1. In addition to an H I shell at low radial velocities immediately surrounding the radio remnant, we detected an extended expanding H I shell, ≈3° in diameter, at a radial velocity of ?25 km s^?1, which closely coincides in coordinates and angular sizes with the outer X-ray shell discovered by Lozinskaya et al. (2000). The Hα emission studied by these authors in the SNR region also has a secondary peak at radial velocities from ?45 to ?20 km s^?1. Since the radial velocities of these two objects differ significantly, their distances can be assumed to differ as well; i.e., a chance projection of two distinct objects is observed.     

Cosmic-ray energetics in the supernova remnant Cassiopeia A

Based on the observed radio spectrum for the supernova remnant Cassiopeia A, we have established that it represents synchrotron radiation of relativistic electrons with a nonpower-law energy spectrum in the form of Kaplan-Tsytovich’s standard distribution. The total density of relativistic electrons is 10^?3 cm^?3, only 20% of which form the radio spectrum. The particle number ratio of the proton-nuclear and electron cosmicray components inside the shell differs significantly from the mean Galactic ratio (100) and probably does not exceed unity.     

New observations of the pulsar wind nebula in the supernova remnant CTB 80

We investigated the kinematics of the pulsar wind nebula (PWN) in the old supernova remnant CTB 80 using the Fabry-Perot interferometer of the 6-m Special Astrophysical Observatory telescope. In addition to the previously known expansion of the system of bright filaments with a velocity of 100–200 km s^?1, we detected weak high-velocity features in the Hα line at least up to velocities of 400–450 km s^?1. We analyzed the morphology of the PWN in the Hα, [S II], and [O III] lines using HST archival data and discuss its nature. The shape of the central filamentary shell, which is determined by the emission in the [O III] line and in the radio continuum, is shown to be consistent with the bow-shock model for a significant (about 60°) inclination of the pulsar’s velocity vector to the plane of the sky. In this case, the space velocity of the pulsar is twice as high as its tangential velocity, i.e., it reaches ?500 km s^?1, and PSR B1951+32 is the first pulsar whose radial velocity about 40 km s^?1 has been estimated from PWN observations. The shell-like Hα-structures outside the bow shock front in the east and the west could be associated with both the pulsar’s jets and the pulsar wind breakthrough due to the layered structure of the extended CTB 80 shell.     

Observational effects in supernova remnants associated with H II regions and dense gaseous clouds

The dependences of various parameters for S-and C-type supernova remnants (SNRs) on their diameters are investigated. Only SNRs with D≤40 pc that expand initially within H II regions and, subsequently, in dense media are considered. The expansion velocities and thermal electron densities of these SNRs were found to decrease with increasing diameter, on average, as D ^?1 and D ^?0.5, respectively. H II regions hamper the detection of SNRs; this effect is particularly pronounced in regions with 270°≤1≤300° and 330°≤1≤360°. The X-ray luminosities of SNRs born in dense media increase by an order of magnitude when their diameters reach ～30 pc. After the SNR diameters reach ～40 pc, their radio and X-ray luminosities decrease sharply.     

Monte Carlo simulations of supernova light curves and the hypernova SN 1998bw

We propose a method for computing the bolometric light curves of type Ia and Ib/c supernovae based on Monte Carlo simulations of unsteady-state radiative transfer. The method is used to analyze the bolometric light curve of the unusual type Ib/c supernova SN 1998bw associated with GRB 980 425. We show that the previously noted inconsistency in the behavior of simulated light curves at early and late stages, which is attributable to asymmetry effects, can be overcome in a spherically symmetric model. Agreement with observations requires complete ⁵⁶Ni mixing and a higher matter density in the central part of the envelope in the velocity range v<5000 km s^?1 compared to standard models.     

Optical observations of type-IIP supernova 2004dj: Evidence for asymmetry of the <Superscript>56</Superscript>Ni ejecta

Photometric and spectroscopic observations of the nearby type-IIP supernova 2004dj are presented. The ⁵⁶Ni mass in the envelope of SN 2004dj was estimated from the light curve to be ≈0.02M_⊙. This estimate is confirmed by modeling the Hα luminosity. The Hα emission line exhibits a strong asymmetry characterized by the presence of a blue component in the line with a shift of ?1600 km s^?1 at the early nebular phase. A similar asymmetry was found in the Hβ, [O I], and [Ca II] lines. The line asymmetry is interpreted as being the result of asymmetric ⁵⁶Ni ejecta. The Hα profile and its evolution are reproduced in the model of an asymmetric bipolar ⁵⁶Ni structure for a spherical hydrogen distribution. The mass of the front ⁵⁶Ni jet is comparable to that of the central component and twice that of the rear ⁵⁶Ni jet. We point out that the asymmetric bipolar structure of ⁵⁶Ni ejecta is also present in SN 1999em, a normal type-IIP supernova.     

Parameters of the classical type-IIP supernova SN 1999em

Based on observations of SN 1999em, we determined the physical parameters of this supernova using hydrodynamic calculations including nonequilibrium radiative transfer. Taking the distance to SN 1999em estimated by the expanding photosphere method (EPM) to be D = 7.5 Mpc, we found the parameters of the presupernova: radius R = 450R_⊙, mass M = 15M_⊙, and explosion energy E = 7 × 10⁵⁰ erg. For the distance D = 12 Mpc determined from Cepheids, R, M, and E must be increased to the following values: R = 1000R_⊙, M = 18M_⊙, and E = 10⁵¹ erg. We show that one cannot restrict oneself to using the simple analytical formulas relating the supernova and presupernova parameters to obtain reliable parameters for type-IIP presupernovae.     

Nonresonant generation of MHD disturbances during supernova explosions in an inhomogeneous interstellar medium

We analyze the nonresonant generation of large-scale magnetic inhomogeneities near a shock front by accelerated particles. The MHD disturbances are generated by the electric current excited by relativistic particles in the preshock medium in the presence of weak large-scale density inhomogeneities. The MHD modes considered can be amplified by other resonant and nonresonant mechanisms related to the presence of relativistic particles. We estimate the magnetic fields and the energies to which charged particles can be accelerated in different phases of the interstellar medium by taking into account the random magnetic fields generated by the mechanism considered.     

Scalability of supernova remnant simulations

The simulation or solution of the supernova remnant evolution may be scaled from one interstellar environment to another. We systematically examine this scalability, the use of which is so far still very limited in astrophysical literature. We show how the scalability is affected by various constraints imposed by physical processes and initial conditions, and demonstrate the use of the scaling as a powerful tool to explore the interdependence among relevant parameters, based on a minimum set of simulations. In particular, we devise a scaling scheme that can be used to adaptively generate numerous seed remnants and plant them into 3D hydrodynamic simulations of the supernova-dominated interstellar medium.     

HI absorption observations of two radio sources near the supernova remnant G 127.1 + 0.5

The compact source 0125 + 628 in the centre of the galactic supernova remnant G 127.1 + 0.5 has been re-observed in HI absorption using the Westerbork Synthesis Radio Telescope (WSRT). The outer arm HI absorption atV = -95km s^-1 has been confirmed. The absorption spectrum is similar to that of the nearby extragalactic source 0123 + 633. We discuss the arguments concerning an extragalactic origin of 0125 + 628 and conclude that it is most likely extragalactic and not an SS 433 type object. The National Radio Astronomy Observatory is operated by Associated Universities Inc. under contract with the National Science Foundation.     

Chandra observations of Tycho’s supernova remnant

We present a newChandra observation of Tycho’s supernova remnant with the Advanced CCD Imaging Spectrometer. Multicolor Xray imaging reveals new details of the outer shock and ejecta. At energies between 4 and 6 keV, the outline of the outer shock is clearly revealed in X-rays for the first time. The distribution of the emission from lines of Si and Fe are confirmed to have a different morphology from each other, and the Si ejecta are shown to extend to the blast shock at several locations. Characteristic spectra of the outer shock and ejecta are also presented.     

Thick radio shell in supernova remnant DA 495 (G 65.7+ 1.2)?

High resolution (11.7 to 64 arcsec) multifrequency radio observations of DA 495 (G 65.7 +1.2) at 20, 49 and 92 cm wavelengths with the VLA, WSRT and OSRT are presented. A map of infrared emission in the surrounding region is also presented. Although the remnant has a minimum near the centre, its brightness distribution does not show limb brightening. Hence it has characteristics of both shell-type SNRs and Crab-type SNR. Alternatively it has an unusually thick shell with inner and outer radii of 125 and 500 arcsec respectively. The volume emissivity within the shell decreases radially outward. Its integrated flux density spectrum is characteristic of a shell-type remnant. The role of the reverse shock in the formation of a thick shell is discussed. The association of the open star cluster NGC6834 with DA 495 is also noted. The parameters of twenty-nine small diameter sources detected around DA 495 are also presented. The radio source 1949 + 291 is associated with an IRAS source. 1948 + 292 may be a Crablike pulsar-driven synchrotron nebula. The radio spectrum of the planetary nebula NGC 6842 is optically thick at 49 cm.     

Smoke rings around supernova 1987a

Detailed observations of the [Oiii]5007 Å emission from the elliptical rings around SN 1987A suggest a model wherein the two faint, outer rings are due to emission from two circular toroids moving outwards (at 25 km s^–1) along a bipolar cone centred on the site of the supernova. The brighter, central ring is expanding radially outward at 8.3 km s^–1. The rings must have been created 2-3 × 10⁴ years before the supernova explosion and are thought to be a consequence of the interaction of stellar winds emanating from the progenitor system during the final stages of its evolution to a supernova.     

Observations of supernovae in the period 1997–1999

Astronomy Letters - We present our photometric observations of the 15 supernovae (SN) discovered in the period 1997–1999; of these, six are type Ia SN, two are peculiar type Ia SN, three are...     

Circumstellar Na I and Ca II absorption lines of type Ia supernovae in the symbiotic scenario

The formation of circumstellar Na I and Ca II resonance absorption lines in a type Ia supernova is studied in the case where the supernova explodes in a binary system with a red giant. The model suggests a spherically symmetric wind and takes into account the nonstationary ionization and heating of the wind by X rays from the shock wave and by gamma rays from radioactive ⁵⁶Ni decay. For wind densities typical of a red giant, the expected optical depth of the wind in Na I lines is shown to be too small (τ < 10^?3) for their detection. Under the same conditions, the optical depth of the predicted Ca II 3934 Å absorption line is sufficient for its detection (τ > 0.1). It is concluded that the Na I and Ca II absorption lines detected in SN 2006X could not be formed in the red giant wind and are most likely related to clouds at distances exceeding the dust evaporation radius (r > 10¹⁷ cm). An upper limit for the rate of mass loss through a stationary wind with velocity u has been obtained from the absence of Ca II absorption lines in SN 2006X unrelated to the similar Na I components: ? < 10^?8 (u/10 km s^?1) M _⊙ yr^?1.     

A rotating collapsar and possible interpretation of the LSD neutrino signal from SN 1987A

We consider an improved rotational mechanism of the explosion of a collapsing supernova. We show that this mechanism leads to two-stage collapse with a phase difference of ～5 h. Based on this model, we attempt a new interpretation of the events in underground neutrino detectors on February 23, 1987, related to the supernova SN 1987A.     

A model of particle acceleration to high energies by multiple supernova explosions in OB associations

The possibility of cosmic-ray (CR) acceleration to energies above 10⁹ GeV per nucleus in extended Galactic OB associations is analyzed. A two-stage acceleration mechanism is justified: at the first stage, the acceleration by separate shock fronts from spatially and temporally correlated supernovae explosions takes place, and, at the second stage, the Fermi acceleration by supersonic turbulence in an extended, strongly perturbed region near the OB association takes place. We calculate the CR energy spectrum, the change in CR chemical composition with energy, and the energy dependence of the mean logarithm of atomic mass, ?lnA?, for the accelerated particles. The calculated values are compared with those observed near the break in the energy spectrum. We estimate the turbulence parameters, which allow the observed features of the energy spectrum and the CR enrichment with heavy elements to be explained.