Supernova 1987A: The envelope mass and the explosion energy

Astronomy Letters - Our study of the photometric and spectroscopic observations of SN 1987A based on the hydrodynamic modeling of its bolometric light curve and nonstationary hydrogen kinetics and...     

Pulsar activity and the morphology of supernova remnants

We use the recently introduced concept of a ‘window’ of magnetic field strengths in which pulsars can be active to explain the variation in morphology of supernova remnants. The striking difference between shell-type and filled-type remnants is attributed to differences in he magnetic field strengths of the neutron stars left by the respective Supernovae. Field strengths of a value permitting pulsar activity result in particle production and Crab-like centrally concentrated remnants. Other field values lead to strong magnetic dipole radiation and consequent shell formation (e.g. Cas A). Several apparent inconsistencies concerning pulsar-supernova associations appear to find a logical explanation on the basis of this hypothesis.     

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.     

Toward Understanding the Formation of Molecular Clouds

Based on a comparison of similar colour indices we investigate the effects of luminosity and metallicity that influence the Strömgren and Vilnius photometric quantities for different spectral types. We notice significant differences for similar indices, apparently due to small deviations of central wavelengths and band-widths of the filters. For the G-K type stars of moderate luminosity we interpret the difference introduced by v and X pass-bands as an log g effect, reflecting the presence of H&;K Ca II stellar lines in these spectral types. We discuss a possible influence of the H&;K Ca II lines on the luminosities derived from the Vilnius classification diagrams.     

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.     

Photoionized Regions Around Supernova Remnants

The radiation produced by the gas cooling behind a fast supernova remnant shock in the interstellar medium is capable of ionizing the undisturbed medium ahead of the shock wave. In this work I investigate the nonequilibrium evolution of these photoionized precursor regions by means of radiation-hydrodynamic simulations of supernova remnant evolution. This revised version was published online in September 2006 with corrections to the Cover Date.     

Long-slit optical spectroscopy of Large Magellanic Cloud radio supernova remnants

We use long-slit spectra from shocked regions of radio supernova remnants (SNRs) in the Large Magellanic Cloud to estimate electron density and derive an average 'metal' abundance of 10^−3.9 based on diagnostic line ratio plots. These simple diagnostics may be especially useful to determine abundances in more distant galaxies. Abundance values listed in this paper, in units of log(x/H) + 12, for nitrogen (7.3) and oxygen (8.2) agree with those reported in the literature. These estimates – which we assume to be dominated by the interstellar medium with little evolutionary interference – were obtained from spectral analysis of ∼50 per cent of known radio SNRs using the double beam spectrograph on the 2.3-m Advanced Technology Telescope at Siding Spring Observatory in Australia and the Cassegrain spectrograph on the 1.9-m Radcliffe telescope at the South African Astronomical Observatory. We also found optical evidence of shocked regions near 2 of 20 radio SNR candidates (J053620−693136 and J053731−662740), strengthening their identification as true remnants.     

A search for OB stars in supernova remnants

A massive binary, in which the primary becomes a supernova, should leave a luminous secondary near the centre of its remnant. Contrary to expectation no statistically significant excess of OB stars is, however, found near the centres of optically visible galactic supernova remnants.     

Broad-band non-thermal emission from molecular clouds illuminated by cosmic rays from nearby supernova remnants

Molecular clouds are expected to emit non-thermal radiation due to cosmic ray interactions in the dense magnetized gas. Such emission is amplified if a cloud is located close to an accelerator of cosmic rays and if energetic particles can leave the accelerator site and diffusively reach the cloud. We consider here a situation in which a molecular cloud is located in the proximity of a supernova remnant which is efficiently accelerating cosmic rays and gradually releasing them in the interstellar medium. We calculate the multiwavelength spectrum from radio to gamma rays which is emerging from the cloud as the result of cosmic ray interactions. The total energy output is dominated by the gamma-ray emission, which can exceed the emission in other bands by an order of magnitude or more. This suggests that some of the unidentified TeV sources detected so far, with no obvious or very weak counterparts in other wavelengths, might be in fact associated with clouds illuminated by cosmic rays coming from a nearby source. Moreover, under certain conditions, the gamma-ray spectrum exhibits a concave shape, being steep at low energies and hard at high energies. This fact might have important implications for the studies of the spectral compatibility of GeV and TeV gamma-ray sources.     

Statistics of Galactic Supernova Remnants

We collected the basic parameters of 231 supernova remnants (SNRs) in our Galaxy, namely, distances (d) from the Sun, linear diameters (D), Galactic heights (Z), estimated ages (t), luminosities (L), surface brightness (∑) and flux densities (S1) at 1-GHz frequency and spectral indices (α). We tried to find possible correlations between these parameters. As expected, the linear diameters were found to increase with ages for the shell-type remnants, and also to have a tendency to increase with the Galactic heights. Both the surface brightness and luminosity of SNRs at 1-GHz tend to decrease with the linear diameter and with age. No other relations between the parameters were found.     

X-ray spectro-imagery of supernova remnants

Supernovae and their remnants play an essential role in the Interstellar Medium as one of the main sources of mechanical energy and heavy element production and as cosmic-ray accelerators. X-ray spectro-imagery is a key approach to look at these issues, as the collision of high velocity ejecta with the ambient medium generates high temperatures of the order of ten million degrees. I present recent results from the XMM-Newton and Chandra X-ray satellites on the elemental composition of young supernova remnants, on the spatial distribution of these synthesized elements and on the constraints obtained on the efficiency of particle acceleration at the shocks. This revised version was published online in September 2006 with corrections to the Cover Date.     

Effect of nearby supernova remnants on local cosmic rays

We study in detail the effect of different particle release times from sources on the cosmic ray (CR) spectrum below 10¹⁵ eV in the Galaxy. We discuss different possible forms of particle injection such as burst-like injection, continuous injection for a finite time, injection from a stationary source and energy-dependent injection. When applied to the nearby known supernova remnants, we find that the observed CR anisotropy data favour the burst-like particle injection model for the CR diffusion coefficient   D ( E ) ∝ E ^a   with   a = 0.3 –0.6  in the local region. In this study we have also found that the contribution of the sources G114.3+0.3 and Monogem dominate if the observed anisotropy is a result of the effect of the nearby sources. Further study shows that we should not neglect the contribution of the undetected old sources to the local CR anisotropy.     

Dynamics and radiation of young type-Ia supernova remnants: Important physical processes

Astronomy Letters - We analyze the physical processes that should be taken into account when modeling young type-Ia supernova remnants (SNRs) with ages of several hundred years in which forward...     

Supernova remnants,planetary nebulae and superbubbles: Prospects for new XMM‐Newton observations

Important results achieved over the last years on supernova remnants, planetary nebulae and superbubbles are briefly reviewed in the context of X‐ray observations. I intend to review the important open scientific questions in these fields, and the specific contributions that can be made by XMM‐Newton. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Observations of the supernova remnants HB 9 and 1C 443 at 34.5MHz

We have observed the extended supernova remnants HB 9 (G 160.5 + 2.8) and IC 443 (G 189.1 + 2.9) at 34.5 MHz with a resolution of 26 arcmin × 40 arcmin. A map of HB 9 is presented. The integrated flux density of HB 9 at 34.5 MHz is 750 ± 150 Jy. The spectral index in the frequency range from 34.5 MHz to 2700 MHz is found to be constant (- 0.58 ± 0.06) without any spectral break such as was reported earlier by Willis (1973). There is no significant variation of the spectral index across the remnant. The integrated flux density of IC 443 at 34.5 MHz is 440 ± 88 Jy. The spectral index in the frequency range from 20 MHz to 10700 MHz is - 0.36 ± 0.04. The reduction in flux at very low frequencies (10 MHz) is attributable to free-free absorption in the interstellar medium and/or in the H II region S 249.     

Distribution of type Ib/c supernovae relative to galactic spiral arms

Type Ib/c supernovae are shown to be concentrated to the inner edges of the spiral arms, with the distributions for type Ib and Ic supernovae being identical. We have found differences between the distributions of type II and Ib/c supernovae relative to spiral arms, suggesting that the type Ib/c presupernovae are, on average, younger.     

On the relationship between pulsars and supernova remnants

We propose that single stars in the mass range 4–6·5M _⊙, that explode as Supernovae of Type I, are totally disrupted by the explosion and form shell-type remnants. More massive single stars which explode as Supernovae of Type II also give rise to shell-type remnants, but in this case a neutron star or a black hole is left behind. The first supernova explosion in a close binary also gives rise to a shell-type supernova remnant. The Crab-like filled-centre supernova remnants are formed by the second supernova explosion in a close binary. The hybrid supernova remnants, consisting of a filled centre surrounded by a shell, are formed if there is an active neutron star inside the shell.     

TeV γ-rays from old supernova remnants

We study the emission from an old supernova remnant (SNR) with an age of around 10⁵ yr and that from a giant molecular cloud (GMC) encountered by the SNR. When the SNR age is around 10⁵ yr, proton acceleration is efficient enough to emit TeV γ-rays both at the shock of the SNR and that in the GMC. The maximum energy of primarily accelerated electrons is so small that TeV γ-rays and X-rays are dominated by hadronic processes,  π⁰  -decay and synchrotron radiation from secondary electrons, respectively. However, if the SNR is older than several 10⁵ yr, there are few high-energy particles emitting TeV γ-rays because of the energy-loss effect and/or the wave-damping effect occurring at low-velocity isothermal shocks. For old SNRs or SNR–GMC interacting systems capable of generating TeV γ-ray emitting particles, we calculated the ratio of TeV γ-ray (1–10 TeV) to X-ray (2–10 keV) energy flux and found that it can be more than  ∼10²  . Such a source showing large flux ratio may be a possible origin of recently discovered unidentified TeV sources.