Chandra observations of SN 1987A: the soft X-ray light curve revisited

We report on the present stage of SN 1987A as observed by the Chandra X-ray Observatory. We reanalyze published Chandra observations and add three more epochs of Chandra data to get a consistent picture of the evolution of the X-ray fluxes in several energy bands. We discuss the implications of several calibration issues for Chandra data. Using the most recent Chandra calibration files, we find that the 0.5-2.0 keV band fluxes of SN 1987A have increased by ~6 x 10 ^-13 erg s^-1 cm^-2 per year since 2009. This is in contrast with our previous result that the 0.5-2.0 keV light curve showed a sudden flattening in 2009. Based on our new analysis, we conclude that the forward shock is still in full interaction with the equatorial ring.Comment: Accepted for publication by ApJ, 7 pages, 5 figure

Observing Supernova 1987A with the Refurbished Hubble Space Telescope

Observations with the Hubble Space Telescope (HST), conducted since 1990, now offer an unprecedented glimpse into fast astrophysical shocks in the young remnant of supernova 1987A. Comparing observations taken in 2010 using the refurbished instruments on HST with data taken in 2004, just before the Space Telescope Imaging Spectrograph failed, we find that the Ly-a and H-a lines from shock emission continue to brighten, while their maximum velocities continue to decrease. We observe broad blueshifted Ly-a, which we attribute to resonant scattering of photons emitted from hotspots on the equatorial ring. We also detect NV~\lambda\lambda 1239,1243 A line emission, but only to the red of Ly-A. The profiles of the NV lines differ markedly from that of H-a, suggesting that the N^{4+} ions are scattered and accelerated by turbulent electromagnetic fields that isotropize the ions in the collisionless shock.Comment: Science, accepted. Science Express, 02 Sept 2010. 5 figures. Supporting online material can be found at http://www.sciencemag.org/cgi/content/full/sci;science.1192134/DC

The X-ray Remnant of SN1987A

We present high resolution Chandra observations of the remnant of SN1987A in the Large Magellanic Cloud. The high angular resolution of the Chandra X-ray Observatory (CXO) permits us to resolve the X-ray remnant. We find that the remnant is shell-like in morphology, with X-ray peaks associated with some of the optical hot spots seen in HST images. The X-ray light curve has departed from the linear flux increase observed by ROSAT, with a 0.5-2.0 keV luminosity of 1.5 x 10^35 erg/s in January 2000. We set an upper limit of 2.3 x 10^34 ergs/s on the luminosity of any embedded central source (0.5 - 2 keV). We also present a high resolution spectrum, showing that the X-ray emission is thermal in origin and is dominated by highly ionized species of O, Ne, Mg, and Si.Comment: 16 pages, 3 figures, Accepted for publication in ApJ Letter

On the Absorption of X-rays in the Interstellar Medium

We present an improved model for the absorption of X-rays in the ISM intended for use with data from future X-ray missions with larger effective areas and increased energy resolution such as Chandra and XMM, in the energy range above 100eV. Compared to previous work, our formalism includes recent updates to the photoionization cross section and revised abundances of the interstellar medium, as well as a treatment of interstellar grains and the H2molecule. We review the theoretical and observational motivations behind these updates and provide a subroutine for the X-ray spectral analysis program XSPEC that incorporates our model.Comment: ApJ, in press, for associated software see http://astro.uni-tuebingen.de/nh

An adjustable law of motion for relativistic spherical shells

A classical and a relativistic law of motion for an advancing shell are deduced applying the thin layer approximation. A new parameter connected with the quantity of absorbed matter in the expansion is introduced; this allows of matching theory and observation.Comment: 15 pages, 10 figures and article in press; Central European Journal of Physics 201

Analysis of the Type IIn Supernova 1998S: Effects of Circumstellar Interaction on Observed Spectra

We present spectral analysis of early observations of the Type IIn supernova 1998S using the general non-local thermodynamic equilibrium atmosphere code \tt PHOENIX}. We model both the underlying supernova spectrum and the overlying circumstellar interaction region and produce spectra in good agreement with observations. The early spectra are well fit by lines produced primarily in the circumstellar region itself, and later spectra are due primarily to the supernova ejecta. Intermediate spectra are affected by both regions. A mass-loss rate of order $\dot M \sim 0.0001-0.001$\msol yr$^{-1}$ is inferred for a wind speed of 100-1000 \kmps. We discuss how future self-consistent models will better clarify the underlying progenitor structure.Comment: to appear in ApJ, 2001, 54

Chandra Observations of SNR 1987A

We report on the results of our monitoring program of the X-ray remnant of supernova 1987A with the {\it Chandra X-Ray Observatory}. We have performed two new observations during the {\it Chandra} Cycle 3 period, bringing the total to six monitoring observations over the past three years. These six observations provide a detailed time history of the birth of a new supernova remnant in X-rays. The high angular resolution images indicate that soft X-ray bright knots are associated with the optical spots, while hard X-ray features are better correlated with radio images. We interpret this in terms of a model in which fast shocks propagating through the circumstellar HII region produce the hard X-ray and radio emission, while the soft X-ray and optical emission arise in slower shocks entering into dense knots in the circumstellar inner ring. New observations begin to show changes in the morphology that may herald a new stage in the development of this incipient supernova remnant. The observed X-ray fluxes increase by nearly a factor of three over the last 30 months. The X-ray remnant is expanding at a velocity of $\sim$5000 km s$^{-1}$.Comment: 8 pages, 6 figures, 2 color figures, To appear in AdSpR (Proceedings 34th COSPAR Synposium E1.4 "High Energy Studies of Supernova Remnants and Neutron stars" For high resolution color figures contact [email protected]

Alignment of the UMLS semantic network with BioTop: Methodology and assessment

Motivation: For many years, the Unified Medical Language System (UMLS) semantic network (SN) has been used as an upper-level semantic framework for the categorization of terms from terminological resources in biomedicine. BioTop has recently been developed as an upper-level ontology for the biomedical domain. In contrast to the SN, it is founded upon strict ontological principles, using OWL DL as a formal representation language, which has become standard in the semantic Web. In order to make logic-based reasoning available for the resources annotated or categorized with the SN, a mapping ontology was developed aligning the SN with BioTop. Methods: The theoretical foundations and the practical realization of the alignment are being described, with a focus on the design decisions taken, the problems encountered and the adaptations of BioTop that became necessary. For evaluation purposes, UMLS concept pairs obtained from MEDLINE abstracts by a named entity recognition system were tested for possible semantic relationships. Furthermore, all semantic-type combinations that occur in the UMLS Metathesaurus were checked for satisfiability. Results: The effort-intensive alignment process required major design changes and enhancements of BioTop and brought up s

Magnetic Flux Expulsion in the Powerful Superbubble Explosions and the Alpha-Omega Dynamo

The possibility of the magnetic flux expulsion from the Galaxy in the superbubble (SB) explosions, important for the Alpha-Omega dynamo, is considered. Special emphasis is put on the investigation of the downsliding of the matter from the top of the shell formed by the SB explosion which is able to influence the kinematics of the shell. It is shown that either Galactic gravity or the development of the Rayleigh-Taylor instabilities in the shell limit the SB expansion, thus, making impossible magnetic flux expulsion. The effect of the cosmic rays in the shell on the sliding is considered and it is shown that it is negligible compared to Galactic gravity. Thus, the question of possible mechanism of flux expulsion in the Alpha-Omega dynamo remains open.Comment: MNRAS, in press, 11 pages, 9 figure