342 research outputs found
Spatially resolved X-ray study of supernova remnants that host magnetars: Implication of their fossil field origin
No full textMagnetars are regarded as the most magnetized neutron stars in the Universe. Aiming to unveil what kinds of stars and supernovae can create magnetars, we have performed a state-of-the-art spatially resolved spectroscopic X-ray study of the supernova remnants (SNRs) Kes 73, RCW 103, and N49, which host magnetars 1E 1841-045, 1E 161348-5055, and SGR 0526-66, respectively. The three SNRs are O- and Ne-enhanced and are evolving in the interstellar medium with densities of >1-2 cm(-3). The metal composition and dense environment indicate that the progenitor stars are not very massive. The progenitor masses of the three magnetars are constrained to be <20 M-circle dot (11-15 M-circle dot for Kes 73, less than or similar to 13 M-circle dot for RCW 103, and similar to 13-17 M-circle dot for N49). Our study suggests that magnetars are not necessarily made from very massive stars, but originate from stars that span a large mass range. The explosion energies of the three SNRs range from 10(50) erg to similar to 2 x10(51) erg, further refuting that the SNRs are energized by rapidly rotating (millisecond) pulsars. We report that RCW 103 is produced by a weak supernova explosion with significant fallback, as such an explosion explains the low explosion energy (10(50)erg), small observed metal masses (M-circle dot similar to 4 x 10(-2) M-circle dot and M-Ne similar to 6 x 10(-3) M-circle dot), and sub-solar abundances of heavier elements such as Si and S. Our study supports the fossil field origin as an important channel to produce magnetars, given the normal mass range (M-ZAMS < 20 M-circle dot) of the progenitor stars, the low-to-normal explosion energy of the SNRs, and the fact that the fraction of SNRs hosting magnetars is consistent with the magnetic OB stars with high field
Tapping Economies of Scale and Scope in Consumer Cooperation - A Case Analysis of Possible Cooperation among selected Cooperatives
No full textBecause of its narrow and negative perspective of safeguarding the interests of only poor consumers against unethical practices of the private traders, consumer cooperation in India seems to have failed, except probably in some isolated pockets. A number of social welfare functions like poverty alleviation and public distribution of essential items of consumption have been imposed on them at the cost of their basic economics. With the basic micro and macro-economic rationale for consumer cooperatives as a positive form of economic organization being lost sight of, they seem to be facing enormous problems both historically as well as currently in a era of economic liberalization. Their worries seem to have been compounded with the threat of impending competition from large private enterpriss - both domestic and foreign, which highlights the need for evolving strategies to rectivy their systemic weaknesses and tackling the competition head on. This case has attempted to document just such an initiative through a round table conference with several doyens of the consumer cooperative movement in India such as Warana Bazar and Amalsad Mandali as well as some fledging consumer cooperatives from West Bengal which are already in existence for some time or contemplating entry into this field. The roundtable conference organized in the spirit of Cooperation among Cooperatives attempted to evolve strategies to capture economies of scale and scope in order to take on the competition, as well as to facilitate dissemination of ideas and information across the country.
THE PLERIONIC SUPERNOVA REMNANT G21.5–0.9 POWERED BY PSR J1833–1034: NEW SPECTROSCOPIC AND IMAGING RESULTS REVEALED WITH THE<i>CHANDRA X-RAY OBSERVATORY</i>
No full text
An Imaging and Spectroscopic Study of the Supernova Remnant RCW 103 (G332.4-0.4) with the CHANDRA X-ray Observatory
No full textThe explosion of a massive star results in an immense expulsion of energy and stellar debris (ejecta) that are heated to extremely high temperatures forming what is known as a super va remnant (SNR). Presented is a CHANDRA 0.5-10 keV X-ray study of the SNR RCW 103, a bright SNR that contains the unusual compact object 1E 161348-5055. This study is the first dedicated and complete imaging and spatially resolved spectroscopic study of the SNR aimed at addressing the intrinsic properties of the SNR, including the explosion energy, ambient density, age, and distance. The SNR's X-ray spectrum is dominated by thermal X-ray emission, requiring globally two components with temperatures at ~0.6 keV and ~0.27 keV and di fferent ionization timescales and abundances. We identify clumpy regions of enhanced abundances suggesting the presence of ejecta. The SNR age is estimated at 1.0-3.7 kyr at a distance of 3.1 kpc.May 201
Structure, simulations, and stability of molecular tornadoes
No full textAn analytic stationary solution for rotating, magnetized, non-self-gravitating filamentary molecular clouds is presented as a model for molecular tornadoes. This model results in monotonically decreasing density profiles for rotating filaments, unlike previous filament models, which suffered radial oscillations in density referred to as density inversions. Whereas previous models consider the effect of self-gravity on molecular clouds, we use estimates derived from observations of the Double Helix Nebula, the Galactic Centre Tornado, and the Pigtail Nebula in the Central Molecular Zone of the Milky Way Galaxy that highly pressure truncated filamentary clouds are at most weakly self-gravitating. The simulation code Athena++ is used to study the time evolution of the model to assess its stability and evolution. Two different sets of boundary conditions are simulated, one which simulates an infinitely long idealized filament and another which simulates a finite filament protruding from a fixed rotating source. Simulations of the model do not develop detectable instabilities until at least twenty-five sound crossing times. However, simulations seeded with white noise with a standard deviation 0.01 in their initial density profiles develop kink instabilities within ten sound crossing timesOctober 202
Searching for nucleus obscuration in the infrared spectra of nearby FR-I radio galaxies
No full textWhy are there so many types of active galactic nuclei (AGN)? Astronomers have proposed numerous AGN unification models to explain the vast array of different AGN types with a single type of object. The most prominent of these features a supermassive black hole’s accretion disk obscured by a torus of discrete dusty clouds. The applicability of this model to low-luminosity AGN such as Fanaroff & Riley class I (FR-I) radio galaxies is controversial. We present a wide-band infrared spectroscopic analysis of ten nearby FR-I radio galaxies. We used Markov-chain Monte Carlo algorithms to fit a set of models to Spitzer /IRS spectra with wide-band behaviour constrained by photometry from 2MASS, Spitzer /IRAC, Spitzer /MIPS, and Herschel /SPIRE. We find one galaxy is best fit by a torus and three others show some thermal mid-infrared component. We conclude that 40% of our FR-I radio galaxies show evidence of obscuring dusty material.October 201
- …
