SGR 1806−20 distance and dust properties in molecular clouds by analysis of flare X-ray echoes

The soft gamma repeater SGR 1806−20 is most famous for its giant flare from 2004, which yielded the highest gamma-ray flux ever observed on Earth. The flare emphasized the importance of determining the distance to the SGR, thus revealing the flare’s energy output, with implications on SGRs energy budget and giant flare rates. We analyse X-ray scattering echoes observed by Swift/X-Ray Telescope (XRT) following the 2006 August 6 intermediate burst of SGR 1806−20. Assuming positions and opacities of the molecular clouds along the line of sight from previous works, we derive direct constraints on the distance to SGR 1806−20, setting a lower limit of 9.4 kpc and an upper limit of 18.6 kpc (90 per cent confidence), compared with a 6–15 kpc distance range by previous works. This distance range matches an energy output of ≈10^(46) erg for the 2004 giant flare. We further use, for the first time, the X-ray echoes in order to study the dust properties in molecular clouds. Analysing the temporal evolution of the observed flux using a dust-scattering model, which assumes a power-law size distribution of the dust grains, we obtain a power-law index of −3.3^(+0.6)_(−0.7) (1σ) and a lower limit of 0.1. µm (2σ) on the dust maximal grain size, both conforming to measured dust properties in the diffused interstellar medium (ISM). We advocate future burst follow-up observations with Swift, Chandra and the planned NuSTAR telescopes, as means of obtaining much superior results from such an analysis

A Dip after the Early Emission of Super-Luminous Supernovae: A Signature of Shock Breakout within Dense Circumstellar Media

The origin of super-luminous supernovae (SLSNe), especially the source of their huge luminosities, has not been clarified yet. While a strong interaction between SN ejecta and dense circumstellar media (CSM) is a leading scenario, alternative models have been proposed. In this Letter, we suggest new diagnostics to discriminate the strong SN-CSM interaction scenario from the others: a decline in the luminosity ('dip') before the main peak of the light curve. This dip is an unavoidable consequence of having a dense CSM within which the shock breakout occurs. If a dense CSM shell is located far at large radii from the progenitor inside, it takes time for the SN ejecta to reach it and the early light curve can be powered by the SN ejecta before the collision. Once the SN ejecta collides with the dense CSM, the electron density and thus the Thomson scattering opacity suddenly increase. Photons become unable to go out of the shock even if there is a source of emission inside, which results in the dip in the light curve. This dip is a solid prediction from the strong interaction scenario irrespective of a power source for the early emission. Eventually the forward shock breaks out from within the dense CSM, and the luminosity increases by the continuous strong SN-CSM interaction, resulting in an SLSN. The possible dip observed in the hydrogen-poor SLSN, 2006oz, could be the first example of this signature and give support to the SN-CSM interaction as the power source of SLSN 2006oz.Comment: 5 pages, 1 figure, 1 table, accepted by The Astrophysical Journal Letter

Migração de consumidores residenciais para o ambiente de contratação livre de energia com uso de dinâmica de sistemas

O mercado livre de energia, onde os consumidores podem escolher seu fornecedor de energia, está aberto para consumidores de grande porte (grupo A), porém as tendências mundiais e da regulamentação brasileira é de abertura do mercado para os consumidores de pequeno porte (grupo B), como os residenciais. A regulamentação prevê a obrigatoriedade da contratação de comercializadores varejistas para os consumidores do grupo A com demanda inferior a 500 kW, o que mostra a tendência desta obrigatoriedade para os consumidores de menor porte (grupo B). O trabalho apresenta a modelagem, com o uso da técnica de Dinâmica de Sistemas, da migração de consumidores residenciais para o ambiente de contratação livre (ACL) considerando o papel do comercializador varejista neste contexto. Com o modelo implementado no software Powersim Studio versão 10, identifica-se políticas relevantes na migração dos consumidores residenciais para o ACL. Os resultados do modelo, através da elaboração de sete cenários, revelam a importância do marketing e da publicidade na conscientização dos consumidores a respeito do ACL, assim como a importância da precificação dos encargos de migração cobrados pelo governo e do custo de contratação cobrado pelo comercializador varejista para não afastar os consumidores com um alto custo inicial de migração.The free energy market, where consumers can choose their energy supplier, is open to large consumers (group A), but global trends and Brazilian regulation are opening the market to small consumers (group B), such as residential. The regulation provides for the obligation to hire retailers for group A consumers with a demand of less than 500 kW, which shows the tendency of this obligation for smaller consumers (group B). The work presents the modeling, using the System Dynamics technique, of the migration of residential consumers to the free contracting environment (ACL), considering the role of the retailer in this context. With the model implemented in Powersim Studio version 10 software, relevant policies are identified in the migration of residential consumers to the ACL. The model's results, through the elaboration of seven scenarios, reveal the importance of marketing and advertising in raising consumer awareness about the ACL, as well as the importance of pricing the migration charges charged by the government and the contracting cost charged by the retailer so as not to alienate consumers with a high initial migration cost