XMM-Newton view of Swift J1834.9-0846 and its Magnetar Wind Nebula

We report on the analysis of two XMM-Newton observations of the recently discovered soft gamma repeater Swift J1834.9-0846, taken in September 2005 and one month after the source went into outburst on 2011 August 7. We performed timing and spectral analyses on the point source as well as on the extended emission. We find that the source period is consistent with an extrapolation of the Chandra ephemeris reported earlier and the spectral properties remained constant. The source luminosity decreased to a level of 1.6x10^34 erg s^-1 following a decay trend of $\propto t^{-0.5}$. Our spatial analysis of the source environment revealed the presence of two extended emission regions around the source. The first (Region A) is a symmetric ring around the point source, starting at 25arcsec and extending to ~50arcsec. We argue that Region A is a dust scattering halo. The second (Region B) has an asymmetrical shape extending between 50arcsec and 150arcsec, and is detected both in the pre- and post-outburst data. We argue that this region is a possible magnetar wind nebula (MWN). The X-ray efficiency of the MWN with respect to the rotation energy loss is substantially higher than those of rotation powered pulsars: $\eta_{\rm X}\equiv L_{\rm MWN,0.5-8 keV}/\dot{E}_{\rm rot}\approx0.7$. The higher efficiency points to a different energy source for the MWN of Swift J1834.9-0846, most likely bursting activity of the magnetar, powered by its high magnetic field, B=1.4x10^14 G.Comment: 10 pages, 10 figures, accepted for publication in Ap

Interactions between the hippocampus, prefrontal cortex, and amygdala support complex learning and memory.

One of the guiding principles of memory research in the preceding decades is multiple memory systems theory, which links specific task demands to specific anatomical structures and circuits that are thought to act orthogonally with respect to each other. We argue that this view does not capture the nature of learning and memory when any degree of complexity is introduced. In most situations, memory requires interactions between these circuits and they can act in a facilitative manner to generate adaptive behavior

A possible magnetar nature for IGR J16358-4726

We present detailed spectral and timing analysis of the hard X-ray transient IGR J16358-4726 using multisatellite archival observations. A study of the source flux time history over 6 yr suggests that lower luminosity transient outbursts can be occurring in intervals of at most 1 yr. Joint spectral fits of the higher luminosity outburst using simultaneous Chandra ACIS and INTEGRAL ISGRI data reveal a spectrum well described by an absorbed power-law model with a high-energy cutoff plus an Fe line. We detected the 1.6 hr pulsations initially reported using Chandra ACIS also in the INTEGRAL ISGRI light curve and in subsequent XMM-Newton observations. Using the INTEGRAL data, we identified a spin-up of 94 s ( = 1.6 × 10-4), which strongly points to a neutron star nature for IGR J16358-4726. Assuming that the spin-up is due to disk accretion, we estimate that the source magnetic field ranges between 1013 and 1015 G, depending on its distance, possibly supporting a magnetar nature for IGR J16358-4726

Statistical properties of SGR 1806-20 bursts

We present statistics of SGR 1806-20 bursts, combining 290 events detected with RXTE/PCA, 111 events detected with BATSE and 134 events detected with ICE. We find that the fluence distribution of bursts observed with each instrument are well described by power laws with indices 1.43, 1.76 and 1.67, respectively. The distribution of time intervals between successive bursts from SGR 1806-20 is described by a lognormal function with a peak at 103 s. There is no correlation between the burst intensity and either the waiting times till the next burst or the time elapsed since the previous burst. In all these statistical properties, SGR 1806-20 bursts resemble a self-organized critical system, similar to earthquakes and solar flares. Our results thus support the hypothesis that the energy source for SGR bursts is crustquakes due to the evolving, strong magnetic field of the neutron star, rather than any accretion or nuclear power.Comment: 11 pages, 4 figures, To appear in ApJ Letter

Spin Tunneling in Magnetic Molecules: Quasisingular Perturbations and Discontinuous SU(2) Instantons

Spin coherent state path integrals with discontinuous semiclassical paths are investigated with special reference to a realistic model for the magnetic degrees of freedom in the Fe8 molecular solid. It is shown that such paths are essential to a proper understanding of the phenomenon of quenched spin tunneling in these molecules. In the Fe8 problem, such paths are shown to arise as soon as a fourth order anisotropy term in the energy is turned on, making this term a singular perturbation from the semiclassical point of view. The instanton approximation is shown to quantitatively explain the magnetic field dependence of the tunnel splitting, as well as agree with general rules for the number of quenching points allowed for a given value of spin. An accurate approximate formula for the spacing between quenching points is derived

Market Entry of a Socially Responsible Retailer

As consumers become more conscious about social issues, they gain an additional "social benefit" when purchasing from a socially responsible retailer (or brand). This trend has motivated more socially responsible retailers (or brands) to enter the market with a "pre-commitment" to donate a certain proportion of their (A) profits or (B) revenues for social causes. In this paper, we present a game-theoretic model where a socially responsible retailer enters the market with an incumbent for-profit retailer and heterogeneous consumers. We examine the socially responsible retailer's pricing strategy and entry conditions, the impact of the socially responsible retailer's entry on the incumbent retailer's profit, and the conditions under which the incumbent retailer should deter (or tolerate) the socially responsible retailer's entry. Our equilibrium analysis generates the following insights. First, even if the incumbent retailer can profitably deter the socially responsible retailer's entry, the incumbent retailer can be better off tolerating it under certain conditions. Second, somewhat interestingly, the incumbent retailer is more likely to deter the type (B) retailer's entry even though such entry is less detrimental to the incumbent retailer

Prompt Optical Detection of GRB 050401 with ROTSE-IIIa

The ROTSE-IIIa telescope at Siding Spring Observatory, Australia, detected prompt optical emission from Swift GRB 050401. In this letter, we present observations of the early optical afterglow, first detected by the ROTSE-IIIa telescope 33 s after the start of gamma-ray emission, contemporaneous with the brightest peak of this emission. This GRB was neither exceptionally long nor bright. This is the first prompt optical detection of a GRB of typical duration and luminosity. We find that the early afterglow decay does not deviate significantly from the power-law decay observable at later times, and is uncorrelated with the prompt gamma-ray emission. We compare this detection with the other two GRBs with prompt observations, GRB 990123 and GRB 041219a. All three bursts exhibit quite different behavior at early times.Comment: 4 pages, 3 figures. Accepted for publication in ApJ Letter

Product Development in Crowdfunding: Theoretical and Empirical Analysis

Problem definition: Crowdfunding goes beyond raising funds. Entrepreneurs often use crowdfunding to solicit feedback from customers in order to improve their products, and may therefore prefer to launch their crowdfunding campaigns using basic versions of their products with fewer features. However, customers may not be persuaded by a campaign if the product appears to be underdeveloped. In view of this trade-off, a key question for entrepreneurs is how much to develop a product before launching a crowdfunding cam- paign. / Methodology/results: Analyzing a game-theoretical model and testing its predictions empirically, we study: 1) how the development level of a product at campaign launch, measured by the initial number of product features, in uences whether customers will make comments that help entrepreneurs improve the product; 2) whether entrepreneurs continue to improve the product during the campaign; and 3) whether the campaign is successful. We show that, as the number of product features at campaign launch increases, the likelihood that customers will make comments and that the product will be improved during the campaign first increases but then decreases. Furthermore, the likelihood of campaign success first increases but then decreases with the number of product features at campaign launch. Finally, by analyzing the interactions between customer feedback, product improvement, and campaign success, we show that customer feedback motivates entrepreneurs to improve the product during the campaign. Moreover, entrepreneurs should take account of the initial number of features and customer feedback when improving the product, because oth- erwise product improvements can harm campaign success. / Managerial implications: Our study provides practical insights on how entrepreneurs can use crowdfunding to aid product development and improve- ment. Specifically, entrepreneurs should avoid overdeveloping their products before crowdfunding campaigns because, as well as decreasing the chance of campaign success, this could hinder their ability to save devel- opment costs (e.g., market research costs) through involving customers in product development

Hard Burst Emission from the Soft Gamma Repeater SGR 1900+14

We present evidence for burst emission from SGR 1900+14 with a power-law high energy spectrum extending beyond 500 keV. Unlike previous detections of high energy photons during bursts from SGRs, these emissions are not associated with high-luminosity burst intervals. Not only is the emission hard, but the spectra are better fit by Band's GRB function rather than by the traditional optically-thin thermal bremsstrahlung model. We find that the spectral evolution within these hard events obeys a hardness/intensity anti-correlation. Temporally, these events are distinct from typical SGR burst emissions in that they are longer (~ 1 s) and have relatively smooth profiles. Despite a difference in peak luminosity of > 1E+11 between these bursts from SGR 1900+14 and cosmological GRBs, there are striking temporal and spectral similarities between the two kinds of bursts, aside from spectral evolution. We outline an interpretation of these events in the context of the magnetar model.Comment: 11 pages (text and figures), submitted to ApJ Letters, corrected erroneous hardness ratio