Sr impurity effects on the magnetic correlations of LaSrCuO

We examine the low-temperature magnetic properties of moderately doped LaSrCuO paying particular attention to the spin-glass (SG) phase and the C-IC transition as they are affected by Sr impurity disorder. New measurements of the low-temperature susceptibility in the SG phase show an increase of an anomalously small Curie constant with doping. This behaviour is explained in terms of our theoretical work that finds small clusters of AFM correlated regions separated by disordered domain walls. The domain walls lead to a percolating sequence of paths connecting the impurities. We predict that for this spin morphology the Curie constant should scale as $1/(2 \xi(x,T=0)^2)$, a result that is quantitatively in agreement with experiment. Also, we find that the magnetic correlations in the ground states in the SG phase are commensurate, and that this behaviour should persist at higher temperatures where the holes should move along the domain walls. However, our results show that incommensurate correlations develop continuously around 5 % doping, consistent with recent measurements by Yamada.Comment: 30 pages, revtex, 8 .ps format figures (2 meant to be in colour), to be published in Physical Review B

A new analysis of the short-duration, hard-spectrum GRB 051103, a possible extragalactic soft gamma repeater giant flare

GRB 051103 is considered to be a candidate soft gamma repeater (SGR) extragalactic giant magnetar flare by virtue of its proximity on the sky to M81/M82, as well as its time history, localization and energy spectrum. We have derived a refined interplanetary network localization for this burst which reduces the size of the error box by over a factor of 2. We examine its time history for evidence of a periodic component, which would be one signature of an SGR giant flare, and conclude that this component is neither detected nor detectable under reasonable assumptions. We analyse the time-resolved energy spectra of this event with improved time and energy resolution, and conclude that although the spectrum is very hard its temporal evolution at late times cannot be determined, which further complicates the giant flare association. We also present new optical observations reaching limiting magnitudes of R > 24.5, about 4-mag deeper than previously reported. In tandem with serendipitous observations of M81 taken immediately before and 1 month after the burst, these place strong constraints on any rapidly variable sources in the region of the refined error ellipse proximate to M81. We do not find any convincing afterglow candidates from either background galaxies or sources in M81, although within the refined error region we do locate two UV bright star-forming regions which may host SGRs. A supernova remnant (SNR) within the error ellipse could provide further support for an SGR giant flare association, but we were unable to identify any SNR within the error ellipse. These data still do not allow strong constraints on the nature of the GRB 051103 progenitor, and suggest that candidate extragalactic SGR giant flares will be difficult, although not impossible, to confir

A new analysis of the short-duration, hard-spectrum GRB 051103, a possible extragalactic soft gamma repeater giant flare

GRB 051103 is considered to be a candidate soft gamma repeater (SGR) extragalactic giant magnetar flare by virtue of its proximity on the sky to M81/M82, as well as its time history, localization and energy spectrum. We have derived a refined interplanetary network localization for this burst which reduces the size of the error box by over a factor of 2. We examine its time history for evidence of a periodic component, which would be one signature of an SGR giant flare, and conclude that this component is neither detected nor detectable under reasonable assumptions. We analyse the time-resolved energy spectra of this event with improved time and energy resolution, and conclude that although the spectrum is very hard its temporal evolution at late times cannot be determined, which further complicates the giant flare association. We also present new optical observations reaching limiting magnitudes of R > 24.5, about 4-mag deeper than previously reported. In tandem with serendipitous observations of M81 taken immediately before and 1 month after the burst, these place strong constraints on any rapidly variable sources in the region of the refined error ellipse proximate to M81. We do not find any convincing afterglow candidates from either background galaxies or sources in M81, although within the refined error region we do locate two UV bright star-forming regions which may host SGRs. A supernova remnant (SNR) within the error ellipse could provide further support for an SGR giant flare association, but we were unable to identify any SNR within the error ellipse. These data still do not allow strong constraints on the nature of the GRB 051103 progenitor, and suggest that candidate extragalactic SGR giant flares will be difficult, although not impossible, to confirm