The Integral Burst Alert System (IBAS)

We describe the INTEGRAL Burst Alert System (IBAS): the automatic software for the rapid distribution of the coordinates of the Gamma-Ray Bursts detected by INTEGRAL. IBAS is implemented as a ground based system, working on the near-real time telemetry stream. During the first six months of operations, six GRB have been detected in the field of view of the INTEGRAL instruments and localized by IBAS. Positions with an accuracy of a few arcminutes are currently distributed by IBAS to the community for follow-up observations within a few tens of seconds of the event.Comment: 7 pages, latex, 5 figures, Accepted for publication on A&A Special Issue on First Science with INTEGRA

Beam alignment techniques based on the current multiplication effect in photoconductors First phase technical summary report

Current multiplication effects in cadmium sulfide photoconductive cell

Non-adiabatic spin torque investigated using thermally activated magnetic domain wall dynamics

Using transmission electron microscopy, we investigate the thermally activated motion of domain walls (DWs) between two positions in permalloy (Ni80Fe20) nanowires at room temperature. We show that this purely thermal motion is well described by an Arrhenius law, allowing for a description of the DW as a quasi-particle in a 1D potential landscape. By injecting small currents, the potential is modified, allowing for the determination of the non-adiabatic spin torque: the non-adiabatic coefficient is 0.010 +/- 0.004 for a transverse DW and 0.073 +/- 0.026 for a vortex DW. The larger value is attributed to the higher magnetization gradients present

Beam Alignment Techniques Based on the Current Multiplication Effect in Photoconductors Summary Technical Progress Report

Beam alignment techniques based on current multiplication effect in photoconductors for application to spacecraft communications syste

Supernova Ejecta in the Youngest Galactic Supernova Remnant G1.9+0.3

G1.9+0.3 is the youngest known Galactic supernova remnant (SNR), with an estimated supernova (SN) explosion date of about 1900, and most likely located near the Galactic Center. Only the outermost ejecta layers with free-expansion velocities larger than about 18,000 km/s have been shocked so far in this dynamically young, likely Type Ia SNR. A long (980 ks) Chandra observation in 2011 allowed spatially-resolved spectroscopy of heavy-element ejecta. We denoised Chandra data with the spatio-spectral method of Krishnamurthy et al., and used a wavelet-based technique to spatially localize thermal emission produced by intermediate-mass elements (IMEs: Si and S) and iron. The spatial distribution of both IMEs and Fe is extremely asymmetric, with the strongest ejecta emission in the northern rim. Fe Kalpha emission is particularly prominent there, and fits with thermal models indicate strongly oversolar Fe abundances. In a localized, outlying region in the northern rim, IMEs are less abundant than Fe, indicating that undiluted Fe-group elements (including 56Ni) with velocities larger than 18,000 km/s were ejected by this SN. But in the inner west rim, we find Si- and S-rich ejecta without any traces of Fe, so high-velocity products of O-burning were also ejected. G1.9+0.3 appears similar to energetic Type Ia SNe such as SN 2010jn where iron-group elements at such high free-expansion velocities have been recently detected. The pronounced asymmetry in the ejecta distribution and abundance inhomogeneities are best explained by a strongly asymmetric SN explosion, similar to those produced in some recent 3D delayed-detonation Type Ia models.Comment: 6 pages, 3 figures, submitted to ApJ Letter

Nonuniform Expansion of the Youngest Galactic Supernova Remnant G1.9+0.3

We report measurements of X-ray expansion of the youngest Galactic supernova remnant, G1.9+0.3, using Chandra observations in 2007, 2009, and 2011. The measured rates strongly deviate from uniform expansion, decreasing radially by about 60% along the X-ray bright SE-NW axis from 0.84% +/- 0.06% per yr to 0.52% +/- 0.03% per yr. This corresponds to undecelerated ages of 120-190 yr, confirming the young age of G1.9+0.3, and implying a significant deceleration of the blast wave. The synchrotron-dominated X-ray emission brightens at a rate of 1.9% +/- 0.4% per yr. We identify bright outer and inner rims with the blast wave and reverse shock, respectively. Sharp density gradients in either ejecta or ambient medium are required to produce the sudden deceleration of the reverse shock or the blast wave implied by the large spread in expansion ages. The blast wave could have been decelerated recently by an encounter with a modest density discontinuity in the ambient medium, such as found at a wind termination shock, requiring strong mass loss in the progenitor. Alternatively, the reverse shock might have encountered an order-of-magnitude density discontinuity within the ejecta, such as found in pulsating delayed-detonation Type Ia models. We demonstrate that the blast wave is much more decelerated than the reverse shock in these models for remnants at ages similar to G1.9+0.3. Similar effects may also be produced by dense shells possibly associated with high-velocity features in Type Ia spectra. Accounting for the asymmetry of G1.9+0.3 will require more realistic 3D Type Ia models.Comment: 6 pages, 4 figures, accepted for publication in ApJ Letters, minor revision

Magnetic induction mapping of magnetite chains in magnetotactic bacteria at room temperature and close to the Verwey transition using electron holography

Off-axis electron holography in the transmission electron microscope is used to record magnetic induction maps of closely spaced magnetite crystals in magnetotactic bacteria at room temperature and after cooling the sample using liquid nitrogen. The magnetic microstructure is related to the morphology and crystallography of the particles, and to interparticle interactions. At room temperature, the magnetic signal is dominated by interactions and shape anisotropy, with highly parallel and straight field lines following the axis of each chain of crystals closely. In contrast, at low temperature the magnetic induction undulates along the length of the chain. This behaviour may result from a competition between interparticle interactions and an easy axis of magnetisation that is no longer parallel to the chain axis. The quantitative nature of electron holography also allows the change in magnetisation in the crystals with temperature to be measured

Observation of thermally-induced magnetic relaxation in a magnetite grain using off-axis electron holography

A synthetic basalt comprising magnetic Fe3O4 grains (~ 50 nm to ~ 500 nm in diameter) is investigated using a range of complementary nano-characterisation techniques. Off-axis electron holography combined with in situ heating allowed for the visualisation of the thermally-induced magnetic relaxation of an Fe3O4 grain (~ 300 nm) from an irregular domain state into a vortex state at 550˚C, just below its Curie temperature, with the magnetic intensity of the vortex increasing on cooling