Search

Nearly 400 years have passed since a supernova was last observed directly in the Milky Way (by Kepler, in 1604). Numerous Galactic supernovae are expected to have occurred since then1, but only one (Cassiopeia A) may have been seen2. The historical record of supernovae is therefore incomplete, as demonstrated by the spatial distribution of young supernova remnants3. The discovery4,5 of γ-ray emission from the decay of 44Ti nuclei associated with Cassiopeia A, the youngest known remnant, has revealed a new way to search for the remnants of other relatively recent supernovae (less than ∼1,000 years old). Here we report the discovery of 44Ti line emission from a previously unknown young supernova remnant, in the direction of the Vela remnant. We estimate a distance of ∼200 parsecs and an age of ∼680 years for the remnant, making it the closest young remnant to the Earth. Why it was not recorded historically remains unknown.

Soft-gamma-ray repeaters (SGRs) are galactic X-ray stars that emit numerous short-duration (about 0.1 s) bursts of hard X-rays during sporadic active periods. They are thought to be magnetars: strongly magnetized neutron stars with emissions powered by the dissipation of magnetic energy. Here we report the detection of a long (380 s) giant flare from SGR 1806-20, which was much more luminous than any previous transient event observed in our Galaxy. (In the first 0.2 s, the flare released as much energy as the Sun radiates in a quarter of a million years.) Its power can be explained by a catastrophic instability involving global crust failure and magnetic reconnection on a magnetar, with possible large-scale untwisting of magnetic field lines outside the star. From a great distance this event would appear to be a short-duration, hard-spectrum cosmic gamma-ray burst. At least a significant fraction of the mysterious short-duration gamma-ray bursts therefore may come from extragalactic magnetars., Comment: 21 pages, 5 figures. Published in Nature

LOCALISED γ-ray sources contribute to the overall galactic emission; some of these sources have been identified with known astronomical objects1,2, while several unidentified γ-ray sources have also been reported3,4. We describe here a search for γ-ray sources using data from the ESA γ-ray satellite COS B which revealed 10 new unidentified sources. These sources seem to be galactic with typical γ-ray luminosities above 100 MeV in excess of 1035 erg s−1.

DURING the past two years results from two different balloon experiments1,2 indicate that the γ-ray emission from the Crab Nebula between 1 and 10 MeV is considerably above the straight line interpolation from lower and higher photon energies. The excess above the power law has been claimed to be factor of 7 between 1 and 3 MeV and of a factor 30 between 3 and 10 MeV. The fact that both experiments yielded nearly identical results gives support to the reality of the excess component. The power in this excess is nearly as large as the total integrated synchrotron power of 2×10−7 erg cm−2 s−1 of the Crab Nebula. It has been speculated that this powerful, narrow-band component may be produced in the pulsar magnetosphere, possibly near the surface of the neutron star2.