The discovery of the unusual supernova SN1998bw, and its possible association with the ␥-ray burst GRB 980425 1-3 , provide new insights into the explosion mechanism of very massive stars and the origin of some classes of ␥-ray bursts. Optical spectra indicate that SN1998bw is a type Ic supernova 3,4 , but its peak luminosity is unusually high compared with typical type Ic supernovae 3 . Here we report our findings that the optical spectra

Nature © Macmillan Publishers Ltd 19988 amounts of 56 Ni (ϳ0.7 solar masses) have to be synthesized in the explosion 16 ; the large energy and 56 Ni mass would be unprecedented for a core-collapse supernova.If one accepts the possibility that GRB980425 and SN1998bw are associated, one must conclude that GRB980425 is a rare type of GRB, and SN1998bw is a rare type of supernova. The radio properties 8,9 of SN1998bw show the peculiar nature of this event independent of whether or not it is associated with GRB980425.The consequence of an association is that the ␥-ray peak luminosity of GRB980425 is L ␥ ¼ ð5:5 Ϯ 0:7Þ ϫ 10 46 erg s −1 (in the 24-1,820 keV band) and its total ␥-ray energy budget is (8:1 ϫ 1:0Þ ϫ 10 47 erg. These values are much smaller than those of 'normal' GRBs which have peak luminosities of up to 10 52 erg s −1 and total energies 5 up to several times 10 53 erg. This implies that very different mechanisms can produce GRBs which cannot be distinguished on the basis of their ␥-ray properties, and that models explaining GRB980425/SN1998bw are unlikely to apply to 'normal' GRBs and vice versa. Ⅺ

We present and discuss the photometric and spectroscopic evolution of the peculiar SN 1998bw, associated with GRB 980425, through an analysis of optical and near-IR data collected at ESOÈLa Silla. The spectroscopic data, spanning the period from day [9 to day ]376 (relative to B maximum), have shown that this supernova (SN) was unprecedented, although somewhat similar to SN 1997ef. Maximum expansion velocities as high as 3 ] 104 km s~1 to some extent mask its resemblance to other Type Ic SNe. At intermediate phases, between photospheric and fully nebular, the expansion velocities (D104 km s~1) remained exceptionally high compared to those of other recorded core-collapse SNe at a similar phase. The mild linear polarization detected at early epochs suggests the presence of asymmetry in the emitting material. The degree of asymmetry, however, cannot be decoded from these measurements alone. The He I 1.083 and 2.058 km lines are identiÐed, and He is suggested to lie in an outer region of the envelope. The temporal behavior of the Ñuxes and proÐles of emission lines of Mg I] j4571, [O I] jj6300, 6364, and a feature ascribed to Fe are traced to stimulate future modeling work. The uniqueness of SN 1998bw became less obvious once it entered the fully nebular phase (after 1 yr), when it was very similar to other Type Ib/cÈIIb objects, such as the Type Ib SN 1996N and the Type IIb SN 1993J, even though SN 1998bw was 1.4 mag brighter than SN 1993J and 3 mag brighter than SN 1996N at a comparable phase. The late-phase optical photometry, which extends up to 403 days after B maximum, shows that the SN luminosity declined exponentially but substantially faster than the decay rate of 56Co. The ultraviolet-optical-infrared bolometric light curve, constructed using all available optical data and the early JHK photometry presented in this work, shows a slight Ñattening starting on about day ]300. Since no clear evidence of ejecta-wind interaction was found in the late-time spectroscopy (see also the work of Sollerman and coworkers), this may be due to the contribution of the positrons since most c-rays escape thermalization at this phase. A contribution from the superposed H II region cannot, however, be excluded.

Abstract. The EPIC focal plane imaging spectrometers on XMM-Newton use CCDs to record the images and spectra of celestial X-ray sources focused by the three X-ray mirrors. There is one camera at the focus of each mirror; two of the cameras contain seven MOS CCDs, while the third uses twelve PN CCDs, defining a circular field of view of 30 diameter in each case. The CCDs were specially developed for EPIC, and combine high quality imaging with spectral resolution close to the Fano limit. A filter wheel carrying three kinds of X-ray transparent light blocking filter, a fully closed, and a fully open position, is fitted to each EPIC instrument. The CCDs are cooled passively and are under full closed loop thermal control. A radio-active source is fitted for internal calibration. Data are processed on-board to save telemetry by removing cosmic ray tracks, and generating X-ray event files; a variety of different instrument modes are available to increase the dynamic range of the instrument and to enable fast timing. The instruments were calibrated using laboratory X-ray beams, and synchrotron generated monochromatic X-ray beams before launch; in-orbit calibration makes use of a variety of celestial X-ray targets. The current calibration is better than 10% over the entire energy range of 0.2 to 10 keV. All three instruments survived launch and are performing nominally in orbit. In particular full field-of-view coverage is available, all electronic modes work, and the energy resolution is close to pre-launch values. Radiation damage is well within pre-launch predictions and does not yet impact on the energy resolution. The scientific results from EPIC amply fulfil pre-launch expectations.