Showing papers by "Christopher Lidman published in 1998"

Discovery of a supernova explosion at half the age of the Universe

Abstract: The ultimate fate of the Universe, infinite expansion or a big crunch, can be determined by using the redshifts and distances of very distant supernovae to monitor changes in the expansion rate. We can now find1 large numbers of these distant supernovae, and measure their redshifts and apparent brightnesses; moreover, recent studies of nearby type Ia supernovae have shown how to determine their intrinsic luminosities2,3,4—and therefore with their apparent brightnesses obtain their distances. The >50 distant supernovae discovered so far provide a record of changes in the expansion rate over the past several billion years5,6,7. However, it is necessary to extend this expansion history still farther away (hence further back in time) in order to begin to distinguish the causes of the expansion-rate changes—such as the slowing caused by the gravitational attraction of the Universe's mass density, and the possibly counteracting effect of the cosmological constant8. Here we report the most distant spectroscopically confirmed supernova. Spectra and photometry from the largest telescopes on the ground and in space show that this ancient supernova is strikingly similar to nearby, recent type Ia supernovae. When combined with previous measurements of nearer supernovae2,5, these new measurements suggest that we may live in a low-mass-density universe.

A hypernova model for the supernova associated with the gamma ray burst of 25 April 1998

Abstract: The discovery of the unusual supernova SN1998bw, and its possible association with the γ-ray burst GRB 9804251,2,3, provide new insights into the explosion mechanism of very massive stars and the origin of some classes of γ-ray bursts. Optical spectra indicate that SN1998bw is a type Ic supernova3,4, but its peak luminosity is unusually high compared with typical type Ic supernovae3. Here we report our findings that the optical spectra and the light curve of SN1998bw can be well reproduced by an extremely energetic explosion of a massive star composed mainly of carbon and oxygen (having lost its hydrogen and helium envelopes). The kinetic energy of the ejecta is as large as +(2–5)× 1052 erg, more than ten times that of previously observed supernovae. This type of supernova could therefore be termed ‘hypernova’. The extremely large energy suggests the existence of a new mechanism of massive star explosion that can also produce the relativistic shocks necessary to generate the observed γ-rays.

SOFI sees first light at the NTT.

Abstract: ing the infrared observing capabilities on La Silla, SOFI has also provided valuable experience within the ‘VLT environment’ now existing at the upgraded NTT telescope in advance of the more complicated installation of ISAAC at the VLT later this year. In addition to the opportunity for testing some of the purely instrumental aspects, this includes some of the new operational features being introduced to ground-based astronomy at the VLT such as automatic

Detection of the lensing galaxy in HE 1104-1805

Abstract: We report on deep IR imaging of the double quasar HE 1104-1805.Anewimagedeconvolutiontechniquehasbeen applied to the data in order to optimally combine the numerous frames obtained. The resulting J and K 0 images allow us to de- tect and study the lensing galaxy between the two lensed QSO images. The near infrared images not only confirm the lensed nature of this double quasar, but also support the previous red- shift estimate of z =1 .66 for the lensing galaxy. No obvious overdensity of galaxies is detected in the immediate region sur- rounding the lens, down to limiting magnitudes of J = 22 and K = 20. The geometry of the system, together with the time delays expected for this lensed quasar, make HE 1104-1805 a remarkable target for future photometric monitoring programs, for the study of microlensing and for the determination of the cosmological parameters in the IR and optical domains.