Search

Future use of type Ia supernovae for cosmology aims not only to determine the equation of state of dark energy, but also to constrain possible variations in its value. To achieve this goal, supernovae need to become better calibrated standard candles — not only to improve the precision of the measurement, but more importantly to gain better control over systematic uncertainties in order to ensure the accuracy of the result. Here we report on a project to quantify the diversity in type Ia supernovae, and to look for trends and/or sub-types that can be used to improve their calibration as standard candles. We implement a version of principal component analysis on type Ia supernova spectra. Although the quantity of data is not sufficient to draw any firm conclusions we show that this method holds promise for, at the very least, effectively separating peculiar supernovae. Whether it can be further used to improve the calibration of normal type Ia’s remains a project for future study. © 2007 American Institute of Physics [ABSTRACT FROM AUTHOR]

If the progenitors of gamma-ray bursts (GRBs) are massive stars, then we expect the GRB rate to follow the cosmic star formation rate at least to moderate redshifts. Here we attempt to quantify selection effects in the measurement of GRB redshifts as a function of the GRB energy release, afterglow luminosity and redshift. We apply these to a sample of 24 GRBs with optical afterglows and measured redshifts, and present the resultant measurement of the GRB rate over 0.2 < z < 5. The GRB rate density evolution is consistent with measurements of the UV luminosity density. Our simulations predict that approximately 50% of searches for optical afterglows result in a nondetection, which is broadly consistent with the observed rate of “dark bursts”. We finally apply our simulations to the case of the Swift satellite mission and show that small robotic telescope projects may be able to identify ∼ 1 GRB beyond z > 7 during the 3 year Swift mission. This rate is largely limited by the relatively poor sensitivity in the near-infrared, but may be increased if small telescopes are coupled with more sensitive NIR imaging in order to uncover a larger fraction of GRBs beyond the most distant known objects at z > 6.5. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

We have developed an automated system for the rapid observation and identification of gamma-ray burst (GRB) afterglows. We expect to observe GRB localisations from the High Energy Transient Explorer within 2 minutes of the GRB, and automatically identify an optical transient within 10 minutes. Such early observations are expected to yield new information on the GRB phenomenon, constrain possible progenitor models and allow rapid spectroscopic follow-up. [ABSTRACT FROM AUTHOR]