My recent paper where we investigate the origin of the infamous correlation between a GRB’s nuFnu spectral peak Epk and its isotropic equivalent energy Eiso has been posted to ArXiv.org. I do this by simulating a realistic population of GRBs and examine how these bursts would appear to a gamma-ray detector here on Earth. I find that a strong observed correlation can be produced between the source frame Epk and Eiso for the detected population despite the existence of only a weak and broad correlation in the original simulated population. The energy dependance of a gamma-ray detector’s flux-limited detection threshold acts to produce a correlation between the source frame Epk and Eiso for low luminosity GRBs, producing the left boundary of the observed correlation. Conversely, very luminous GRBs are found at higher redshifts than their low luminosity counterparts due to the standard Malquest bias, causing bursts in the low Epk, high Eiso regime to go undetected because their Epk values would be redshifted to energies at which most gamma-ray detectors become less sensitive. I argue that it is this previously unexamined effect which produces the right boundary of the observed correlation. Therefore, the origin of the observed correlation is a complex combination of the instrument’s detection threshold, the intrinsic cutoff in the GRB luminosity function, and the broad range of redshifts over which GRBs are detected. These simulations serve to demonstrate how selection effects caused by a combination of instrumental sensitivity and the cosmological nature of an astrophysical population can act to produce an artificially strong correlation between observed properties.

The full paper can be found at the link below:
http://adsabs.harvard.edu/abs/2011arXiv1110.6173K

Our recent paper on the effects of time dilation on gamma-ray burst pulses has now been posted on ArXiv.org. In the paper we explain that the observed lack of time dilation in the temporal profiles of high redshift GRBs is due to an instrumental bias that effects the duration measurement of transient signals in the presence of background noise. We find that the observer frame duration of individual pulses does not increase as a function of redshift as one would expect from a cosmologically expanding Universe. In fact, the duration of individual pulses is seen to decrease as their signal-to-noise decreases with increasing redshift, as only the brightest portion of a high redshift GRB’s light curve is accessible to the detector. We show that this fundamental duration bias implies that the measured durations and associated Eiso estimates for GRBs detected near an instrument’s detection threshold should be considered lower limits to their true values. The full paper can be found at the link below.

http://adsabs.harvard.edu/abs/2011arXiv1110.6175K

Our recent paper on the origins of the M-Z relation for long gamma-ray burst host galaxies has now been posted on ArXiv.org. In the paper we explain the observed offset between the GRB and SDSS defined M-Z relations as being due to a bias towards finding transient events in low metallicity, high star forming galaxies. If low metallicity galaxies produce more stars than their equally massive, high-metallicity counterparts, then transient events that closely trace the SFR in a galaxy would be more likely to be found in these types of galaxies. You can read all about it at the link below: