Stephen Holland's Recent News

October 31, 2012

Our paper on A Correlation Between the Intrinsic Brightness and Average Decay Rate of Swift/UVOT Gamma-Ray Burst Optical/Ultraviolet Light Curves has been published in Monthly Notices of the Royal Astronomical Society. A copy of the paper is a available here.

This Figure shows the average decay indices and luminosities of 61 GRB optical and ultraviolet afterglows taken from the second Swift UVOT GRB afterglow catalogue. The decay indices and luminosities were measured at 200 s after the BAT trigger. The solid red line is the best fit to the data and the dashed blue lines are the 3-σ deviations. The best fit gives

log₁₀(L₂₀₀ = (-3.626 ± 0.004)α₂₀₀ + (28.08 ± 0.13)

with a probability that we can reject the null hypothesis (no correlation) of 99.998%. It is not clear what physical mechanism is responsible for this correlation.

August 28, 2012

Our paper on Swift observations of the Type IIb supernova SN2009mg has been published in Monthly Notices of the Royal Astronomical Society. A copy of the paper is a available here.

The upper panel of this Figure shows the v-band light curve of SN2009mg (green). light curves for the prototype SNe IIb SN1993J (black) and SN2008ax (red). The late-time decay of SN2009mg is not consistent with the supernova remnent being powered by the radioactive decay of ⁵⁶Co. This suggests that gamma-rays are leaking out of the ejecta. It also implies that the progenitor mass was less than that of typical SNe IIb progenitors. The lower panel shows the b-v colour evolution for these three supernovae.

June 25, 2012

Our paper presenting evidence that the transient X-ray source Swift J2058.4+0516 was a star being torn apart by a supermassive black hole has been published in the Astrophysical Journal. A copy of the paper is a available here.

This Figure shows a the spectral energy distribution of Swift J2058.4+0516 to those of various blazars and the unusual event Swift J164449.3+573451. This latter source was originally thought to be a gamma-ray burst, but is not thought to be the death thoes of a star being torn apart by a supermassive black hole. We find that Swift J2058.4+0516 has many properties, including its spectral energy distribution, that are very similar to what are expected when a supermassive black hole tears a star apart.