Optimal co-addition of imaging data for rapidly fading gamma-ray burst afterglows

A. N. Morgan, D. E. Vanden Berk, P. W.A. Roming, J. A. Nousek, T. S. Koch, A. A. Breeveld, M. De Pasquale, S. T. Holland, N. P.M. Kuin, M. J. Page, M. Still

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4 Scopus citations


We present a technique for optimal co-addition of image data for rapidly varying sources, with specific application to gamma-ray burst (GRB) afterglows. Unweighted co-addition of rapidly fading afterglow light curve data becomes counterproductive relatively quickly. It is better to stop co-addition of the data once noise dominates late exposures. A better alternative is to optimally weight each exposure to maximize the signal-to-noise ratio (S/N) of the final co-added image data. By using information about GRB light curves and image noise characteristics, optimal image co-addition increases the probability of afterglow detection and places the most stringent upper limits on nondetections. For a temporal power-law flux decay typical of GRB afterglows, optimal co-addition has the greatest potential to improve the S/N of afterglow imaging data (relative to unweighted co-addition) when the decay rate is high, the source count rate is low, and the background rate is high. The optimal co-addition technique is demonstrated with applications to Swift Ultraviolet/Optical Telescope (UVOT) data of several GRBs, with and without detected afterglows.

Original languageEnglish (US)
Pages (from-to)913-923
Number of pages11
JournalAstrophysical Journal
Issue number2
StatePublished - Aug 20 2008

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


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