GRB 090926A was detected by both the Gamma-ray Burst Monitor and Large Area Telescope (LAT) instruments on board the Fermi Gamma-ray Space Telescope. Swift follow-up observations began ~13 hr after the initial trigger. The optical afterglow was detected for nearly 23 days post trigger, placing it in the long-lived category. The afterglow is of particular interest due to its brightness at late times, as well as the presence of optical flares at T0+105 s and later, which may indicate late-time central engine activity. The LAT has detected a total of 16 gamma-ray bursts; nine of these bursts, including GRB 090926A, also have been observed by Swift. Of the nine Swift-observed LAT bursts, six were detected by UVOT, with five of the bursts having bright, long-lived optical afterglows. In comparison, Swift has been operating for five years and has detected nearly 500 bursts, but has only seen ~30% of bursts with optical afterglows that live longer than 105 s. We have calculated the predicted gamma-ray fluence, as would have been seen by the Burst Alert Telescope (BAT) on board Swift, of the LAT bursts to determine whether this high percentage of long-lived optical afterglows is unique, when compared to BAT-triggered bursts. We find that, with the exception of the short burst GRB 090510A, the predicted BAT fluences indicate that the LAT bursts are more energetic than 88% of all Swift bursts and also have brighter than average X-ray and optical afterglows.
- gamma-ray burst: general, gamma-ray burst: individual: GRB 090926A, shock waves, Astrophysics - High Energy Astrophysical Phenomena
Swenson, C. A., Maxham, A., Roming, P. W. A., Schady, P., Vetere, L., Zhang, B. B., Zhang, B., Holland, S. T., Kennea, J. A., Kuin, N. P. M., Oates, S. R., Page, K. L., & De Pasquale, M. (2010). GRB 090926A and Bright Late-time Fermi Large Area Telescope Gamma-ray Burst Afterglows. Astrophysical Journal, 718(1), L14-L18. https://doi.org/10.1088/2041-8205/718/1/L14