Evolution of the afterglow optical spectral shape of GRB 201015A in the first hour: evidence for dust destruction
Komesh T. Grossan B. Maksut Z. Abdikamalov E. Krugov M. Smoot G.F.
1 April 2023Oxford University Press
Monthly Notices of the Royal Astronomical Society
2023#520Issue 46104 - 6110 pp.
Instruments, such as the ROTSE, TORTORA, Pi of the Sky, MASTER-net, and others have recorded single-band optical flux measurements of gamma-ray bursts starting as early as ∼ 10 s after gamma-ray trigger. The earliest measurements of optical spectral shape have been made only much later, typically on hour time-scales, never starting less than a minute after trigger, until now. Beginning only 58 s after the Swift BAT triggered on GRB201015A, we observed a sharp rise in optical flux to a peak, followed by a power law temporal decay, ∝ t−0.81 ± 0.03. Flux was measured simultaneously in three optical bands, g, r, and i, using our Burst Simultaneous Three-channel Imager on the Nazarbayev University Transient Telescope at Assy-Turgen Astrophysical Observatory telescope. Our data during the decay show strong colour evolution from red to blue, with a change in the optical log slope of +0.72 ± 0.14; during this time the X-ray log slope remained constant. We did not find evidence for a two-component jet structure or a transition from reverse to forward shock or a prompt emission component that would explain this change in slope. We find that the majority of the optical spectral slope evolution is consistent with a monotonic decay of extinction, evidence of dust destruction. Assuming a constant source spectral slope and an Small Magellanic Cloud-like extinction curve, we derive a change in the local extinction Alocalv from ∼0.8 mag to 0.3 mag in ∼2500 s. This work shows that significant information about the early emission phase is being missed without such early observations with simultaneous multiband instruments.
burst: individual: GRB 201015A , dust, extinction , gamma-ray
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Energetic Cosmos Laboratory, Nazarbayev University, Astana, 010000, Kazakhstan
Faculty of Physics and Technology, Al-Farabi Kazakh National University, Almaty, 050040, Kazakhstan
Space Sciences Laboratory, University of California, Berkeley, 94720, CA, United States
Department of Physics, Nazarbayev University, 53 Kabanbay Batyr ave, Astana, 010000, Kazakhstan
Fesenkov Astrophysical Institute, Almaty, 050020, Kazakhstan
Institute for Advanced Study, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, 999077, Hong Kong
Université Sorbonne Paris Cité, Laboratoire APC-PCCP, Université Paris Diderot, 75013, France
Department of Physics, University of California, 94720, CA, United States
Université de Paris, Laboratoire Astroparticule et Cosmologie, Paris, F-75013, France
Donostia International Physics Center, University of the Basque Country UPV/EHU, San Sebastian, E-48080, Spain
Energetic Cosmos Laboratory
Faculty of Physics and Technology
Space Sciences Laboratory
Department of Physics
Fesenkov Astrophysical Institute
Institute for Advanced Study
Université Sorbonne Paris Cité
Department of Physics
Université de Paris
Donostia International Physics Center
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