GRB 060418 and 060607A: the medium surrounding the progenitor and the weak reverse shock emission

Abstract

We constrain the circum-burst medium profile with the rise behavior of the very early afterglow light curves of gamma-ray bursts (GRBs). Using this method, we find a constant and low-density medium profile for GRB 060418 and GRB 060607A, which is consistent with the inference from the late afterglow data. In addition, we show that the absence of the IR flashes in these two GRB afterglows is consistent with the standard external reverse shock model, which thus renders models like the highly magnetized GRB outflow being unnecessary to a certain extent.

7 pages including 3 eps figures. Expanded version to appear in MNRAS main Journal. References added. Main conclusions are unchanged

References in corpus (7)

• Polarisation studies of the prompt gamma-ray emission from GRB 041219a using the Spectrometer aboard INTEGRAL
• The Remarkable Afterglow of GRB 061007: Implications for Optical Flashes and GRB Fireballs
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• Early Optical Polarization of a Gamma Ray Burst Afterglow
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• The nature of the X-Ray Flash of August 24 2005
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• Fitting orbits to tidal streams with proper motions
• Challenging GRB models through the broadband dataset of GRB060908
• Interpretation and implication of the non-detection of GeV spectrum excess by Fermi gamma-ray Space Telescope in most GRBs
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• Gamma rays from a reverse shock with turbulent magnetic fields in GRB 180720B
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• GRB Optical and X-ray Plateau Properties Classifier Using Unsupervised Machine Learning
• X-ray plateaus followed by sharp drops in GRBs 060413, 060522, 060607A and 080330: Further evidences for central engine afterglow from Gamma-ray Bursts
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