Multi-wavelength observations of GRB 111228A and implications for the fireball and its environment
- Key Laboratory of Space Astronomy and Technology, National Astronomical Observatories, Chinese Academy of Sciences (China)
- GXU-NAOC Center for Astrophysics and Space Sciences, Department of Physics, Guangxi University, Nanning 530004 (China)
- Institute of Astronomy, National Central University, Chung-Li 32054, Taiwan (China)
- Yunnan Observatories, Chinese Academy of Sciences, P.O. Box 110, 650011 Kunming (China)
- Department of Mathematics and Science, National Taiwan Normal University, Lin-kou District, New Taipei City 24449, Taiwan (China)
Observations of very early multi-wavelength afterglows are critical to reveal the properties of the radiating fireball and its environment as well as the central engine of gamma-ray bursts (GRBs). We report our optical observations of GRB 111228A from 95 s to about 50 hr after the burst trigger and investigate its properties of the prompt gamma-rays and the ambient medium using our data and the data from the Swift and Fermi missions. Our joint optical and X-ray spectral fits to the afterglow data show that the ambient medium features a low dust-to-gas ratio. Incorporating the energy injection effect, our best fit to the afterglow light curves with the standard afterglow model via the Markov Chain Monte Carlo technique shows that ϵ{sub e}=(6.9±0.3)×10{sup −2}, ϵ{sub B}=(7.73±0.62)×10{sup −6},E{sub K}=(6.32±0.86)×10{sup 53} erg, n=0.100±0.014 cm{sup −3}. The low medium density likely implies that the afterglow jet may be in a halo or in a hot ISM. A chromatic shallow decay segment observed in the optical and X-ray bands is well explained with the long-lasting energy injection from the central engine, which would be a magnetar with a period of about 1.92 ms inferred from the data. The E{sub p} of its time-integrated prompt gamma-ray spectrum is ∼26 KeV. Using the initial Lorentz factor (Γ{sub 0}=476{sub −237}{sup +225}) derived from our afterglow model fit, it is found that GRB 111228A satisfies the L{sub iso}−E{sub p,z}−Γ{sub 0} relation and bridges the typical GRBs and low luminosity GRBs in this relation.
- OSTI ID:
- 22887024
- Journal Information:
- Astrophysical Journal, Vol. 817, Issue 2; Other Information: Country of input: International Atomic Energy Agency (IAEA); Since 2009, the country of publication for this journal is the UK.; ISSN 0004-637X
- Country of Publication:
- United Kingdom
- Language:
- English
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