Kui-Yun Huang

National Central University, Таоюань, Taiwan, Taiwan

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Publications (2)8.06 Total impact

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    ABSTRACT: 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 sec to about 50 hours after the burst trigger and investigate its properties of the prompt gamma-rays and the ambient medium using our data and the data observed with {\em Swift} and {\em Fermi} missions. Our joint optical and X-ray spectral fits to the afterglow data show that the ambient medium features as low dust-to-gas ratio. Incorporating the energy injection effect, our best fit to the afterglow lightcurves with the standard afterglow model via the Markov Chain Monte Carlo (MCMC) technique shows that $\epsilon_e=(6.9\pm 0.3)\times 10^{-2}$, $\epsilon_B=(7.73\pm 0.62)\times 10^{-6}$, $E_{\rm K}=(6.32\pm 0.86)\times 10^{53}\rm erg$, $n=0.100\pm 0.014$ cm$^{-3}$. The low medium density likely implies that the afterglow jet may be in a halo or in a hot ISM. Achromatic 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 13 ms inferred from the data. The $E_p$ of its time-integrated prompt gamma-ray spectrum is $\sim 26$ KeV. Using the initial Lorentz factor ($\Gamma_0=476^{+225}_{-237}$) derived from our afterglow model fit, it is found that GRB 111228A satisfies the $L_{\rm iso}-E_{\rm p,z}-\Gamma_0$ relation and bridges the typical GRBs and low luminosity GRBs in this relation.
    Full-text · Article · Dec 2015 · The Astrophysical Journal
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    ABSTRACT: Observations were made of the optical afterglow of GRB 051028 with the Lulin observatory 1.0m telescope and the Wide-Field Telescope for GRB Early Timing (WIDGET) robotic telescope system. $R$-band photometric data were obtained on 2005 October 28 (UT), or 0.095–0.180 d after the burst. There is a possible plateau in the optical light curve around 0.1 d after the burst; the afterglow of GRB 051028 resembles optically bright afterglows (e.g., GRB 041006, GRB 050319, GRB 060605) in shape of the light curve, but not in brightness. The brightness of the GRB 051028 afterglow is 3 mag fainter than that of one of the dark events, GRB 020124. Optically dark GRBs have been attributed to dust extinction within the host galaxy or a high redshift. However, a spectrum analysis of the X-rays implies that there is no significant absorption by the host galaxy. Furthermore, according to a theoretical calculation of the Ly$\alpha$ absorption to find the limit of the GRB 051028’s redshift, the expected $R$-band absorption is not high enough to explain the darkness of the afterglow. The present results disfavor either the high-redshift hypothesis or the high-extinction scenario for optically dark bursts; rather, they are consistent with the possibility that the brightness of the optical afterglow is intrinsically dark.
    Full-text · Article · Jul 2007 · Publications- Astronomical Society of Japan