Won-Kee Park

The unusual γ-ray burst GRB 101225A from a helium star/neutron star merger at redshift 0.33

C. C. Thöne1,2,∗, A. de Ugarte Postigo, C. L. Fryer, K. L. Page, J. Gorosabel, M. A. Aloy, D. A. Perley, C. Kouveliotou, H. T. Janka, P. Mimica, J. L. Racusin, H. Krimm, J. Cummings, S. R. Oates, S. T. Holland, M. H. Siegel, M. De Pasquale, E. Sonbas, M. Im, W.-K. Park, D. A. Kann, S. Guziy, L. Hernández Garcı́a, A. Llorente, K. Bundy, C. Choi, H. Jeong, H. Korhonen, P. Kubanek, J. Lim, A. Moskvitin, T. Muñoz-Darias, S. Pak, I. Parrish 1 IAA CSIC, Glorieta de la Astronomı́a s/n, 18008 Granada, Spain 2 Niels Bohr International Academy, Niels Bohr Institute, Blegdamsvej 17, 2100 Copenhagen, Denmark 3 Dark Cosmology Centre, Niels Bohr Institute, Univ. of Copenhagen,Long γ-ray bursts (GRBs) are the most dramatic examples of massive stellar deaths, often associated with supernovae. They release ultra-relativistic jets, which produce non-thermal emission through synchrotron radiation as they interact with the surrounding medium. Here we report observations of the unusual GRB 101225A. Its γ-ray emission was exceptionally long-lived and was followed by a bright X-ray transient with a hot thermal component and an unusual optical counterpart. During the first 10 days, the optical emission evolved as an expanding, cooling black body, after which an additional component, consistent with a faint supernova, emerged. We estimate its redshift to be z = 0.33 by fitting the spectral-energy distribution and light curve of the optical emission with a GRB-supernova template. Deep optical observations may have revealed a faint, unresolved host galaxy. Our proposed progenitor is a merger of a helium star with a neutron star that underwent a common envelope phase, expelling its hydrogen envelope. The resulting explosion created a GRB-like jet which became thermalized by interacting with the dense, previously ejected material, thus creating the observed black body, until finally the emission from the supernova dominated. An alternative explanation is a minor body falling onto a neutron star in the Galaxy.

A tale of two GRB-SNe at a common redshift of z=0.54

We present ground-based and Hubble Space Telescope optical observations of the optical transients (OTs) of long-duration Gamma Ray Bursts (GRBs) 060729 and 090618, both at a redshift of z= 0.54. For GRB 060729, bumps are seen in the optical light curves (LCs), and the late-time broad-band spectral energy distributions (SEDs) of the OT resemble those of local Type Ic supernovae (SNe). For GRB 090618, the dense sampling of our optical observations has allowed us to detect well-defined bumps in the optical LCs, as well as a change in colour, that are indicative of light coming from a core-collapse SN. The accompanying SNe for both events are individually compared with SN1998bw, a known GRB supernova, and SN1994I, a typical Type Ic supernova without a known GRB counterpart, and in both cases the brightness and temporal evolution more closely resemble SN1998bw. We also exploit our extensive optical and radio data for GRB 090618, as well as the publicly available Swift-XRT data, and discuss the properties of the afterglow at early times. In the context of a simple jet-like model, the afterglow of GRB 090618 is best explained by the presence of a jet-break at t-to > 0.5 d. We then compare the rest-frame, peak V-band absolute magnitudes of all of the GRB and X-Ray Flash (XRF)-associated SNe with a large sample of local Type Ibc SNe, concluding that, when host extinction is considered, the peak magnitudes of the GRB/XRF-SNe cannot be distinguished from the peak magnitudes of non-GRB/XRF SNe. --------------------------------------------------------------------------------

Preliminary design of IGRINS (Immersion GRating INfrared Spectrograph)

The Korea Astronomy and Space Science Institute (KASI) and the Department of Astronomy at the University of Texas at Austin (UT) are developing a near infrared wide-band high resolution spectrograph, IGRINS. IGRINS can observe all of the H- and K-band atmospheric windows with a resolving power of 40,000 in a single exposure. The spectrograph uses a white pupil cross-dispersed layout and includes a dichroic to divide the light between separate H and K cameras, each provided with a 2kx2k HgCdTe detector. A silicon immersion grating serves as the primary disperser and a pair of volume phased holographic gratings serve as cross dispersers, allowing the high resolution echelle spectrograph to be very compact. IGRINS is designed to be compatible with telescopes ranging in diameter from 2.7m (the Harlan J. Smith telescope; HJST) to 4 - 8 m telescopes. Commissioning and initial operation will be on the 2.7m telescope at McDonald Observatory from 2013.

DISCOVERY OF A FAINT QUASAR AT z ∼ 6 AND IMPLICATIONS FOR COSMIC REIONIZATION

Recent studies suggest that faint active galactic nuclei may be responsible for the reionization of the universe. Confirmation of this scenario requires spectroscopic identification of faint quasars (

FOCAL REDUCER FOR CQUEAN (Camera for QUasars in EArly uNiverse)

M_{1450}>-24

A Catalog of New M33 Star Clusters Based on Hubble Space Telescope WFPC2 Images

mag) at

NEAR-IR PHOTOMETRIC STUDY OF THE FU ORIONIS OBJECT HBC 722

z \gtrsim6

AUTO-GUIDING SYSTEM FOR CQUEAN (CAMERA FOR QUASARS IN EARLY UNIVERSE)

, but only a very small number of such quasars have been spectroscopically identified so far. Here, we report the discovery of a faint quasar IMS J220417.92+011144.8 at z~6 in a 12.5 deg

AGES OF M33 STAR CLUSTERS BASED ON THE HUBBLE SPACE TELESCOPE/WFPC2 PHOTOMETRY

^{2}

The optical rebrightening of GRB100814A: an interplay of forward and reverse shocks?

region of the SA22 field of the Infrared Medium-deep Survey (IMS). The spectrum of the quasar shows a sharp break at