The rapid development of our understanding of gamma-RAY bursts, the most energetic known events in the universe, has been enabled by the unprecedented coordination between precise localization…

The rapid development of our understanding of gamma-RAY bursts, the most energetic known events in the universe, has been enabled by the unprecedented coordination between precise localization satellites (e.g. bepposax, batse, swift & fermi) and rapid ground-based follow-up efforts. The ground-based follow-up campaigns have relied on networks of observatories ranging from automated, intermediate aperture telescopes to target-of-opportunity observations at 10-m class observatories. The majority of the ground-based follow-up effort to-date has been in optical wavelengths but there is much to be gained with expanded wavelength coverage. Near-IR (NIR) observations, in particular, are important for determining the nature of so-called dark grbs, which have no detectable optical counterpart. They are thought to be either highly extinguished populations or objects at very high redshift where the lyman break pass through the optical pass-bands. Given the link between long duration grbs, extremely massive STARS and star formation, grbs represent a promising probe of both high redshift populations and their associated dust-enshrouded environments. The recent swift discovery of GRB090423 at z-8.2, the most distant object ever detected, is one such example of a GRB that can serve as a valuable probe of the early universe. We propose to perform follow-up NIR imaging observations of swift-detected gamma-RAY bursts (grbs) and hard x-RAY sources. The observations will be obtained with the 4-m united kingdom infrared telescope (ukirt) at mauna KEA, hawaii with GRB observations executed in too observing mode and BAT hard x-RAY survey sources in a scheduled observing mode. Since grbs fade rather rapidly, immediate NIR follow-up observations are necessary to ensure the optical/NIR identification of dark grbs. The expected NIR afterglow during the early phase (k - 17-19 MAG) are just faint enough that efficient follow-up observations require 4-m class telescopes. The grbs that will be followed up will be those that occur during the nights allocated for the intermediate wide, medium-deep survey (IMS) led by a group of collaborators from seoul national university. The IMS is a j-band imaging survey of 200 square degrees to the depth of j - 23 AB MAG, with the main scientific goals of (i) discovering quasars at z > 7 to understand the mass growth history of super-massive black holes, and (II) studying galaxy clusters and over-densities at i < z < 4 to constrain the galaxy formation and evolution models. About 25 - 30 nights are allocated for the IMS, and we expect that 3-4 GRB events to occur during such a period. Upon swift detection, grbs will be immediately followed up in NIR passbands. Extended follow-up imaging of interesting GRB will continue throughout the IMS campaign to measure NIR light-curves and host galaxy characterization. In addition to the GRB follow-up, NIR observations of hard x-RAY transients detected in the BAT all-sky x -RAY survey offers the possibility of characterizing a new subclass of long, smooth grbs that are not identified as bursts. The nature of these sources, whether extending a continuum of long or short duration grbs or unveiling an entirely new high energy transient phenomena. The observation and analysis of both the GRB and x-RAY transient NIR data, including light curve analysis, spectral energy distribution fitting and host galaxy characterization will be performed by the PI and a visiting post-doctoral scholar involved in the project. Undergraduate students will be engaged in all aspects of the NIR project as well as an optical/polarimetry follow-up campaign with the l-m table mountain observatory targeting the brighter subset of the GRB and x -RAY samples.