2007PASJ...59...67H

begin{HTML}We report on a deep search for ¹²CO (J=3–2) line emission from the host galaxy of GRB980425 with the Atacama Submillimeter Telescope Experiment (ASTE). We observed five points of the galaxy, covering the entire region. After combining all of the spectra, we obtained a global spectrum with a rms noise level of 3.3 mK in the T_mb scale at a velocity resolution of 10 km s^-1. No significant emission was detected, though we found a marginal emission feature in the velocity range corresponding to the redshift of the galaxy. We derived 3 s upper limits on the global properties: the velocity-integrated CO (3-2) intensity of I_CO(3-2) < 0.26 K km s^-1, by adopting a velocity width of 67 km s^-1; an H₂ column density of N(H₂) < 3 x 10²⁰ cm^-2; a molecular gas mass of M(H₂) < 3 x 10⁸ M_☉, by assuming a CO line luminosity to H² molecular gas mass conversion factor of X_CO = 5.0 x 10²⁰ cm^-2 (K km s^-1)^-1; and a star-formation rate of SFR < 0.1M_☉ yr^-1, based on the Schmidt law. The SFR is consistent with the previous results of Hα and mid-IR observations, thereby suggesting that there is no significant obscured star formation in the host galaxy of GRB980425. This result implies that there is a variety of GRB hosts with regard to the presence of obscured star formation.