用阿塔卡玛亚毫米望远镜实验寻找GRB 980425主星系的CO（J=3-2）辐射
A Search for CO(J=3-2) Emission from the Host Galaxy of GRB 980425 with the Atacama Submillimeter Telescope Experiment
摘要：
利用阿塔卡玛亚毫米波望远镜实验（ASTE）对GRB 980425的主星系CO（J=3-2）谱线进行了深入的探测。我们观察到银河系的五个点覆盖了整个区域。在将所有的谱组合起来之后，我们得到了一个在10 km s^-1的速度分辨率下，在T_mb尺度上均方根噪声水平为3.3 mK的全球谱。没有显着的发射被检测到，虽然我们发现一个边缘的发射功能的速度范围对应的星系的红移。我们得到了整体性质的3 σ上限：采用67 km s^-1的速度宽度，I_CO（3 - 2）的速度积分CO（3 - 2）强度< 0.26 K km s^-1; N（H_2）的H_2柱密度< 3 x 10^20 cm^-2; M（H_2）的分子气体质量< 3 x 10^8 M_sun，假设CO谱线光度与H_2分子气体质量的转换因子X_CO = 5.0 x 10^20 cm^-2（K km s^-1）^-1;根据施密特定律，恒星形成速率SFR < 0.1 M_sun yr^-1。SFR与以往的H_α和中红外观测结果一致，表明GRB 980425的宿主星系中没有明显的恒星形成。这一结果意味着，有各种各样的伽玛射线暴的主机方面的存在被掩盖的恒星形成。
英文摘要：
We report on a deep search for CO(J=3-2) line emission from the host galaxy of GRB 980425 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 the rms noise level of 3.3 mK in T_mb scale at a velocity resolution of 10 km s^-1. No significant emission was detected, though we find a marginal emission feature in the velocity range corresponding to the redshift of the galaxy. We derive 3 sigma 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; the H_2 column density of N(H_2) < 3 x 10^20 cm^-2; the molecular gas mass of M(H_2) < 3 x 10^8 M_sun, by assuming a CO line luminosity to H_2 molecular gas mass conversion factor of X_CO = 5.0 x 10^20 cm^-2 (K km s^-1)^-1; and the star formation rate of SFR < 0.1 M_sun yr^-1, based on the Schmidt law. The SFR is consistent with the previous results of H_alpha and mid-IR observations, thereby suggesting that there is no significant obscured star formation in the host galaxy of GRB 980425. This result implies that there is a variety of GRB hosts with regard to the presence of obscured star formation.
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