Tomonori Totani

No Evidence for Variability of Intervening Absorption Lines toward GRB 060206: Implications for the Mg II Incidence Problem

We examine variability of absorption line strength of intervening systems along the line of sight to GRB 060206 at zu2009=u20094.05, by the low‐resolution optical spectra obtained by the Subaru telescope from six to ten hours after the burst. Strong variabilities of Fe II and Mg II lines at zu2009=u20091.48 during tu2009=u20095–8u2009hours have been reported for this GRB [8], and this has been used to support the idea of clumpy Mg II cloudlets that was originally proposed to explain the anomalously high incidence of Mg II absorbers in GRB spectra compared with quasars. However, our spectra with higher signal‐to‐noise ratio do not show any evidence for variability in tu2009=u20096–10u2009hours. There is a clear discrepancy between our data and Hao et al. data in the overlapping time interval. Furthermore, the line strengths in our data are in good agreement with those observed at t∼2u2009hours by Thone et al. [22]. Therefore we conclude that there is no strong evidence for variability of intervening absorption lines toward GRB 060206, significantly ...

Evaluation of large pixel CMOS image sensors for the Tomo-e Gozen wide field camera

Tomo-e Gozen (Tomo-e) is a wide field optical camera for the Kiso 1.05 m f/3.1 Schmidt telescope operated by the University of Tokyo. Tomo-e is equipped with 84 chips of front-illuminated CMOS image sensors with a microlens array. The field of view is about 20 square degrees and maximum frame rate is 2 fps. The CMOS sensor has 2160x1200 pixels and a size of pixel is 19 microns, which is larger than those of other CMOS sensors. We have evaluated performances of the CMOS sensors installed in Tomo-e. The readout noise is 2.0 e- in 2 fps operations when an internal amplifier gain is set to 16. The dark current is 0.5 e-/sec/pix at room temperature, 290K, which is lower than a typical sky background flux in Tomo-e observations, 50 e-/sec/pix. The efficiency of the camera system peaks at approximately 0.7 in 500 nm.