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Astron. Astrophys. Suppl. Ser. 138, 433-434

What did ASCA see in the GRB 970828 afterglow?

A. Yoshida1 - M. Namiki1 - C. Otani1 - N. Kawai1 - T. Murakami2 - Y. Ueda2 - R. Shibata2 - S. Uno2

Send offprint request: A. Yoshida

1 - The Institute of Physical and Chemical Research, 2-1, Hirosawa, Wako, Saitama 351-0198, Japan
2 - Institute of Space and Astronautical Science, 3-1-1, Yoshinodai, Sagamihara, Kanagawa 229-8510, Japan

Received January 21; accepted July 5, 1999


The ASCA satellite made a quick followup observation of GRB 970828 and detected its fading X-ray afterglow at the position localized by the All-Sky Monitor on the Rossi XTE satellite. Because of the quickness, the afterglow was still rather bright ($\sim 4\ 10^{-13}$ ergs cm-2s-1: 2-10 keV), and ASCA obtained the data of good quality. We found the spectral features of the absorption which implies a column density of $4.1\ 10^{21}$ cm-2 at z=0, together with an emission line at $\sim 5$ keV. The line could be red shifted Fe K$_{\alpha}$ line. Hence, it suggests a relatively small red shift $z \approx 0.33$ for this GRB.

Key words: gamma-rays: bursts

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