------------------------------------------------------------------------
From: Atsushi MIYAZAKI  amiya@nro.nao.ac.jp 
To: gcnews@zia.aoc.nrao.edu
Subject: submit intradsgras.tex ApJL 2004 accepted

% astro-ph/0407252  
% Accepted for publication in ApJL 2004

%% preprint2 produces a double-column, single-spaced document:
\documentclass[preprint2]{aastex}

\newcommand{\sgras}{Sgr~A$^{\ast}$}
\newcommand{\dsos}{$\Delta S/S$}
\newcommand{\sm}{\hbox{$M_{\odot}$}}

\begin{document}

\title{Intra-day Variation of Sagittarius~A$^{\ast}$ 
at Short Millimeter Wavelengths}
\author{Atsushi Miyazaki}
\affil{Nobeyama Radio Observatory
\footnote{Nobeyama Radio Observatory (NRO) is a branch of 
the National Astronomical Observatory, 
National Institutes of Natural Sciences, JAPAN. }, 
National Astronomical Observatory of Japan, \\
Minamimaki, Minamisaku, Nagano 384-1305, Japan}
\email{amiya@nro.nao.ac.jp}
\author{Takahiro Tsutsumi}
\affil{National Astronomical Observatory of Japan, 
2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan}
\email{tsutsumi@alma.mtk.nao.ac.jp}
\and
\author{Masato Tsuboi}
\affil{Nobeyama Radio Observatory, 
National Astronomical Observatory of Japan, \\
Minamimaki, Minamisaku, Nagano 384-1305, Japan}
\email{tsuboi@nro.nao.ac.jp}

\begin{abstract}
We have performed the monitoring observations of flux density 
of Sagittarius~A$^{\ast}$ 
at short millimeter wavelengths (100 and 140~GHz bands) 
on seven years in the period from 1996 to 2003 
using the Nobeyama Millimeter Array (NMA). 
We found intra-day variation of \sgras\ in March 2000 flare.  
The flux density at the peak of the flares increases 100--200\% 
at 100~GHz and 200--400\% at 140~GHz (\dsos), respectively.  
The two-fold increase timescale of the flare 
is estimated to be about 1.5 hours at 140~GHz.  
The intra-day variation at mm-wavelengths 
has similar increase timescale as those in the X-ray and infrared flares 
but has smaller amplitude.  
This short timescale variability suggests that 
the physical size of the emitting region 
is smaller than 12~AU ($\approx 150~R_{\rm s}$).  
The decay timescale of the flare was at most 24 hours.  
Such a light curve with rapid increase and slow decay is similar to 
that often observed in outburst phenomena with ejections.  
\end{abstract}

\keywords{galaxies: nuclei---Galaxy: center---radio continuum: galaxies}

\end{document}