Investigating the submillimetre variability of Sagittarius A* with SCUBA

D. Pierce-Price1, J. S. Richer2, T. Jenness1, J. S. Greaves3, W. S. Holland3

1 Joint Astronomy Centre, 660 North A`ohoku Place, Hilo, Hawaii 96720, USA
2 Cavendish Astrophysics, Cavendish Laboratory, Madingley Road, Cambridge CB3 9JB, UK
3 Astronomy Technology Centre, Blackford Hill, Edinburgh EH9 3HJ, UK

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We present an analysis of variability in submillimetre continuum observations of Sagittarius A*. The observations were made with the Submillimetre Common-User Bolometer Array (SCUBA) on the James Clerk Maxwell Telescope (JCMT) during a wide-field 2.8 deg x 0.5 deg survey of the Galactic Centre ``Central Molecular Zone'' (CMZ) at 850 and 450 microns. This survey is also presented here. It traces the temperature-weighted column density of dust in the CMZ, with a resolution of 8 arcsec at 450 microns and 15 arcsec at 850 microns, and a sensitivity of 15-20 M_sun of gas and dust per beam. The survey shows extremely rich extended structure, including GMCs, filaments, and partial shells throughout the CMZ.

Our average flux densities for Sagittarius A* are lower than some previous results, such as those of Serabyn et al. (1997), but show the presence of the submillimetre excess above the quasi-monoenergetic synchrotron radio spectrum. Direct comparison of the flux densities with previous results is difficult due to apparent variability in the submillimetre excess. We detected a  50 pct increase in the 850 micron flux density of Sagittarius A* between April 1998 and August 1999. To investigate this further, we have used additional data from the SCUBA/JCMT archive to calculate flux densities for other dates.