fl149.kundu01 Posted: 25-Oct-93 Updated: 24-Jul-94 Events specified: flaring XBPs
1,2 1 1 3 M.R.Kundu , K.Shibasaki, S.Enome, N.Nitta
1 NRO 2 U.MD. 3 LPARL
The BP flares are considered to be elementary flares.It is important to know if these elementary flares produce both thermal and nonthermal emissions. The X-ray emission from flaring BPs is believed to be thermal.Evedence for non- thermal emission in these flares comes from metric observations in the form of type IIIs.It is important to know if there is microwave emission associated with flaring XBPs and if it is thermal or nonthermal.One should be able to determine BP flare parameters (density,temperature,etc.) by combining SXT observations with the microwave data.On the Yohkoh/SXT images of July 31,1992, we have identified at least 6 XBPs-3 near active regions and 3 in coronal holes.They also appear weakly on 17GHz Nobeyama Radioheliograph maps.We believe that some of the coronal hole XBPs were flaring.We have analyzed the 17GHz maps for this day (July 31,1992) to see if there are 17GHz emissions associated with the XBP flares.Quiescent(with time variability) BPs in coronal holes have been detected in microwaves in the past using the VLA at 20 and 6 cm wavelengths.However,to our knowledge no flaring BPs in microwaves have been reported in the literature.This is the first time XBPs are reported to be detected at the highest radio frequency of 17GHz.This detection will provide us some information on the height structure of the miniature loops that constitute the coronal bright points.17GHz measurements combined with Yohkoh/ SXT measurements will provide some information on the physical parameters of the flaring BPs.
Update 24-Jul-94
A paper has been accepted for publication in Ap.J. Letters.
DETECTION OF 17 GHz RADIO EMISSION FROM X-RAY BRIGHT POINTS
M. R. KUNDU1, K. SHIBASAKI2, S. ENOME2, N. NITTA3 1Department of Astronomy, University of Maryland, College Park, MD 20742 USA 2Nobeyama Radio Observatory, Minamisaku-gun, Nagano 384-13, Japan 3Lockheed Palo Alto Research Laboratory, Palo Alto, CA 94304 USA
Abstract
Using observations made with the Nobeyama radio heliograph (NRH) at 17 GHz and the Yohkoh/SXT experiment, we report the first detection of 17 GHz signatures of coronal X-ray bright points (XBP's). This is also the first reported detection of flaring bright points in microwaves. We have dectected four BP's at 17 GHz out of eight identified in SXT data on July 31, 1992, for which we looked for 17 GHz emission. For one XBP located in a quiet mixed-polarity region, the peak times at 17 GHz and X-rays are very similar, and both are long lasting -- about 2 hours in duration. There is a second BP (located near an active region) which is most likely flaring also, but the time profiles in the two spectral domains are not similar. The other two 17 GHz BPs are quiescent with fluctuations superposed upon them. For the quiet region XBP, we believe that the 17 GHz emission is thermal.