ar064.krucker01 Posted: 08-Feb-94 Updated: 30-Sep-94, 27-Dec-94, 16-Sep-95, 24-Feb-96, 07-Jul-96, 10-Nov-96 Events specified: Noise storm between 14:00 and 15:10 UT on 30-Jul-92
S.Krucker, M.J. Aschwanden, T.S. Bastian, A.O. Benz, K.T. Strong
During the summer of 1992 & 1993 we have simultaneous measurements of the solar radio emission with the VLA and the frequency-agile spectrometer (PHOENIX) near Zurich and YOHKOH. From our broadband spectral observation we are able to classify the radio emission and select type I noise storm, in particular specific phases of the storm, such as drifting chains. The VLA has spacially resolved data at 333 MHZ and 1445 MHz measrued at the same time. We have an interesting series of a chain on 92/07/30 1400-1510 UT, when the storm bursts drifted through the VLA frequency and moved spatially in the VLA images.
The YOHKOH soft X-ray imaging data can help us to understand the origin of the emission. As we know the density of the radio sources (assuming plasma emission), we hope to locate the radio source in the YOHKOH picture and to study the magnetic configuration. In particular, we plan to determine the plasma temperature of the suspected region and follow it in time. Noise storms are suspected to be associated with minor, but quasi-continous energy releases.
Update 10-Nov-96
The paper 'Fine structure of the X-ray and radio emissions of the quiet solar corona'(Arnold O. Benz, S\"am Krucker, Loren W. Acton, and Tim S. Bastian) has been accepted to be published in A&A. The abstract of the revised version of the paper has not been changed.
Additionally, we are finishing a letter with the title 'X-ray and radio microflares in the magnetic network of the quiet sun'. (S\"am Krucker, Arnold O. Benz, Tim S. Bastian, and Loren W. Acton) We will submit it to ApJ Letters. The abstract is as following:
The temporal variations in the soft X-ray (SXR) emission and the radio emission above the solar magnetic network are investigated using Yohkoh SXR images of the quiet corona with a deep exposure and VLA observations in the centimeter radio range. The SXR data show several brightenings with an extrapolated occurrence probability of one brightening per 3~seconds on the total solar surface. During the roughly 10~minutes of enhanced flux, the total radiative losses of the observed plasma are around $10^{25}$~erg per event. Compared to previously reported X-ray bright points, these events are two or more orders of magnitude smaller. For all of the four SXR events with simultaneous radio observations, a corresponding radio source correlating in space and time can be found. There are several similarities between solar flares and the SXR/radio events presented in this letter: (i) In 3 of 4 events, the centimetric radio emission is shorter in duration and peaks several tens of second earlier than the SXR emission. (ii) The ratio of the total energies radiated in SXR and radio is similar as observed in flares. (iii) One radio event shows a degree of polarization significantly different from zero. (iv) The variations in temperature and emission measure during the SXR enhancements are consistent with evaporation of cooler material from the transition region and/or the chromosphere. Therefore, these events are defined as SXR and radio microflares in the magnetic network of the quiet Sun.
Update 07-Jul-96
Our paper 'Yohkoh observation of the source regions of solar narrowband, millisecond spike events' (S. Krucker, A.O. Benz, and M.J. Aschwanden) has been accepted on June 3, 1996 to be published in Astronomy & Astrophysics. The abstract has slightly changed in the revised version:
The source regions of metric spike events are investigated on Yohkoh soft X-ray (SXR) maps. The spikes are identified by the spectrometer Phoenix between 300~MHz and 360~MHz and are associated with groups of type~III bursts at lower frequencies reaching also the decametric range. The Very Large Array (VLA) provides simultaneously spatial informationat 333~MHz, 1446~MHz and 4866~MHz. Similar to the previous VLA observation of a metric spike event, the new data are consistent with a high altitude of the spike sources of about $5^.10^{10}$cm above the photosphere. The additionally available SXR data for one of the presented events give the following new informations: (i) The spike sources occur near open field lines and near regions of a slightly enhanced SXR flux relative to the ambient plasma. (ii) Contrary to SXR observations of type~III bursts without metric spike activity, no SXR jet is observed. (iii) At low altitude, a weak SXR enhancement occurs, peaking about 60~s after the spike event. The SXR source and the spike sources can be connected by potential field lines. The observations corroborate a model in which a metric spike event is attributed to an energy release region at high altitude, while upwards propagating electrons produce type~III bursts and downward moving electrons are responsible for SXR emission of heated plasma.
The second on-going project ('Yohkoh observations of radio noise storm') is still not finished. At the moment it is unclear when we will find time to finish it. We will inform you about it in our next report.
Update 24-Feb-96
We have submited our new paper with the title 'Yohkoh observation of the source regions of solar narrowband, millisecond spike events' (S. Krucker, A.O. Benz, and M.J. Aschwanden) to Astronomy and Astrophysics. The abstract is as following:
The source regions of metric spike events are investigated on Yohkoh soft X-ray (SXR) maps. The spikes are identified by the spectrometer Phoenix between 300~MHz and 360~MHz and are associated with groups of type~III bursts at lower frequencies reaching also the decametric range. The Very Large Array (VLA) provides simultaneously spatial information at 333~MHz, 1446~MHz and 4866~MHz. Similar to the previous VLA observation of a metric spike event, the new data are consistent with a high altitude of the spike sources of about $5^.10^{10}$cm above the photosphere. The additionally available SXR data for one of the presented events give the following new informations: (i) The spike sources occur most probably on open field lines with a slightly enhanced SXR flux relative to the ambient plasma. (ii) Contrary to SXR observations of type~III bursts without metric spike activity, no SXR jet is observed. (iii) At low altitude, a weak SXR enhancement occurs peaking about 60~s after the spike event. The SXR source and the spike sources can be connected by potential field lines. The observations corroborate a model in which a metric spike event is attributed to an energy release region at high altitude, while upwards propagating electrons produce type~III bursts and downward moving electrons are responsible for SXR emission of heated plasma. Additionally, a possible relation of spikes to impulsive 2-10~keV solar electron events observed in interplanetary space and to high coronal flares is discussed.
Update 16-Sep-95
Our paper "YOHKOH,VLA and PHOENIX observations ..." was accepted to be published in Solar Physics (August 95). The final version of the abstract is as following:
The data is presented of a solar type~I noise storm observed on 92/07/30 with the radio spectrometer Phoenix of ETH Z\"urich, the Very Large Array (VLA) and the soft X-ray (SXR) telescope on board the Yohkoh satellite. The spectrogram was used to ident ify the type~I noise storm. In the VLA images at 333~MHz a fully left circular polarized (100\%~LCP) continu um source and several highly polarized (70\% to 100\%~LCP) burst sources have been located. The continuum and the bursts are spatially separated by about 100" and apparentl y lay on different loops as outlined by the SXR. Continuum and bursts are separated in perpendicular direction to the ma gnetic field configuration. Between the periods of strong burst activities, burst-like emissions are also su perimposed on the continuum source. There is no obvious correlation between the flux density of the continuum and the bursts. The burst sources have no systematic motion, wh ereas the the continuum source shows a small drift of $\approx$~0.2"/min along the X-ray l oop in the long-time evolution. The VLA maps at higher frequency (1446~MHz) show no source corresponding to the type~I event. The soft X-ray emission measure and temperature was calculated. The type~I continuum source is located (in projection) in a region with enhanced SXR emissi on, a loop having a mean density of $\langle n_e \rangle = (1.5 \pm 0.4)^.10^9\,\mbox{cm$^{-3}$}$ and a temperature of $T = (2.1 \pm 0.1)^.10^6 \mbox{K}$. The centroid positions of the left and right circularly polarized components of the burst sources are separated by 15"-50" and seems to be on different loops. T hese observations contradict the predictions of existing type~I theories.
At the moment we are working on two project:
(1) We are looking at some more data of radio noise storms. We have
found simultaneous data of noise storms in radio and SXR on
92/07/20, 92/08/18 and 93/08/05. In one event (93/08/05)
there are images with long exposure times (5 s and more),
in which we found a weak enhanced SXR emission at one foot point of
the type I emitting loop.
(2) The second project is an investigation on metric spikes (92/08/18).
The centroids of the radio emission are found to be situated along
a weak SXR emitting structure reaching high altitudes,
which seems to be along an open
field line or along a very large loop. The approximated density
in the source is compatible with fundamental plasma emission,
but not with emission at harmonics.
We hope to finish these two projects until the end of this year.
Update 27-Dec-94
We have finished the revised version of our paper and we have already resend it to Solar Physics. The referee have been suggestingsome helpful comments. The title and abstract of our paper has slightly changed:
TITLE:
Location of type I radio continuum and bursts on Yohkoh soft X-ray maps
ABSTRACT:
The data is presented of a solar type~I noise storm observed on 92/07/30 with the radio spectrometer Phoenix of ETH Z\"urich, the Very Large Array (VLA) and the soft X-ray (SXR) telescope on board the Yohkoh satellite. The spectrogram was used to identify the type~I noise storm. In the VLA images at 333~MHz a fully left circular polarized (100\%~LCP) continuum source and several highly polarized (70\% to 100\%~LCP) burst sources have been located. The continuum and the bursts are spatially separated by about 100" and apparently lay on different loops as outlined by the SXR. Continuum and bursts are separated in perpendicular direction to the magnetic field configuration. Between the periods of strong burst activities, burst-like emissions are also superimposed on the continuum source. There is no obvious correlation between the flux density of the continuum and the bursts. The burst sources have no systematic motion, whereas the the continuum source shows a small drift of $\approx$~0.2"/min along the X-ray loop in the long-time evolution. The VLA maps at higher frequency (1446~MHz) show no source corresponding to the type~I event. The soft X-ray emission measure and temperature was calculated. The type~I continuum source is located (in projection) in a region with enhanced SXR emission, a loop having a mean density of
At the moment we are looking for more type I events in our data (in the spectral data and in the VLA data), and compare it with the Yohkoh orbits and pointings. The idee, or wish, is to find simultanous data in radio and SXR before, during and after the type I event (In our paper we just had Yohkoh images before the event occured). This would allow to compare spatialy resolved data from the thermal emission (SXR) and the non-thermal emission (radio) during the entire type I event. Therefore we are strongly interested in an ongoing cooperation.
Update 30-Sep-94
Our proposal is ar064.krucker01 ("YOHKOH,VLA and PHOENIX observations of a solar noise storm..."). We have finished the first version of our paper and we will submit it to Solar Physics. The paper should be published in one volume containing all the publications from the CESRA meeting 1994, Potsdam. The abstract of our paper is the following:
Abstract: The presented data of a solar type~I noise storm was observed on 92/07/30 with the radio spectrometer Phoenix of ETH Z\"urich, the Very Large Array (VLA) and the soft X-ray telescope on board the Yohkoh satellite. The spectrogram was used to identify the type~I noise storm. In the VLA images at 333~MHz a fully left circular polarized (100\%~LCP) continuum source and several highly polarized (70\% to 100\%~LCP) burst sources have been observed. The continuum and the bursts are spatially separated by about 100" and apparently lay on different loops as outlined by the SXR. Continuum and bursts are separated in perpendicular direction to the magnetic field configuration. Between the periods of strong burst activities, burst-like emissions are also superimposed on the continuum source. There is no obvious correlation between the flux density of the continuum and the bursts. The burst sources have no systematical motion, whereas the the continuum source shows a small drift of $\approx$~0.2"/min along the X-ray loop in the long-time evolution. The VLA maps at 1446~MHz show no source corresponding to the location of the type~I event. From the Yohkoh/SXT images the soft X-ray emission measure and temperature was calculated. The type~I continuum source is located in a region with enhanced SXR emission, coinciding with a loops having a mean density of n_e = (1.5 +- 0.4)10^9 cm-3 and a temperature of T = (2.1 +- 0.1)10^6 K. The centroid positions of the left and right circularly polarized components of the burst sources are separated by 15"-50" and seems to be on different loops. These observations contradict the predictions of existing type~I theories.