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Physics, Astronomy and Electronics Work Bench Catalog of dynamic electromagnetic spectra observed with Callisto, Phoenix-3 and ARGOS Christian Monstein1 1 Institute of Astronomy, ETH Zurich, Switzerland e-mail: [email protected] Draft 30.04.2011 / Updated 15.12.2013 Abstract. This catalog demonstrates dynamic electromagnetic spectra observed by Callisto radio spectrometers. In the first part natural spectra are presented while in the second part we concentrate on artificial (man-made) spectra. This catalog shall help the scientist to detect and identify weak flares in highly interfered spectra. In addition, Callisto spectrometers have proven to be a cheap and reliable instrument for radio frequency monitoring of terrestrial interference. Key words. Callisto, spectrum, cross modulation, inter- ference, solar flares. 1. Introduction A catalog of different electromagnetic spectra is presented for the convenient interpretation of dynamic radio obser- vations of solar flares in view of ISWI (International Space Weather Initiative). Spectra are observed at different loca- tions worldwide and with different antenna systems within the e-Callisto network (Benz , 2004). Observations took place since 2004. The catalog consists of spectrograms all produced in the same way: bad channels with high σ elim- inated, background subtracted, and zoomed to the inter- esting part. Fig. 1. Noise storm of solar radio emission observed at Bleien 2. Solar spectra observatory, Switzerland. Antenna = dish 7m, circularly po- larized. A chain of type I bursts is shown. In the collection below most of the typical solar radio bursts will be presented and shortly discussed. A detailed description of the physics behind the bursts can be found bandwidths of a few MHz and lifetimes extending from 0.1 in the publication by Kundu (Kundu , 1965). seconds to 1 second. Chains of bursts last nearly 1 minute (Fig. 1). At frequencies below 40 MHz drifting bursts of bandwidth up to 30 MHz and lifetimes less than a second 2.1. Type I bursts (noise storm) may predominate. A noise storm consists of long series of short and narrow- band bursts continuing over hours or days. Polarization is 2.2. Type II bursts (slow drift) always high (circular) and the sign of the polarization can change within one day. The bursts are superimposed on After large flares narrow bands of intense radiation drift a background of slowly varying enhanced radiation which sometimes slowly, and often irregularly, towards lower fre- has been described as a "continuum", although it is possi- quencies. Figure 2 shows a typical example. The spectra ble that the background may itself be composed of a large occasionally show the presence of a second harmonic in number of overlapping bursts (?). Noise storms are nor- frequency, but are often so complex as to preclude such mally spread over a large frequency band but are rarely identifications. in rare cases type II bursts show a char- seen above 350 MHz. On many occasions the bursts have acteristic called 'herring bones' as illustrated in Figure 2 Christian Monstein: Callisto spectra Fig. 2. Type II solar radio flare with harmonics observed at Fig. 4. Two low-frequency isolated type III solar radio bursts Ooty observatory, India. Antenna = logarithmic-periodic linear observed at Bleien observatory, Switzerland. Antenna = polarized. logarithmic-periodic CLP-5130. Fig. 3. Type II solar radio flare with harmonics and 'herring Fig. 5. Group of type III solar radio bursts observed at Bleien bones', observed at Bleien observatory, Switzerland. Antenna observatory, Switzerland. Antenna = log-per CLP-5130, lin- = parabolic dish 7m, circular polarized. early polarized. Some type III are reverse drifting. 2.4. Type IV bursts 3. (xxxEs gibt ein viel schneres Beispiel von Birr am 22. September 2011xxx). The velocity of the solar disturbance The continuum radiation is a steady enhancement of the giving rise to these slow-drift bursts may be deduced from background level over a wide band of the spectrum, and is their rate of change of frequency. This velocity is of the or- often followed by a noise storm (type I). At times, however, der of 1000 km/s and corresponds to superalfvenic shocks an extremely intense form of continuum radiation is ob- originating in the flare or coronal mass ejection (CME) served covering a frequency band of more then 300 MHz, and moving through the corona. see figure 7. It often occurs during and after great out- bursts, and may last 10-300 minutes. The wavy, periodic 2.3. Type III bursts (fast drift) intensity variations in frequency are not caused by stand- ing waves in the receiving system. They are not properties Fast drifting bursts, a very commonly occurring phe- of the type IV burst. This can be confirmed by compar- nomenon, have typical durations of a second. The duration ing the same flare from observations at different locations increases at lower frequency and the drift rate (MHz/s) de- (e-Callisto network). creases. Type III bursts typically occur in groups of 3 to 10 with a total duration of less than 60 sec, as illustrated 2.5. Type V bursts in Figures 4-6. The radio emission is caused by flare ac- celerated electron beams propagating through the corona Type V bursts are always associated with type III bursts at high velocity (up to half the speed of light). and follow them for a few tens of seconds. They appear Christian Monstein: Callisto spectra 3 Fig. 6. Large group of type III solar radio flare observed at Fig. 8. Type V solar radio burst observed at Ooty observatory, Humain observatory, Belgium. Antenna = log-per CLP-5130, India. Antenna = home made, linearly polarized, pointing to linearly polarized. Probably a U-burst on the left side near zenith. 11:31UT. Fig. 9. DCIM (decimetric) solar radio burst with pulsations observed at Bleien observatory, Switzerland. Antenna = 7m Fig. 7. Type IV solar radio flare (continuum) observed in dish, circularly polarized RHCP, pointing to sun. Badary observatory near Irkutsk, Russian Federation. Antenna = log-per CLP-5130, linearly polarized. like a flag attached at low frequency to the type III burst, see Figure 8 near 07:39:30UT. The emission is quasi con- tinuous with a bandwidth of less than the type III burst. Duration is typically less than 1 minute. The exciter is the electron beam that is partially scattered at high altitude. 2.6. Type DCIM/P bursts Decimetric bursts are quite frequent and cover frequency ranges of up to a one GHz. In figure 9 we can see pulsa- tions in right circular polarization while at the same time Fig. 10. DCIM (decimetric) solar radio burst with continuum left circular polarization is not pulsed but shows contin- observed at Bleien observatory, Switzerland. Antenna = 7m uum, see figure 10. The origin of the emission needs to be dish, circularly polarized LHCP, pointing to sun. investigated further. 4 Christian Monstein: Callisto spectra Fig. 11. DCIM (decimetric microwave) solar radio flare with Fig. 12. Gyro-synchrotron solar radio radiation observed in L- fiber structures observed at Bleien observatory, Switzerland. band at Bleien observatory, Switzerland. Antenna = 5m dish, Antenna = 5m dish, pointing to sun. linearly polarized, pointing to sun. 2.7. Type DCIM/F burst Intermediate drift burst of a DCIM event produced by a X6.9 flare covering hundreds of MHz frequency up to 4 GHz. In figure 11 we can see fiber-like struc- tures. Therefore also the name fiber burst. This flare was recorded with Phoenix-3, a FFT-spectrometer. 2.8. Synchrotron radiation Decimetric continuum or synchrotron radiation during ac- tive sun produce intensive broad band noise, see figure 12. Contrary to other sources in astrophysics, the majority of solar flare electrons reach only mildly relativistic energies. Thus the emission is called gyro-synchrotron. These elec- trons easily radiate due to gyration without any collisions Fig. 13. U-burst in intensity (LHCP+RHCP). Antenna = 7m with other particles. They radiate via the cyclotron (non- dish, circular polarized, pointing to sun. relativistic), synchrotron, and possibly inverse-Compton radiation mechanisms. The gyro-synchrotron radiation mechanism depends on the strength of the magnetic fields. These fields are present everywhere, but they tend to be stronger in those places where electrons are accelerated to the solar corona following a loop-shaped magnetic field high energies, thus helping the high efficiency with which that turns back to the chromosphere. these electrons emit radiation 2.9. Type U burst 2.10. Interference from ground reflection The U-burst, first identified by Maxwell and Swarup and Interference from ground happens only in linear horizon- Haddock (Maxwell, 1958), is a type of solar event lasting tal polarization if the ground is reflective due to water, up to about 10 sec in which the frequency or the emis- metal or plants. Also buildings or other large construc- sion first drifts rapidly downwards, then increases again. tions may led to interference effects. This happens mainly On the dynamic spectrum the burst has appearance of an during sun-rise and sun-set when the elevation of the sun inverted letter U, see figure 13.The frequency drift rate at is low, thus when the reflected radiation and the direct ra- the sides of the 'U' is of the same order as that observed diation are both in the beam of the antenna, see figure 14. in ordinary type III bursts; the U-burst is now generally Detectable interference from solar radiation proves that regarded as sub-class of type III, and is believed to be gen- the quiet solar flux can be measured. Thus, the system is erated by plasma waves set up by fast electron streams in sensitive down to quiet solar flux. Christian Monstein: Callisto spectra 5 Fig. 14. Interference due to reflection of the solar radiation Fig.

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