Significance variations of lunar radio flux at the wavelength of 2.46 cm were detected in Irbene (Latvia) during the maxima of Leonid shower on the Moon in 2000 and 2001. These results were interpreted as detection of lunar radio emission of seismic origin. However, radio observations of the Moon at the wavelength of 6 cm in Ukraine did not show any signal enhancement of lunar radio flux on November 17–19, 2001. Except meteoroid impacts, the eclipses can lead to increasing of intensity of non-thermal radio emission due to formation of micro cracks in lunar regolith when the regolith temperature during eclipses is quickly changes. The results of simultaneous observations of the full lunar eclipse at the wavelengths of 18 cm and 1.35 cm in Simeiz (Ukraine) and Pushchino (Russia) on November 8–9, 2003 are presented. According to these observations the correlation between fluctuations of lunar radio flux at both wavelengths is absent. Thus, the previously detected fluctuations of lunar flux at the wavelength of 2.6 cm may have the instrumental origin. Lunar origin of detected fluctuations could be confirmed by simultaneous observations at two radio telescopes. Our future goal is try to detect the lunar radio emission of seismic origin at the lower frequencies, because the intensity of such emission during the earthquakes increases with a decreasing frequency

Berezhnoy, A.A.

Khavroshkin, O.B.

Kovalenko, A.V.

Smirnov, G.T.

Volvach, A.E.

Kinematika i fizika nebesnyh tel (Online)

Наукова електронна бібліотека періодичних видань НАН України (Vernadsky National Library of Ukraine)

THE LUNAR RADIO FLUX DURING LEONID METEOR SHOWERSAND LUNAR ECLIPSEA. E. Volvach1, A. A. Berezhnoy2, O. B. Khavroshkin3,A. V. Kovalenko4, G. T. Smirnov41Radio Astronomy Laboratory, Crimean Astrophysical ObservatoryRT-22, Katsively, 98688 Yalta, Ukrainee-mail: volvach@crao.crimea.ua2Advanced Institute for Science and Engineering, Waseda University3-4-1 Okubo, Tokyo 169-0071 Japan3Institute of Earth Physics10 B. Gruzinskaya Str., 123810 Moscow, Russia4Pushchino Radioastronomical ObservatoryPushchino, 142290 Moscow Region, RussiaSigniﬁcance variations of lunar radio ﬂux at the wavelength of 2.46 cm were detected in Irbene(Latvia) during the maxima of Leonid shower on the Moon in 2000 and 2001. These results wereinterpreted as detection of lunar radio emission of seismic origin. However, radio observations ofthe Moon at the wavelength of 6 cm in Ukraine did not show any signal enhancement of lunarradio ﬂux on November 17–19, 2001. Except meteoroid impacts, the eclipses can lead to increasingof intensity of non-thermal radio emission due to formation of micro cracks in lunar regolith whenthe regolith temperature during eclipses is quickly changes. The results of simultaneous observa-tions of the full lunar eclipse at the wavelengths of 18 cm and 1.35 cm in Simeiz (Ukraine) andPushchino (Russia) on November 8–9, 2003 are presented. According to these observations the cor-relation between ﬂuctuations of lunar radio ﬂux at both wavelengths is absent. Thus, the previ-ously detected ﬂuctuations of lunar ﬂux at the wavelength of 2.6 cm may have the instrumentalorigin. Lunar origin of detected ﬂuctuations could be conﬁrmed by simultaneous observations attwo radio telescopes. Our future goal is try to detect the lunar radio emission of seismic origin atthe lower frequencies, because the intensity of such emission during the earthquakes increases witha decreasing frequency.INTRODUCTIONMeteoroid impacts onto the Moon might be observable from the Earth. The meteoroid stream most likely tobe detectable is the Leonids, remnants of the comet 55P/Tempel–Tuttle. Optical ﬂashes from Leonid meteorshitting the dark side of the Moon were observed in 1999 [6]. An unsuccessful attempt to detect ﬂashes of radioemission at the wavelength of 3.6 cm during optical ﬂashes caused by Leonid’s impacts onto the Moon in 1999was carried out by [5].The main component of the lunar radio emission is the thermal radiation. The lunar thermal radiation hasbeen rather well investigated and it allowed us to estimate the density and electric properties of the porous lunarregolith, as well as the temperature regime of the surface layers. The frequency of electromagnetic radiationof the seismic origin measured before earthquakes ranges from 1 kHz to 1 MHz [3]. Radio emission of seismicorigin can also be detected on the Moon.Variability of lunar radio emission at 13 and 21 cm was detected on July 29 – August 2, 1999 [4]. Duringthe Leonid meteoroid shower in 2000 and 2001 the variability of lunar radio ﬂux at the wavelength of 2.46 cmwas detected in Irbene (Latvia) [1]. The increasing of amplitude of the lunar radio ﬂux variations duringLeonid shower is interpreted as a result of excitation of the seismic waves on the Moon and the transformationof the seismic energy into the electromagnetic radiation. In this article we present the results of the Moonobservations in Ukraine during Leonid shower in 2001 and in Japan in November 1999.Except for meteoroid impacts, the eclipses can lead to increasing of intensity of non-thermal radio emissiondue to formation of micro cracks in lunar regolith when the regolith temperature quickly changes during eclipses.c© A. E. Volvach, A. A. Berezhnoy, O. B. Khavroshkin, A. V. Kovalenko, G. T. Smirnov, 200482Fig. 1b.Fig. 1a. Fig. 2a.Fig. 2b.Figure 1. Periodogramms of radio ﬂux from the Moonon November 18, 2001. Curve 1a shows the results of ob-servations at 09:50–10:45 UT, curve 1b those of at 14:00–14:55 UTFigure 2. Periodogramms of radio ﬂux from Cyg A andthe sky on November 18, 2001. Curve 2a shows the re-sults of the sky observations in Simeiz at 8:32–8:38 UT,curve 2b those of Cyg A at 13:49–13:55 UTThe results of simultaneous observations of the full lunar eclipse are presented at the wavelengths of 18 cm and1.35 cm in Simeiz and Pushchino on November 8–9, 2003.OBSERVATIONSDuring Leonid meteor showersThe observations of the Moon at the frequency of 8.2 GHz during Leonid meteor shower in 1999 were carried outusing the 32 m radio telescope of the Kashima Space Research Center, Japan (36◦N, 141◦ E) on November 15,16, and 18. The bandwidth of the receiver is 800 MHz, the output time constant is 0.021 ms. Then the averagingof data was performed with a new output time constant equal to 1 s. The antenna was guided to the center ofthe lunar disc. The detailed description of the observations is given in [5]. The calibration sources and sky werenot observed in Kashima. That’s why the additional observations of the Moon at the frequency of 8.415 GHzwere carried out on May 7, 2003 at RT-22 in Crimea (44◦N, 35◦ E). The bandwidth of the receiver is 2 MHz,the output time constant is 1 s. The value of the sensitivity threshold for this time resolution is equal to 0.05 K.The antenna feed was left circular polarized. The antenna was guided to the center of the lunar disc. Forcalibration purposes the observations of the sky near the Moon and Vir A were also carried out. The durationof interrupted observations of each object is 20 min.During November 17–19, 2001 the observations of the Moon at the wavelength of 6.2 cm were carried outin Simeiz. The frequency and the bandwidth of the receiver in Simeiz are 4.866 GHz and 2 MHz, respectively.The diameter of the radio telescope is 22 m, the output time constant is 1 s. The antenna feed was left circularpolarized. The antenna was guided to the center of the lunar disc. The duration of interrupted observations ofthe Moon is 1 hour.83To verify whether the variations are attributed to the Moon we performed several tests that included recor-ding signals from strong calibration source Cyg A and recording atmospheric radio emission, when the radiotelescope tracked a position on the sky several degrees oﬀ the Moon and Cyg A.During lunar eclipseDuring November 8–9, 2003 the simultaneous observations of the Moon were carried out in Pushchino (55◦N,38◦ E) and in Simeiz (44◦N, 35◦ E). The frequency and the bandwidth of the receiver in Simeiz are 1.666 GHzand 2 MHz, respectively. The frequency and the bandwidth of the receiver in Pushchino are 22.283 GHz and6 MHz, respectively. The diameter of both radio telescopes is 22 m, the output time constant is 1 s. The antennafeed was left circular polarized in both cases. The antenna was guided to the center of the lunar disc.To verify whether the variations are attributed to the Moon we performed several tests that included recor-ding signals from strong source Cyg A that is known to be without fast variations and recording the atmosphericradio emission, when the radio telescope tracked a position on the sky several degrees oﬀ the Moon and Cyg A.RESULTSThe mean amplitude of sporadic ﬂuctuations of lunar radio ﬂux at the frequency of 8.2 GHz was about ﬁverelative units on November 16 and 18, 1999. The amplitude of ﬂuctuations of lunar radio ﬂux did not increaseat the time of predicted maximum of Leonid meteor shower on the Moon. The amplitude of ﬂuctuations oflunar radio ﬂux was equal to 200–300 relative units on November 16, 1999 at 9:20–10:50 UT. It can be explainby instrumental eﬀects because Leonid activity was too low at that time interval.The amplitudes of peak-to peak variations of signal from the Moon at the frequency of 8.4 GHz in Simeiz areequal to 2 K and comparable to those from the sky and Vir A. Fourier analysis shows the absence of periodicitiesof signal from all three objects.The results of the Moon observations at the wavelength of 6.2 cm are quite diﬀerent from those of atthe wavelength of 2.46 cm. The amplitude of lunar radio ﬂux variations at the wavelength of 6.2 cm in Simeizis equal to 1–2 K during November 17–19, 2001 and did not increase at the time of predicted maxima of Leonidshower on the Moon. The amplitude of these variations is comparable with that of the sky and Cyg A. Spectralanalysis shows the existence of periodicities of radio ﬂux both from the Moon and from Cyg A and also fromthe sky. The values of periods vary chaotically versus time. All these facts conﬁrm instrumental origin ofdetected variations.According to simultaneous observations of the full lunar eclipse at the wavelengths of 18 cm and 1.35 cm inSimeiz and Pushchino on November 8–9, 2003 the correlation between ﬂuctuations of lunar radio ﬂux at bothwavelengths is absent.DISCUSSIONThe Moon observations at the wavelengths of 3.6 and 6.2 cm do not give support to the lunar origin of detectedvariations. It can be explained by weak intensity of lunar radio emission caused by meteoroid bombardmentat the wavelengths of 3.6 and 6.2 cm in comparison with that at the wavelength of 2.46 cm. To conﬁrmthe detecting seismic origin of lunar radio emission at the wavelength of 2.46 cm the additional simultaneousobservations of the Moon at this wavelength are required by using two diﬀerent radio telescopes.The important feature of the variable lunar radio ﬂux is its periodicity. The values of periods are situatedbetween 1.5 and 12 min at the wavelengths of 2.46, 13, and 21 cm [1]. The spectral analysis of the radio signalsvariations from the sky, the Moon and Cyg A at the wavelength of 6.2 cm shows a general increase of the spectraldensity towards lower frequencies. The periods of oscillations of lunar radio ﬂux at the wavelength of 6.2 cmrange from 1 to 15 min (see Fig. 1). The amplitude of spectral power of the spectra at the wavelength of 6.2 cmfrom the sky and Cyg A is comparable with that from the Moon; the spectral maximum of the atmosphericﬂuctuations is at periods less than 2 min (see Fig. 2). Unfortunately, the observations of the sky and Cyg Ahave been carried out only during 5 min, but it is not enough to study of possible periodicities at 3–15 minrange, where the lunar radio ﬂux shows periodicities. There is fast variability of the values and intensities ofspectral peaks from the Moon, from the sky, and also from Cyg A. It is known that Cyg A has not variability ofits radio ﬂux in 1 min range. This means that the instrumental eﬀects can explain the periodicities of lunar ﬂuxat the wavelength of 6.2 cm. Thus, previously detected periodicities of lunar ﬂux at other wavelengths must bechecked again with simultaneous observations at two isolated antennas.During impacts of meteoroids with the Moon the thermal radiation emits from the impact-produced ﬁreball.Just after an impact, the seismic waves are excited, and a part of the seismic energy is transformed to the radioemission. The unsuccessful search for the impact-produced radio ﬂashes was performed. The upper limit forthe strongest radio ﬂashes is equal to 3 K based on the Simeiz data. We can estimate the upper limit of intensity84of the impact-produced radio ﬂashes as 2 · 10−8 J Hz−1 at the wavelength of 6.2 cm. We can suppose that radioﬂashes accompanying optical emission have the same duration as optical ﬂashes (0.1 s). Let us assume thatthe mass of the biggest meteoroid collided with the Moon at the time interval of our radio observations is 2.5 kgas estimated by Ortiz et al. 2002. Using the model of Yanagisawa & Kisaichi [6] for thermal radiation fromD ′ ﬂash, caused by the impact of 2.5 kg meteoroid, we can estimate that the ﬂux of thermal radiation fromsuch impact does not exceed 5 · 10−15 J Hz−1 at the wavelength of 6.2 cm. Thus, the ﬂux of thermal radiationfrom the impact-produced ﬁreballs is too low for detection by radio telescopes. This estimation is conﬁrmedwith the radio ﬂashes absence at the frequency of 8.2 GHz at the moments of big meteoroids impacts detectedby Yanagisawa & Kisaichi [6].The further theoretical, observational, and experimental study of the radio emission of the Moon is necessaryto better understand the nature of the detected variations of lunar radio ﬂux. The future study of the seis-mic origin of lunar radio emission must be performed at a few radio telescopes for accurate determination ofan inﬂuence of the atmospheric ﬂuctuations and instrumental eﬀects. Monitoring of the lunar radio ﬂux cangive information about the time of maximal intensity of the strongest meteoroid showers on the Moon. Un-fortunately, these moments were not estimated independently with other techniques. For example, the timedetermination of Leonid shower maxima on the Moon based on detection of the optical ﬂashes on the Moonis practically diﬃcult due to poor statistics. For study of the meteoroid bombardment intensity on the Moonwith optical techniques, the methods for detection of the weak ﬂashes must be developed. The LUNAR-A andSELENE spacecrafts are planned to launch to the Moon in nearest years. The LUNAR-A penetrators withsensitive seismometers will be installed on the lunar surface; these instruments can determine the moments ofstrong moonquakes and the maxima of meteor showers on the Moon. As a correlation between seismic radioemission and earthquakes is veriﬁed by Diakonov & Ulitin on Earth [2], we can expect the appearance of radioemission of the seismic origin during moonquakes. During moonquakes the release of radioactive gases Rn andPo from lunar interiors can occur, the SELENE alpha particle spectrometer can detect such events.Except for meteoroid impacts, the eclipses can lead to increasing of the intensity of non-thermal radioemission due to formation of micro cracks in lunar regolith when the regolith temperature during eclipses isquickly changes. According to these observations a correlation between the ﬂuctuations of lunar radio ﬂuxat both wavelengths is absent. Thus, the previously detected ﬂuctuations of the lunar ﬂux at the wavelengthof 2.6 cm may have instrumental origin. The lunar origin of detected ﬂuctuations could be conﬁrmed bysimultaneous observations using two radio telescopes.CONCLUSIONPreviously, it was reported that the strong oscillations of the lunar ﬂux at the wavelength of 2.46 cm occurredat the moments of the predicted maxima of Leonid meteor shower on the Moon in 2000 and 2001. Butthe observations of the Moon at the wavelength of 2.46 cm were carried out at the unique antenna. An absenceof the coincidence data obtained with other radio telescopes means that the instrumental origin of the detectedﬂuctuations can’t be exclude. To conﬁrm the lunar origin of the variable lunar radio emission the simultaneousobservations of the Moon must be carried out at a few radio telescopes during the lunar eclipses and the strongmeteor showers. The radio ﬂashes caused by collisions of kg meteoroids with the Moon were not detected atthe wavelengths of 3.6 and 6.2 cm, the upper limit for the intensity of such ﬂashes is estimated. In the future it ishighly desirable the simultaneous study of the meteoroid bombardment and the seismic activity of the Moon withLUNAR-A penetrators, SELENE alpha particle spectrometer, single dish radio observations, and by monitoringof the optical ﬂashes.Our future goal is try to detect the lunar radio emission of seismic origin at the lower frequencies, becausethe intensity of such emission during earthquakes increases with a decreasing frequency.[1] Berezhnoy A. A., Bervalds et al. // Baltic Astronomy.–2002.–11.–P. 507.[2] Diakonov B. P., Ulitin R. V. // Rep. Russian Acad. Sci.–1992.–264.–P. 322.[3] Gokhberg M. B., Morgunov V. A., Pokhotelov O. A. Earthquake prediction – Seismoelectromagnetic phenomena.–Amsterdam: Gordon and Breach Publishers, 1995.–P. 193.[4] Khavroshkin O. B., Tsyplakov V. V., Poperechenko B. A., et al. // Rep. Earth Sci.–2001.–376.–P. 90.[5] Osaki H., Okubo H., Koyama Y. // J. Commun. Res. Lab.–2001.–48.–P. 159.[6] Yanagisawa M., Kisaichi N., et al. // Icarus.–2002.–159.–P. 31.85

The lunar radio flux during Leonid meteor showers and lunar eclipse

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The lunar radio flux during Leonid meteor showers and lunar eclipse

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