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  • 1
    Electronic Resource
    Electronic Resource
    On the variability timescales and magnetic field in OJ 287 (1996)
    Springer
    Astrophysics and space science 240 (1996), S. 195-204 
    Details
    ISSN: 1572-946X
    Keywords: BL Lac ; Synchrotron radiation ; Black hole ; Relativistic jet ; Magnetic field
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The continuum spectrum of OJ 287, like most other BL Lac objects, is featureless- no emission or absorption lines are observed. However, OJ 287 shows variations at different timescales in flux and polarization at various wavelength bands. Using the available variability data one can estimate the sizes of the emission regions in the source from light travel time arguments. We assume the emission mechanism to be synchrotron radiation by high energy electrons with single power law energy distribution. Theoretical synchrotron spectrum in the frequency range 1011–1017 H z is compared with the observed spectral shape, obtained from new multifrequency quasi-simultaneous observations, to estimate the lower and upper cut off frequencies. These frequencies are used to obtain theoretical values of the variability timescales and magnetic field in the emission region. We obtain a value of 0.93 G for the magnetic field and 5.184×104 sec for the cooling time from the quiescent continuum spectrum. The shock-in-jet model explains the spectrum where shocks accelerate the particles and amplify the magnetic field in the jet. This timescale is compared with the one obtained from observed short timescale variability (20 minutes) with proper beaming correction. The short timescale variations (200 minutes in the source frame), possibly caused by an additional, ‘flaring’, component of the source, are also used to calculate compressed magnetic field. The observed and theoretically estimated variability timescales and the shape of the spectrum suggest that there are more than one emission components in OJ 287.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00639584
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  • 2
    Electronic Resource
    Electronic Resource
    Peculiar oscillations in the microwave emission of Jupiter during the impact of K fragment of comet Shoemaker-Levy 9 (1996)
    Springer
    Earth, moon and planets 75 (1996), S. 127-133 
    Details
    ISSN: 1573-0794
    Keywords: Oscillation ; microwave emission ; Jupiter ; Shoemaker-Levy 9 ; magnetospheric radiation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract In this article we report the peculiar oscillations in the intensity of microwave (4.15 GHz) emission seen during the impact of K fragment of comet Shoemaker-Levy 9 on July 19, 1994. The oscillations begin at 10h 13m 25s UT suddenly with a frequency of ~0.3 Hz and gradually the frequency of these oscillations increases to ~ 1 Hz. The oscillations are not due to local atmosphere or the radio interference from signals of geostationary satellite. They are intrinsic to the microwave emission from Jupiter during the impact of K fragment. Peak-to-peak amplitude of the oscillations is about 34% of the total microwave emission from Jupiter. If we assume that only 50% of the microwave emission is non-thermal and only the non-thermal emission suffered oscillations, then the oscillations are about 68% of the non-thermal emission from Jupiter. The observations also indicate that there are three continuum enhancements during this event and periodic oscillations almost all through. The third enhancement was the largest and during this enhancement there were some additional aperiodic variations. The aperiodic variations were of the order of few minutes and were possibly generated by the gravity waves. The periodic oscillations could be synchrotron emission modulated by the plasma oscillation in the outer magnetosphere. kg]Key words
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00054508
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    Paper (German National Licenses)
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