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An attempt is made to search for a consistent model to explain the electromagnetic spectrum of the Crab nebula (Tau A). It is assumed that there is a continuous injection of electrons at the centre of the nebula with an energy spectrumE
–1.54 as evidenced by radio data. This spectrum must steepen to a slope larger than 2 at some energyE
i
in order to ensure that the energy input into electrons remains finite. The spectrum must also steepen beyond an energyE
c
depending on the magnetic field because of synchrotron energy losses. Two types of models are considered: Class I, in which the whole nebula is characterised by a uniform magnetic field, and Class II, in which besides the general fieldH
0, small filamentary regions of strong fieldH
s
are postulated.In models of Class I, the best fit to the observed data is obtained whenE
t
>E
c
andH
05×10–4 gauss. However, this predicts a decrease in X-ray source size beyond 40 KeV. There are two possibilities of Class II model depending on the residence time of electrons in strong field regions being small or large. The former case explains the flattening in the optical spectrum.Experiments to distinguish between the various models are indicated.Presented at the International Conference on Cosmic Rays, Budapest, 1969. 相似文献
4.
The dynamical masses of dwarf-spheroidals, spiral and elliptical galaxies, dwarf irregular binaries, groups of galaxies and
clusters are shown to lie in a band about the M ∼ ρR3
line. The value of ρ is approximately the same as that estimated for unseen matter in the solar neighbourhood. The clusters themselves
lie about theM ∼ R
-3
line derived for a self-gravitating neutrino gas; their masses are distributed around the maximum Jeans-mass, MJmax. corresponding to mv - 10 eV in an expanding universe. The present day length scales of clusters and the dispersion in the velocities observed
within them are understood in terms of a 100-fold expansion subsequent to the initial growth of the fluctuations at MJmax. These systematics on theR-M plane imply that the initial condensations in the expanding universe are on the scale of the rich clusters of galaxies, these
condensations were triggered dominantly by the gravitation of the neutrinos and the constant density of al systems arises
naturally due to the embedding of these systems in the large scale neutrino condensations. If the neutrino density falls off
asr
-2 beyond the cluster edge till the distributions from different clusters overlap, then the mean density of the neutrinos approximately
equals the closure density of the universe. 相似文献
5.
K. S. Gothe T. P. Prabhu P. R. Vishwanath B. S. Acharya R. Srinivasan V. R. Chitnis P. U. Kamath G. Srinivasulu F. Saleem P. M. M. Kemkar P. K. Mahesh F. Gabriel J. Manoharan N. Dorji T. Dorjai D. Angchuk A. I. D’souza S. K. Duhan B. K. Nagesh S. K. Rao S. K. Sharma B. B. Singh P. V. Sudersanan M. Tashi Thsering S. S. Upadhya G. C. Anupama R. J. Britto R. Cowsik L. Saha A. Shukla 《Experimental Astronomy》2013,35(3):489-506
An array of seven atmospheric Cherenkov telescopes was commissioned at a high altitude site in Hanle in the Ladakh region of the Himalayas. The array called HAGAR has been designed to observe celestial γ-rays of energy >100 GeV. Each telescope is altitude-azimuth mounted and carries seven parabolic mirrors whose optic axes are co-aligned with the telescope axis. The telescopes point and track a celestial source using a PC-based drive control system. Two important issues in positioning of each HAGAR telescope are pointing accuracy of telescope axis and co-alignment of mirrors’ optic axes with the telescope axis. We have adopted a three pronged strategy to address these issues, namely use of pointing models to improve pointing accuracy of the telescopes, RA-DEC scan technique to measure the pointing offsets of the mirrors and mechanical fine-tuning of off-axis mirrors by sighting a distant stationary light source. This paper discusses our efforts in this regard as well as the current status of pointing and monitoring of HAGAR telescopes. 相似文献
6.
Extensive and meticulous observations of the rotation curves of galaxies show that they are either flat or gently going up,
but rarely decreasing, at large galactocentric distances. Here we show that the gravitational potential which would lead to
such rotation curves arises naturally when the visible matter modelled as a collisionless Maxwellian gas is embedded in a
dark halo of collisionless particles with a much higher dispersion in velocities. 相似文献
7.
If the dwarf spheroidals are embedded in an extended cloud of dark matter then their density profiles can be reproduced by
assuming a Maxwellian distribution of velocities for the constituent stars. The observed luminosity profiles of dwarf spheroidals
imply densities for the dark matter in the range 10-26 to 10-25 g cm-3, and mass-to-luminosity ratios which are typically an order of magnitude greater than those of globular clusters. Neutrinos
of mass ∼ 10 eV and (v) ∼ 1000 km s-1 can provide this requisite density for the background. 相似文献
8.
Singh Jagdev Cowsik R. Raveendran A. V. Bagare S. P. Saxena A. K. Sundararaman K. Krishan Vinod Naidu Nagaraja Samson J. P. A. Gabriel F. 《Solar physics》1997,170(2):235-252
An experiment to search for short-period oscillations in the solar corona was conducted during the total solar eclipse of 1995 October 24 at Kalpi, India. The intensity in the continuum, centred around 5500 Å and with a passband having a half-width of 240 Å, was recorded at a counting rate of 20 Hz using a thermoelectric-liquid cooled photomultiplier. The power-spectrum analysis of the data reveals that most of the power is contained in 6 frequencies below 0.2 Hz. A least-square analysis gives the periods of the 6 frequency components to be 56.5, 19.5, 13.5, 8.0, 6.1, and 5.3 s. These oscillations are found to be sinusoidal, and their amplitudes are found to lie in the rangeinebreak 0.2–1.3% of the coronal brightness. Assuming these oscillations to be fast magnetosonic modes, the calculations indicate the availability of enough flux for the heating of the active regions in the solar corona. 相似文献
9.
Cowsik Ramanath Singh Jagdev Saxena A.K. Srinivasan R. Raveendran A.V. 《Solar physics》1999,188(1):89-98
Encouraged by the detection of high-frequency, low-amplitude continuum intensity oscillations in the solar corona during the total solar eclipse of 1995, we designed and fabricated a six-channel photometer incorporating low-noise Hamamatsu R647 photomultipliers. Fast photometry at five different locations in the solar corona was performed at Don Bosco Mission, Venezuela during the total solar eclipse of 26 February 1998. Three interference filters with passbands of about 150 Å and centered around 4700, 4900, and 5000 Å were used. The photometric data were recorded at a rate of 20 Hz in three channels and 50 Hz in the remaining three channels. The power spectrum analysis of one of the channels that recorded appreciable counts indicates the existence of intensity oscillations in the frequency range 0.01–0.2 Hz. A least-squares analysis yields 90.1, 25.2, and 6.9 s periods for the three prominent components which have amplitudes in the range 0.5–3.5% of the coronal brightness. These periods and their amplitudes are similar to those detected in the coronal intensity oscillations during the 1995 eclipse. 相似文献
10.
Ramnath Cowsik 《Journal of Astrophysics and Astronomy》1986,7(1):1-6
The theoretical expectation of the high mass of >400 eV for the particles constituting the dark matter in dwarf-spheroidals
as an artifact of the implicit assumption that the density of particles vanishes at the visible edge. On the contrary if our
Galaxy and the dwarf-spheroidals are embedded in a neutrino condensation of the dimensions of the cluster thenm
- 10 eV can accommodate all the observations. 相似文献
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