11,719 research outputs found
Secondary periodicities of microbursts of TeV gamma rays from the Crab pulsar
Observations were made during the past several years on the Crab pulsar using the Ooty atmospheric Cerenkov array with the aim of detecting possible emission of ultra high energy gamma rays by the pulsar. During the course of these observations, it was found that the Crab pulsar emits TeV gamma rays in bursts of short duration. The microbursts of TeV gamma rays from the Crab pulsar, which were seen in the data of at least three years, also reveal interesting secondary periodicities. It was noticed at first that some bursts could be connected with the others that occurred during the same night or during the next two nights with integral number of cycles of periods 43 + or - 1 minute. Ten possible periods in the vicinity of 43 minutes were determined for all the combinations of bursts for each year. The best values of periods thus obtained were different from year to year. But when, instead of the real time, the number of Crab cycles elapsed between the bursts was used as the unit of time, two values of burst periods - 77460 and 77770 Crab cycles - were found to be significant in the data of at least two years. A Monte Carlo simulation using 1500 trial periods chosen randomly within + or - 5 minutes of the original burst period did not reveal any value of the period as significant
An overview of the current understanding of Gamma-ray Bursts in the Fermi era
Gamma-ray bursts are the most luminous explosions in the Universe, and their
origin as well as mechanism are the focus of intense research and debate. More
than three decades since their serendipitous discovery, followed by several
breakthroughs from space-borne and ground-based observations, they remain one
of the most interesting astrophysical phenomena yet to be completely
understood. Since the launch of Fermi with its unprecedented energy band width
spanning seven decades, the study of gamma-ray burst research has entered a new
phase. Here we review the current theoretical understanding and observational
highlights of gamma-ray burst astronomy and point out some of the potential
promises of multi-wavelength observations in view of the upcoming ground based
observational facilities.Comment: 45 pages, 18 figures; Special issue of the Bulletin of the
Astronomical Society of India on Transients from Radio to Gamma rays,
December, 2011, eds. D.J. Saikia and D.A. Gree
Science and technology in agricultural development - a key to the future
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Observations on TeV gamma rays from Geminga and PSR 0950+08
The Geminga (2 CG 195+04) which exhibits a periodicity with a period of 59 to 60 s in its emission of X-rays, GeV gamma rays and TeV gamma rays was studied. During the winter of 1984 to 1985, this object was observed to see if it emits TeV gamma rays with a periodicity approx 60 s. The observations were carried out at two different sites separated by 11 Km with the Ooty Atmospheric Cerenkov Array split into two parts. Data were collected during clear moonless nights for a total duration of 15.3 hours spread over 2 months. Since the first time derivative of period is believed to be large and uncertain. The total data are subdivided into segments of duration not more than 3 days each to steer clear of the effects of P in the phase analysis. If TeV gamma ray signals are seen in each of these segments, it is possible to derive P from observed data
Equipartition of Current in Parallel Conductors on Cooling Through the Superconducting Transition
Our experiments show that for two or more pieces of a wire, of different
lengths in general, combined in parallel and connected to a dc source, the
current ratio evolves towards unity as the combination is cooled to the
superconducting transition temperature Tc, and remains pinned at that value
below it. This re-distribution of the total current towards equipartition
without external fine tuning is a surprise. It can be physically understood in
terms of a mechanism that involves the flux-flow resistance associated with the
transport current in a wire of type-II superconducting material. It is the fact
that the flux-flow resistance increases with current that drives the current
division towards equipartition.Comment: Revised version of J.Phys. Condens.Matter; vol. 18(2006) L143-L147 14
pages including 3 figures; provided an explanation in terms of the physical
mechanism of flux flow induced resistance that is proportional to the
impressed current. We are adding a simple, physically robust derivation of
our equipartition without taking resort to the minimum dissipation principl
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