H. L. Duorah

The synthesis of26Al during combined hydrogen and helium-burning reactions

We have studied the synthesis of26Al during combined hydrogen and helium-burning processes in high temperature and density conditions. The possible sites for these processes are believed to be the neutron star surfaces where the density ranges from ρ=104−107 g cm−3 and temperature range from 108−8×108 K. The screening effect which leads to an enhancement of nuclear reaction rates is taken into account whenever necessary. A detailed calculation of the abundances of26Al and27Al isotopes is presented here. Finite amounts of26Al is found to be produced atT=2×108 K and ρ=108 g cm−3 due to these combined reactions. This situation is likely to be realized during the γ-ray burst events on neutron star surface. The amount of material processed in the burst sources is very little compared to the amount of material processed in Novae or Supernovae. Thus it is suggested that rather than contributing to the overall amount of26Al, γ-ray bursts are likely to contribute more significantly to the inhomogeneity of26Al distribution in interstellar medium.

Two X-ray sources model of Cyg X-3

A model of Cyg X-3, as a binary cocooned star system with two sources of X-rays, one above the polar caps of the neutron star — the usual pulsar radiation — and the other around the equatorial plane of the magneto-bounding surface formed due to the interaction of the infalling plasma and the magnetic field of the neutron star, is made. The X-ray, γ-ray, and IR radiation light curves are considered from the shadow effect. An upper limit on the mass of the neutron star is estimated from the consideration of periodic derivative purely due to mass loss. A comparison is made with the results of Elsneret al. (1980) and Ghoshet al. (1981), which they derived from the consideration of period derivative purely from apsidal motion.

A model of rapid burster MXB 1730-335

A model of rapid burster MXB 1730-335, the source of type II X-ray burst is proposed, based on the Rayleigh-Taylor instability due to interaction of relativistic electrons produced by the rapid rotation of a highly magnetized neutron star, and the infalling accreted matter through the magnetic funnel at the poles. Conclusions are made that type II X-ray burster may be a constant source of cosmic rays and such a mechanism may be the progenitor of some forms of nebulae.Permanent address: Imphal College, Imphal, Manipur.

Study of IGM through high energy radiation from blazar

The high energy gamma rays from blazar affects the intergalactic medium (IGM) to large distances at different redshifts. The blazar radiation has been taken as the result of synchrotron and Inverse Compton scattering of electrons. It is found that the intergalactic medium is clumpy. Our estimated values lie within the suggested limit of ΩIGM ≊ 0.03 at redshift z = 3.

Nuclear reactions on accreting neutron star surface

The production of X-rays and gamma-rays in bursts is believed to be due to the rapid burning of matter accreted onto a neutron star surface from its companion, most probably a giant star. The accreted matter consists mainly of hydrogen and helium and a very small amount of heavy elements. Due to the infall of matter, the temperature at the bottom layers is raised to a value of the order of 108 K. The neutron star surface density is>107 g cm−3. As hydrogen burning is a slow process under any temperature and density conditions, we consider the helium-burning reactions as the source of gamma-rays in the neutron star surface. Under high-density conditions the ordinary laboratory reaction rates should become modified. At high-density conditions, the strong screening effect due to the polarising cloud of electrons around the ions become important and enhances the reaction rates considerably. The helium-burning reactions are calculated under such conditions. The abundances of helium-burning products such as12C, 116O, and20Ne, etc., are computed. Under high-density and temperature conditions carbon is found to be more abundant than oxygen. Neon is completely absent in almost all the relevant physical conditions in which a strong screening effect is operative. It is suggested that explosive burning of accreted helium of 10−13M⊙ will account for the observed energy of gamm-ray burst.

Explosive hydrogen burning in supernovae

Rapid proton capture is supposed to be responsible for the synthesis of a number of proton-rich nuclei. This process of hydrogen burning is considered here for mass elements, the atomic numbers of which range fromZ=10 toZ=20. The possible site for this process is assumed to be the outer envelope of the supernova at a proton number density (np)ranging fromnp=1022 cm−3 tonp=1028 cm−3 at temperatures in the range ofT=2–3×109 K.The capture path is determined by considering that a dynamical equilibrium between (p, γ) and (γ,p) reactions exists between the reacting nuclei. In this situation, the abundances of elements become proportional to the lifetime of β+ decaying nuclei at the waiting points.It is suggested that these rapid proton-capture reactions are responsible for the production of a number of nuclei in the rangeA≲40 during supernova outbursts.

Binary star model of the γ-ray burst with special reference to that on 5 March, 1979 and subsequent bursts on 6 March, 4 April, and 24 April, 1979

The peculiar γ-ray burst phenomenon of 5 March, 1979, and the other subsequent bursts on 6 March, 4 April, and 24 April, 1979, are studied, using the physically more realistic exponentially increasing accretion rate on a highly magnetized neutron star from its companion, and the conclusions that pycnonuclear reaction flash for the first and thermonuclear flashes for the subsequent bursts as the most probable model for this series of bursts, are made.We further conclude that a huge γ-ray burst is a sequel to rapid X-ray transient or type-I X-ray bursts, i.e., an almost exactly similar burst as on 5 April, 1979 will never repeat from the same source, instead rapid X-ray transient burst, or type-I X-ray burst will be occured. A rough estimate gives that the next burst will occur within ∼0.5 yr since 24 April, 1979.

Studies on the evolved carbon cores

Physical conditions prevalent in a degenerate carbon plasma lead to the enhancement of the carbon-carbon thermonuclear reaction rates. Nuclear energy generation rate in the carbon core is thereby augmented. The possible dissipation of energy due to pair-annihilation neutrinos, plasma neutrinos and neutrino bremsstrahlung are considered. Neutral current contribution to these weak processes are also taken into account. It is suggested that the enhanced nuclear gene-ration rate in the evolved core might halt the core collapse for a time, thus necessitating a reassessment of the phenomenon of core collapse as a precursor of carbon detonation supernova events.