R. R. Daniel

A search for energetic neutrons emitted during solar flares

On the basis of solar flare forecasts, balloon flights were made from Hyderabad, India (vertical geomagnetic threshold rigidity of 16.9 GV), to detect the possible emission of high energy neutrons during solar flares. The detector comprised of a central plastic scintillator, completely surrounded by an anticoincidence plastic scintillator shield. The instrument responds to neutrons of about 15–150 MeV and gamma rays of about 5–30 MeV with about the same efficiency. The detector was flown to an atmospheric depth of 25 g cm-2 on February 26, 1969; while the balloon was at ceiling a flare of importance 2B and one of 1N occurred. No perceptible flare associated increase in the counting rate was observed. Using the observed counting rates, an upper limit of 1.2 × 10-2 neutrons cm-2 sec-1 is obtained for the first time for a flare of importance 2B for neutrons of energy 15–150 MeV. The corresponding upper limit for gamma rays of energy 5–30 MeV is found to be ∼ 10-2 photons cm-2 sec-1. The neutron flux limits are compared with the recent calculations of Lingenfelter.

The energy spectrum of cosmic ray electrons between 10 and 1000 GeV

Measurements made by the Bombay Group on the fluxes of cosmic ray electrons in the energy range 10–1000 GeV have been compared with those of other workers in the same energy domain with a view to understand the present confused situation on the existing observations at these high energies. Such an analysis clearly brings out the current situation in its true perspective and highlights the care and emphasis to be placed on future experimentation in this important field.

Atmospheric gamma rays in the energy region 40–1000 GeV

A large stack of lead-emulsion sandwich detector assembly was flown over Hyderabad, India. High energy gamma rays at the float altitude were unambiguously identified from the cascades they induced, and their energies reliably determined by improved methods. From an analysis of 163 gamma rays of energy ≳ 30 GeV, it is found that the differential energy spectrum is represented by the power lawJr(E)= 129·4E−2·62±0·12 photons m−2 sr−1sec−1 GeV−1 at an effective atmospheric depth of 14·3 g cm−2; this is the first reliable balloon measurement of atmospheric gamma rays in the energy range 40–1000 GeV. After correcting for the gamma rays radiated by the primary cosmic ray electrons, the production spectrum of gamma rays, resulting from the collisions of cosmic ray nuclei with air nuclei, at the top of the atmosphere isPr(E, 0)=8·2 × 10−4 E2.60±0.09 photons g−1sr−1sec−1 GeV−1. The atmospheric propagation of the electromagnetic component due to the cascade process is also derived from the gamma ray production spectrum.

Near infrared photometry of some RS CVn systems and candidates

Infrared observations in the J, H, and K bands were made on eleven RS CVn systems. Infrared (IR) excess ≳0.3 mag in the J, H, and K bands was observed from the three systems UX Ari, HR 1099 and σ CrB. Similar observations were also made on the RS CVn candidates HD 26354, 39937, 42449, 51268, and 86005.The IR excess in the RS CVn systems for which near infrared photometric data are available is found to be correlated with the maximum of optical wave amplitude of these systems.The observed excess cannot be explained on the basis of a single process such as: (i) emission from cool spots on the photosphere; (ii) free-free emission from an optically thin circumstellar plasma; or (iii) dust grain emission from circumstellar material.

A 750 mm balloon-borne telescope for far-infrared astronomical observations

A balloon-borne 750 mm Cassegrain telescope has been developed for far-infrared (FIR) astronomical observations. This telescope uses a three-axis stabilised balloon platform with approximately 30 sec of arc (RMS) pointing accuracy. Design and overall properties of this telescope system are presented. Some of the special features of the payload are highlighted, viz., cheap and lightweight mirrors made in epoxy resin; the in-flight relative phase adjustment facility between the detector signal processing system and the secondary mirror chopper. This telescope was flown at an altitude of 32 km on December 10, 1980 for conducting far-infrared observations. The telescope flight details and performance are presented and compared with the design goals. To illustrate the scanning capability of the telescope, a map of Orion-A obtained using it is presented.

Energetic neutrons and gamma rays measured on the Aryabhata satellite

An experiment to measure energetic neutrons and gamma rays in space was launched in the first Indian scientific satellite,Aryobhata, on April 19, 1975. From this experiment, the first measurements in space of the Earth’s albedo fiux of neutrons of energy between 20 and 500 MeV have been made; the values obtained for two mean geomagnetic vertical cut-off rigidities of 5.6 and 17.0 GV are (6.3±0.4)×10−2 and (1.4±0.3)×10−2 neutrons cm−2 sec−1 respectively. These measurements confirm that protons arising from cosmic ray albedo neutron decay, can adequately account for the protons in the inner radiation belt. Observations on gamma rays of energy between 0.2 and 24 MeV have enabled the determination of the total background gamma ray flux in space as a function of latitude. This in turn has permitted useful information on the diffuse cosmic gamma rays. We have also observed four events that showed sudden increases in the gamma ray counting rates between 0.2 and 4.0 MeV. Observational details of these events are given.

The diffuse cosmic gamma rays

A careful and objective analysis is made of the available experimental observations which claim evidence for the existence of a shoulder in the spectrum of the diffuse cosmic gamma rays in the energy range of 1–40 MeV. In this, special cognisance is taken of the experimental data and theoretical calculations of the Bombay Group. These considerations cast serious doubts on the reliability of the high flux values obtained by many experimenters in this energy region emphasizing thereby the need for great caution in interpreting the shoulder as due to cosmological effects with far reaching implications.

Far-Infrared (100–200 μm) Photometry of HII Regions with a 1m Balloon Borne Telescope

A 1m balloon-borne telescope has been developed at TIFR for far-infrared (FIR) astronomical observations. The telescope was successfully flown on March 2, 1985 from Hyderabad, India. During the flight RCW 57, RCW 108, RCW 122, W 31, G 351.6-1.3 and Carina nebula were observed. This paper describes the telescope, its performance and very preliminary results from this flight.

Infrared observations of beta Cephei and delta Scuti stars

We have made near-infrared photometric observations of nine β-Cephei and eight δ-Scuti stars inJ, H, andK bands. The observed fluxes are in good agreement with those expected according to their spectral types. We conclude that these stars do not have any anomalous emission in these near-infrared bands.

Cross-sections for the (4He, 3H) stripping reaction on Fe, Al, C and glass targets at an energy of 120 MeV

Fe, Al, C and Glass targets have been irradiated with 120 MeV helium ions. The cross sections for the stripping reaction (4He, 3H) on these target nuclei have been determined, with nuclear emulsions, as 85 ± 30, 65 ± 20, 38 ± 15 and 41 ± 15 mb, respectively.