003175   Bhattacharaya D;Ravi Shankar B T (NO, Raman Research Institute, Bangalore-560 080) : Imaging with the scanning sky monitor on ASTROSAT. Bull Astr Soc India 2002, 30(3), 833-4.

Describes the status of the development of software for coded mask imaging with the Scanning Sky Monitor aboard the proposed Indian multiwavelength astronomy satellite ASTROSAT.

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003174   Ballabh G M;Alladin S M (Astronomy Dep, Osmania University, Hyderabad-500 007) : Fluctuations in moon's period and its relationship with the perigees of the moon and the sun. Bull Astr Soc India 2002, 30(3), 601-4.

Just as the regression of the nodes of the lunar orbit is connected with the periodicity in the eclipse phenomenon, the advance of perigee is connected with the periodicity in the fluctuations of Moon's synodic period. From the data for 495 synodic months it is found that the gross fluctuation pattern repeats itself after about 112 synodic months, which is close to the period of one complete revolution of the Moon's perigee. Within each gross fluctuation pattern there are eight smaller cycles of about 14 synodic months. The causes of these features are suggested in terms of the angles between the new moon and the perigees of the Moon and Sun. The dependence of the amplitude of variation with respect to various angular separations can possibly be understood by the fact that the tidal effect on the Moon varies with its relative from the Sun.

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003173   Ashok N M;Banerjee D P K;Varricatt W P (Astronomy and Astrophyics Div, Physical Research laboratory, Ahmedabad-380 009) : Near-infrared spectroscopy of nova Sagittarii 2001. Bull Astr Soc India 2002, 30(3), 683-5.

Near-infrared spectra of the very fast He/N-type nova, Nova Sagittarii 2001 (V4643 Sgr) obtained in the early decline phase and the period 110 to 170 days after the discovery date are presented. The spectrum in the early decline phase is dominated by emission lines of hydrogen and accompanied by fluorescence excited O I line at 1.129 μm. These lines have broad symmetric emission wings with full width at zero intensity (WZI) corresponding to a velocity of <126> 10,000 km s^-1. About 120 days after the discovery the K band spectrum is dominated by emission lines due to Si VI and Si VII at 1.963 μm and 2.476 μm indicating that the nova had entered the coronal phase. The line ratios of Brackett series deviate substantially from case B values indicating optical depth effects.

3 illus, 7 ref

003172   Anupama G C;Sahu D K (NO, Indian Institute of Astrophysics, Bangalore-560 034) : Observations of the type IIp supernova 2001 X during the plateau phase. Bull Astr Soc India 2002, 30(3), 751-4.

The photometric and spectroscopic observations indicate the supernova to be of type II-P and also the observations were made during the plateau phase. The photospheric temperatures obtained based on spectra are very similar to those obtained for the type II-P supernova SN1999em at similar phases.

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003171   Anandarao B G (NO, Physical Research Laboratory, Ahmedabad-380 009) : Near-infrared investigations of star forming regions. Bull Astr Soc India 2002, 30(3), 631-6.

Initiated an observational programme on star formation using the 256x256 HgCdTe Infrared Array Camera(NICMOS 3) at the 1.2 m IR telescope in Mt. Abu. The observations, being made in the spectral region 1-2.5 μm, involve broad/narrow band imaging photometry of selected small molecular clouds and medium resolution spectroscopy (with the grating spectrograph of NICMOS 3) of some bright young stellar objects. Developed a medium resolution Fabry-Perot Imaging Spectrometer for mapping of regions of emission in a selected emission line. Reports here some of the recent results obtained.

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003170   Ahuja A L;Gupta Y;Kembhavi A K;Kulkarni V (NO, IUCAA, Post Bag 4, Geneshkhind, Pune-411 007) : Tracking pulsar dispersion measures using the GMRT. Bull Astr Soc India 2002, 30(3), 701-2.

Presents preliminary results from an ongoing program of accurate pulsar dispersion measure (DM) measurements using the GMRT. From simulatneous dual frequency observations, are able to determine DMs to accuracies of 1 part in 10⁴ and better. For 4 of the 12 pulsars studied, finds mean DM value to be significantly different from the expected value. For most of the pulsars, detects significant variations of the DM on time scales of weeks to months.

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003169   Agrawal V;Sreekumar P (Space Astronomy and Instrumentation Div, ISRO Satelite Centre, Bangalore-560 017) : Spectral evolution of LMXB GX 349+2. Bull Astr Soc India 2002, 30(3), 675-6.

Z sources are the brightest low-mass X-ry binaries (LMXB) believed to contain magnetized neutron stars. They trace a `Z' shaped track in their X-ray colour-colour diagram. It is thought that the accretion rate increases systematically along this track. According to `unified model' proposed to explain combined spectral and timing properties of this class of sources, the systematic variation with accretion rate of spectral parameters such as the optical depth and the comptonization parameter can explain the `Z' shaped track. Made detailed spectral and timing analysis of the Z source GX 349+2 using RXTE archival data of the period 29 September to 13 October 1998 to investigate the spectral variations along the Z track.

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001042   Poonia S;Soni S N (X-ray Lab, Phys Dep, Jai Narain Vyas Univ, Jodhpur-342 003) : Lα satellites in X-ray emission spectra of middle-Z elements. Indian J pure appl Phys 2002, 40(11), 786-94.

The X-ray satellite spectra arising due to a certain transition array have been calculated. Auger transition energies and their relative intensities have been estimated by considering cross sections of singly ionized. States and then of subsequent Coster-Kronig and shake-off process. The calculated spectra have been compared with the measured satellite energies in Lα spectra. Their intense peaks have been identified as the observed satellite lines. The one-to-one correspondence between the peaks in calculated spectra and the satellites in measured spectra has been established on the basis of the agreement between the separations in the peak energies and those in the measured satellite energies. Satellites observed in the Lα region of the X-ray spectra of various elements, named α₃, α₄ and α5 in order of increasing energy are mainly emitted by stated.The satellite α₃ in all these spectra can be assigned to the super-position. This must be most intense one out of all these satellites, contributing in order of decreasing intensity. Possible contributions of other transitions have been discussed.

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000166   Yadav K K;Chouhan N;Kaul S R;Koul R (Bhabha Atomic Research Centre, Nuclear Research Laboratory, Trombay, Bombay - 400 085) : Multinode data acquisition and control system for the 4-element TACTIC telescope array. Bull Astr Soc India 2002, 30(1), 403-6.

An interrupt driven multinode data acquisition and control system has been developed for the 4-element gamma-ray telescope array, TACTIC. Computer networking technology and the CAMAC bus have been integrated to develop this icon-based, userfriendly failsafe system. Describes the salient features of the system.

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000165   Vishwanath P R;Acharya B S;Bhat P N;Chitnis V R;Majumdar P;Rahman M A;Singh B B (NO, Tata Institute of Fundamental Research, Homi Bhabha Road, Colaba, Mumbai - 400 005) : Performance studies of the PACT experiment. Bull Astr Soc India 2002, 30(1), 367-71.

Monte Carlo calculations have been done to understand various characteristics like the energy threshold, collection area etc of the recently commissioned PACT. The energy threshold of the array for gamma rays is found to be about 900 GeV. A larger collection area than many other experiments is a reflection of the large extant of the array.

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000164   Vishwanath P R (Tata Institute of Fundamental Research, , Colaba, Mumbai-400 005) : Very high energy γ-rays from Galactic sources. J Astrophys Astr 2002, 23(1-2), 45-51.

The field of Very High Energy (VHE) gama ray astronomy using the Atmospheric Cerenkov Technique has entered an interesting phase with detection of various galactic and extragalactic sources. Among galactic sources, only the Crab nebula has been established as a standard candle. Most observations on pulsars are in agreement as to the necessity for the GeV spectra to steepan at <60>200 GeV. While the Imaging method for increase of sensitivity has been successful with many results, an alternate technique-Wavefront Sampling Technique - is also being used by an increasing number of experiments. The recently commissioned experiment at Pachmarhi (PACT) in India is presented as an example of this technique. Preliminary results from this experiment show detection of VHE γ-ray emission from the Crab nebula at a high significance and Crab and Geminga pulsars at <62> 1.5 TeV which could be the second component of the Outer Gap pulsar models.

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000163   Vishwanath P R (NO, Tata Institute of Fundamental Research, Homi Bhabha Road, Mumbai 400 005) : Review of obervational results on very high energy (99>(F255>-ray emission from pulsars. Bull Astr Soc India 2002, 30(1), 95-104.

Radio pulsars have played a very important part in the growth of VHE (Very high energy) χ-ray astronomy. Apart from their ability to accelerate particles to very high energies, the modest sensitivity of the first generation atmospheric Cerenkov telescopes could be increased with the time signature of the pulsars. The main inference from the telescopes of the 80s was that the time-averaged emission spectra from the lower energies had to steepen in the GeV-TeV energy region. This conclusion has been reinforced in the 90s from experiments with much better sensitivities. However, results from several experiments from the past and the more sensitive experiments at present can be reconciled by invoking a possibly different component arising in the TeV region.

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000162   Viotti R F;Antonelli L A;Rebecchi S;Rossi C (Istituto di Astrofisica Spaziale, CNR, 00133 Roma, Italy, , ) : High energy phenomena in Eta Carinae. J Astrophys Astr 2002, 23(1-2), 19-22.

Investigates with BeppoSAX the long term behaviour of the harder X-ray component of the supposed supermassive binary system η Car along its 5.52 year cycle. In March 1998 during egress from the last December 1997 eclipse, this component was the same as outside eclipse, but for a large (x 3.5) increase of NH_h, that can be attributed to the presence or formation of opaque matter in front of the source near periastron. Unexpectedly, at that time the iron 6.7 ke V emission line was 40% stronger. BeppoSAX has for the first time found hard X-ray tail extending to at least 50 keV, that cannot be adequately fitted with an additional hotter thermal component. The 2-100 keV spectrum of η Car is instead well fitted with an absorbed power law spectrum with photon index 2.53, suggesting non-thermal emission as an alternative model for the core source.

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000161   Vinod Krishan (Indian Institute of Astrophysics, , Bangalore - 560 034) : Compton cross sections in highly dense plasmas. Bull Astr Soc India 2002, 30(1), 261-8.

The properties of the electromagnetic radiation undergo a fundamental change in the presence of a medium in general and a plasma in particular. Specially the dispersion relation is modified in a way that in a plasma, the square of the four-momentum of a photon is not zero. In an unmagnetized plasma, it is equal to the square of the plasma frequency. Further, the electron-photon coupling vertex along with the energy momentum conservation laws are also modified if the Compton processes occur in a plasma. As a result the cross sections of the three Compton processes, viz., the Compton scattering, the electron-position pair annihilation and production become functions of the plasma density. The cross sections are found to change significantly in highly dense plasmas.

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000160   Verma M K (Physics Dep, Indian Institute of Technology, Kanpur-208 016) : On generation of magnetic field in astrophysical bodies. Curr Sci 2002, 83(5), 620-2.

Comparison has been made in the energy transfer rates in magnetohydrodynamic turbulence using field-theoretic method. Calculation shows that there is a large energy transfer rate from the large-scale velocity field to the large-scale magnetic field. The growth of large-scale magnetic energy is primarily due to this transfer. The above conclusion was reached without any linear approximation like that in α-dynamo.

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000159   Upadhya S S et al (NO, Tata Institute of Fundamental Research, Homi Bhabha Road, Colaba, Mumbai - 400 085) : Distributed data acquisition system for Pachmarhi array of Cerenkov telescope. Bull Astr Soc India 2002, 30(1), 411-6.

Pachmarhi Array of Cerenkov Telescopes consists of 25 Telescopes distributed within an area of 8000 m². The array is divided into 4 sectors. The array was designed to detect and process faint Cerenkov light flashes that lasts for a few nanoseconds, produced in the atmosphere by celestial VHE χ-rays or cosmic rays. The arrival time and amplitude of fast tiny pulses were measured and recorded from each of 175 photo-tubes in a shortest possible time. A distributed Data Acquisition System and a Master Data Acquisition System. The distributed data acquisition and monitoring system were built using PC's which are networked through LAN. The entire software for DDAS was developed in-house in C language under LINUX environment. Most of the hardware were designed and fabricated in-house. The design features, implementation strategy as well as the performance of the whole system have been discussed.

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000158   Tonwar S C (NO, Tata Institute of Fundamental Research, Mumbai) : Cosmic ray astrophysics in the knee region and implications for gamma ray astronomy. Bull Astr Soc India 2002, 30(1), 147-61.

Following the discovery of ultra high energy cosmic rays with energies of PeV and higher in the 1950's and detailed studies on the energy spectrum in the TeV-PeV-EeV regions in 1960's there has been enormous interest in learning about the nature of astrophysical sources capable of accelerating particles to these extremely high energies and about their propagation in the interstellar and intergalactic space. Direct observational studies on cosmic ray sources through detection of PeV energy χ-rays have yielded very scanty information due to the absence of steady sources above the presently detectable flux limits. Therefore , indirect information on the nature of cosmic ray sources and acceleration processes has to be obtained from measurements on the energy spectra of various nuclear groups. The presence of the `knee` at E ~ 3 x 10¹⁵eV is very significant and it is important to obtain accurate information on the chemical composition of cosmic ray flux around the `knee` to understand the nature of cosmic ray sources contributing to this part of the energy spectrum. The present status of UHE χ-ray astronomy has been summarised and some of therecent experimental results on energy spectra and composition have been discussed.

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000157   Tickoo A K et al (Bhabha Atomic Research Centre, Nuclear Research Laboratory, Mumbai - 400 085) : Towards absolute gain calibration of the TACTIC imaging element. Bull Astr Soc India 2002, 30(1), 381-4.

Imaging element of the 4-element TACTIC telescope array has been in operation at Mt. Abu since 1987, for carrying out detailed investigations of χ-ray sources in the TeV energy range. In order to characterize the progenitor particle (χ-ray / cosmic ray), a relative gain calibration system, based on a high intensity LED, has been in operation. However, for calorimetric purpose, an absolute gain calibration system is necessary and has been developed for on-line calibration of 4 out of 349-pixels of its imaging camera, using Am²⁴¹ -based light pulsers. The details of the scheme followed and the results obtained so far are presented.

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000156   Suthar R L;Guha S;Biswas P K;Koul R;Aggarwal N K (Bhabha Atomic Research Centre, Central Workshop, Mumbai-400 085) : Mechanical design improvements in the "TACTIC" gamma ray telescope. Bull Astr Soc India 2002, 30(1), 407-9.

The basic mechanical design of the TACTIC (TeV Atmospheric Cerenkov Telescope with Imaging Camera) telescope was received from the Lebedev Institute of the Academy of Physical Sciences, Moscow, in November 1990. A large number of mechanical design improvements and additions were incorporated in the basic design of the telescope and the first (Imaging) unit of an array of four telescopes was made operational in 1997. Three Vertex units were erected thereafter and are operational at present. Improvements/additions incorporated in the TACTIC array of four telescope have been described.

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000155   Suthar R L;Guha S;Bandopadhyay K;Manjunatha A;Mishra V K;Koul R;Bhat C L (Central Workshop, Nuclear Research Laboratory, Bhabha Atomic Research Centre, Trombay, Mumbai 400 085) : Salient mechanical design features of the proposed 17 meter diameter MACE imaging gamma-ray telescope. Bull Astr Soc India 2002, 30(1), 223-7.

A low-threshold energy, high-sensitivity χ-ray telescope MACE (for Major Atmospheric Cerenkov Experiment) is proposed to be built in India for explorations of χ-ray sky in 100's keV - 10's GeV photon energy range, hitherto inaccessible from ground. Mechanical design aspects of this major telescope and the scientific motivation have been dealt with.

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000154   Sreekumar P (NO, ISRO Satellite Centre, Bangalore-560 017) : Diffuse gamma ray emission: Implications on cosmic ray origin. Bull Astr Soc India 2002, 30(1), 61-71.

The Compton Gamma Ray Observatory (CGRO) produced the first full sky survey in gamma rays resulting in significantly improved data on the spectral and spatial distribution of diffuse gamma-rays from the galaxy of the sun. The intense diffuse gamma-ray emission arising from the Galaxy is understood as primarily arising from the interaction of energetic cosmic rays with the interstellar matter and radiation and is an excellent tool to study cosmic ray spectral characteristics and its distribution within the Galaxy. Comparison of the new data with simple cosmic ray models have led to important conclusions on the spectrum of cosmic-ray protons and electrons. Current understanding of these models and its implications for a galactic origin of cosmic rays have been discussed,

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000153   Sreekantan B V (NO, National Institute of Advanced Studies, I.I.Sc Campus, Bangalore - 560 012) : Historical aspects of gamma ray astronomy. Bull Astr Soc India 2002, 30(1), 5-10.

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000152   Smith D A (NO, Centre d'Etudes Nucleaires de Bordeauz-Gradignan, ) : Non-imaging gamma ray telescopes. Bull Astr Soc India 2002, 30(1), 183-92.

Despite continual improvement of the Atmospheric Cherenkov Technique, the number of astrophysical gamma ray sources that have been studied from the ground remains small (less than a half-dozen), due mainly to the nature of the cosmic accelerators themselves. For most Active Galactic Nuclei of the blazar class, the energy range in which imagers are sensitive lies beyond the inverse Compton peak, where the flux falls rapidly with increasing energy. A few galactic sources are very bright in EGRET but the spectra roll over (e.g. Geminga), while many have no break in the EGRET data but are intrinsically weak. The Crab nebula is an exception, along with some others. Increasing the data sample thus requires a lower energy threshold, increased flux sensitivity, or a combination of the two. Long term progress will come with the imager arrays (HESS & VERITAS, beginning in 2002). Reviews work-in-progress aimed at reaching the 50 GeV range using solar plants.

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000151   Sinha S;Sreekumar P;Kasturirangan K (ISRO Satellite Center, , Bangalore-560 017) : SROSS C-2 detection of gamma ray bursts and the SGR 1627-41. J Astrophys Astr 2002, 23(1-2), 73-9.

The GRB monitor (GRBM) on board the Indian SROSS C-2 satellite has detected 53 classical gamma ray bursts since its launch in May, 1994 till its re-entry in July, 2001. For a subset of 26 events, locations were obtained from simultaneous observations by other gamma-ray detectors in space. The sky distribution of these 26 SROSS C-2 bursts is consistent with isotropy. The distribution of event durations shows evidence for bimodality. There is an evidence for a moderate hardness ratio-intensity (HIC) correlation in the data. The SROSS C-2 GRBM has also detected three episodes of emission from the SGR 1627-41.

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000150   Sinha S (ISRO Satellite Centre, , Bangalore-560 017) : Exact solution of the gamma ray burst arrival time analysis problem. J Astrophys Astr 2002, 23(1-2), 129-35.

An analytical solution of the GRB arrival time analysis is presented. The errors in the position of the GRB resulting from timing and position errors of different satellites are calculated. A simple method of cross-correlating gamma ray burst time-histories is discussed.

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000149   Shanthi K;Kaul C L;Kaul R K;Tickoo A K;Bhat C L (NO, Academic Staff College, Mumbai Univ, Mumbai) : Gamma ray bursts at high energies: detection ranges and event rates. Bull Astr Soc India 2002, 30(1), 422-34.

The Gamma-Ray Burst (GRB) detection rates at energies ≥ 20 GeV, have been estimated for the 3 atmospheric Cerenkov telescope systems of the GRACE project at Mt. Abu, under the assumption that the bursts have a cosmological origin and a continuous power-law spectrum in the MeV-TeV energy range. The attenuation of high energy gamma-ray photons in a burst, during its propagation in the intergalactic space, has been taken into account by assuming two extreme scenarios of the Extragalactic Background Radiation (EBR) fields.

1 illus, 11 ref

000148   Shanth K;Bhat C L (Academic Staff College, University of Mumbai, Mumbai - 400 098) : Reclassification of gamma ray burst based on their brightness distributions. Bull Astr Soc India 2002, 30(1), 445-8.

Reclassification of the cosmic gamma-ray bursts has been done into two distinct classes on the basis of their brightness distributions. While one class is found to be compatible with a homogeneous and monoluminosity source population with simple cosmological effects folded into the brightness distribution function, the other, smaller population is not consistent with such a scenario and may need a consideration of source evolutionary effect.

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000147   Sarala S;Jain P (Physics Department, IIT, Kanpur-208 016) : Circular statistical method for extracting rotation measures. J Astrophys Astr 2002, 23(1-2), 137-41.

Proposes a new method for the extraction of Rotation Measures from spectral polarization data. The method is based on maximum likehood analysis and takes into account the circular nature of the polarization data. The method is unbiased and statistically more efficient than the standard X² procedure.

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000146   Sapru M L;Satyabhama N;Koul M K;Tickoo A K; Bhat C L (Bhabha Atomic Research Centre, Nuclear Research Laboratory, Mumbai - 400 085) : Threshold energy estimates of TACTIC array. Bull Astr Soc India 2002, 30(1), 435-40.

Using the CORSIKA-code based simulation studies, results on the χ-ray and the cosmic-ray proton trigger-thresholds for the Imaging-Element and the 3 Vertex-Elements of the TACTIC atmospheric Cerenkov telescope array have been presented. The thresholds have been derived for several, potentially useful trigger-configurations.

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000145   Sahni V C (Physics Group, Bhabha Atomic Research Centre, Trombay, Mumbai 400 085) : The GRACE facility. Bull Astr Soc India 2002, 30(1), 213.

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000144   Sagar R (NO, Indian Institute of Astrophysics, Bangalore - 560 054) : Observations of GRB afterglows from Nainital: evidence in favour of jet model. Bull Astr Soc India 2002, 30(1), 237-48.

Broad band optical photometric observations of five Gamma-ray burst (GRB) afterglows (GRB 990123, GRB 991208, GRB 991216, GRB 000301 and GRB 000926) are taken from Nainital during 1999 and 2000. These in combination with the published observations including at other wavelengths are used to study their flux decays, broad spectral energy distributions and energetics in the light of fireball plus blast wave synchrotron emission models. Their early time flux decay constant is ~ 1.1 which becomes ≥ 2 at later times. All are having a relatively flat spectral index with values ranging from 0.73 to 0.95. Observations of these afterglows support the model of non-isotropic synchrotron emission from the centre of these GRBs which reduces the budget of isotropic energy emission from <62> 10⁵³ erg to 10⁵² erg. This, as well as the other observations indicate that GRBs originate most likely from the collapse of massive stars rather than the merging of compact objects.

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000143   Sachdev S;Uday Shankar N (NO, Raman Research Institute, Sadashivanagar, Bangalore-560 080) : Wide-field imaging with the Mauritius radio telescope. J Astrophys Astr 2001, 22(2-3), 229-49.

Mauritius Radio Telescope (MRT) is a Fourier Synthesis T-shaped array operating at 151.5 MHz. The primary objective of the telescope is to produce a sky survey in the declination range - 70° to -10°. A 512 channel digitial complex correlation receiver is used to measure the visibility function. The visibilities have to be measured with four different delay settings to image the entire declineation range, keeping the effects of band width decorrelation to less than 20% on the longest baseline. To have a reasonable surveying sensitivity this has to be done in one observation schedule. However the existing correlator system which can measure visibility with only one presettable delay setting for each interaction time, cannot meet this requirement. A recirculator system which enables visibility measurements with four different delay settings in one integration time using the existing correlator has been designed and installed to mkae the MRT an efficient surveying instrument. Describes the recirculator system, and the scheme that use a MRT to calibrate the visibilities measured with different delay setting. The observations carried out for the full sky survey and a section of the wide field image made using the new system are described.

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000142   Sachdev S;Uday Shankar N (NO, Raman Research Institute, Sadashivanagar, Bangalore-560 080) : Detection, excision and statistics of interference at the Mauritius radio telescope. J Astrophys Astr 2001, 22(2-3), 213-27.

A technique to detect man-made interference in the visibility data of the Mauritius Radio Telescope (MRT) has been developed. This technique is based on the understanding that the interference is generally `spiky' in nature and has Fourier components beyond the maximum frequency which can arise from the radio sky and can therefore be identified. The sum of magnitude of visibilities on the baselines measured at a given time to improve detectability is taken. This is then high-pass filtered to get a time series from which the contribution of the sky is removed. Interference is detected in the high-pass data using an iterative scheme. In each iteration, interference with amplitudes beyond a certain threshold is detected. These points are then removed from the original time series and the resulting data are high-pass filtered and the process repeated. Studies the statistics of the strength, numbers time of occurrence and duration of the interference at the MRT also. The statistics indicate that most often the interference excision can be carried out while post-integrating the visibilities by giving a zero weight to the interference points.

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000141   Roychowdhury S;Nath B B (Raman Research Institute, , Bangalore-560 080) : Heating of the intracluster medium by quasar outflows. J Astrophys Astr 2002, 23(1-2), 101-05.

Studies the possibility of quasar outflows in clusters and groups of galaxies heating the intracluster gas in order to explain the recent observation of excess entropy in this gas. Shows that radio galaxies alone cannot provide the energy required to explain the observations but the inclusion of Board Absorption Line (BAL) outflows can do so, and that in this scenario most of the heating takes place at Z <126> 1-4, the `preheating' epoch being at a lower redshift for lower mass clusters.

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000140   Rowell G P (Max Planck Institut fur Kernphysik, , D-69029 Heidelberg) : Cosmic rays from SNRs and TeV gamma-ray astronomy. Bull Astr Soc India 2002, 30(1), 25-35.

Origin of Galactic cosmic rays is still a burning question that forms a major motivation for developments in ground-based gamma-ray astronomy. SNRs are long-thought to be sites for the acceleration of Galactic cosmic rays, and evidence for gamma-ray and non-thermal X-ray production from some SNRs suggest that they may be capable of accelerating particles to multi-TeV energies. Yet, along with this, and in the same overall model framework (diffusive shock acceleration), is the need to accommodate upper limits at TeV energies imposed on other examples. This review presents an update on the status of SNR observations at TeV energies, their interpretation, and discusses the relevant parameters and issues of next generation ground-based instruments relating to their ability to confirm SNRs as Galactic cosmic ray sources.

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000139   Razdan A;Haungs A;Rebel H;Bhat C L (Nuclear Research Laboratory, , BARC Mumbai - 400 085) : Novel image and non-image parameters for efficient characterisation of atmospheric Cerenkov images. Bull Astr Soc India 2002, 30(1), 357-60.

Comparative study of the classification potential of various image and non-image parameters which are measurable with the TACTIC array focal plane instrumentation has been made. The image parameters include conventional Hills parameters and multifractal dimensions and wavelet moments. Similarly the parameters derived from non-image Cerenkov data consist of pulse profile rise time and base width and the relative ultraviolet to visible light fluxes off the Cerenkov events. It is shown by the artificial neural net approach that suitable combinations of these parameters can bring about an efficient segregation of various event types, even for modest sized data samples of progenitor gamma-rays and cosmic ray hadrons.

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000138   Ramaprakash A N (Inter University Centre for Astronomy and Astrophysics, , Pune - 411 007) : Multi-band monitoring and polarimetry of GRB afterglows with the IUCAA telescope. Bull Astr Soc India 2002, 30(1), 249-54.

The IUCAA 2m telescope which is scheduled to be available for observations in early 2002, will initially have two instruments at its f/10 Cassegrain focii - the IUCAA Faint Object Spectrograph Camera (IFOSC) and the Near Infrared PICNIC Imager (NIPI). Both of these instruments are planned to have polarimetric capabilities too, with the ability to measure two orthogonal polarization components simultaneously. Apart from monitoring the afterglow light curves, these instruments will provide the opportunity to observe afterglow linear polarization and perhaps its variation. Such observations are necessary to constrain the large number of models that have been suggested predicting afterglow polarization. Measurement of polarization will also provide a better handle in understanding the beaming nature or otherwise of GRB ejecta.

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000137   Rakshit S;Deodhare D (Centre for Art Intell & Robotics, , Bangalore-560 001) : Algorithm for fast registration of radar images. Def Sci J 2002, 52(3), 243-51.

Radar imagery provides an all-weather and 24h coverage, making it ideal for critical defence applications. Multiple images need further processing. Such situation arise for battlefield surveillance based on satellite imagery. The registration has to be done between an earlier (reference) image and a new (live) image. The registration transformation is mainly a global translation. Radar images are not as feature-rich as optical images and the image content variation can be as high as 90 per cent. Seasonal variations can significantly alter the radar signatures of ground, vegetation, and water bodies. This necessitates a novel approach different from the techniques developed for optical images. An algorithm has been developed that leads to fast registration radar images, even in the presence of specular noise and significant scence content variation. The key features of this approach are adaptability to sensor/terrain types, ability to handle large content variations and false positive rejection. Shows that this algorithm allows for various cost-performance trade-offs, making it suitable for a wide variety of applications. The algorithm, in various cost-performance configurations, is tested on a set of ERS images. Results of such tests have been reported, indicating the performance of the algorithm for various cost-performance trade-offs.

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000136   Rahman M A;Bhat P N;Acharya B S;Chitnis V R (NO, Tata Institute of Fundamental Research, Colaba, Mumbai - 400 005) : Gamma ray and hadron generated Cerenkov photon spectra at various observation altitudes. Bull Astr Soc India 2002, 30(1), 335-40.

Studies the propagation of Cerenkov photon generated by very high energy χ-rays and hadrons in the atmosphere. Photon production height distributions derived from semi-empirical methods agreed with those obtained by Monte Carlo simulations. The Cerenkov photon spectra at various observation altitudes were obtained after applying wavelength dependent corrections for the attenuation of photons in the atmosphere. The calculations were done both for χ-ray and hadron primaries of various energies. The spectra were found to be dependent on altitude as well as primary energy. The peak of the photon spectrum seemed to shift towards the shorter wavelength with increasing primary energy at a given altitude. The fraction of the UV component in the Cerenkov spectrum was estimated. The hadron generated Cerenkov spectra were richer in UV light at higher altitude.

4 illus, 14 ref

000135   Porwal S;Pradhan B K;Sharma J K;Jain S C (Def Electronics Applic Lab, , Dehradun-248 001) : Search and render algorithm for three-dimentsional terrain visualisation of large dataset. Def Sci J 2002, 52(3), 277-84.

There exists a wide class of algorithm for 3-D modelling and visualisation of terrain. These techniques are not very useful for flight simulation application. A very large terrain has to be modelled for flight simulators and primitive techniques do not support large data handling. The terrain keeps on changing rapidly, so in flight simulator application, rendering of each frame must be very fast. Describes an algorithm which handles very large dataset and can generate 3-D frames quickly. A flight simulator application can be designed using this technique.

8 illus, 1 table, 10 ref

000134   Paul B;Kitamoto S (Tata Institute of Fundamental Research, Homi Bhabha Road, Colaba, Mumbai-400 005) : Superorbital period variations in the X-ray pulsar LMC X-4. J Astrophys Astr 2002, 23(1-2), 33-8.

Reports the discovery of a decay in the superorbital period of the binary X-ray pulsar LMC X-4. Combining archival data and published long term X-ray light curves, found a decay in the third period in this system (P <126> 30.3 day, P <126>-2x10^-5 ss^-1). Along with this result, a comparison of the superorbital intensity variations in LMC X-4, Her X-1 and SMC X-1 is also presented.

2 illus, 11 ref

000133   Pandey J C;Singh K P;Sagar R;Drake S A (State Observatory, , Naini Tal-263 129) : Photometric variability of four coronally active stars. J Astrophys Astr 2002, 23(1-2), 9-14.

Presents photometric observations of four stars that are optical counterparts of soft X-ray/EUV sources, namely 1ES 0829+15.9, 1ES0920-13.6, 2RE J110159+223509 and 1ES 1737+61.2. Discovered periodic variability in two of the stars, viz., MCC 527 (1ES 0829+15.9; Period = 0^d.828±0.0047) and HD 81032 (1ES 0920-13.6; Period = <126> 57.02±0.560 days). HD 95559 (2RE J110159+223509) is found to show a period of 3^d. HD 160934 (1ES1737+61.2) also shows photometric variability but needs to be monitored further for finding its period. These stars most likely belong to the class of chromospherically activer stars.

2 illus, 1 table, 10 ref

000132   Osborne J L;Aye M;Chadwick P M;Daniel M K; McComb T J L;McKenny J M;Nolan S J;Orford K J;Rayner S M (Physics Dep, University of Durham, South Road, Durham DH1 3LE, United Kingdom) : Importance of atmospheric monitoring in Cherenkov experiments. Bull Astr Soc India 2002, 30(1), 51-9.

A review is presented of Monte Carlo simulations of the effects of differing atmospheric structure and absorption models on the Imaging Atmospheric Cerenkov Telescope signal. Methods of monitoring the atmosphere are discussed.

^iia9 ref

000131   Negi D S;Kaushik V K;Manocha O P (Def Electronics Applic Lab, , Dehradun-248 001) : PAN-PAN change detection system for satellite imageries. Def Sci J 2002, 52(3), 329-36.

System has been built and tested for automated change detection between multi-temporal panchromatic images. Discusses the implementation issues, associated tools, and finally summarises initial tests on IRS 1C/1D and other high-resolution images. Key characteristics of this system are integration of technologies having high degree of registration, normalisation of the effects of radiometry; selectivity to specific type of changes, refinement of changes by thresholding, and assignment of presence and absence of object and tools for updation/deletion of change mask. A semi-automatic technique for selection of control points in an image having affine distortion has been implemented. Linear regression is used for normalisation of the images. Two change detection techniques, namely image subtraction and image rotatioing have been used to find the global change mask. Selective threshold is used to generate target mask. Target mask is shown in two colours to depict presence and absence of the object. Method based on ratioing has been found to be more sensitive to spectral variations and provides better detection of changes.

11 illus, 6 ref

000130   Narasimha D;Kanekar N;Chengalur J N (Tata Institute of Fundamental Research, , Mumbai-400 005) : Tracking the shadows through GMRT. J Astrophys Astr 2002, 23(1-2), 165-71.

The structures of faint high redshift galaxies cannot be observed directly. But if a luminous quasar is located farther along their line of sight, high resolution absorption lines offer a valuable and reliable probe to their structure. GMRT is suited to monitor the absorption spectra, if the redshifted neutral hydrogen or OH doublet fall in one of the windows of the telescope. OH doublet absorption spectra for the system B0218+357, taken at GMRT this year at resolution of approx. 9.5 km/sec with an rms noise of the order of 1 mJy have been presented. Based on the study of the OH doublet and 21 cm neutral hydrogen line it has been infered that, in the lensing spiral galaxy of B0218+357, neutral hydrogen and OH coexist in tenous clouds and there is possibly a hole in the central part of the galaxy. In constrast, the gas is seen in high density clouds in the lens in an otherwise similar system PKS1830-211

2 illus, 3 ref

000129   Nandi A;Chakrabarti S K (S N Bose National Centre for Basic Science, Salt Lake, Calcutta-700 098) : Understanding the behavior of high enrgy X-rays from the black hole candidate GRS 1915+105. Bull Astr Soc India 2002, 30(1), 327-30.

Black Hole candidate GRS 1915+105 shows a very interesting behaviour at high energy X-rays. It shows Quasi-Periodic Oscillations (QPO) at high energies. The spectral slopes at high energies vary and carry information about the winds and jets produced at the centrifugal barrier. These aspects of the observations with explanation from theoretical models have been discussed.

2 illus, 11 refs

000128   Nair S (Raman Research Institute, , Bangalore-560 080) : Class B 1359+154: modelling lensing by a group of galaxies. J Astrophys Astr 2002, 23(1-2), 115-8.

The recently discovered gravitationally lensed system CLASS B1359+154 appears to have six detectable images of a single background source at a redshift of 3.235. A group of galaxies acts as the lens, at a redshift of <126> 1. Identifies two distinct, physically plausible image configurations, a 7-image one and a 9-image one. Mass models are constructed corresponding to realizations of these two configurations. Both models call for, in addition to non-singular galaxy-type lenses, a larger scale mass component that resembles the extended dark matter distributions seen in relatively low-redshift galaxy groups. It is observationally impossible to study the extended X-ray emission from a group at such a high redshift, hence lensing studies are of some interest. A lensed system with a high image multiplicity does not necessarily admit of a unique lensing interpretation; discrimination is possible with additional observable details.

4 illus, 5 ref

000127   Naik S;Paul B (Tata Institute of Fundamental Research, , Mumbai-400 005) : Spectral properties of the X-ray binary pulsar LMC X-4 during different intensity states. J Astrophys Astr 2002, 23(1-2), 27-31.

Presents spectral variations of the binary X-ray pulsar LMC X-4 observed with the RXTE/PCA during different phases of its 30.5 day long third period. Only out-of-eclipse data were used for the study. The 3-25 keV spectrum, modeled with high energy cut-off power-law and iron line emission is found to show strong dependence of the intensity state. Correlations between the Fe line emission flux and different parameters of the continuum are presented.

2 illus, 15 ref

000126   Nagase F (The Institute of Space and Astronautical Science, , Japan) : Spectroscopic studies of X-ray binary pulsars. J Astrophys Astr 2002, 23(1-2), 59-65.

Several new features of X-ray binary pulsars are revealed from recent observations with ASCA, RXTE, BeppoSAX and other X-ray observatories. Among these, some recent progress in spectroscopic studies of accreting X-ray pulsars in binary systems (XBPs) are reviewed. Discussed soft excess features observed in the energy spectra of XBPs and proposed that it is a common feature for various sub-classes of XBPs. Presented some recent results of high resolution spectroscopy with ASCA and Chandra.

2 illus, 32 ref

000125   Murthy J (Indian Institute of Astrophysics, Koramangala, , Bangalore-560 034) : Upper limits on O VI emission from Voyager observations. J Astrophys Astr 2002, 23(1-2), 23-6.

Examined 426 Voyager fields distributed across the sky for O VI (<108><108> 1032/1038 Angstrom) emission from the Galactic diffuse interstellar medium. No such emission was detected in any of our observed fields. Most constraining limit was a 90% confidence upper limit of 2600 photons cm^-2sr^-1s^-1 on the doublet emission in the direction (1, b)=(117.3, 50.6). Combining this with an absorption line measurement in nearly the same direction allows us to place an upper limit of 0.01 cm^-3 on the electron density of the hot gas in this direction. Placed 90% confidence upper limits of less than or equal to 10,000 photons cm^-2sr^-1s^-1 on the O VI emission in 16 of our 426 observations.

1 illus, 1 table, 15 ref