000124   Mukhopadhyay P K (Electronics division, Bhabha atomic research centre, Trombay, Mumbai - 400 085) : Signal processing instrumentation of gamma - ray telescopes of the GRACE Project. Bull Astr Soc India 2002, 30(1), 215-21.

The TACTIC Cerenkov telescope has recently been commissioned at Mt. Abu, Rajasthan. The signal processing electronics of the 349 element imaging camera was a totally indigenous development. A number of groups from Electronics Division and NRL, BARC participated in the development of the various subsystems of the imaging camera which included multichannel detector bias supply, fast amplifier, charge to digital converter, 50MHz scaler, programmable trigger generator and acquisition electronics. Most of the multichannel electronic modules followed either the NIM or the CAMAC standard. In the second phase of GRACE project, two further telescopes, namely MACE and MYSTIQUE have been proposed.

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000123   Mukherjee R (Dep of Physics and Astronomy, Barnard College, Columbia University, New York, NY 10027, USA) : EGRET gamma-ray sources: observations and physics. Bull Astr Soc India 2002, 30(1), 73-83.

High energy astronomy above 30 MeV received a significant impetus from the observations of EGRET (Energetic Gamma-Ray Experiment Telescope) onboard the Compton Gamma Ray Observatory (CGRO). Until June 2000, when CGRO was de-orbitted, EGRET produced a wealth of important astrophysical results, and was responsible for the detection of more than 270 point sources of γ-rays. These sources include active galaxies, pulsars, the normal galaxy LMC, as well as the large majority of sources that remain unidentified. In addition , EGRET has detected the high energy emission from a few γ-ray bursts (GRBs). Reviews some of the important results from EGRET.

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000122   Mitra A (Theoretical Physics Division, , BARC, Mumbai - 400085) : On the nature of the compact condensations at the centre of galaxies. Bull Astr Soc India 2002, 30(1), 173-82.

There are many observational evidences for the existence of massive compact condensations in the range 10⁶-10¹⁰ M at the core of various galaxies and in particular in the core of High Energy Gamma Ray emitting galaxies. At present such condensations are commonly interpreted as Black Holes (BHs). While such Black Hole Candidates (BHCs) must be similar to BHs in many respects, they, actually, can not be BHs because existence of Black Holes would violate the basic tenet of the General Theory of Relativity (GTR) that the worldline of a material particle must be timelike at any regular region of spacetime. On the other hand, general relativistic collapse of massive bodies should lead to EternallyCollapsing Configurations (ECOs). While ECOs may, have strong intrinsic magnetic field. Despite many practically be as compact as corresponding BHs, they will have a physical surface. Also while BHD do not have any intrinsic magnetic field, ECO's may claims actually there is no real evidence for the "Event Horizon" (EH) of supposed BHs and on the other hand, there are tentative evidence for the existence of strong magnetic field in several BHCs (or ECOs). The presence of such intrinsic magnetic field may render the task of explaining high energy radiation phenomenon in many Active Galactic Nuclei easier.

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000121   Mayya Y S;Srivatsava G P;Koul R (Bhabha Atomic Research Centre, Control Instrumentation Division, Mumbai 400 085) : MACE telescope: Servo design aspects. Bull Astr Soc India 2002, 30(1), 229-35.

The design parameters of the servo system for the MACE imaging Cerenkov telescope, based on functional, performance, operational and safety requirements of the system are briefly discussed. The servo system is designed around electronically commutated motors using fully digital controllers, pc - compatible hardware and software and ethernet connectivity for remote monitoring and control.

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000120   Manna A;Chakrabarti S;Mukhopadhayay p (Bhabha Atomic Research Centre, Electronics Division, Mumbai - 400 008) : A new computer-controlled multi-channel high voltage supply system for GRACE. Bull Astr Soc India 2002, 30(1), 425-8.

The high energy gamma ray telescopes being set up by the Bhabha Atomic Research Centre (BARC) at Mt. Abu, Rajasthan, as part of the GRACE project, require a very large number (~ 1000) of programmable high voltage power supplies for biasing photomultiplier tubes for the detection and characterization of the atmospheric Cerenkov events. These HV supplies need to be very compact, lightweight and rugged, as they will be mounted on the base of the moving telescopes. Describes the design aspects of the overall HV system and the performance of the prototype HV supplies Each HV modules have been developed for such applications. In the new design, the inverter switching frequency of the HV supplies has been increased threefold as compared to the earlier design, and surface mounted devices have been used to achieve overall size and weight reductions. The system consists of multiple HV modules, each containing 16 independently programmable HV module has an on-board micro-controller for doing control and supervisory functions and is interconnected via a serial I²C bus. The HV supplies have built in over voltage/current, thermal overload protections with output voltage readback and adjustable slew rate control facilities.

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000119   Maneva G M;Temnikov P P (NO, Institute for Nuclear Research and Nuclear Energy, 72 Tzarigradsko chaussee Blvd., 1784 Sofia, Bulgaria) : Application of neural network for the gamma-hadron discrimination. Bull Astr Soc India 2002, 30(1), 255-60.

Artificial Neural Network (ANN) method is applied for the analysis of raw data from the gamma ray CELESTE experiment. Preliminary results show that, in the energy range 30-300 GeV, a good discrimination between showers generated by primary photons or hadrons could be obtained.

4 illus, 9 ref

000118   Manchanda R K (NO, Tata Institute of Fundamental Research, Colaba, Mumbai 400 005) : Hard X-ray spectrum of Mkn 421 during the active phase. J Astrophys Astr 2001, 22(2-3), 145-154.

Spectral measurement of Mkn 421were made in the hard X-ray energy band of 20-200 ke V using a high sensitivity, large area scintillation counter telesope on November 21, 2000 and these coincided with the onset of an active X-ray phase as seen in the ASM counting rates on board RXTE. The observed spectrum can not be fitted to a single power law similar to the PDS data of Beppr oSAX. The data can be fitted both by a two component power law function or a combination of an exponential function with a power law component at the high energies above 80 ke V. Identifies these components with those arising from the synchrotron self Compton and the high energy power-law tail arising from the upgrading of the thermal photons due to multiple Compton scattering a la Cyg X-1. A comparision with the earlier data clearly suggests a spectral variability in the hard X-ray spectrum of the source. Proposes a continuously flaring geometry for the source as the underlying mechanism for energy release.

3 illus, 27 ref

000117   Majumdar P;Acharya B S;Bhat P N;Chitnis V R; Rahman M A;Singh B B;Vishwanath P R (NO, Tata Institute of Fundamental Research, Homi Bhabha Road, Colaba, mumbai - 400 085) : Angular resolution of Pachmarhi array of Cerenkov telescopes. Bull Astr Soc India 2002, 30(1), 389-75.

Pachmarhi Array of Cerenkov Telescopes (PACT) consisting of a distributed array of 25 telescopes is used to sample the atmospheric Cerenkov Photon showers. The shower front is fitted to a plane and the direction of arrival of primary particle is obtained. The accuracy in the estimation of the arrival direction of showers has been estimated to be ~ 0°.1 using `split` array method.

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000116   Le Gallou R;Smith D A (NO, Centre d'Etudes Nucleaires de Bordeaux, Gradignan-33175 France) : Observations of Mrk 421 with the CELESTE Heliostat Array. Bull Astr Soc India 2002, 30(1), 281-3.

Since CELESTE first began routine observations in November 1999 in the 50 GeV range Mrk 421 has been a prime target. Here the authors report the preliminary average integral flux measurement obtained with 31.5 hours of ON-source time of (7 ± 3) x 10^<-10> cm^<-2> s^<-1>.

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000115   LE Floc'h E;Mirabel I F;Duc P A (Service d'Astrophysique, CEA-Saclay, France, , ) : Preliminary results on VLT K-band imaging observations of GRB host galaxies. J Astrophys Astr 2002, 23(1-2), 119-22.

Obtained K-band imaging observations of Gamma-Ray Burst (GRB) host galaxies with the near-infrared spectro-imager ISAAC installed on the Very Large Telescope at Paranal (Chile). The derived K magnitudes, combined with other photometric data is used to investigate the R-K colors of GRB hosts. Did not find any extremely reddened starbursts in sample, despite the capability of GRBs to trace star formation even in dusty regions. Observed R-K colors are on the contrary typical of irregular and spiral blue galaxies at high redshift.

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000114   Le Coultre P (ETH, , CH-8093 Zurich, Switzerland) : Astronomy with charged particles. Bull Astr Soc India 2002, 30(1), 163-72.

The L3+C experiment takes advantage of the high precision muon spectrometer of the L3 detector installed at LEP, CERN, Geneva, to measure precisely cosmic ray muons. Several physics topics in the field of astrophysics and particle physics are being studied. A description of the detector is given. The possibility to record high energy gamma ray bursts, or burst signal from point sources is discussed.

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000113   Lazzati D (Institute of Astronomy, University of Cambridge, Madingley Road, CB3 OHA Cambridge, England) : The importance of multispectral band observations of gamma-ray bursts. Bull Astr Soc India 2002, 30(1), 11-6.

Gamma-Ray Bursts are one of the best examples to show how multiwavelength observations can help in our understanding of the universe. Gamma-Ray Bursts were a mystery for more than thirty years, during which they could be observed only in the hard X-ray/soft γ-ray band. Nowadays, bursts are observed from the gamma-ray to the optical frequencies and a completely new phenomenon, the afterglow, is observed down radio frequencies. This extension of the band led to a much deeper understanding of the bursts. The importance of the multiwavelength observations that led to the present understanding of the bursts have been shown, as well as the possible new observations that are foreseen to clarify some obscure points of the burst and afterglow astrophysics.

44 ref

000112   Kulgod S V;Pious L;Chadda V K;Kaul S R;Yadav K K;Koul R (Bhabha Atomic Research Centre, Nuclear Research Laboratory, Mumbai - 400 085) : Active mirror alignment control system for the MACE telescope. Bull Astr Soc India 2002, 30(1), 421-4.

The conceptual design of an active mirror control system for the MACE telescope, being set up by the Bhabha Atomic Research Centre at Mt. Abu is described. Preliminary results obtained from recent laboratory trials are also described.

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000111   Koul M K;Charagi S K;Rannot R C;Sapru M L; Bhat C L (Bhabha Atomic Research Centre, Nuclear Research Laboratory, Mumbai - 400 085) : Optimum image parameter ranges for TACTIC imaging element; guidance from simulations. Bull Astr Soc India 2002, 30(1), 361-6.

Present some results on the performance characteristics of the TACTIC Imaging Element (IE) as predicted by extensive simulation studies. The main features studied are the optimum image parameter ranges for selection of gamma-ray showers from point-sources, corresponding Quality factor (Q) and the gamma-ray image threshold energy of the experiment.

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000110   Koul D K;Koul M K;Tickoo A K;Bhat C L (Bhabha Atomic Research Centre, Nuclear Research laboratory, Mumbai - 400 085) : Spot size of 17m-diameter MACE reflector in presence of surface inaccuracies. Bull Astr Soc India 2002, 30(1), 373-6.

The MACE (for Major Atmospheric Cerenkov Experiment), an imaging Cerenkov telescope for gamma-ray astronomy investigations in the sub-TeV energy bracket, plans to use a 17 m-diameter high quality reflecter mounted with a high definition imaging camera in its focal plane. The spot size of the MACE has been estimated for, both, on- and off-axis cases, considering an ideal mirror surface. The effect on this spot-size due to surface smoothness errors has been investigated.

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000109   Kaul R K;Bhat C L (Bhabha Atomic Research Centre, Nuclear Research Laboratory, Mumbai-400 085) : Observations of Mkn 421 with TACTIC. Bull Astr Soc India 2002, 30(1), 297-300.

The TACTIC imaging element has observed the extragalactiv BL Lac object Mkn 421 for ~ 78h during Jan. - April 2001. Analysis of the overall data set, using the dynamic supercuts methodology, has revealed the presnece of a ~ 7.5 σ strong signal of Eγ≥ 1 TeV. The signal is found to be variable on a day-to-day basis and is more or less absent during April 2001.

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000108   Katysheva N A;Shugarov S Y;Pavlenko E P; Abolmasov P V (Sternberg Astronomical Institute, , Moscow, Russia) : The investigation of nova-like variable MV Lyr during the 1999-2001 years. J Astrophys Astr 2002, 23(1-2), 15-8.

Peculiar nova-like MV Lyr was investigated. The CCD-observations of MV Lyr were continued in Crimea during the outbursts and quiescent states. Last year its behavior became non-typical for `anti-dwarf novae'. The length of its first deep minimum was 10 years. A modern state is characterized by very strong outbursts and very often changes of the stages. The periods 0.^d 128 and 0.^d136 were obtained for 1998 and 1999 years accordingly. A relation between the photometric period and the brightness possibley exists.

3 illus, 9 ref

000107   Kamath K et al (Bhabha Atomic Research Centre, Nuclear Research Laboratory, Trombay, Mumbai - 400 085) : Large-area wide angle (LAWA) Cerenkov detector for MYSTIQUE array. Bull Astr Soc India 2002, 30(1), 377-80.

An ultra-sensitive, multidetector wide angle atmospheric Cerenkov telescope array is being set up at Mt. Abu for cosmic γ-ray studies in tens of TeV energy region. The design feature of the Cerenkov light detector, along with its efficiency, based on simulation and prototype testing studies, are presented.

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000106   Joshi U C;Baliyan K S;Ganesh S (Physical Research Laboratory, , Ahmedabad - 380 009) : Variability study of Mrk-421 in near IR bands from Mt. Abu observatory. Bull Astr Soc India 2002, 30(1), 301-4.

Mrk421 is the nearest, and brightest blazar detected in almost all the spectral windows, including high energy γ-rays. It exhibits short and long timescale variations at all frequency bands. Though it has been observed extensively at various wavebands, a lot more observations, preferrably simultaneous, are required to help understand the physical mechanisms of energy generation and structure of the relativistic jet by looking for correlations between the emissions at different wavelengths. Observations in near infrared made during April 23 - 27, 2001, using the Mt Abu IR Telescope (MIRT) have been reported. The source has been found to be in its quiescent phase during this observation period.

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000105   Hirotani K;Shibata S (NO, NASA/Goddard Space Flight Center, Greenbelt, MD 20771, USA) : Electrodynamic structure of an outer-gap accelerator: Gamma-ray emission from the crab pulsar. Bull Astr Soc India 2002, 30(1), 193-9.

A stationary pair production cascade in the outer magnetosphere of a spinning neutron star has been investigated. The charge depletion due to a global current, causes a large electric field along the magnetic field lines. Migratoryelectrons and/or positrons are accelerated by this field to radiate curvature gamma-rays, some of which collide with the X-rays to materialize as pairs in the gap. The replenished charges partially screen the electric field, which is self-consistently solved together with the distribution functions of particles and gamma-rays. If no current is injected at either of the boundaries of the accelerator, gap is located around the conventional null surface, where the local Goldreich-Julian charge density vanishes. It is found that the gap position shifts outwards (or inwards) when particles are injected at the inner (or outer) boundary. Applying the theory to the Crab pulsar, it is demonstrated that the pulsed TeV flux does not exceed the observational upper limit for moderate infrared photon density and that the gap should be located near to or outside of the conventional null surface so that the observed spectrum of pulsed GeV fluxes may be emitted via curvature process.

2 illus, 24 ref.

000104   Griffin R F (NO, The Observatories, Madingley Road, Cambridge CB3 OHA, England) : Spectroscopic binaries near the north galactic pole paper 24: HD 106104, 109281, 109463 and 110743. J Astrophys Astr 2001, 22(2-3), 187-211.

Four stars have been under observation with photoelectric radial-velocity spectrometers for many years. They have proved to be binaries with periods of 30, 1828, 1514 and 822 days respectively; the orbits are of modest eccentricity a part from that of HD 110743 which is indistinguishable from a circle. The mass functions are small, and no companion has been observed for any of the stars. HD 110743, a K dwarf, is much the nearest of the four, and its orbit is of short enough period for the photocentric motion to have been recognised by Hipparcos. An eleventh-magnitude star rather more than 1' away from HD 106104 is shown to be genuine physical companion, with practically identical radial velocity, proper motion and distance modulus, although the project separation is about 13,000 AU.

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000103   Goyal A;Sapru M L;Kaul R K;Bhat C L (NO, Nuclear Research Laboratory, Mumbai - 400 085) : Atmospheric parameter monitoring at Mt. Abu. Bull Astr Soc India 2002, 30(1), 441-4.

Several atmospheric / meteorological parameters, including atmospheric dust load, sky condition and solar UV. (γ = 270 -310 nm) radiation flux have been monitored on a daily basis at the GRACE observatory site in Mt. Abu for several years. The results of preliminary analysis of these data, especially the diurnal and seasonal variations in various parameters and their effect on observations with the TACTIC imaging Cerenkov telescope array have been reported.

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000102   Gothe K S et al (NO, Tata Institute of Fundamental Research, Homi Bhabha Road, Colaba, Mumbai - 400 005) : Auxiliary control systems for Pachmarhi array of Cerenkov telescope. Bull Astr Soc India 2002, 30(1), 397-402.

Pachmarhi Array of Cerenkov Telescopes (PACT) consists of 25 Telescopes deployed over an area of 100 m x 80 m. The experiment is based on atmospheric Cerenkov technique to detect Very High Energy celestial γ-rays using wavefront sampling method. Each telescope consists of 7 large area parabolic mirrors mounted para-axially on an equatorial mount and a fast photo-multiplier tube at the focus of each mirror. For efficient operation of the experiment, 3 automated control systems were developed and installed, viz. Automated Computerized Telescope Orientation System (ACTOS) to control the pointing and tracking of individual telescopes, Automatic Photo-multiplier Exposure System (APES) to facilitate the exposure of photo-tubes only during observations, and Computerized Automated Rate Adjustment and Monitoring System (CARAMS) to ensure uniform gains for all the phototube - mirror system. The design features and performance of each of these systems are discussed.

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000101   Golap K;Uday Shankar N (Physics Dep, University of Mauritius, Reduit, Mauritius) : Deconvolution of wide-field image from a non-coplanar T-array. J Astrophys Astr 2001, 22(2-3), 251-62.

Deconvolution of wide-field images is a well-knwon problem with many interesting algorithms. Describes the solution developed for deconvolving wide-field images from the Maruritius Radio Telescope (MRT). MRT is a non-coplanar, Fourier synthesis T array operating at 151.5 MHz. The non-coplanarity of the MRT produces dirty images that are convolvd by a position dependent point spread function (PSF). Focuses mainly on the methods developed for estimating the PSF of the array from the dirty images and translating the PSF estimated at a given declination to the PSF at another declination.

5 illus, 11 ref

000100   Gizani N A B;Garrett M A;Leahy J P (Centro de Astronomia e Astrofisica da Univ. de Lisboa, , O A L Portugal) : The multiwavelength study of two unique radio galaxies. J Astrophys Astr 2002, 23(1-2), 89-93.

Presents the usage of multi-frequency and multi-band radio, VLA, observations as well as X-ray observations in order to study the environment around two powerful radio galaxies, namely Hercules A and 3 C310. Environment both in pc- and kpc-scales has been studied. Chosen these two radio galaxies as they present similar and unique characteristics, compared to the ones from our general knowledge about double radio galaxies associated with active galactic nuclei.

2 illus, 14 ref

000099   Ghosh S K;Mookerjea B;Rengarajan T N;Tandon S N;Verma R P (NO, Tata Institute of Fundamental Research, Bombay-400 005) : Far infrared mapping of three galactic star forming regions : W3(OH), S209 & S187. J Astrophys Astr 2001, 22(2-3), 173-85.

Three galactic star forming regions associated with W3(OH), S209 and S187 have been simultaneously mapped in two trans-IRAS far infrared (FIR) bands centered at <126> and 200 μm using the TIFR 100 cm balloon borne FIR telescope. These maps show extended FIR emission with structures. The HIRES processed IRAS maps of these regions at 12, 25, 60 and 100μm have also been presented for comparison. Point-like sourcs have been extracted from the longest waveband TIFR maps and searched for assoications in the other five bands. The diffuse emission from these regions have been quantified, which turns out to be a significant fraction of the total emission. the spatial distribution of cold dust (T<60> 30K) for two of these sources (W3(OH) & S209), has been determined reliably from the maps in TIFR bands. The dust temperature and optical depth maps show complex morphology. In general, the dust around S209 has been found to be warmer than that in W3(OH) region.

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000098   Fleury P (IN2P3/Ecole Polytechnique, 91128, Palaiseau, , ) : Observation of Markarian 421 by the CAT imaging telescope. Bull Astr Soc India 2002, 30(1), 291-6.

The CAT imaging telescope has been exploited since 1997 for the observation of Mrk-421 among other sources. After a brief review of the characteristics of the CAT telescope, the event reconstruction method has been described. Recent analysis results, with emphasis on the determination of the energgy spectrum, its shape and its dependence upon the level of activity of the blazar have been described.

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000097   Fleury P (IN2P3/Ecole Polytechnique, 91128, , Palaiseau) : Introduction to Markarian 421 special session. Bull Astr Soc India 2002, 30(1), 277-9.

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000096   Fleury P (NO, Ecole Polytechnique, 91128 Palaiseau) : Gamma astronomy from space and from ground. Bull Astr Soc India 2002, 30(1), 37-49.

Ground based observations has come of age with the advent of the Whipple imaging telescope 10 years ago. The decade that followed has been a period of consolidation, with several detectors of performance comparable to that of the Whipple, mostly HEGRA and CAT in the Northern hemosphere and Cangaroo and Mark-6 in the South. A few important results have been obtained, but the number of firmly established sources remain quite scarce. EGRET has collected an impressive amount of data mostly concerning the blazars, but it has left many questions open, and many of the observed sources remain unidentified. The new decade will bring in major progress, with the new satellites AGILE and GLAST and with large arrays of telescopes in both hemispheres. In the same time, new ground based techniques are under study either for better angular coverage or lower energy threshold. Finally, new sites are setting in, which have to find their part to play in this context.

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000095   Finley J P (Dep of Physics, Purdue University, West Lafayette, IN, 47907, USA) : VHE Gamma-ray astronomy: present status and future challenges. Bull Astr Soc India 2002, 30(1), 17-23.

Reports the status of VHE gamma-ray astronomy at the start of the new millennium. The decade of the 90's saw rapid development of the field and many new detectors and proposed facilities have been discussed. The growth of the field in the new millennium will continue and the catalogue of TeV sources will increase by at least an order of magnitude. While many advances are expected some "thorny" problems, which have been around for quite a while, may still prove to be a challenge in the future.

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000094   Dhekne P S (Bhabha Atomic Research Centre, Computer Division, Mumbai-400 085) : Integrated instrumentation & computation environment for GRACE. Bull Astr Soc India 2002, 30(1), 269-75.

The project GRACE (Gamma Ray Astrophysics with Coordinated Experiments) aims at setting up a state of the art Gamma Ray Observatory at Mt. Abu, Rajasthan for undertaking comprehensive scientific exploration over a wide spectral window (10's keV - 100's TeV) from a single location through 4 coordinated experiments. The cumulative data collection rate of all the telescopes is expected to be about 1 GB/hr, necessitating innovations in the data management environment. As real-time data acquisition and control as well as off-line data processing, analysis and visualization environment of these systems is based on the use of computers, communications and the Internet. A single, unified environment using Web based technologies has been proposed. This new environment will allow researchers better access to facilities, improve resource utilization and enhance collaborations by having identical environments for online as well as offline usage from any location. An implementation strategy for a platform independent web-based system that supplements automated functions with video-guided interactive and collaborative remote viewing, remote control through virtual instrumentation console, remote acquisition of telescope data, data analysis, data visualization and active imaging system has been presented. This end-to-end web-based solution will enhance collaboration at the national and international level using the telescope systems of the GRACE project.

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000093   de Jager O C (Unit for space Physics, Potchefstroom University for CHE, Potchefstroom 2520, South Africa) : Pulsar Observations above 1 GeV with future ground-based gamma-ray telescopes. Bull Astr Soc India 2002, 30(1), 85-93.

Explores the potential of present and future ground based γ-ray telescopes to detect GeV to multi-GeV pulsed emission from EGRET pulsars. Five types of telescopes can in principle detect such emission. The two most promising are the "5@5" stereo array (5 telescopes, each with a diameter of 20 m; proposed site: Chile, 5 km a.s.1.) and a single 30 meter dish at a conventional altitude (e.g. 2.2 km). These two detectors (in the conceptual phase) should be able to detect pulsed GeV emission within a few seconds, but may not realize before the launch of GLAST. Pre-GLAST results are however expected from experiments under construction: MAGIC (17 m single dish, La Palma) and H.E.S.S. (four 11 m diameter dishes, Namibia). Existing solar type arrays: CELESTE (France - in operation) and STACEE (USA - in operation). To date no confirmed pulsed γ-ray emission from radio pulsars has been seen from any ground-based γ-ray telescope. In the case of the solar-type arrays, a clever triggering technique may reveal the spectral tail of the pulsed γ-ray emission from pulsars such as Crab and PSR B1951+32, but more luck is expected from the MAGIC and H.E.S.S. type arrays. Compares the pulsed rates and detection times required for MAGIC, H.E.S.S., and "5@5" given the trigger studies performed up to date.

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000092   Das S;Chakrabarti S K (S N Bose National Center for Basic Sciences, , Block-JD; Sector-III, Salt Lake, Kolkata-700 098) : Standing shocks around black holes and estimation of outflow rates. J Astrophys Astr 2002, 23(1-2), 143-7.

Obtains shock locations in an accretion flow by using an analytical method. One can obtain the spectral properties, quasi-periodic oscillation frequencies and the outflow rates when the inflow parameters are known. Since temperature of the CENBOL decides the spectral states of the black hole, and also the outflow rate, the outflow rate is directly related to the spectral states.

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000091   Cowsik R;Srinivasan R;Prabhu T P (NO, Indian Institute of Astrophysics, Bangalore 560 034) : Introduction to the Indian astronomical observatory, Hanle. Bull Astr Soc India 2002, 30(1), 105-14.

Situated in the high-altitude cold desert of Changthang Ladakh bordering Himarchal Pradesh and Tibet Indian Astronomical Observatory, Hanle (32°46'46"N, 78°57"51"E; 4500 m above msl), provides excellent opportunities for developing astronomical facilities at a variety of frequencies. In addition it provides environment and logistics for a range of scientific experiments which benefit from its unique location. A 2-m telescope of new advanced technology design has been installed at the observatory. The telescope saw its first light on the night of September 26/27 2000 and has been operating with a CCD imager. The telescope will be remotely operable from the Centre for Research and Education in Science and Technology of IIA at Hosakote near Bangalore over the next few months. All the necessary infrastructure including 20 kw/h power through generators, 1 Mbps dedicated satellite communication link (to be upgraded to 2 Mbps and a 128 kbps redundant link to be established), liquid nitrogen plant, etc. have been already developed. The Government of Jammu & Kashmir has transferred over 600 acres of land to the observatory. The infrastructure developed for the observatory is already being used for other scientific experiments by national and international institutions. Determination of atmospheric opcaity at mm wavelengths, geodynamic and seismological experiments, aerosol background and other aeronomical experiments are being conducted.

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000090   Choudhury M;Rao A R (Tata Institute of Fundamental Research, , Mumbai-400 005) : X-ray spectroscopy of Cygnus X-3. J Astrophys Astr 2002, 23(1-2), 39-43.

Analysed the X-ray spectra of the highly variable X-ray source Cygnus X-3 over a wide energy range from 5 keV to 150 keV using data selected from the RXTE archives. Separate analysis of the low and hard states show the presence of a hard powerlaw tail in both the states. Present the result of the wide band spectral study of the source.

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000089   Chitre A;Joshi U C (NO, Indian Institute of Science, Bangalore-560012) : H α emission line morphologies in Markarian starburst galaxies. J Astrophys Astr 2001, 22(2-3), 155-72.

Presents broad band R and narrow band Hα exmission line imges of a sample of optically selected starburst galaxies from the Markarian lists. The emission line morphology is studied and global properties like luminosities, equivalent widths and star formation rates are derived. The radial distribution of Hα flux and the EW are determined using concentric aperture photometry on the emissiion line and the continuum images. Hα flux is genrally found to peak in the nuclear region and fall off outwards. The EW is found to peak off-centre in most of the cases implying that though the intensity of emission is maxiumum at the nucleus, the star formation avtivity relative to the underlying continuum often peaks away from the centrer in Markarian starburst galaxies.

5 tables, 6 illus, 21 ref

000088   Chitnis V R;Bhat P N (NO, Tata institute of Fundamental Research, Homi Bhabha Road, Colaba, Mumbai - 400 005) : Estimation of vital shower parameters in wavefront sampling technique. Bull Astr Soc India 2002, 30(1), 345-9.

Wavefront sampling experiments record arrival times of Cerenkov photons with high precision at various locations in Cerenkov pool using a distributed array of telescopes. This photon front can be fitted with a spherical surface travelling at a speed of light and originating from a single point on the shower axis. Radius of curvature of the spherical shower front (R) is approximately equal to the height of shower maximum from observation level. R varies with the primary energy (E) and provides a method of estimating the primary energy. One can estimate the arrival times at each telescope using the radius of curvature, arrival direction of the primary and the core location. This enables parameters for each shower. This alleviates the difficulty of systematics arising out of the plane wavefront approximation for the Cerenkov front. Another outstanding problem in the field of atmospheric Cerenkov technique is the difficulty in locating the shower core. This method seems to solve both these problems and provides an elegant method to determine the arrival direction as well as the core location from timing information alone. Using the Cerenkov photon density information and the core position the energy of the primary can be estimated if the nature of the primary is known. Combining the two independent estimates of the primary energy, the energy resolution can be further improved. Application of this methodology to simulated data and the results have been presented.

3 illus, 4 ref

000087   Chitnis V R;Bhat P N (NO, Tata institute of Fundamental Research, Homi Bhabha Road, Colaba, Mumbai - 400 005) : Gamma-hadron separation using Cerenkov photon density fluctuations. Bull Astr Soc India 2002, 30(1), 341-4.

In atmospheric Cerenkov technique γ-rays are detected against abundant background produced by hadronic showers. In order to improve signal to noise ratio of the experiment, it is necessary to reject a significant fraction of hadronic showers. The temporal and spectral diffferences, the lateral distributions and density fluctuations of Cerenkov photons generated by γ-ray and hadron primaries are offten used for this purpose. Differences in Cerenkov photon density fluctuations at the observation level based on Monte Carlo simulations have been studied. Various types of density fluctuations like the short range (or local), medium range fluctuations and flatness parameter have been studied. The estimated quality factors reflect the efficiencies with which the hadrons can be rejected from the data. It has been found that around 80% of proton showers can be rejected while retaining about 70% of γ-ray showers in the data, based only on the differences in the flatness parameter. Density fluctuations particularly suited for wavefront sampling observations seemed to be a good technique to improve the signal to noise ratio.

1 table, 6 ref

000086   Chitnis V R;Bhat P N (NO, Tata Institute of Fundamental Research, Homi Bhabha Road, Colaba, Mumbai - 400 005) : Longitudinal shower development and its signature at observation level. Bull Astr Soc India 2002, 30(1), 351-5.

From a study of Cerenkov photon arrival times at various core distances at the observation level it has already been established that the photon front is well fitted with a spherical surface travelling at the speed of light and originating from a fixed point on the shower axis. The radius of curvature as measured at the observation level has been found to be roughly equal to the height of shower maximum from the observation level. Relationship between the radius of curvature of the shower front (R), the height of electron maximum (h_e), the Cerenkov photon maximum (h_C) and the average production height of Cerenkov photons complement of (h) has been studied. Cerenkov pulse width (w) has always been used as a parameter to study cascade development especially at tens of PeV energies. Relation between the w and h_e at TeV energies for γ-ray and proton primaries has been discussed.

3 illus, 7 ref

000085   Chattopadhyay I;Chakrabarti S K (S N Bose National Centre for Basic Sciences, , Block-JD, Sector-III, Kolkata-700 098) : Radiatively driven winds from effective boundary layer around black holes. J Astrophys Astr 2002, 23(1-2), 149-53.

Matter accreting onto black holes suffers a standing or oscillating shock wave in much of the parameter space. The post-shock region is hot, puffed up and reprocesses soft photons from a Keplerian disc to produce the characteristic hard tail of the spectrum of accretion discs. The post-shock torus is also the base of the bipolar jets. Author study the interaction of these jets with the hard photons emitted from the disc. Shows that radiative force can accelerate outflows but the drag can limit the terminal speed. Introduces an equilibrium speed v_eq 'as a function of distance, above which the flow will experience radiative deceleration.

2 illus, 15 ref

000084   Chattopadhyay I;Chakrabarti S K (NO, S N Bose National Centre for Basic Sciences, Kolkata - 700 098) : Shocks in winds from accretion discs and the formation of high energy particles. Bull Astr Soc India 2002, 30(1), 313-6.

Effects of radiation momentum deposition on jets and outflows from the disks have been studied and it has been shown that if disks are perturbed, jets could have propagating shock waves which may accelerate particles to observed slopes.

^ssc3 illus, 12 ref

000083   Chakrabarti S K (NO, S N Bose National Centre for Basic Sciences, Salt lake, Calcutta 700098) : Advective flow paradigm of disks and outflows around black holes. Bull Astr Soc India 2002, 30(1), 125-34.

For the past fifty years, accretion process has been studied on normal stars and compact objects like black holes and neutron stars. Modern development of the subject has been presented and it has been shown that the advective disk paradigm comprises the most complete solution presented so far. Predictions made by this paradigm and have been discussed and it has been shown how the observations support these predictions.

48 ref

000082   Bottcher M (Physics and Astronomy Department, Rice University, MS 108, Houston, TX 77005-1892, USA) : Physics input from multiwavelength observation of AGN. Bull Astr Soc India 2002, 30(1), 115-24.

The current status of leptonic jet models for blazars is reviewed. Differences between the quasar and BL-Lac subclasses of blazars may be understood in terms of the dominance of different radiation mechanisms in the gamma-ray regime. Spectral variability patterns of different blazar subclasses appear to be significantly different and require different intrinsic mechanisms causing gamma-ray flares. Recent results of long-term multiwavelength monitoring of PKS 0528+134, 3C 279, and Mrk 501 are interpreted in the framework of leptonic jet models. Short-term variability patterns give important additional clues about the source geometry and the relevant radiation mechanisms in blazars Challenges for future observational efforts are discussed.

^iia55 ref

000081   Bhattacharyya S;Sahayanathan S;Kaul C L (Nuclear Research Laboratory, Bhabha Atomic Research Centre, , Mumbai-400 085) : Effect of particle acceleration process on the flare characteristics of blazars. J Astrophys Astr 2002, 23(1-2), 95-9.

Following the kinetic equation approach, study the flare processes in blazars in the optical-to-X-ray region, considering energy dependent acceleration time-scale of electrons and synchrotron and adiabatic cooling as their dominant energy loss processes.

1 illus, 7 ref

000080   Bhattacharya D (Raman Research Institute, , Bangalore-560 080) : Evolution of neutron star magnetic fields. J Astrophys Astr 2002, 23(1-2), 67-72.

Reviews the current status of the theoretical models of the evolution of the magnetic fields of neutron stars other than magnetars. It appears that the magnetic fields of neutron stars decay significantly only if they are in binary systems. Three major physical models for this, namely spindown-induced flux expulsion, ohmic evolution of crustal field and diamagnetic screening of the field by accreted plasma, are reviewed

26 ref

000079   Bhat P N;Acharya B S;Chitnis V R;Majumdar P; Rahman M A;Singh B B;Vishwanath P R (NO, Tata Institute of Fundamental Research, Homi Bhabha Road, Colaba, Mumbai 400 005) : TeV gamma-ray flares from Mkn 421 detected by the Pachmarhi array of Cerenkov telescopes. Bull Astr Soc India 2002, 30(1), 285-90.

Pachmarhi Array of Cerenkov Telescopes (PACT), based on wave front sampling techniqe, has been used for detecting TeV gamma rays from galactic and extra-galactic γ-ray sources. The Blazar, Mkn 421 was one such extra-galactic source observed during the winter nights of 2000 and 2001. A preliminary analysis of the data taken during the nights of January, 2000 and 2001 was carries out. Results show a significant gamma ray signal from this source during both these periods above a threshold energy of 900 GeV. The source was contemporaneously observed by CAT imaging telescope during the first episode of January 2000 while HEGRA CT1 was observing the source during the second episode. Both these observations have detected variable γ-ray emission from this source and flaring activity during both these periods have been reported. The light curve in the TeV gamma ray range derived from the first PACT observations during both these episodes is in agreement with that reported by other experiments. The analysis procedure and the preliminary results have been presented and discussed.

2 illus, 1 table, 13 ref

000078   Bhat P N (NO, Tata Institute of Fundamental Research,, Homi Bhabha Road, Colaba, Mumbai 400 005) : Wavefront sampling technique: VHE γ-ray experiments. Bull Astr Soc India 2002, 30(1), 135-45.

Atmospheric Cerenkov technique is the only method which has been successfully used to probe the sky in the TeV energy band. However it has certain intrinsic drawbacks arising primarily out of the presence of cosmic rays which out-number γ-rays by around a factor of ~ 1000. Second generation experiments in the field have developed some novel techniques by which a bulk of the cosmic ray could be rejected thus increasing the signal to noise ratio. Thus the field emerged from an era when the confidence level of positive results were rarely larger than a few standard deviations. The underlying technique responsible for this phenomenal success was the ability to identify the primary species from the Cerenkov images recorded at the observation level, first demonstrated by simulation techniques, that the spatial sampling of Cerenkov photons too is potentially a viable as well as a powerful technique which is yet to be fully exploited. Several Cerenkov telescope arrays are now in advanced stages of operation which employ this technique in order to reduce the cosmic ray background. This technique, also called the wavefont sampling technique, is being employed for studying TeV γ-rays at the Pachmarhi Array of Cerenkov Telescopes (PACT).Progress made by the PACT team in trying to achieve a significant signal to noise ratio by this method has been discussed.

^iia3 illus, 3 tables, 14 ref

000077   Bhat N et al (Bhabha Atomic Research Centre, Nuclear Research Laboratory, Mumbai - 400 085) : Recent results on crab nebula and Mkn-421 observations with TACTIC imaging element. Bull Astr Soc India 2002, 30(1), 385-8.

The results of recent observational campaigns on the Crab Nebula and Mkn-421, carried out with the 349-pixel Imaging Element of the TACTIC array, are presented alongwith the details of the data analysis. Analysis of the recorded events reveals presence of significant signals from both these sources.

3 illus, 7 ref

000076   Bhat N D R;Camilo F;Cordes J M;Nice D J; Lorimer D R;Chatterjee S (National Astronomy and Ionosphere Center, , Arecibo Observatory, U S A) : Arecibo observations of Parkes multibeam pulsars. J Astrophys Astr 2002, 23(1-2), 53-7.

The on-going Parkes multibeam survey has been astoundingly successful, and its discovery of over 600 pulsars has opened up new avenues for probing the Galaxy's electron content and magnetic field. Reports on recent observations made with the Arecibo 305-m telescope, where 80 distant, high dispersion measure pulsars (of which 35 are from the multibeam survey) were studied at multiple frequency bands in the range 0.4-2.4 GHz, in order to determine their scattering properties, rotation measures and spectral indices. The results will be used to meet a variety of science goals; viz., creating an improved model of the electron density, mapping out the Galactic magnetic field, and modeling the pulsar population.

2 illus, 7 ref

000075   Bhat C L;Kaul R K (Bhabha Atomic Research Centre, Nuclear Research Laboratory, Mumbai - 400 085, ) : (NULL). Bull Astr Soc India 2002, 30(1), 201-11.

The recent advances in the field of very high energy (VHE) or TeV gamma-ray astronomy, culminating in the unambiguous detection of several galactic and extragalactic sources, owes itself largely to the successful exploitation of the Cerenkov imaging technique in the mono-and stereo operation modes. In this method , substantially improved detection sensitivities are achieved by recording the two - dimensional Cerenkov light distribution patterns in the focal plane of one or more light collectors and rejecting ≥ 99 percent background cosmic ray - initiated events on the basis of their distinct image shape and orientation characteristics. The basic methodology of the Cerenkov imaging technique particularly in the context of the TACTIC and MACE imaging systems, which are being set up at Mt. Abu. The special design features of these two systems and the astrophysical problems likely to be addressed have been highlighted.

^iia11 illus, 38 ref