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The Compton Gamma Ray Observatory (CGRO) completed a full sky survey in November 1993 during which the number of known gamma-ray pulsars more than doubled. During this survey the Compton Telescope (COMPTEL) observed the classical isolated pulsars Crab and Vela and detected PSR 1509-58. Attempts to detect the newly discovered pulsars, Geminga, PSR 1706-44 and PSR 1055-52, in the COMPTEL energy range provide only upper limits. The results of these analyses are presented together with the outcome of a search for further candidate radio pulsars whose ephemerides are given in the Princeton Pulsar Catalogue.

The Compton Gamma-Ray Observatory (C-GRO) has completed a full-sky survey during which the number of known γ-ray pulsars has more than doubled. COMPTEL has observed the classical pulsars Crab and Vela on several occasions and has derived detailed pulse patterns and spectral parameters in the 0.7-30 MeV energy interval. The new C-GROγ-ray pulsars have different properties in terms of energy spectra and light-curve shapes, and, in fact, only the Crab is seen by all four C-GRO instruments. This raises intriguing questions about the particle acceleration processes and beaming taking place in the neutron magnetosphere. We have examined the COMPTEL data to add information on these objects in the 0.7-30 MeV energy interval and present evidence for the detection of one of them, PSR B1509-58. We have also undertaken a search for candidate radio pulsars whose ephemerides are well defined. The results of these analyses are presented.Subject headings: gamma rays: observations — pulsars: general

Summary.Pulsar measurements performed by the experiment COMPTEL, aboard the Compton Gamma Ray Observatory, are described. The main results refer to the Crab and Vela pulsars whose pulse shape characteristics are given in some detail and light curves are compared with those above 50 MeV, as observed by the COS-B satellite. No other gamma-ray pulsars have been detected to date by COMPTEL, the upper limit on the pulsed signal from Geminga being compatible with indications by other experiments.

We describe a method of analysis for the reconstruction of the arrival direction of a high-energy photon impacting on the top of the atmosphere by using the directions of the particles on the shower front as measured by a ground-based array of tracking chambers uniformly distributed on a square surface; as an example, an array with enclosed surface of (120×120) m2 has been considered. Estimates on the accuracy of reconstruction are given, after application of the method to computer-simulated shower directions as a function of the number of «smapling» detectors and of their accuracy in the measurement of the «local» shower direction.

We report the third consecutive detection of Vela X-1 as a source of VHE gamma-rays ( E γ > 1 TeV ) with a 99.92 % significance. The pulsed emission shows a broad sinusoidal light curve at a period similar to the X-ray value, with a large negative period derivative over the 60 days of observation. We also report our observations on Cen X-3 in which we were able to confirm the orbitally modulated, pulsed VHE gamma-ray emission from Cen X-3 at the 2σ level. Finally, the possible detection of stable material at one of the Lagrangian points in the system PSR1957+20 is reported. We found indications from VHE gamma-ray data (at the 3σ level) of a DC enhancement at the L4 Lagrangian point. This indication was then independently confirmed at the 99.9% level from COS-B data. This enhancement of radiation in the binary orbit may indicate the existence of stable material with a column density of about 50 g/cm 2 at the Lagrangian point L4.

We discuss the feasibility of a telescope consisting in a sampling array for extensive air showers measure combined with a muon tracking device. The sampling array will extend over a surface of ≥ 10 7 m 2 while the muon tracking device will cover ≥ 10 4 m 2 . The telescope should be done with resistive plates counters and would become a very powerful device to study high energy neutrinos and gamma rays astronomy as well as cosmic ray physics up to the highest energy (≥ 10 19 eV ) region.

An experiment is described in which air shower measurement are carried out by means of a «track detector» placed in a test location near the center of a conventional array telescope currently in use for gamma-ray astronomy. This array, consisting of scintillators (GREX, operated at Haverah Park (U.K.) by the Department of Physics of the University of Leeds), provides, in the usual way, for each shower it selects, its own estimates of shower direction and shower particle density at the test location. Estimates of the muon density at the test location are provided by a large muon detector in operation nearby. The scintillator array triggers this muon detector and it is able to provide flexibly tailored trigger signals for the track detector. This detector named PLASTEX (acronym for Palermo Leeds Air Shower Tracking Experiment), consisting of tracking chambers above and below a thin sheet of lead, designed to provide data on charged particles incident from the air, on the stopping, scattering and multiplication of these particles in the lead sheet and on charged particles created in the lead sheet by shower photons. From these data estimates are derived of the densities and directional properties of the electrons, photons and muons striking the track detector. These results are to be compared with those given by the conventional detectors and with theoretical predictions given by simulations that are being carried out. The objective is to develop and assess optimal procedures for employing clusters of PLASTEX-type detectors as telescopes for the observation of UHE cosmic rays, including cosmic gammarays, over a very wide energy range.

It is discussed the persisting necessity for a change in paradigm in science and in the common way of thinking, from the exophysical perspective, typical of the classic realism, to an endophysical one, where the mutual interaction between us and the environment is not neglected. The necessity clearly results from the continuous debate on the interpretation of Quantum Mechanics in relation with the investigation of the microworld and from the unresolved problem of the compatibility of the linear, reversible and unstructured time of physics with the highly structured time of our perception endowed with an irreversible arrow. The necessity in the proposed change in paradigm is still clearer if we focus our attention to the formation of a representation of the external world in our mind, a process similar to that observed in nature in all complex self-organizing physical systems – including living organisms and human societies – producing order in competition with the second principle of thermodynamics. In such a conceptual schema, in fact, the acquisition of knowledge in man occurs in continuous and strict interaction with the environment and the result is always a new situation in which both man (with his representation of the world) and the environment are irreversibly changed.

One of the main activities of human beings has always been to understand the laws ruling the external world, in order to keep it under control as much as possible. A theoretical scenario for an overall representation of the world provides a practical tool for this purpose. Such a scenario is usually built by combining knowledge obtained from everyday observations into a general framework containing all those a priori beliefs necessary for a complete and satisfactory global view of the world. New knowledge, however, is not always compatible with existing scenarios, and gives rise to questions requiring answers capable of eliminating any recognized contradictions. New and careful observations do provide the desired answers, but at the cost of modifying, sometimes drastically, existing scenarios. In the long run this results in a reduction of our a priori beliefs, with the advantage of achieving a more precise and complete representation of the universe.

Preface. 1: History. The History of Neutron Stars: From Early Speculations to Current Problems F. Pacini. 2: Neutron Star Structure. Internal Constitution of Neutron and Strange Stars N.K. Glendenning. Topics in the Theory of Matter at Sub-Nuclear Densities C.J. pethick, D.G. Ravenhall. Dynamics of the Neutron Star Interior M.A. Alpar. Pulsar Magnetic Fields and Glitches M. Ruderman. 3: Radio Pulsars. Detection of Radio Emission from Pulsars: A Pulsar Observation Primer D. Bhattacharya. The Experimental Determination of the Limiting Spin Period of Neutron Stars N. D'Amico. Radio Pulsar Population Properties D.R. Lorimer. Energetic Young Radio Pulsars J.F. Bell. Young Nerutron Stars in Supernova Remnants D.A. Frail. Gamma-Ray Emission from CGRO Pulsars G. Kanbach. Time Averaged Pulse Phase Resolved Spectra of the Vela Pulsar Measured by COMPTEL at MeV Energies L. Kuiper, et al. New Views of the Vela Pulsar Jet C.B. Markwardt, H.B. OEgelman. Kinematics of Low-Mass X-Ray Binaries and Millisecond Pulsars R. Ramachandran, D. Bhattacharya. Unusual Increase in the 325 Mhz Flux Density of PSR B0655+64 T.J. Galama, et al. High-Energy Emission from Binary Pulsars M. Tavani. Relativistic Winds and Jets M. Salvati. Pulsar Electrodynamics, Atoms in Strong Magnetic Fields F. Simoes, A.A. da Costa. 4: X-Ray Binaries. Neutron Stars and Black Holes in X-Ray Binaries J. van Paradijs. Kilo-Hertz Quasi-Periodic Oscillations in Low-Mass X-Ray Binaries M. Van der Klis. Long-Term Behavior of Accretion Powered Pulsars M.H. Finger. GRO J1744-28: The Bursting Pulsar C. Kouveliotou. The 5-9 Second X-RayPulsars L. Stella, et al. First Results from a Systematic Search for New X-Ray Pulsators in ROSAT PSPC Fields S. Covino, P. Giommi. Thermonuclear Burning on Rapidly Accreting Neutron Stars L. Bildsten. Results from the PDS Experiment Aboard the BeppoSAX Satellite E. Palazzi, et al. The Astrophysical Key Source SS 433 W. Kundt. High-Energy Emission from Accreting Neutron Stars S. Zane, et al. 5: Evolution of Binaries with Compact Components. Coalescing Binary Neutron Stars F.A. Rasio. Modelling Gamma-Ray Bursts M. Tavani. The Effects of Kick Velocities on the Formation of Low-Mass X-Ray Binaries V. Kalogera. Transients and the Evolution of Low-Mass X-Ray Binaries A.R. King. An Evolutionary Picture for Short Orbital Period Millisecond Binary Pulsars E. Ergma, et al. 6: X-Rays from Single Neutron Stars. On the X-Ray Emission Properties of Rotation Powered Pulsars W. Becker, J. Trumper. Thermal Evolution of Isolated Neutron Stars D. Page. Evolution of Thermal Structure and Radiation Spectrum of Cooling Neutron Stars Yu.A. Shibanov, et al. Atomic Ionization and Opacities in Pulsar Atmospheres: Hydrogen Atmospheres J. Ventura, et al. The Observability of Old Neutron Stars Accreting the Interstellar Medium A. Treves, et al. Search for Old Neutron Stars in Molecular Clouds: Cygnus Rift and Cygnus OB7 T. Belloni, et al. Author Index. Subject Index. Object Index.

Using the COMPTEL data of the first 5 years of the CGRO mission we have derived the average pulsed spectrum of the Crab Pulsar, as well as phase-resolved spectra of the pulsed emission of the Crab Pulsar. The spectra in the COMPTEL energy range (0.75 to 30 MeV) are compared to those in the neighboring energy bands. The pulsed flux has been examined for its stability. Pulsed lightcurves have been derived for different energy intervals. Preliminary results of this analysis are presented.

The imaging Compton Telescope (COMPTEL) is sensitive in the energy range of 0.75 to 30 MeV. COMPTEL observed the Crab several times during the Compton Gamma Ray Observatory (CGRO) sky survey and CGRO Phase II. Both the Crab pulsar and nebula are detected over the entire COMPTEL energy range. The phase-averaged energy spectra of the Crab Pulsar and Nebula are presented. The combined observations provide sufficient statistics for a phase-resolved analysis of the Crab pulsar spectrum.

A large international collaboration from the high energy astrophysics community has proposed the Tracking and Imaging Gamma Ray Experiment (TIGRE) for future space observations. TIGRE will image and perform energy spectroscopy measurements on celestial sources of gamma rays in the energy range from 1 to 100 MeV. This has been a difficult energy range experimentally for gamma ray astronomy but is vital for the future considering the recent exciting measurements below 1 and above 100 MeV. TIGRE is both a double scatter Compton and gamma ray pair telescope with direct imaging of individual gamma ray events.Multi‐layers of Si strip detectors are used as Compton and pair converters CsI(Tl) scintillation detectors are used as a position sensitive calorimeter. Alternatively, thick GE strip detectors may be used for the calorimeter. The Si detectors are able to track electrons and positrons through successive Si layers and measure their directions and energy losses. Compton and pair events are completely reconstr...

A maximum likelihood method is described which was used to make a search for gamma‐ray bursts in 3 dimensions: 2 space coordinates and time, without relying on any previous knowledge about the event. Extensive Monte Carlo simulations have been performed to evaluate the statistical significance of potential bursts utilizing the EGRET experimental conditions. Applications to the EGRET observational data show that a) the May 3, 1991 burst is detectable by our method at a 6.5 σ significance level and b) a burst of the intensity of the ‘‘superbowl’’ burst is detectable at a 14 σ significance level.

During the first year of observation by the Compton Gamma Ray Observatory, the Crab pulsar was in the field of view of COMPTEL four times. COMPTEL is sensitive to gamma radiation in the energy interval 0.7–30 MeV. The light curves that were obtained for each observation showed slight differences in appearance. A statistical analysis of the signal and the noise in the light curve has been performed to check whether the variation in shape is due to intrinsic source behaviour, which would obviously have theoretical implications, or simply due to statistical variations. The result of this analysis shows the latter to be the case.

The COMPTEL telescope aboard the Compton Gamma‐Ray Observatory, sensitive to low‐energy γ‐rays between about 0.7 and 30 MeV, has detected the pulsed signal of the Vela pulsar (PSR0833‐45) in the 10–30 MeV range with a significance of 12 σ. The two main peaks in the light curve resemble the sharp peaks detected earlier in high‐energy γ‐rays. A combination of timing and spatial analysis, lowering the COMPTEL source detection threshold, enabled the detection of PSR0833‐45 down to 0.75 MeV. The energy spectrum of the total pulsed emission connects smoothly to that measured simultaneously at higher energies by EGRET (and the time‐averaged COS‐B spectrum) and to the OSSE spectrum and ROSAT detection at lower energies. The combined spectrum cannot be represented by a single power law; bends/breaks are required at two or three energies to represent the data from the EGRET high‐energy γ‐rays down to the ROSAT soft X‐rays. Spectral between 1 and 30 MeV are also shown for the sum of the emission from the two main pe...

The paper describes the software package SAST developed for detection and description of periodicities and other irregular time structures in gamma-ray timing data. The package has been successfully used for the analysis of the photon arrival times measured by the COS-B satellite for gamma-ray astronomy and of the times derived from some observations of the Cerenkov telescope at the Potchefstroom University (South Africa).

The COMPASS system is a large software package, involving several subsystems, whose development has been ‘shared’ by the four institutes of the COMPTEL Collaboration.

Pulsed γ radiation from the Geminga pulsar was recorded by the COS B satellite from 50 MeV to 5 GeV between 1975 and 1982. It has been analysed to derive the source spectral properties as a function of time and phase. The two main peaks are separated by 0.50 ± 0.01 in phase. Significant pulsed emission has also been detected in both phase regions between the two main peaks. Significant spectral differences with phase have been found; the emission from the first peak is slightly softer than from the second one and the Interpeak 2 radiation is extremely soft. The first peak emission remained stable within the statistics over 7 years while the flux from the other phase intervals changed significantly with time. The phase dependence of the variability implies that all the observed source emission should be pulsed and that it consists of four discrete beams with different apertures and spectra. The beams characteristics are strikingly similar to those of four γ-ray beams generated by the Vela pulsar.Subject headings: gamma rays: observations — pulsars: individual (Geminga, Vela)

A reanalysis of the original 1985 TeV data on PSR 1802 - 23 by DeJager (1987) is reported which reveals a significance for pulsed emission of 98.6 percent, which is seven times less significant than the original claim of 99.8 percent. The tracking mode was used to collect nine times more data during 1986, 1987, and 1988, and the total time ON-source during these three years was also nine times that of 1985. In spite of this, no signal is detected from this pulsar when searching for both steady pulsed emission and transient emission. No indications are found of any DC enhancements. The flux upper limit for steady pulsed TeV gamma rays is 2.6 x 10 to the -11th/sq cm/s, corresponding to an upper limit in TeV gamma-ray luminosity of 1.2 x 10 to the 35th ergs/s. The original detection may therefore be considered as a once-only event or more probably as a statistical fluctuation. 15 refs.

Les donnees du telescope Cerenov de Potchefstroom, du satellite COS B et du telescope Compton MPE sont analysees pour detecter la presence d'un signal de rayonnement gamma en direction du pulsar binaire a eclipse PSR 1957+20. Une emission Rγ possible au point lagrangien L 4 est determinee pour deux des trois ensembles de donnees.

Measurements of pulsars in the energy domain above ~ 1 keV have provided in the last few years new and interesting results. This paper presents a review of the observational features of PSR 0531+21 and PSR 0833–45 (the Crab and Vela pulsars). Searches for pulsed emission from old radio pulsars in the same energy domain are also reviewed and results assessed. The comparison of the observed features with each other and with the corresponding features observed at lower energies reveals similarities and differences capable to constrain theoretical models with special regard to the geometry of the emission mechanisms.

The Crab pulsar (PSR0531 + 21) was one of the earliest identified sources of high-energy γ radiation1–6. As such it was selected as the first object of detailed study by ESA's γ-ray astronomy satellite COS B, launched in August 1975. The experiment and mission have been described elsewhere7. In the first 6 yr of operation COS B has made five observations (each of 30–40 days duration) in which PSR0531 + 21 was within 15° of the centre of the field of view. The first of these confirmed the result of the SAS 2 experiment that the γ-ray light curve for energies above a few tens of MeV consisted essentially of two equally strong peaks but the later measurements found a decrease in the strength of the second peak relative to the first. No change was observed in the 2–12 keV X-ray light curve simultaneously measured by COS B. The total data from the five observations contain the first evidence of interpulse emission between the two peaks in the energy range 50–3,000 MeV.

The problem of the automatic selection from background events of electron pairs due to gamma-ray conversion in a multiplate spark chamber is dealt with by means of a direct non-parametric pattern recognition method. The method is applied to the data obtained in a gamma-ray astronomy experiment using a balloon-borne optical spark chamber. A filter operation is initially introduced to exclude clearly evident spurious events; the remaining spark chamber images are then reduced to their most significant zone in order to lower time and cost of subsequent analysis. The feature selection is performed by using a “training set” of labeled events and the classification made introducing a pre-established linear threshold decision function. Results are presented giving the percent of correct classification as a function of the threshold value chosen.

In the framework of an experiment of search for fast pulsars inside the error boxes of the COS-B gamma-ray sources, a special effort has been done to observe with the best possible sensitivity the X-ray source 1E0630+178 believed to be a neutron star on the basis of the high ratioLx/Lo between X-ray and optical luminosity. The object, which is located inside the error box of the gamma-ray source 2CG195+04 (Geminga) was observed at 318, 430, 1387 and 1414 MHz with long integration times and low sampling rate. The most sensible observation is that at 430 MHz for which a limiting flux threshold of 0.6 mJy has been reached for periods down to 2 ms. The power spectrum does not indicate the presence of any pulsation effect and so is, at slightly higher limiting flux thresholds, for all other frequencies.

The paper describes a non-parametric analysis to obtain the phase histogram of a pulsar as seen in the satellite reference frame; the method requires only an approximate knowledge a priori of the pulsar period and of the position of the satellite. Results are presented on the derivation of the X-ray (2–12 keV) and gamma-ray ( E >50 MeV) pulsar phase histograms relative to NP-0532 as observed by the COS-B satellite.

When we talk of Gamma-Ray Astronomy we refer in general to celestial photons covering the energy domain from a fraction of MeV up to the highest detected energies at hundreds or thousands of GeV. The six to seven decades altogether spanning the overall energy range constitute a very wide domain to be compared with those of the optical (less than one decade) or of the neighbouring X-Ray Astronomy (about two decades). The observational technique varies widely with changing energy; detector performances and characteristic parameters are not, in general, comparable.

A gamma-ray telescope with a 850 cm2 multiplate spark chamber as a detector, has been used in an experiment of six balloon flights to investigate the Crab Nebula Pulsar 0532. The triggering signal is provided by a plastic scintillator-directional Čerenkov counter system. The spark chamber events are photographed by a stereo camera. The time of arrival of each event is recorded in UTC time with one millisecond accuracy, to search for a possible pulsed gamma emission from NP0532 above 50 MeV.

WE have investigated the gamma-ray emission from the Crab Nebula in a series of balloon flights of a multiplate spark chamber triggered by a Cerenkov detector-scintillator coincidence system1. The previously quoted gamma-ray energy threshold for pulsed emission from the Nebula and NP 0532 (refs. 1, 2) is ∼50 MeV; a detailed investigation of the telescope efficiency as a function of energy has now shown that the efficiency extends down to 20 MeV.

The internal working model on attachment dimensions changes with significant emotional experiences. The purpose of this study was to evaluate if and how the internal working models correlate with primary headaches. Attachment dimensions of subjects suffering from primary headaches were studied. One hundred and fourteen subjects [68 with migraine, 23 with tension–type headache (according to ICHD–I criteria), 23 with chronic daily headache (according to Silberstein’s criteria)], were studied and compared with a control group of 57 subjects (matched in sex, age and social level) not suffering from any primary headache. Attachment dimensions were investigated using the Adult Attachment Questionnaire (AAQ) and the Attachment Style Questionnaire (ASQ). Headache sufferers seem to be characterised by attachment styles of the “insecure” type. In particular they seem to feel extremely ill at ease if there is an expectation of reduction of interpersonal distance.

A systematic search for fast radio pulsars in some of the error boxes of the γ-ray satellite COS B1 unidentified point sources2–4 on the 305-m Arecibo Observatory radiotelescope was started 3 years ago. The motivation for the search and the method and limitations are given elsewhere5. One of the search areas covered was the γ-source 2CG065+00. We report here the discovery of a 6.13317-ms pulsar in a binary system with a 120-day orbital period inside the error box of this source. The initial search observation (23 July 1980) with a sampling rate of 4.167 ms produced an aliased (76.93 Hz) detection at 430 MHz. Confirmatory observations made in March 1983, showed a variable pulse frequency indicating a Doppler shift due to a periodic orbit around another object6. A compilation of measured system parameters and the underlying assumptions are given in Table 1.

PULSARS seem to play a major role as γ-ray emitters. Of the 13 objects listed in the first COS B catalogue1 the two brightest, CG185-5 and CG263-2, have been identified with the Crab (PSR0531+21) and Vela (PSR0833–;45) pulsars respectively. This privileged role of pulsars as identified γ-ray sources could be simply related to observational reasons: in fact, because of the poor angular resolution intrinsic to the γ-ray telescopes, the only possibility of identification for individual sources is the time structure of the emission, and the periodical pattern of pulsars is particularly suited. On the other hand, for PSR0531+21 and PSR0833−45, the observed pulsed energy release is essentially in the γ-ray channel, with a ratio between the γ and radio luminosity as high as ∼106.

The fully samples Columbia 1/sup 0/ CO survey and the Berkeley H I survey are compared with the COS B gamma-ray survey. As a first step, the study is limited to the high-energy gamma-rays (Eapprox.300 MeV). It is found that a simple model, in which uniformly distributed cosmic rays interact with the interstellar gas, as traced by H I and CO, can account for almost all the observed gamma-rays. Furthermore, if the contribution from point sources to the gamma-ray flux is significant, these sources must have a galactic distribution similar to that of CO. The analysis permits calibration of the ratio between H/sub 2/ column density and integrated CO line intensity: N(H/sub 2/)/W/sub CO/ = (1-3) 10/sup 2/0 molecules cm/sup -2/ K/sup -1/ km/sup -1/ s.

When we talk of Gamma-Ray Astronomy we refer in general to ce lestial photons covering the energy domain from a fraction of MeV up to the highest detected energies at hundreds or thousands of GeV. The six to seven decades altogether spanning the overall energy range constitute a very wide domain to be compared with those of the optical (less than one decade) or of the neighbouring X-Ray Astronomy (about two decades). The observational technique varies widely with changing energy; detector performances and characteristic parameters are not, in general, comparable. All of this has inevitably introduced, for the Gamma-Ray field, an additional subdivision in at least three sub-sectors: Low and Medium Energy : 0.1 to 20–30 MeV. Intermediate and High Energy: 30 MeV to 5–10 GeV. Very High Energy : the region beyond.

We discuss some of the basic steps of the analysis for the detection and description of short periodicities in the photon counting regime (typical of gamma-ray astronomy), focusing the attention to those aspects where a certain degree of subjectivity by the analyst may lead to erroneous conclusions. As a statistical test for the detection of the periodic signal, the use of the Hm-test is suggested in ail exploratory cases when information on the expected light curve shape is lacking. The bin free kernel density estimator (KDE) and cluster analysis are used for the description of intensities, the location and significance of structures on the light curve and are proposed as alternatives to the histogram technique which is easy to use, but since the construction of the histogram is largely based on subjective considerations, it may lead to wrong interpretations especially in the case of weak signal and low counting statistics.

The photon arrival times detected by COS-B around the direction of the Crab pulsar have been analyzed by an adaptive cluster method in order to search for short bursts of gamma-ray emission from the source. As a result, two clusters of 3 and 6 photon arrival times within 264 s and 1813s respectively were found with the corresponding residual phases having close correlation with the peaks of the Crab pulsed emission. The comparison with a similar analysis performed by using photon arrival times not correlated with the Crab direction shows that the events have chance occurrence probabilities of about 10-3 and therefore may be consistent with (rare) random fluctuations of the background. Finally, 3 σ upper limits on the existence of bursts of emission from the Crab are given.