OPTIMA: A Photon Counting High-Speed Photometer

OPTIMA is a small, versatile high-speed photometer which is primarily intended for time resolved observations of young high energy pulsars at optical wavelengths. The detector system consists of eight fiber fed photon counters based on avalanche photodiodes, a GPS timing receiver, an integrating CCD camera to ensure the correct pointing of the telescope and a computerized control unit. Since January 1999 OPTIMA proves its scientific potential by measuring a very detailed light-curve of the Crab Pulsar as well as by observing cataclysmic variable stars on very short timescales. In this article we describe the design of the detector system focussing on the photon counting units and the software control which correlates the detected photons with the GPS timing signal.     

Short Gamma Ray Bursts as electromagnetic counterpart of coalescing binary systems

Coalescing binary systems, consisting of two collapsed objects, are among the most promising sources of high frequency gravitational waves signals detectable, in principle, by ground-based interferometers. Binary systems of Neutron Star or Black Hole/Neutron Star mergers should also give rise to short Gamma Ray Bursts, a subclass of Gamma Ray Bursts. Short-hard-Gamma Ray Bursts might thus provide a powerful way to infer the merger rate of two-collapsed object binaries. Under the hypothesis that most short Gamma Ray Bursts originate from binaries of Neutron Star or Black Hole/Neutron Star mergers, we outline here the possibility to associate short Gamma Ray Bursts as electromagnetic counterpart of coalescing binary systems.     

OPTIMA: A Photon Counting High-Speed Photometer

OPTIMA is a small, versatile high-speed photometer which is primarily intended for time resolved observations of young high energy pulsars at optical wavelengths. The detector system consists of eight fiber fed photon counters based on avalanche photodiodes, a GPS timing receiver, an integrating CCD camera to ensure the correct pointing of the telescope and a computerized control unit. Since January 1999 OPTIMA proves its scientific potential by measuring a very detailed light-curve of the Crab Pulsar as well as by observing cataclysmic variable stars on very short timescales. In this article we describe the design of the detector system focussing on the photon counting units and the software control which correlates the detected photons with the GPS timing signal. This revised version was published online in July 2006 with corrections to the Cover Date.     

A high speed photometer in the optical region for lunar occultation studies

High speed photometry during the lunar occultation of a stellar system provides an effective means of achieving high angular resolution in one dimension at the sub arc second level which is well suited for resolving close binary projected separations in the range of 10–100 milliarc seconds. An optical fast photometer designed for such a purpose is described and some results from the initial observations taken with the system including the resolution of a projected separation of 55 milli arcsecond in one binary system are detailed.     

Study on the possible detection of Gamma Ray Bursts with the ANTARES neutrino telescope

The ANTARES telescope, currently in construction, is aiming to detect high energy neutrinos. Data from the first line of the detector, which became operational recently, demonstrates that the nominal time and space resolutions are achieved. Various models predict the emission of high energy neutrinos from astrophysical sources such as Supernova Remnants, Microquasars, Active Galactic Nuclei and Gamma Ray Bursts. With the custom designed data acquisition system of this detector, in combination with the existing satellite alert systems, the ANTARES telescope has an increased sensitivity for neutrinos from Gamma Ray Bursts compared to conventional time independent sources. Gabrielle Lelaizant on behalf of the ANTARES Collaboration.     

High-speed energy-resolved STJ photometry of the eclipsing binary UZ For

We present high-time-resolution optical photometry of the eclipsing binary UZ For using a superconducting tunnel junction (STJ) device, a photon-counting array detector with intrinsic energy resolution. Three eclipses of the ∼18-mag 126.5-min orbital binary were observed using a 6×6 array of tantalum STJs at the 4.2-m William Herschel Telescope on La Palma. The detector presently provides individual photon arrival-time accuracy to about 5 μs, and a wavelength resolution of about 60 nm at 500 nm, with each array element capable of counting up to ∼5000 photon s⁻¹. The data allow us to place accurate constraints on the accretion geometry from our time- and spectrally resolved monitoring, especially of the eclipse ingress and egress. We find that there are two small accretion regions, located close to the poles of the white dwarf. The positions of these are accurately constrained, and show little movement from eclipse to eclipse, even over a number of years. The colour of the emission from the two regions appears similar, although their X-ray properties are known to be significantly different: we argue that the usual accretion shock may be absent at the non-X-ray-emitting region, and instead the flow here interacts directly with the white dwarf surface; alternatively, a special grazing occultation of this region is required. There is no evidence for any quasi-periodic oscillations on time-scales of the order of seconds, consistent with relatively stable cyclotron cooling in each accretion region.     

High time-resolution spectroscopic imaging using intensified CCD detectors

The micro‐channel plate intensified CCD photon counting detector developed at University College London has been upgraded to allow time-resolved spectroscopic optical data to be acquired on periodical sources such as pulsars. First observing trials have been carried out, acquiring spectroscopic data on the Crab pulsar. The detector was phase locked to the pulsar period and a temporal resolution of 41.4 μs employed. The phase locking allowed the coaddition of time slices over a large number of pulsar periods to build up quantifiable spectroscopic data when observing in a flux-limited regime.     

The Investigation of Optical Variability on Time Scales of 10-7-102S: Hardware, Software, Results

We present a hardware/software complex for photometric observations with high time resolution. The hardware consists of a detector, a recording system which is a "time - coded" converter, a PC/AT 486 computer and a tape recorder. As a detector we can use any device that provides its output in such a way that for every detected quantum there is a correspondent standard impulse with additional information on the quantum - space coordinates, frequency, polarization, etc. A special "time - coded" converter "Quantochron" registers the quanta arrival times with an accuracy of ± 20 nanoseconds stores in the computer the 16-bit codes as well as the 16-bit codes of additional information. At present, the photometer complex allows to register without distortion the flux events up to 380 kHz. We describe the special methods and software capable of searching and analyzing any type of photon flux intensity variations. The results of the high time resolution investigations of a number of relativistic and fast variable objects, such as black hole candidates, LMXB, pulsars and flare stars, are presented.     

Search for correlations of GRB and cosmic rays

It is possible that violent processes resulting in Gamma Ray Bursts produce also high energy photons and cosmic rays. The possible correlations of very short GRB with, e.g., CMB, cosmic rays is briefly discussed. We have also begun preparation of the experiment correlating in real time data from Maze cosmic ray detector and Pi of the Sky robotic telescope.     

Spectroscopic studies of X-ray binary pulsars

Several new features of X-ray binary pulsars are revealed from recent observations with ASCA, RXTE, BeppoSAX and other X-ray observatories. Among these, I will review in this paper some recent progress in spectroscopic studies of accreting X-ray pulsars in binary systems (XBPs). First, I will discuss soft excess features observed in the energy spectra of XBPs and propose that it is a common feature for various subclasses of XBPs. Next I will present some recent results of high resolution spectroscopy with ASCA and Chandra.     

Phase Resolved High Speed Photometry and Spectroscopy of Pulsars

We describe the implementation of two High Time Resolution modes for ESO's new generation CCD controller FIERA. These new modes have been used to perform phase-resolved high speed photometry and spectroscopy of pulsars with the FORS instruments at the VLT.     

ULTRACAM: an ultrafast, triple-beam CCD camera for high-speed astrophysics

ULTRACAM is a portable, high-speed imaging photometer designed to study faint astronomical objects at high temporal resolutions. ULTRACAM employs two dichroic beamsplitters and three frame-transfer CCD cameras to provide three-colour optical imaging at frame rates of up to 500 Hz. The instrument has been mounted on both the 4.2-m William Herschel Telescope on La Palma and the 8.2-m Very Large Telescope in Chile, and has been used to study white dwarfs, brown dwarfs, pulsars, black hole/neutron star X-ray binaries, gamma-ray bursts, cataclysmic variables, eclipsing binary stars, extrasolar planets, flare stars, ultracompact binaries, active galactic nuclei, asteroseismology and occultations by Solar System objects (Titan, Pluto and Kuiper Belt objects). In this paper we describe the scientific motivation behind ULTRACAM, present an outline of its design and report on its measured performance.     

Optical properties of Small Magellanic Cloud X-ray binaries

This work represent the first major study of the optical and infrared characteristics of the mass donor companions to the X-ray pulsars in the Small Magellanic Cloud (SMC). In this work several new counterparts have been identified, and possible ones confirmed, as companions to X-ray pulsars in the SMC giving a total of 34 such objects now identified. In addition this work presents three new binary periods and confirms two X-ray periods using optical data for objects in this group. This homogeneous sample has been studied as a group to determine important general characteristics that may offer an insight into the evolution of such systems. In particular, the spectral class distribution shows a much greater agreement with those of isolated Be stars, and appears to be in some disagreement with the galactic population of Be stars in Be/X-ray binaries. Studies of the long-term optical modulation of the Be star companions reveal an extremely variable group of objects, a fact which will almost certainly make a major contribution to the pronounced X-ray variability. The spatial distribution of these systems within the SMC is investigated and strongly suggests a link between massive star formation and the H  i density distribution. Finally, studies of the circumstellar disc characteristics reveal a strong link with optical variability offering important clues into the long-term stability of such discs.     

Radio Afterglows of Gamma Ray Bursts

This review focuses on the physics of Gamma Ray Bursts probed through their radio afterglow emission. Even though radio band is the least explored of the afterglow spectrum, it has played an important role in the progress of GRB physics, specifically in confirming the hypothesized relativistic effects. Currently radio astronomy is in the beginning of a revolution. The high sensitive Square Kilometer Array (SKA) is being planned, its precursors and pathfinders are about to be operational, and several existing instruments are undergoing upgradation. Thus, the afterglow results from detection statistics and follow up programs are expected to improve in the coming years. We list a few avenues unique to radio band which if explored to full potential have the promise to greatly contribute to the future of GRB physics.     

CCD Time-Resolved Photometry of Four Newly Discovered CVs

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Jets from Young Stars and Compact Objects Environments

Several classes of cosmic objects, such as Young Stellar Objects, Active Galactic Nuclei, Micro-Quasars, Pulsars and probably Gamma Ray Bursts, display powerful winds and jets; for some of them the flow is even ultrarelativistic. For all these classes of objects, the magnetic field is supposed to play a major role in launching and collimating the flow, together with the angular momentum transfer. It probably plays an important role for the turbulent transport in accretion disks also. Regarding the high energy radiation of relativistic jets and the cosmic ray generation, the magnetic field is of course the acceleration agent and could produce the Ultra High Energy Cosmic Rays in some extragalactic objects. The main growth points of these topics are presented, mostly in the case of black hole environments; the case of Young Stellar Objects is more complicated because of the interaction of the stellar magnetosphere with the accretion disk, and the models for this interaction are not yet founded on a reliable theory.     

Recent advances and low cost concept for the gamma-ray lens project MAX

Until recently, focusing of gamma-radiation was regarded as an impracticable task. Today, gamma-ray lenses have become feasible and present promising perspectives for future instrumentation. For the first time in high energy astronomy the signal/noise ratio will be dramatically improved as gamma-rays are collected on the large area of a lens from where they are focused onto a small detector. Besides an unprecedented sensitivity, MAX will feature very high angular and energy resolution. The conjunction of this new technique of Gamma Ray focusing and the new possibilities brought by the developping formation flying technology will allow a great step for Gamma Astronomy. This paper will describe after a short recall of the scientific objectives of MAX, the design of the MAX formation flying concept and the associated main design drivers and constraint.     

Exploring accretion theory with X-ray binaries in the Small Magellanic Cloud

The understanding of the accretion process on to compact objects in binary systems is an important part of modern astrophysics. Theoretical work, primarily that of Ghosh & Lamb, has made clear predictions for the behaviour of such systems which have been generally supported by observational results of considerably varying quality from galactic accreting pulsar systems. In this work, a much larger homogeneous population of such objects in the Small Magellanic Cloud is used to provide more demanding tests of the accretion theory. The results are extremely supportive of the theoretical models and provide useful statistical insights into the manner in which accreting pulsars behave and evolve.     

脉冲星参数统计和演化

统计分析了目前发现的几种脉冲星的自转周期和表面磁场以及空间的分布情况,揭示出毫秒脉冲星比普通射电脉冲星、LMXB(低质量X射线双星)比HMXB(高质量X射线双星)的空间分布要更加弥散;孤立毫秒脉冲星自转周期分布的峰值为4.7 ms,而普通脉冲星的相应值为0.6 s,双星中毫秒脉冲星这一值为3.5 ms; FERMI脉冲...     

KR Cygni: a near-contact eclipsing binary?

In this study we present photometric observations of the eclipsing binary KR Cyg made in 1999 and 2000. The observations of the eclipsing binary KR Cyg have been carried out in B, V and R colours at the Ege University Observatory. A new seasonal light curves are presented. New times of minima and ephemerides are given. Based on a statistical analysis of the times of minima obtained by photoelectric photometry, the orbital period of the system is found to be constant. The photometric mass ratio of the system is well determined. The corresponding light curves were analyzed by the Wilson-Devinney code. This revised version was published online in July 2006 with corrections to the Cover Date.