Astronomy Experiment Research Articles

60-Channel 10 $\mu$s Time-Resolution Counter Array for Long Term Continuous Event Counting

Experiments in nuclear physics, biomedicine and astronomy often require pulse-counting electronics for large numbers of channels. This paper describes an event-counting system attached to 60 channels of an innovative monolithic array of single- photon avalanche diodes (SPADA) intended for astronomical use. The system can capture events with pulse-counting rates of up to 20 MHz, a minimum integration time of 10 mus, which results in a data acquisition rate of 100 000 frames per second. It can also store several hours' worth of data. This performance is achieved in a system that offers a high degree of flexibility, is small in size and has a low cost. The implementation is based on a commercial-off-the-shelf (COTS) single board, fitted with an FPGA and a DSP. This board is connected to a PC by means of an IEEE 1394 high-speed serial link which stores the collected data and functions as a TCP/IP server. The data acquisition parameters, as well as the collected data, can be accessed by means of a custom-designed interface running on a TCP/IP client. A proof-of-concept system has been assembled and some test stand results are presented and discussed.

Experimental approaches for 100 TeV astronomy

The high energy end of γ-ray source spectra might provide important clues regarding the nature of the processes involved in γ-ray emission. Several galactic sources with hard emission spectra extending up to more than 30 TeV have already been reported. Measurements around 100 TeV and above should be an important goal for the next generation of high energy γ-ray astronomy experiments. Here we present several techniques providing the required exposure (∼ 100 km2 ⋅ h). We focus our study on three Imaging Atmospheric Cherenkov Technique (IACT) based approaches: low elevation observations, large field of view telescopes, and large telescope arrays. We comment on the advantages and disadvantages of each approach and report simulation based estimates of their energy ranges and sensitivities.

Small IRAIT Telescope: photometry and asteroseismology at Dome C

Inhalt (u.a.): M. BREGER: Delta Scuti stars: Observational aspects; M.S. Cunha: Theory of rapidly oscillating Ap stars; M. SACHKOV et al.: Vertical structure of pulsations in roAp stars; G. HOUDEK: Theoretical asteroseismology of solar-like oscillations; B.L. POPIELSKI: Core modes as a seismic probe of mixing beyond the convective core; M. GODART: Temperature gradients in the core overshooting region; W.A. DZIEMBOWSKI – J. DASZYŃSKA-DASZKIEWICZ – A.A. PAMYATNYKH: Interpretation of the Be star HD 163868 oscillation spectrum based on the MOST observations; D. KILKENNY: Pulsating Hot Subdwarfs – An Observational Review; M.H. MONTGOMERY: Mapping Convection using Pulsating White Dwarf Stars; M. ROTH: The Network Activities in HELAS; I. KUDZEJ et al.: A New Slovak Observatory 500 km from Vienna; W.W. WEISS: Microsatellites; G. KOPACKI – S. FRANDSEN: RR Lyrae stars in M4

The role of voluntary organizations in astronomy popularization: a case study of Khagol Mandal

AbstractWe present a case study of “Khagol Mandal,” a voluntary organization primarily based in Mumbai, India. In the 20 years since its inception, Khagol Mandal has given more than 1000 public outreach programmes. The volunteers strive to go beyond amateur level by means of various study tours, astronomical experiments and workshops. These activities have inspired a number of students to take professional astronomy careers. With a volunteer force, probably largest in India or even south Asia, Khagol Mandal is well poised to take advantage of the archival data of large telescopes. With a little guidance from senior researchers, organizations like Khagol Mandal can provide a solution to the ever-increasing need for manpower for ancillary science from these large-scale facilities.

Interaction between electromagnetic radiations and West Ford needle clusters: Models and application

Radar observations of small space debris made with the Goldstone radar facility has shown that a population of small particles do exist at an altitude larger than 2000 km. This population has been identified with clusters of copper needles created upon the deployment of the West Ford needles project, by MIDAS satellites in 1961 and 1963. This set of particles is either not taken into account in the debris models or only add to other populations. However, it could affect, for instance, the space borne astronomical experiments. In order to assess this threat it is necessary to model their physical and geometric characteristics. A preliminary modelling using spheres suggests that some improvement is needed. We propose a better approach with long conductive circular cylinders as a model for the clusters. The interaction of solar light with these particles allows us to estimate the spurious flux scattered inside space borne instruments. We conclude that for a given spatial configuration light flashes can affect seriously the operating mode of high-sensitivity instruments.

Class Transitions in Black Holes

A black hole spectrum is known to change from the hard state to the soft state when the energy spectral index α (FE ∝ E-α) in, say, 2–20 keV range changes from α ~ 0.5 to ~ 1.5. However, this 'classical' definition which characterizes black holes like Cyg X-1, becomes less useful for many objects such as GRS 1915+105 in which the spectral slope is seen to vary from one to the other in a matter of seconds and depending on whether or not winds form, the spectral slope also changes. The light curves and the colour-colour diagrams may look completely different on different days depending on the frequency and mode of switching from one spectral state to the other. Though RXTE observations have yielded wealth of information on such 'variability classes' in GRS 1915+105, very rarely one has been able to observe how the object goes from one class to the other. In the present review, we discuss possible origins of the class transition and present several examples of such transitions. In this context, we use mostly the results of the Indian X-ray Astronomy Experiment (IXAE) which observed GRS 1915+105 more regularly.

Solar X-ray Spectrometer (Soxs) Mission on Board GSAT2 Indian Spacecraft: The Low-Energy Payload

The first space-borne solar astronomy experiment of India, namely “Solar X-ray Spectrometer (SOXS)”, was successfully launched on 08 May 2003 on board geostationary satellite GSAT-2 of India. The SOXS is composed of two independent payloads, viz. SOXS Low-Energy Detector (SLD) Payload and SOXS High-Energy Detector (SHD) Payload. The SOXS aims to study the full-disk integrated X-ray emission in the energy range from 4 keV to 10 MeV. In this paper we present the first report on the SLD instrumentation and its in-orbit performance. The SLD payload was designed and developed at the Physical Research Laboratory in collaboration with various centers of Indian Space Research Organisation (ISRO). The basic scientific aim of the SLD payload is to study solar flares in the energy range from 4 to 60 keV with high spectral and temporal resolution. To meet these requirements, the SLD payload employs state-of-the-art solid state detectors, the first time for a solar astronomy experiment, viz. Si PIN (4 –25 keV), and cadmium–zinc–telluride (4 –60 keV). With their superb high-energy resolution characteristics, SLD can observe iron and iron–nickel complex lines that are visible only during solar flares. In view of its 3.4∘ FOV, the detector package is mounted on a Sun Aspect System, for the first time, to get uninterrupted observations in a geostationary orbit. The SLD payload configuration, its in-flight operation, and the response of the detectors are presented. We also present the first observations of solar flares made by the SLD payload and briefly describe their temporal and spectral mode results.

First Measurements of the Infrared Sky Brightness at Dome C, Antarctica

ABSTRACTDome C, Antarctica, (75° south, 123° east, 3250 m) is one of the coldest and driest locations on Earth, with exceptionally low winds throughout the atmosphere. It therefore has the potential to be an ideal site for astronomical observations. It is also an excellent site for the validation of satellite instruments. A Fourier transform infrared interferometer was deployed at Dome C during two austral summer seasons (2003 January and 2003 December/2004 January) for the purpose of acquiring satellite validation data. However, these data are also useful for understanding the infrared characteristics of the atmosphere for future astronomical experiments at Dome C. The Polar Atmospheric Emitted Radiance Interferometer measured the downwelling infrared radiance from the atmosphere (sky brightness) from 3 to 20 μm. Over 100 radiosondes were also launched during this time period. Typical measured values of the sky brightness in the clearest portions of the M, N, and Q bands are 0.9, 43, and 310 Jy arcsec−2, respectively. The lowest measured values of sky brightness within these bands are 0.4, 34, and 200 Jy arcsec−2. The spectral region of the Q band from about 18.7 to 19 μm is expected to be an excellent window for observations made from the Antarctic Plateau. The sky brightness has been measured between 10.60 and 11.30 μm in the N band for comparisons to earlier studies at South Pole Station; the values in this band are similar to those in the 8.20–8.40 μm band. For the period of time covered by our observations, the sky brightness in the dark portions of the N band was less than about 50–60 Jy arcsec−2 for about 10% of the time, and less than about 75 Jy arcsec−2 for about 50% of the time. During a 5 day period of clear skies, the mean sky brightness was 47.7 Jy arcsec−2, with a variation about this mean of 4.4 Jy arcsec−2 (1 σ). Calculations of the summertime atmospheric transmission under clear skies over Dome C show that portions of the M, N, and Q bands have transmission greater than 95%, with some spectral regions greater than 99%.

A modelling of the interaction between electromagnetic radiation and West Ford needles clusters: a preliminary study

Radar observations of small space debris made with the Goldstone radar facility have shown that a population of small particles do exist at an altitude larger than 2000 km. This population has been identified with clusters of copper needles created upon the deployment of the West Ford needles project, by MIDAS satellites in 1961 and 1963. This set of particles is either not taken into account in the debris models or only added to other populations. But owing to their specific physical and geometrical properties, the sunlight they scatter could affect, for instance, the spaceborne astronomical experiments. In order to assess this threat it is necessary to model their physical and geometric characteristics. A preliminary modelling using spheres suggests that some improvement is needed. We propose a better approach with long conductive cylinders as a model for the clusters. The interaction of solar light with these particles allows us to estimate the spurious flux scattered inside spaceborne instruments. We conclude that for a given spatial configuration light flashes can affect seriously the operating mode of high sensitivity instruments.

The Crab Nebula and Pulsar between 500 GeV and 80 TeV: Observations with the HEGRA Stereoscopic Air Cerenkov Telescopes

The Crab supernova remnant has been observed regularly with the stereoscopic system of 5 imaging air Cherenkov telescopes that was part of the High Energy Gamma Ray Astronomy (HEGRA) experiment. In total, close to 400 hours of useful data have been collected from 1997 until 2002. The spectrum extends up to energies of 80 TeV and is well matched by model calculations in the framework of inverse Compton scattering of various seed photons in the nebula including for the first time a recently detected compact emission region at mm-wavelengths. The observed indications for a gradual steepening of the energy spectrum in data is expected in the inverse Compton emission model.The average magnetic field in the emitting volume is determined to be $(161.6\pm0.8mathrm{stat}\pm18_\mathrm{sys}) \mu$G. The presence of protons in the nebula is not required to explain the observed flux and upper limits on the injected power of protons are calculated being as low as 20 % of the total spin down luminosity for bulk Lorentz factors of the wind in the range of $10^4-10^6$.The position and size of the emission region have been studied over a wide range of energies. The position is shifted by 13\arcsec to the west of the pulsar with a systematic uncertainty of 25\arcsec. No significant shift in the position with energy is observed. The size of the emission region is constrained to be less than 2\arcmin at energies between 1 and 10 TeV. Above 30 TeV the size is constrained to be less than 3\arcmin.No indications for pulsed emission has been found and upper limits in differential bins of energy have been calculated reaching typically 1-3 % of the unpulsed component.

Evidence of Class Transitions in GRS 1915+105 from Indian X‐Ray Astronomy Experiment Data

GRS 1915+105 shows at least 12 distinct classes of light curves. By analyzing the data obtained from the Indian X-ray Astronomy Experiment (IXAE) instrument on board the IRS-P3 satellite, we show that on several days, transitions between one class to another were observed. On these days, the so-called κ class went to ρ class and the χ class went to ρ class. In the frequency-time plane, such transitions exhibited change in quasi-periodic oscillation (QPO) frequency. We could detect that low-frequency QPOs occurred in anticipation of a class transition several hundred minutes before the actual transition.

Effects of /spl gamma/-rays on JFET devices and circuits fabricated in a detector-compatible Process

This work is concerned with the effects of /spl gamma/-rays on the static, signal and noise characteristics of JFET-based circuits belonging to a fabrication technology made available by the Istituto per la Ricerca Scientifica e Tecnologica (ITC-IRST), Trento, Italy. Such a process has been tuned with the aim of monolithically integrating the readout electronics on the same highly resistive substrate as multielectrode silicon detectors. The radiation tolerance of some test structures, including single devices and charge sensitive amplifiers, was studied in view of low-noise applications in industrial and medical imaging, X- and /spl gamma/-ray astronomy and high energy physics experiments. This paper intends to fill the gap in the study of gamma radiation effects on JFET devices and circuits belonging to detector-compatible technologies.

On the Magnetic Fields and Particle Acceleration in Cassiopeia A

We investigate the nonthermal X-ray emission from Cas A, using BeppoSAX, Compton Gamma Ray Observatory OSSE, and Chandra data. For the hard X-ray continuum we test the model proposed by Laming, which invokes nonthermal bremsstrahlung from electrons accelerated by lower hybrid plasma waves. The justification for this model comes from our determination of a lower limit to the average magnetic field of B > 0.5 mG. For such high magnetic fields, the synchrotron losses are severe enough that most of the electron populations responsible for the radio emission have maximum electron energies well below the limit for which X-ray synchrotron emission is important. However, we do suggest that the rim surrounding Cas A, seen in Chandra continuum images, is X-ray synchrotron emission. The width of this rim of 15-4'' can be used to infer the magnetic field near the shock front, for which we estimate B = 0.08-0.16 mG and electron energies of ~57-40 TeV. This magnetic field strength is lower than the average magnetic field but higher than what may be expected from shocked interstellar medium, suggesting either a high magnetic field in the wind of the progenitor or rapid postshock field amplification by nonlinear growth of plasma waves. Combining the two magnetic field measurements, we have constructed a simple two-zone model. Most of the radio emission comes from inside Cas A, where the magnetic field is strong. In contrast, the inverse Compton emission is dominated by emission from near the shock front. Only for our lower limit on the magnetic field strength near the shock front is it possible to explain the recent detection of TeV emission by the High Energy Gamma Ray Astronomy experiment with inverse Compton emission, for which, in addition, we have to assume a rather high far-infrared photon density that should be twice as high as our best estimate of ~70 cm-3. Pion decay is therefore likely to be the dominant emission from Cas A at TeV energies.

New measurements of orbital period change in Cygnus X-3

A nonlinear nature of the binary ephemeris of Cygnus X-3 indicates either a change in the orbital period or an apsidal motion of the orbit. We have made extended observations of Cygnus X-3 with the Pointed Proportional Counters (PPCs) of the Indian X-ray Astronomy Experiment (IXAE) during 1999 July 3-13 and October 11-14. Using the data from these observations and the archival data from ROSAT, ASCA, BeppoSAX and RXTE, we have extended the data base for this source. Adding these new arrival time measurements to the published results, we make a comparison between the various possibilities, (a) orbital decay due to mass loss from the system, (b) mass transfer between the stars, and (c) apsidal motion of the orbit due to gravitational interaction between the two components. Orbital decay due to mass loss from the companion star seems to be the most probable scenario.

X-ray properties of the microquasar GRS 1915105 during a variability class transition

We present a detailed X-ray study of the microquasar GRS 1915+105 during a variability class transition observed in 2000 June with the Pointed Proportional Counters (PPCs) of the Indian X-ray Astronomy Experiment (IXAE). We supplement this observation with data from the RXTE archives. The source made a transition from a steady low–hard state to a regular oscillatory behaviour in the light curve known as bursts or class ρ (variability classes from Belloni et al.) between 2000 May 11 and 17 and reverted back to the low–hard state on 2000 June 27. A gradual change in the burst recurrence time from about 75 s to about 40 s was observed, which then increased to about 120 s during the ∼40 d of class ρ. The regular bursts disappeared from the X-ray light curves and the class transition was observed to occur within 1.5 h on 2000 June 27 with the PPCs. A correlation is found between the observed quasi-periodic oscillation frequency at 5–8 Hz in the quiescent phase and the average X-ray intensity of the source during the class ρ. We notice a strong similarity between the properties of the source during the class ρ and those during the oscillatory phase of the observations of class α, which contains a long stretch (∼1000 s) of steady low–hard state in the light curve along with the regular periodic bursts. From the timing and spectral analysis, it is found that the observed properties of the source over tens of days during the class ρ are identical to those over a time-scale of a few hundreds of seconds in the class α. Examining the light curves from the beginning of the RXTE/PCA and RXTE/ASM observations, it is found that the change of state from radio-quiet low–hard state to high state occurs through the X-ray classes ρ and α, which appear together during the state transition. It is further inferred that the source switches from low–hard state to the class ρ through the intermediate class α.

The French balloon programme: capabilities and scientific programmes

CNES, the French Space Agency, makes available to the French and European scientific communities a comprehensive ballooning capacity with vehicles adapted to different scientific objectives as required by the scientists, and world-wide operational services. In addition, it provides funds to French scientific groups to develop balloon-borne instruments and fly them either individually or in the frame of coordinated campaigns. The main fields of research presently covered by the French scientific balloon programmes are astronomy, stratospheric dynamics and chemistry for science and satellite data validation, and troposphere dynamics. This paper shall briefly present these capabilities as well as the programmes and campaigns carried out during the past two years. It will give more detailed information on some experiments using different types of balloons such as the THESEO 1999 and 2000 campaigns for the study ozone destruction processes, the CLAIRE and ARCHEOPS astronomy experiments, the MUTSI, INDOEX and MAP balloon campaigns using small pressurised balloons for atmospheric dynamic studies. The results of the third flight of the 2-meter PRONAOS IR and sub-mm astronomy observatory will be presented in a separate paper. Finally, this paper will also put emphasis on an original technical development named AEROCLIPPER, devoted to atmosphere/ocean experiments, as well as on future scientific and technological trends as defined by the French scientific community.

Trans-Pacific Demonstrations (TPD): remote astronomy demonstration and results

In 1993, a proposal at the Japan-US Science, Technology, and Space Applications Program (JUSTSAP) workshop led to a subsequent series of satellite communications experiments and demonstrations, under the title of Trans-Pacific High Data Rate Satellite Communications Experiments. The first phase of this was a joint collaboration between government and industry teams in the United States and Japan that successfully demonstrated distributed high definition video (HDV) post-production on a global scale using a combination of high data rate satellites and terrestrial fiber optic asynchronous transfer mode (ATM) networks [1-3]. This was followed by the Phase-2 Internet Protocol (IP) based experiments and demonstrations [4-7] in tele-medicine and astronomical distance education, using another combination of two high data rate satellites and terrestrial fiber optic networks. This paper describes the Phase-2 remote astronomy experiment in detail. This experiment established a heterogeneous ground- and space-based network between Japan and several sites in the US, which was used by students, scientists, and educators to provide real-time interaction and collaboration with the 14-inch Telescopes in Education (TIE) telescope and associated data archive. The remote astronomy activity demonstrated collaborative observation and distance education at multiple locations around the globe and the transparent operations of distributed systems technologies over a combination of broadband satellites and terrestrial networks. The use of Internet Protocol related technologies allowed the general public to be an integral part of the exciting activities, helped to examine issues in constructing a global information infrastructure with broadband satellites, and afforded an opportunity to tap the research results from the (reliable) multicast and distributed systems communities. In this paper, we describe the network infrastructure at both the technical and user levels, review the operation of the experiment, and summarize our lessons learned. We find that such networking, while still somewhat complex to construct on highly distributed scales, can provide educators and students with a unique collaborative environment which greatly enhances the educational experience.

Simultaneous X‐Ray and TeV Gamma‐Ray Observation of the TeV Blazar Markarian 421 during 2000 February and May

We present the results of simultaneous observations of the TeV blazar Markarian 421 at X-ray and TeV gamma-ray energies with the Rossi X-Ray T iming Explorer and the stereoscopic Cerenkov telescope system of the High Energy Gamma-Ray Astronomy (HEGRA) experiment, respectively. The source was monitored from 2000 February 2 to 16 and from 2000 May 3 to 8. In both energy bands several —ares with very rapid —ux variability were observed. In the X-ray band, the —ux increased and decreased with e-folding times as short as about 5 hr. The 3¨20 keV photon index varied between values of 2.2 and 2.9. For —ve pointings the data show statistically signi—cant evidence for spectral curvature. The photon index varied substantially on very short timescales: on 2000 February 11 it hardened within 1.6 hr by *! 0.18, and on February 14 it softened within 1.6 hr by *! 0.2. The TeV observations of February 7/8 showed statistically signi—cant evidence for substantial TeV —ux variability on a 30 minute timescale. The TeV energy spectrum averaged over all the observations of the campaign shows a similar steep slope as in earlier HEGRA observations: TeV)~! with dN/dE N 0 (E/1 N 0 (25 ^ 1 stat ) ] 10~12 photons cm~2 s~1 TeV~1 and Within statistical errors no evidence for a curvature of ! 2.94 ^ 0.06 stat . the TeV energy spectrum is found. We show the results of modeling the data with a time-dependent homogeneous synchrotron self-Compton model. The X-ray and TeV gamma-ray emission strengths and energy spectra together with the rapid —ux variability strongly suggest that the emission volume is approaching the observer with a Doppler factor of 50 or higher. The diUerent —ux variability timescales observed at X-rays and TeV gamma rays indicate that a more detailed analysis will require inhomogeneous models with several emission zones. Subject headings: BL Lacertae objects: individual (Markarian 421) ¨ galaxies: jets ¨ gamma rays: observations

IXAE observations of the X-ray pulsar XTE J1946+274

We report results from two observations of the transient binary X-ray pulsar XTE J1946+274 with the Indian X-ray Astronomy Experiment (IXAE) made in September 18-30 1999 and June 28-July 7 2000. The pulsar has a ~80 days orbital period during which the X-ray intensity varies almost sinusoidally between intensity levels of 5 and 50 mCrab. The mid-time of the two observations with the IXAE are separated by an orbital phase of 0.56 and were in the decaying and rising parts of its orbital modulation, respectively. During both the observations, strong pulsations with 15.8 s period are detected in the 2-6 and 6-18 keV energy bands of IXAE. The pulse profiles in both the observations are double peaked and identical with a similar pulse fractions of ~30% in the two energy bands. The pulse periods and its local derivatives are obtained from the IXAE observations. The known pulse period history shows small deviations from an otherwise nearly constant spin-up trend of the pulsar since its discovery. If the measured local period derivatives are a sum of a nearly constant spin-up of the pulsar and effect of its orbital motion, it suggests that the orbit of this Be X-ray binary is eccentric. The RXTE-ASM light curve shows a continuous detection of 10 orbital modulation of the source since its discovery.

ITAL]MIDCOURSE SPACE EXPERIMENT[/ITAL][ITAL]Midcourse Space Experiment[/ITAL] Survey of the Galactic Plane

The Midcourse Space Experiment (MSX) surveyed the entire Galactic plane within |b| ≤ 5° in four mid-infrared spectral bands between 6 and 25 μm at a spatial resolution of ~183. The survey was redundant within |b| ≤ 45 with four-fold coverage over two-thirds of the area. These survey data were combined to create 1680 15 × 15 images that cover the region with 6'' pixel spacing in each of the spectral bands. The images preserve the inherent resolution of the data but have up to twice the sensitivity of a single scan. The individual survey observations had to be extensively conditioned to achieve the co-add advantage. The noise equivalent radiance (NER) at 8.3 μm, the most sensitive MSX mid-infrared spectral band, varies from ~1.3 MJy sr-1 in the inner Galaxy to 3 times that at the latitude limits in the outer Galaxy; the sensitivities of the other MSX mid-infrared bands are 10–25 times less. Additionally, 36 lower resolution 10° × 10° images were generated in each band that span the full latitude and longitude range of the survey. These panoramic images have a resolution of ~12 with 36'' pixel spacing and a six-fold improvement in NER, making them an ideal product for comparison with radio surveys of the Galactic plane. An ancillary set of images has been created from other MSX astronomy experiments that lie within 10° of the Galactic plane. These images either extend the latitude coverage of the survey or provide deeper probes of Galactic structure either by themselves or when added to the survey images.