ELECTRONIC NEWSLETTER OF THE HIGH ENERGY ASTROPHYSICS DIVISION OF THE AAS

Newsletter No. 69 November 1996
IN THIS ISSUE:

Notes from the Editor - K. Hurley
1996 Senior Review - G. Riegler
First Results from BEPPOSAX - L. Piro
CHIANTI Atomic Database - K. Dere
SEUS Web Page - F. Harrison
ACE Science Workshop - R. Mewaldt
Aspen Workshop on Gamma-Ray Bursts - D. Lamb
Obituaries - HETE, MARS 96, and CUBIC - HETE Team, K. Hurley, and D. Burrows
Future Meetings
Notes from the Editor
by Kevin Hurley, Secretary-Treasurer (khurley@sunspot.ssl.berkeley.edu)
This will be my last newsletter. The new secretary-treasurer will be Alan Marscher, Boston University. His e-mail address is marscher@buast0.bu.edu.
The 1996 Senior Review
by Guenther Riegler
NASA used the recommendations from the Senior Review 1996 to prioritize and assign funding among the eight programs considered. Since some previously unassigned funds were available for assignment, it was possible to extend U.S. participation in the ISO project to FY00, extend participation in ASCA to FY00, participation in ROSAT to FY99, and GRO and XTE to FY00.
We have now initiated a similar comparative review process for ten Space Physics MO&DA programs, and will probably initiate a similar process for planetary science missions in 1997 or 1998.
FINAL REPORT
Senior Review of
Astrophysics Mission Operations and
Data Analysis Programs
Submitted to:
Chief Scientist, Research Program Management Division
Office of Space Science
NASA Headquarters
Submitted by: J. N. Bregman, A. K. Dupree (Chair), D. J. Helfand,
S. Kulkarni, C. F. McKee, P. Szkody, P. A. Vanden Bout, D. W. Weedman

I. INTRODUCTION
The 1996 Senior Review of Astrophysics Mission Operations and Data Analysis Programs was convened on July 29-31, 1996. The Senior Review panel was charged with ranking the expected scientific returns of eight Astrophysics missions -- ASCA, CGRO, EUVE, ISO, ROSAT, SAX, SVLBI, and XTE -- for two periods of two years each: FY '97-'98 and FY '99-'00.
The paradigm of evaluating on the basis of "science per dollar", while difficult, is necessary in an era when funds for space science are extremely limited. It is sobering to realize that the drive for cost savings could lead to termination of observatories while they are still obtaining valuable data, or to an early reduction of operations immediately after prime phase. The scientific returns from these Astrophysics missions are reduced in order to save an amount that is typically a few percent of the cost to construct and launch the mission.
Although new missions will arrive bringing powerful new capabilities, satellites launched previously remain vigorous and long-lived and their impressive scientific accomplishments accumulate. A delicate balance must be achieved in order that the enthusiasm and high interest of both astronomers and the public for space science discoveries proceeds undiminished.
We note that a major shift has occurred in the missions considered by this Senior Review. The majority of the missions, six out of nine, represent US access to observations from the satellites of other nations. In the last Senior review only two out of eleven missions were non-US. With non-US missions, US scientists are frequently able to obtain observations which are scientifically outstanding and extremely cost-effective.
II. RECOMMENDATIONS
During its deliberations, the Committee arrived at a ranking of Astrophysics missions (see accompanying table and Section III) as well as five general policy recommendations:
1. SCOPE OF CHARGE
The Committee believes that meaningful optimization of total scientific effort occurs only when broad comparisons are possible.
The last Senior Review in 1994 requested that the 1996 Review "consider the full range of science supported by the Astrophysics MO&DA program, including the LTSA, ADP, and ATP programs." This activity was not scheduled for this Senior Review because we concentrated on programs with near-term concerns, such as mission extensions or severe underfunding. However, this Committee urges that such a charge be included in the scope of the Astrophysics Senior Review in 1998.
In addition, we urge in the strongest terms that the relevant portions of the HST and AXAF MO&DA budgets (including Science Center, Guaranteed Time Investigators, and Guest Investigator funding) be included for review and prioritization along with the other missions and programs in the next Astrophysics Senior Review Committee. It is simply not possible to recommend an optimal distribution of precious funds for science exploitation of astrophysics missions when the largest part of the budget is declared off-limits.
Finally, the MO&DA items for other missions not directly included for consideration should also be provided to the Senior Review Committee so that the competed missions can be evaluated in the context of the total program. We emphasize this scope since it is clear the the diminishing MO&DA funds may require drastic recommendations. To make the best use of restricted funds, the Astrophysics Senior Review should weigh all programs rather than be bounded arbitrarily.
Given the newly unified Office of Space Science, our Committee urges that similarly rigorous MO&DA comparisons be undertaken as soon as possible within each discipline in OSS, so that in the future, Astrophysics missions are not subjected to stricter reviews than other OSS missions.
2. MULTIPLE SOFTWARE SYSTEMS
The Committee is concerned about the proliferation of multiple software systems and the resultant incompatibilities for reduction and analysis of mission data. Some of this proliferation results from the access of US investigators to mission data from experiments of other countries; other examples occur among NASA's own satellites. Such a situation not only adds complexity, cost, and barriers to fast and efficient reduction and scientific analysis of results for the Guest Observers, but also contributes to the overall support costs of missions. Thus, less science is produced for the funds invested.
The Committee strongly urges that the activities of the former Science Operations MOWG for Astrophysics be reinstated. Their careful scrutiny and oversight of the plans and operations of the data handling and support for missions can bring pressure to bear for similar and compatible software.
3. GUEST INVESTIGATOR PROGRAMS
For missions no longer in their prime phase, or missions without significant NASA participation (e.g. ASCA, SAX, ROSAT, EUVE), this Review Committee recommends transferring the funds for Guest Investigators into the ADP budget line. Although this recommendation will require two proposals from a Guest Investigator for an ongoing mission, one for observing time and another for funds, we believe that the opportunity to combine Guest Investigator grants for analysis of data from different missions, and to access both archival and new data will result in stronger scientific programs, and allow a GI to propose for one program with continuity and scientific focus. The present schedule in which proposals for observing time are due in the summer-fall, and the ADP program deadlines occur the following January, also works well for GI's seeking funding for new satellite observations.
Addressing a related issue, the Committee believes that a program of Astrophysics Fellows, perhaps similar to the Hubble Fellows, can lead to enhanced return on our investment in space science missions. Outstanding young scientists, competitively selected, and allowed to be independently creative, can broaden and enrich NASA's current research efforts. We encourage NASA to explore the initiation of a such a broad Fellowship program.
4. COST EFFICIENT OPERATIONS
In past years, the Committee has encouraged individual missions to conserve allotted funds in order to derive the most scientific benefit through an extended mission life. This Committee endorses that philosophy, and asks NASA to reward such savings by allowing those programs that have accumulated savings to use them for mission extensions.
5. REVIEW OF DATA CENTERS
The Committee believes it worthwhile to evaluate periodically the performance of all science services in order to optimize their science usefulness and their cost effectiveness. Specifically, the Infrared Processing and Analysis Center (IPAC) and the High Energy Astrophysics Science Archive and Research Center (HEASARC) were set up in the late 80's after recommendations from the science community. It is time now to initiate periodic comparative reviews and/or recompetitions of all discipline and mission science centers. These actions should assure that the science centers serve today's science needs, use today's technology, and fit today's financial constraints.
III. COMMENTS ON INDIVIDUAL MISSIONS
Missions are listed in alphabetical sequence.
Advanced Satellite for Cosmology and Astrophysics (ASCA)
Science Strengths
The ASCA mission is an imaging spectroscopic telescope with large collecting area, that has led to study of a broad range of astronomical objects at a relatively low cost because satellite control and mission operations is provided by the Japanese ISAS. This mission has made major contributions for a very wide range of astronomical sources. In the near future, one of the prime science goals is the study of gas orbiting supermassive black holes in active galactic nuclei (AGN), which will be accomplished by observing the shape and time variation of the Fe K-alpha line. The gas scintillation proportional counters (GSPCs), the primary instrument for hard sources, continue to operate without degradation. Another important large project will be to understand the many bright but previously unknown X-ray sources that were discovered by the ROSAT All-Sky Survey, only recently released. Important observations are continuing to be obtained for supernova remnants, X-ray binaries, cataclysmic variables, clusters of galaxies, stars, and AGNs. In addition to their scientific value, these observations will be of significant assistance in planning observations by future X-ray observatories such as AXAF and XMM.
The ASCA Guest Observer Facility has worked well with the Japanese team at ISAS to plan, obtain, and distribute a large amount of data to a substantial user community.
Science Weaknesses
For extended sources, the point spread function of the instrument complicates the extraction of spectral quantities. Shortcomings in the calibration of the detectors at low energies have hampered the analysis of spectra. The performance of the X-ray CCDs (the SISs) has decreased in terms of the number of CCDs that can be used simultaneously and their spectral resolution, although they continue to obtain valuable data.
Recommendation
ASCA continues to produce exceptional science, a situation that we expect to continue for several years. The high ranking of this program (2/8) reflects the range of scientific goals that are being addressed at moderate cost, due to the collaboration with the Japanese. The program should be maintained at a vigorous level through the launch of AXAF, and at a declining level through FY2000. We strongly encourage a continuation of efforts to cross-calibrate ASCA with other current missions (i.e., XTE, EUVE, ROSAT, and SAX) and with AXAF in 1998. Also, we recommend that important data products, such as spectra and light curves, be produced by the ASCA GOF for access through the archive. It is recommended that funds for analysis of new observations will be competed for through the ADP program, which is being augmented to accommodate this need.
Compton Gamma Ray Observatory (CGRO)
Science Strengths
CGRO covers six decades of frequency of the electromagnetic band, from about 30 keV to 30 GeV, and has brought gamma ray observations into the main stream of astronomy. Launched in 1991, CGRO has been responsible for many significant discoveries. Notable are the isotropy of the gamma ray bursts (GRB), the discovery of gamma ray quasars, gamma ray pulsars, direct detection of recently formed elements (nucleosynthesis), and mapping of the diffuse emission from our Galaxy, from the Universe in the 511-keV annihilation line and the 26Al lines. Long term studies of accretion powered pulsars and the discovery and follow-up of X-ray transients have also been very productive enterprises.
The proposed future programs include the continued operation of all the instruments except EGRET which has a lifetime of 1 year, limited by a consumable (spark-chamber gas). BATSE detects, on average, about one burst a day. Over the next five years, the BATSE catalog can be doubled to 3000 bursts and this may lead to new constraints on repetition (or lack of it) and the burst distribution on large scales. By means of BACODINE, crude positions of gamma ray bursts are made available on the Internet for prompt follow up at radio and optical wavelengths.
Continued imaging of the Galactic plane in the 26Al line by COMPTEL will improve the significance of the detections. Imaging in the 44Ti line may show us sites of the youngest supernovae. New transients keep appearing on the sky and CGRO is well suited to their detection and detailed study. Finally, we note that GRO will be the only gamma-ray mission that will be operational during the next solar maximum which starts in 1999, although the Committee did not feel it had the competence to judge the scientific significance of this capability.
Science Weaknesses
Gamma ray sources are quite faint. Thus significant improvements in detection sensitivities would require very long integration times and a mission duration comparable to the prime time phase duration of five years. While BATSE will be useful for the detection of new transients there are other recent missions that have significant overlap in the area of transient detection and accretion powered pulsars. BATSE is quite limited in its ability to localize Gamma-Ray Bursts, and it is unclear that the mystery of Gamma-Ray Bursts will be resolved simply by increasing the size of the present sample.
Recommendation
CGRO has achieved, indeed exceeded, its stated goals, but it now is entering an era of diminishing science returns. It is desirable to maintain the BATSE capability until there is another mission available to address the nature of Gamma-Ray Bursts. Within this priority, the four instruments aboard GRO should continue to operate as long as possible. The Committee recommends that beginning in FY97, Instrument PI teams compete with Guest Investigators for all science grants support.
The solar community needs to be consulted about the importance of observations with CGRO during solar maximum.
It is crucial that efforts concentrate on techniques such as BACODINE that hold the promise of individual source identifications. The Committee encourages the GRO Project to maximize the effectiveness of the ground-based component of the BACODINE network.
The PI instrument teams should make a more vigorous effort to archive their data in a useful way in the HEASARC. The instrument teams should work with the HEASARC to produce software tools needed to access the archival GRO data.
Extreme Ultraviolet Explorer (EUVE)
Science Strengths
EUVE fills a unique spectral region that is replete with a rich spectrum of atomic and ionic lines representing a wide sampling of energies from 10^4 to over 10^7K. Both spectroscopy and photometry are possible covering the region 70 to 700A. During its prime mission, followed by its extended mission phase, the scientific returns from EUVE have been impressive. Significant contributions to many areas of astrophysics have resulted, among them cool star coronas, hot star photospheres, white dwarf atmospheres, cataclysmic variables, and the structure of the interstellar medium. Spectroscopy in the EUV region provides a complement to low resolution observations of ASCA for point sources. EUVE has developed innovative and cost-savings approaches to satellite operations, and has dealt well with software, data distribution, and educational outreach.
Science Weaknesses
Balanced against these strong points, the Committee finds that the scientific case for extending the EUVE mission a second time is not as compelling in comparison to plans for other missions in the competition. Many of the brightest targets accessible to EUVE have been measured; remaining targets will require long integration times. Some of the programs proposed for this EUVE extended mission could be carried out more effectively in other ways.
Recommendation
For the final years of EUVE, the Committee encourages observations that focus on the unique strengths of the mission, such as the study of nearby objects. The Committee recommends that EUVE mission operations continue through FY'97. Funds for the EUVE Guest Observer program will be distributed via the ADP program in order to allow analysis of EUVE data alone or in conjunction with other observations. Given the present budget constraints, only reduced funding for EUVE operations is available through FY97 unless additional funds are found. Within available funds, EUVE should be encouraged to explore ways to extend science observations as long as possible.
Infrared Space Observatory (ISO)
Science Strengths
The ESA Infrared Space Observatory, launched in November 1995, is the major infrared space mission of this decade. It has a complex suite of instruments for imaging, photometry, and spectroscopy at various resolutions between 2.5 and 240 micron. Already, it has achieved an extraordinary variety of observations affecting nearly all areas of astronomy. These observations are providing insight into solar system objects, cool or obscured stars, protostellar and protoplanetary regions, dusty and primeval galaxies, active galaxies, and the chemistry of the interstellar medium in the Milky Way and other galaxies. Not only will outstanding science be done, but this science will point the way to areas of infrared astronomy which will be the most exciting frontiers for SIRTF and will produce a knowledgeable community of US infrared astronomers to optimize the planning and use of SIRTF.
US astronomers participate in this billion dollar mission with guaranteed time as members of ISO instrument teams and as members of US Key projects. In addition, a large number of US astronomers (135 PIs from 56 institutions) successfully competed for ISO guest observer time, receiving 34% of the available open time. The return to the US community will be further enhanced by the significantly longer lifetime now anticipated for ISO (24 months vs 16 months), which means there will be a second opportunity for proposals. In addition, the support of proposals and data analysis provided in the US through IPAC enhances the overall efficiency of US involvement, and allows the potential for longer term data analysis and archiving tools that will benefit the entire ISO user community. In the judgment of our Senior Review, ISO is proving an outstanding success, and we are extremely pleased at the extent of involvement by US astronomers.
Science Weaknesses
The ISO instruments are complex, sensitivity is lower than expected for some instruments, and calibration is more difficult than expected because of on-orbit changes in the detectors. Nevertheless, the interface provided by IPAC between US users and the European instrumentation teams and the data analysis tools being developed at IPAC will eventually lead to adequate results for US observers.
Recommendation
This 1996 Senior Review ranks ISO number one among the missions considered in terms of scientific productivity relative to the NASA investment. In our view, the scientific return can be greatly leveraged with further modest investments. For this reason, we recommend an augmentation of both the data analysis funds for US Guest Observers as well as for the science operations, data analysis, and archiving tools at IPAC.
The needs at IPAC are more urgent since these tools need to be developed in advance of the actual observations. For the observers, the enhanced funding can await the time after observations are actually obtained. Because of the unexpectedly large number of US users, current staffing at IPAC cannot meet demand. Also, because of incomplete European plans for a data archive, IPAC must begin developing an archive.
Consequently, we recommend that the FY 97 and FY 98 ISO-related funding for IPAC be at a level of 3.6M (1M above the currently approved NASA plan for FY 97 and 0.8M above for FY 98), with the extra funding to be used only for archive development and support of US GTOs and GOs. Augmentation is recommended for data analysis funding to GOs in FY 98 (1.8M increase to 3.5M) and FY 99 (0.8M increase to 2.8M).
It appears that the cost per FTE is significantly higher at IPAC than at other data centers we examined. We strongly urge IPAC to explore methods to reduce their cost per FTE.
Roentgensatellit (ROSAT)
Science Strengths
The ROSAT mission has been extraordinarily effective in addressing many issues in X-ray astronomy, at extremely low cost to NASA. ROSAT's unique capabilities - spatial resolution of ~5 arcsec over a 40 arcmin field of view - justify continuing US participation in observations. The large amounts of HRI observing time available enable acquisition of extremely valuable high-resolution maps of large supernova remnants, crowded star clusters, the Magellanic clouds and other nearby galaxies, and clusters of galaxies. Having a large library of such pathfinder images in the ROSAT data base will greatly increase the efficiency of AXAF.
The extensive set of unique PSPC observations is an irreplaceable trove of data on tens of thousands of faint point sources, plus many complex extended emitting and absorbing objects. It will be the basis for many studies of stellar and extragalactic astronomy, diffuse x-ray emission, supernova remnants, and galactic structure. The ROSAT Bright Source Catalog, which was recently released, includes a number of sources that can be imaged with the HRI. The recent observation of X-rays from Comet Hyakutake demonstrates ROSAT's continuing capability for making surprising discoveries.
Science Weaknesses
With the loss of the PSPC, ROSAT has virtually no spectroscopic capability. ROSAT's sensitivity is limited to soft x-rays.
Recommendation
ROSAT continues to provide an excellent opportunity to derive important and long-lasting science at an unusually low cost to NASA. The Panel recommends funding for the US ROSAT effort at approximately $1M/year for 1997-99. In addition, we recommend that some support be given to Guest Investigators on ROSAT by allowing them to propose through the ADP program. ROSAT should continue operation through the launch of AXAF, and the data archive should be completed by the end of FY 99.
SAX - (Satellite per Astronomia X "Beppo"))
Science Strengths
The unique capability of the Italian-Dutch BeppoSAX satellite is its ability to measure simultaneously, with cross-calibrated instruments, the spectrum of both galactic and extragalactic objects from 0.1 to over 100 keV. The principal science goals include measurement of the broadband spectrum of AGN, broad-band spectral monitoring of galactic X-ray binaries, and detection of X-ray (2-30 keV) counterparts to gamma-ray bursts using the Wide Field Camera.
Science Weaknesses
The effective area of the low and medium energy instruments is smaller than for other current and near-future missions; e.g., the proposed studies of external galaxies, supernova remnants, faint point sources, galaxies clusters, and stars are likely to be made with ROSAT, ASCA, AXAF, XMM, and ASTRO-E. Timing observations of bright sources can be better achieved with XTE. The approved US programs are, in general, good uses of SAX's capabilities, but do not appear to offer breakthrough opportunities.
Recommendation
It is clear that the software situation needs improvement, although there seems to be a path to providing both analysis software for US users and basic datasets for a usable archive at relatively modest costs. Given the excellent record of the HEASARC in providing cost-effective analysis tools and user-friendly archives, the Committee feels that MO&DA funding for SAX should be focused there. The Committee believes that the establishment of a SAX archive will give US scientists access to a valuable observational capability and an important archive of high energy astrophysics data at extremely modest cost. US SAX investigators should have an opportunity to propose to the ADP program for support to carry out their SAX Guest Investigator programs.
Space Very Long Baseline Interferometry (SVLBI)
Science Strengths
The Japanese VSOP mission provides a space radio telescope that together with an international array of ground-based telescopes, comprises the first Space Very Long Baseline Interferometry (SVLBI) facility. The basic scientific strength of the mission lies in the gain of a factor of three in angular resolution at the three operating frequencies compared with ground-based arrays. This improvement in angular resolution makes possible a number of important and interesting investigations. Examples include: a test of the predicted limit to source brightness temperature imposed by inverse Compton cooling, study of superluminal motions closer to the central engines of active galactic nuclei (AGN), study of accretion disk structures on subparsec scales via H2O maser emission, and imaging of galactic maser spot shapes.
Science Weaknesses
Ground-based observations at the same spatial resolution provided by SVLBI, although at higher frequencies and of admittedly poorer quality, have not yielded significant new information on AGN's. The small size (8m) of the space element means the amount of interesting science will be limited by the availability of the largest ground-based telescopes and may be restricted to the brighter 100 sources of the roughly 1000 that can be imaged by SVLBI.
Recommendation
The proposal requests data analysis support for only those PI's ineligible for NSF support - (14) individuals at JPL, IPAC, and SAO. Data analysis is complex for SVLBI and will require, at least initially, travel to NRAO-Socorro for training. Science support is important for SVLBI scientists at Federally Funded Research and Development Centers (FFRDC) who have been awarded observing time, and should be provided during the prime phase of the VSOP mission.
Overall ranking of SVLBI in this Senior Review and the constraints of the budget argue for funding at roughly one-third of the level requested.
Rossi X-Ray Timing Explorer (RXTE)
Science Strengths
The Rossi-XTE is in the first year of its prime science mission, and the first 6 months of operation have produced new and exciting results on the millisecond variability of neutron stars, bursting pulsars and the long-term variability and spectra of AGN and X-ray transients. The prime advantages of XTE over other X-ray missions are its capability for observations on extremely short timescales, its broad bandpass, and its flexible scheduling, which allows rapid observation of transient phenomena as well as long term monitoring studies of variable X-ray sources. The All Sky Monitor provides the capability for notification of new X-ray transients and the production of long term light curves for bright sources. The panel was pleased with the rapid availability of 100% open time for the entire community. The wide range of target capabilities has led to a large proposal response from the scientific community.
Science Weaknesses
The satellite and detectors were designed for observation of the brightest compact sources, so targets at low flux levels (many ROSAT sources, galaxies, SNR) are not suitable. The high and variable background is a limiting problem for many programs. No argument is made for how many sources need to be observed to achieve the scientific objectives (e.g. how many AGNs need to be observed, and for how long, in order to significantly advance the field.) It is too early to tell if the detection of Millisecond Quasi-Periodic Oscillators (MS QPOs) will solve fundamental problems with neutron stars or are merely manifestations of neutron star "weather".
Recommendation
Since this mission is still operating in its prime phase, and is accomplishing its expected science goals, the mission should be funded at adequate levels to ensure operations and data analysis during its prime mission years. After year 2, the user support should be reduced as expertise is transferred to the Guest Observers. At the next Senior Review, a reassessment of the accomplishments in terms of remaining prime science should be done. In light of the limited range of problems to be addressed by XTE and extreme demands on available funding, FTE support must be reduced in future years.
TABLE 1
Astrophysics Senior Review 1996
Numerical Rank Order of Eight Astrophysics MO&DA Programs
[Average of Panel Member rankings on a scale of 1 (highest rank) to 8]

Program    97-98     99-00

ISO     1.0     2.3

ASCA     2.8     2.5

ROSAT     3.8     4.3

XTE     4.0     4.5

GRO     4.8     4.6

SVLBI     6.0     5.3

SAX     6.5     5.1

EUVE     7.1     7.3

First Results from BEPPOSAX
L. Piro(*) on behalf of the BeppoSAX team
(*) BeppoSAX Mission Scientist
Istituto Astrofisica Spaziale, C.N.R., Via E. Fermi 21, 00044
Frascati, Italy
e-mail: saxsci@alpha1.ias.fra.cnr.it
Abstract
The X-ray satellite BeppoSAX, a major programme of the Italian space agency (ASI) with participation of the Dutch space agency (NIVR), was successfully launched from Cape Canaveral on April 30, 1996. After a 2 month period devoted to engineering check out that confirmed the nominal functionality of the satellite and the scientific payload, we have performed a series of observations of celestial objects to calibrate the instruments and verify their scientific performance. Here we will present some preliminary results obtained in this phase on:
1) the X-ray pulsar Vela X-1 and the AGNs 3C273 and NGC 4151, as examples of the broad spectroscopy of bright and weak sources,
2) the observation of the Galactic center to show the capabilities of monitoring wide regions of the sky, and
3) some light curves of gamma-ray bursts.
They confirm the expected scientific capabilities of the mission.
1. Introduction
The X-ray satellite SAX, named BeppoSAX after launch in honour of Giuseppe (Beppo) Occhialini, is the first X-ray mission with a scientific payload covering more than three decades of energy - from 0.1 to 300 keV - with a relatively large area, good energy resolution, and with imaging capabilities (resolution of about 1 arcmin) in the range 0.1-10 keV. This capability, in conjunction with the presence of wide field instruments primarily for discovering transient phenomena which can then be observed with the broad band instruments, provides an unprecedented opportunity to study the broad band behaviour of several classes of X-ray sources.
The broad band capability is provided by a set of instruments co-aligned with the Z axis of the satellite; these Narrow Field Instruments (hereafter NFI) are:
MECS (Medium Energy Concentrator Spectrometers): a medium energy (1.3-10 keV) set of three identical grazing incidence telescopes with double cone geometry (Citterio et al. 1985, Conti et al. 1994), with position sensitive gas scintillation proportional counters in their focal planes (Boella et al. 1996a).
LECS (Low Energy Concentrator Spectrometer): a low energy (0.1-10 keV) telescope, identical to the other three, but with a thin window position sensitive gas scintillation proportional counter in its focal plane (Parmar et al 1996).
HPGSPC, a collimated High Pressure Gas Scintillation Proportional Counter (4-120 keV, Manzo et al. 1996).
PDS, a collimated Phoswich Detector System (15-300 keV, Frontera et al 1996)
Access to large regions of the sky (~1000 square degrees) with a resolution of 5' in the range 2-30 keV is provided by two coded mask proportional counters (Wide Field Cameras, WFC, Jager et al. 1996), perpendicular to the axis of the NFI and pointed in opposite directions.
Finally, the anticoincidence scintillator shields of the PDS (GRBM) will be used as a gamma-ray burst monitor in the range 60-600 keV with a fluence greater than about 10^-6 erg cm^-2 and with a temporal resolution of about 1 ms.
More details on the mission and its instruments can be found in Piro, Scarsi & Butler (1995), Boella et al. (1996b), in the special session devoted to BeppoSAX of the SPIE Vol. 2517 and on line at:
http://www.sdc.asi.it
2. The Science Verification Phase
The goal of the Science Verification Phase was to verify the expected scientific capabilities of the mission and to calibrate the instruments. To this aim a series of objects with well known properties were selected and observed.
2.1 Broad Band Spectroscopy with the NFI
2.1.1 The X-ray pulsar Vela X-1
Figure 1. The spectrum of Vela X-1 from the MECS, HPGSPC and PDS fitted with a power law with exponential cut-off. The residuals show the presence of an iron line and absorption edge as well as an absorption feature around 60 keV.
Figure 2. The best fit to the Vela X-1 spectrum obtained with a power law with 2 cyclotron lines at about 30 and 60 keV, an iron line and absorption edge (see text).
In figure 1 we show the spectrum of the X-ray pulsar Vela X-1 in the range 3-200 keV obtained in a 30 ksec observation with the MECS, HPGSPC and PDS. The data are fitted with a power law with absorption and an exponential cutoff. The residuals show large deviations from the model. The most noticeable are those due to the presence of an iron line and absorption edge in the 6-8 keV region and an absorption feature around 60 kev. Following the results from GINGA (Mihara 1995) we fit the spectrum with a power law with two cyclotron absorption lines, plus an iron line and iron edge. This model provides a satisfactory fit to the data (figure 2). The values of the cyclotron lines are remarkably similar to those obtained by Mihara in a fit employing the same model. The first line is at around 27 keV, with an optical depth of about 0.2, whereas the optical depth of the second harmonic at 54 keV is about 10 times larger. The two lines are rather broad, being respectively about 15 keV and 35 keV. Further analysis is ongoing to study different models and phase-resolved spectra.
2.1.2 The AGN 3C273 and NGC 4151
Figure 3. The spectrum of 3C273 by the LECS, MECS, and PDS fitted with a simple power law with absorption.
One of the scientific objectives of BeppoSAX is to measure the broad band spectrum of relatively faint sources such as AGNs. In figure 3 we show the spectrum of 3C273 observed with the LECS, MECS and PDS fitted with a simple power law with absorption. This BeppoSAX observation is a joint program with RossiXTE and ASCA aimed at cross-calibrating the satellites.
The X-ray spectrum of NGC 4151 is the most complex observed so far in AGNs, being characterized by narrow and broad spectral features from soft to hard X-rays (e.g. Perola et al. 1986, Warwick et al. 1995, Zdziarski et al. 1996). It is thus the best candidate to verify the unique capability of BeppoSAX to disentangle spectral features over the 0.1-200 keV energy range.
Figure 4. The spectrum of NGC 4151 observed by the LECS, MECS and PDS (from left to right) fitted with a complex model: a power law, a soft X-ray component, a complex absorbing medium, and a high energy cut-off.
Figure 5. The spectrum of NGC 4151 in the MECS around the iron complex region. The best fit model is the same as that in fig.1 to show in the residuals the clear presence of the iron line and absorption edge.
Figure 6. The model needed to fit the BeppoSAX spectrum of NGC 4151 (see text)
In figure 4 we show the spectrum of the LECS (7 ksec of effective exposure time), MECS (about 55 ksec) and PDS (about 35 ksec) fitted with a complex model of the broad continuum components. The presence of an iron line and iron absorption edge is very clear in the residuals of the MECS (figure 5). In figure 6 we show the best fit model spectrum required to fit the data, composed of an intrinsic power law with an exponential cut-off around 70 keV; an absorbing medium with a column density ~10^23 cm^-2 which is likely producing the observed iron fluorescence line and the iron absorption edge; this medium has a complex structure, well described by a leaky absorber, that allows a fraction (~20%) of the intrinsic power law continuum to be transmitted without strong absorption. However, to be consistent with the spectrum (and lack of variability, see Perola et al. 1986) in soft X-rays, this component needs to be absorbed by a further, uniform absorbing screen with N_H ~ 10^22 cm^-2. Finally, a soft component, possibly of thermal origin (kT ~ 0.4 keV), external to the uniform absorber, is present below 1 keV.
2.2 Monitoring a large region of the X-ray sky: transients and gamma-ray bursts
One of the primary scientific goals of BeppoSAX is the observation of transient phenomena in the sky. Two set of instruments are devoted to this purpose: the two WFC and the GRBM.
Figure 7. The WFC observation of the Galactic center region.
In figure 7 we show a 40 degree by 40 degree image centered on the Galactic center as observed by one of the WFC. The field shows 27 sources distributed along the galactic plane. To our knowledge this is the largest field ever imaged in X-rays in a single observation.
An exciting example of the capability of BeppoSAX to observe transient phenomena is the simultaenous observation of the gamma-ray burst GB960720 by the WFC and the GRBM (Piro et al. 1996a http://www.sdc.asi.it/first/iaucirc.html ). The light curve in the GRBM is shown in figure 7. The WFC image allows a localization of the event within a few arcmin. This observation has triggered a series of follow-up observations in different energy bands (e.g. Frail et al. IAUC 6472; Murakami et al. IAUC6481). We have carried out a deep observation of the field with the NFI, that has led to the discovery of a previously unknown X-ray source in the WFC error box (Piro et al. 1996b http://www.sdc.asi.it/first/grb.html ). It is not yet clear whether this source is actually related to GB960720 (see also Greiner et al. IAUC 6487). Along with the imaging information, the wide band energy range covered simultaneously by the WFC and the GRBM provides important information on the evolution of the burst at different energies.
In figure 8 we show some examples of gamma-ray burst light curves, in the different energy ranges of the two instruments.
Figure 8. A sample of light curves of gamma-ray bursts observed by the GRBM
References
Boella G. et al. 1996a, A&A Suppl. Ser., in press.
Boella G. et al. 1996b, A&A Suppl. Ser., in press.
Citterio O. et al. 1985, SPIE Proc. 597, 102
Conti G. et al. 1994, SPIE Proc. 2279, 101
Frontera et al. 1996, A&A Suppl. Ser., in press.
Jager R. et al. 1996, A&A Suppl. Ser., in press.
Manzo G. et al. 1996, A&A Suppl. Ser., in press.
Mihara 1995 PhD Thesis, Riken IPCR CR-76.
Parmar A. et al., 1996, A&A Suppl. Ser., in press.
Perola G.C. et al. 1986, ApJ 306, 508
Piro L., Scarsi L. & Butler R.C., 1995, SPIE Proc. 2517, 169
Piro L. et al. 1996a, IAU circ. 6467
Piro L. et al. 1996b, IAU circ. 6480
Warwick R.S., Done C. & Smith D.A. 1995, MNRAS 275, 100
Zdziarski, A. A., Johnson, W. N. & Magdziarz P. 1996, MNRAS 283, 193
CHIANTI Atomic Database Package
by Ken Dere
We would like to announce the release of the first version of the CHIANTI atomic database package. CHIANTI includes a comprehensive set of the most up-to-date atomic data available for calculating astrophysical emission line spectra at wavelengths greater than 50 Angstroms as a function of both density and temperature. IDL procedures to calculate synthetic spectra, density and temperature sensitive line ratios, etc are also included. A paper describing the CHIANTI atomic database package has recently been submitted to Astronomy and Astrophysics Supplements and is authored by K. P. Dere, E. Landi, H. E. Mason, B. C. Monsignori Fossi and P. R. Young. CHIANTI will continue to be developed in the future and, in particular, is being extended to cover the X-ray region of the spectrum.
CHIANTI is available by anonymous ftp to louis14.nrl.navy.mil in the pub/chianti directory and through our WWW page http://wwwsolar.nrl.navy.mil/chianti.html. The README file should provide the necessary information for downloading the files and getting started. If you have any questions or would like to be put on a mailing list to be informed of the status of the CHIANTI database, please email Ken Dere at dere@halcyon.nrl.navy.mil.
SEUS Web Page
by Fiona Harrison
The Structure and Evolution of the Universe Subcommittee (SEUS) of the SScAC would like to point out the existence of a web page http://www.srl.caltech.edu/seus which is intended to provide the community information about the meetings of this subcommittee, the roadmap process, and information about current and proposed missions relevent to the SEU science theme. We are maintaining a public bulletin board at this site intended for community input on missions, science, technology and other items of interest. This bulletin board will be reviewed regularly by SEUS members and by the SEUS chairman, Roger Blandford.
ACE Science Workshop
by Richard Mewaldt
First Announcement
ACE Science Workshop
January 7, 8, & 9, 1997
Pasadena, CA
A scientific workshop for NASA's Advanced Composition Explorer (ACE) mission will be held on January 7, 8, and 9, 1997 on the campus of the California Institute of Technology. ACE includes nine instruments that will measure the elemental, isotopic, and ionic charge state composition of nuclei with Z=1 to 28 from solar wind energies (~1 keV/nuc) to galactic cosmic ray energies (~500 MeV/nuc). It will be launched in August 1997 into orbit about the inner Lagrangian (L1) point, where it will provide unprecedented measurements of energetic nuclei of solar, interplanetary, and galactic origin, and also provide real-time solar wind and other interplanetary data.
The January workshop will include fifteen invited speakers that will discuss the broad range of scientific objectives that ACE can address. The scientific community is invited to present ideas for the use of ACE data in a poster session, and by participation in several splinter sessions that will focus on topics involving solar wind origin and acceleration, the composition of the solar corona, interstellar material observable as pick-up ions and anomalous cosmic rays, solar/interplanetary particle acceleration, and the origin, acceleration, and transport of galactic cosmic rays. A special issue of Space Science Reviews is also planned.
To get on the mailing list for additional workshop announcements send your name and address by e-mail to: acemeet@srl.caltech.edu or fax it to Debby Kubly at 818-449-8676.
Questions about the scientific program can be addressed to any of the following members of the organizing committee:
Jon Ormes (301-286-8801; ormes@lheavx.gsfc.nasa.gov),
Bill Feldman (505-667-7372; wfeldman@lanl.gov),
George Gloeckler (301-953-5412; gloeckler@umdsp.umd.edu),
Glenn Mason (301-405-6203; mason@sampx2.umd.edu),
Richard Mewaldt (818-395-6612; mewaldt@srl.caltech.edu),
Eberhard Moebius (603-862-3097; moebius@rotor.unh.edu).
Aspen Workshop on Gamma Ray Bursts
by D. Lamb
A second workshop on gamma-ray bursts will be held at the Aspen Center for Physics from 18 August - 6 September 1997. The co-organizers are Don Lamb (University of Chicago), Michael Briggs (Marshall Space Flight Center), and Igor Mitrofanov (Institute of Space Research, Moscow).
A number of morning seminars will be given to provide an overview and a framework for discussing important issues, but most of the action will take place in small working groups and in discussions between individual participants during other mornings and in the afternoons.
The workshop will focus on the predictions of galactic corona and cosmological models, and the evidence for and against these models. Specific issues that are likely be discussed at the workshop include whether or not galactic corona models can accomodate the degree of isotropy of bursts on the sky that is observed; whether or not cosmological tests are overwhelmed by source evolution; whether or not various cosmological tests are consistent with each other; whether or not there is a lack of bright galaxy optical counterparts; whether or not burst spectra show lines, and if so, whether or not the lines are consistent with what is expected if they are due to cyclotron resonant scattering in strong magnetic fields; whether or not burst sources repeat; and what are the best next steps to take to try to get to the bottom of this mysterious phenomenon.
Persons interested in participating in the workshop should apply through the regular admissions process of the Aspen Center for Physics. This can be done electronically through the Aspen Center for Physics Web page at http://andy.bu.edu/aspen or by sending a completed application form (which can be obtained from the Center Web page) to Aspen Center for Physics, 700 West Gillespie Street, Aspen, CO 81611, U.S.A.
Obituaries - HETE, MARS 96, and CUBIC
HETE - by J.-L. Atteia, T. Cline, E. Fenimore, K. Hurley, M. Matsuoka, D. Lamb, G. Ricker, and S. Woosley
Tragically, the High Energy Transient Experiment (HETE) was lost during launch on November 4th when the third stage of the Pegasus rocket failed to separate from the payload containing HETE (and SAC-B). Although the third stage of the rocket and the attached payload did achieve orbit, HETE was "trapped" inside the can supporting SAC-B. Unable to see, communicate, or recharge its batteries, HETE died one day later. Before HETE died, the NOAA VHF tracking station at Wallops Island and a radio antenna at Los Alamos National Laboratory managed to detect radio transmissions from HETE, verifying that, insofar as we can tell, HETE was operating as planned.
It is perhaps worthwhile to review briefly the history and some of the unique aspects of the HETE mission. HETE began as an idea in workshops at San Diego and at Santa Cruz in the early 1980's. The name and the three instruments were laid out in the Santa Cruz conference proceedings in 1983. At first the HETE concept was broad, with a mass and size requiring a dedicated Delta-class launcher, and expensive, with costs in excess of $100M. In 1986, the HETE concept was sharply re-focused on determining accurate gamma-ray burst positions and carrying out multi-wavelength observations from a single small satellite. Japanese and French collaborators were invited to join the effort, enhancing both the scientific capability and the cost effectiveness of the mission. The HETE Team eventually grew to encompass several countries and dozens of people. It also came to include ground-based observers around the world.
HETE was a ground-breaking mission in many ways. First, the idea of multi-wavelength observations across 6 orders of magnitude in energy (UV, X-ray, gamma-ray) was a novel way to study gamma-ray bursts. Seeing correlated behavior in these three energy bands would highly constrain possible models. HETE also had improved sensitivity in the mid-x-ray band (~2-20 keV) compared to BATSE and could have provided new information about the x-ray behavior of gamma-ray bursts, as well as interesting secondary science studies of x-ray bursts and flare stars. Perhaps the most exciting HETE innovation was the idea of getting word of a gamma-ray burst to these observers in seconds, so that they could turn their telescopes on the burst while it was still happening. HETE would have done that, and in doing so, might have solved the problem of what gamma-ray bursts are.
Programmatically, HETE was the prototype of the "faster, cheaper" mission, an approach now endorsed by NASA. HETE pioneered an entirely new mission management philosophy, in which a fixed price was set for the mission, and the scientists involved were given the freedom and the responsibility of making trade-off or de-scoping decisions, if needed in order to meet the fixed price. HETE pioneered the operation of a NASA astrophysics satellite through direct up/down links from primary and secondary ground stations established by the scientists involved, rather than through a NASA center. As a result, HETE came to involve a network of dozens of observatories scattered worldwide that were dedicated to rapidly responding to HETE detections.
Although the original HETE hardware is now dead, the ideas underlying the mission and the unique synergy of individuals, laboratories, and countries that really constitute HETE are very much alive. Most importantly, the scientific motivation for HETE remains. We have thus begun to consider and to discuss with NASA the possibility of resurrecting the HETE mission. Our Japanese and French colleagues enthusiastically support this possibility. The existence of complete blueprints for the spacecraft and flight spares for parts of the instruments, as well as the experience gained by building HETE, would allow us to refly HETE for a small fraction of what has already been spent. For a total of approximately $6.5 M, a new HETE could be ready to fly in 28 months.
The HETE Team will be happy to provide additional supporting information. Material on the technical and scientific status of HETE, photos of the HETE hardware, details of the Pegasus XL launch failure, and a description of the worldwide HETE Burst Alert Network is also available on the HETE Web page located at
http://space.mit.edu/HETE/ .
MARS 96 by K. Hurley
According to a Russian saying, "a tragedy never comes alone". This proved to be true on November 16 when, after a nominal launch into low Earth orbit, the fourth stage of the Proton rocket carrying the Russian Mars 96 mission failed to place it into an interplanetary orbit to Mars. The spacecraft re-entered and burned up over the South Pacific. Onboard were three gamma-ray burst detectors which would have completed the Third Interplanetary Network. One was a scintillator array provided by the CESR in Toulouse, France, which was similar to instruments placed aboard the ill-fated Phobos 1 and 2 missions. The second was the Precision Gamma-Ray Spectrometer, a Los Alamos/IKI collaboration. PGS comprised a germanium detector for studies of the Martian surface, and was equipped with a trigger system and a fast memory for studying gamma-ray bursts. The third was the Gamma Ray Burst Monitor, an experiment developed by UC Berkeley Space Sciences Laboratory, Lawrence Berkeley Laboratory, Lawrence Livermore National Laboratory, and Goddard Space Flight Center, in collaboration with IKI. GRBM (also known as "Burstman") was a prototype for a small, low cost instrument which could be placed on mass-constrained planetary missions.
CUBIC by David Burrows
The Pegasus that launched HETE contained a double payload. The second satellite was the Argentinian/US SAC-B, and among other instruments, it carried CUBIC (Cosmic Unresolved Background Instrument Using CCD's), to measure the spectrum of the soft X-ray diffuse background over the energy range 0.2 - 10 keV over a large part of the sky. The CUBIC home page http://www.astro.psu.edu/xray/cubic/ contains more information on this experiment.
Future Meetings
by K. Hurley
A very complete list of astronomical meetings exists on the Hawaii web site http://cadcwww.dao.nrc.ca/meetings/meetings.html Here is my partial list of meetings that I have received notices for.
189th AAS, Toronto, Canada, January 12-16, 1997. Of special interest to HEAD members are the Rossi Prize Lecture, the HEAD business meeting, and the special HEAD sessions, all on Tuesday, January 14.
Contact: http://www.aas.org/meetings/aas189/program/index.html
Science with BeppoSAX (First Results from the Science Verification Phase), andBeppoSAX Scientific Software and Calibration (Demonstration sessions on software and calibration of BeppoSAX)
January 21-22, 1997, Rome, Italy.
Contact: mcappi@tesre.bo.cnr.it
All-Sky X-Ray Observations in the Next Decade - A Workshop for ASM and GRB Missions in the X-ray Band, March 3-5, 1997, Wako, Japan
Contact: http://www.riken.go.jp/lab-www/cosmic/workshop.html
Fourth Compton Symposium, Williamsburg VA, April 28-30, 1997.
Contact: kurfess@osse.nrl.navy.mil or
http://osse-www.nrl.navy.mil/cgrosymp.htm
X-ray Surveys Workshop, Potsdam, Germany, June 18-20, 1997
Contact: http://xray.gsfc.nasa.gov/xsurvey/xsurvey.html
25th International Cosmic Ray Conference, Durban, South Africa, July 28 - August 8, 1997.
Contact: http://www.puk.ac.za/fskdocs/icrc97
Aspen Center for Physics 1997
Numerous informal workshops, including Formation and Evolution of Extrasolar Planets and Brown Dwarfs (May 26- June 6), Microlensing, Dark Matter, and Galactic Structure (May 26 - June 13), Nonlinear Dynamics in Astrophysics and Geophysics (June 2 - June 13), and Gamma-Ray Bursters (August 18 - September 5),
http://andy.bu.edu/aspen/ , or jane@acp1.zgsw.com, or phone (970) 925 2585
23rd General Assembly of the IAU, Kyoto, Japan, August 18-30, 1997.
A Joint Discussion on High Energy Transients will be part of the program, as well as a symposium on hot astrophysical plasmas, five other symposia, and about 15 joint discussions, on a wide range of astronomical topics. Anyone interested in presenting a paper or poster should contact Virginia Trimble, chair of the SOC (vtrimble@astro.umd.edu). IAU membership forms were distributed in the August AAS newsletter, and there is an opportunity to apply for travel funds from a block NSF/AAS grant. The IAU itself provides some travel support for young astronomers and those from soft-currency projects.
Contact: iau@iap.fr
Fourth Huntsville Symposium on Gamma-Ray Bursts
15-19 September 1997 - Huntsville, AL
Contact: C. Meegan (meegan@ssl.msfc.nasa.gov)
http://www.batse.msfc.nasa.gov/information/4hgrbs
The Active X-ray Sky, Emphasing Results from BeppoSAX and RXTE,
October 22-24, 1997, Rome, Italy
Contact: saxsci@alpha1.ias.fra.cnr.it
HEAD 1997 meeting, November 4-7, 1997, Stanley Hotel, Estes Park, CO
Contact: eureka@netcom.com, or http://www.eurekasci.com


HEADNEWS, the electronic newsletter of the High Energy Astrophysics Division of the American Astronomical Society, is issued by the Secretary-Treasurer, at the University of California Space Sciences Laboratory, Berkeley, CA 94720-7450. The HEAD Executive Committee Members are:
Neil Gehrels, Chair (gehrels@lheavx.gsfc.nasa.gov)
Gordon Garmire, Vice-Chair (garmire@astro.psu.edu)
David Burrows (burrows@astro.psu.edu)
Lynn Cominsky (lynnc@charmian.sonoma.edu)
Chuck Dermer (dermer@osse.nrl.navy.mil)
Martin Elvis, Member and Past Chair (elvis@cfa.harvard.edu)
Kevin Hurley, Secretary-Treasurer (khurley@sunspot.ssl.berkeley.edu)
Chryssa Kouveliotou (kouveliotou@batse.msfc.nasa.gov)
Chip Meegan (meegan@ssl.msfc.nasa.gov)
Paula Szkody (szkody@astro.washington.edu)
Please send newsletter correspondence to khurley@sunspot.ssl.berkeley.edu