An Einstein Observatory High Resolution Imager (HRI) image of Tycho's supernova remnant.
The HRC is a natural extension of proven technology based on microchannel plate imaging x-ray detectors. Because of the relative maturity of the HRC design we have made only a few changes in the instrument, and these tend to be simplifications of the design to improve reliability and/or to reduce cost. The HRC is the instrument of choice for reading out the Low Energy Transmission Grating Spectrometer (LETGS), and we have worked to improve the interface with this instrument.
Our scientific observing program covers many of the objectives
of the AXAF mission as stated in the original Announcement of
Opportunity including observations of the x-ray background,
quasars, active galaxies, clusters of galaxies, galactic winds,
globular clusters, x-ray pulsars, compact objects, x-ray binaries,
star formation regions, and stellar coronae. These data will be
used to help determine the nature of celestial objects from normal
stars to quasars, to improve our understanding of the physical
processes in and between objects, and to better understand the
history and evolution of the Universe.
Our observing program emphasizes the unique capabilities of the HRC
such as high angular resolution, low energy response, and
sub-millisecond timing and makes modest use of the LETGS expected
to be included in AXAF. While we have proposed to initiate
investigations for several specific topics, there are innumerable
observations available for the astronomical community to propose as
general observers. For example, studies of nearby galaxies (e.g.,
M31, SMC, LMC) can be carried out effectively with the HRC. These
include determination of the luminosity function, time variability
distribution and, insofar as possible, identification of
galactic sources for which the high spatial and temporal resolution
of the HRC is required. The HRC is also well suited for detailed
mapping of supernova remnants and for measuring the expansion rate
of young SNRs, such as SN1987a and Cas A, over the lifetime of
AXAF. Within each of the specific areas of investigation covered
by this proposal, the IPI time limitations leave a wealth of
observational opportunities for general observers. Examples in the
galaxy cluster area include detailed studies of nearby clusters,
systematic measurements of cluster gas temperatures, and
determination of the prevalence of gaseous galactic coronae as a
function of cluster gas density.
The power of the HRC derives from the following set of
characteristics:
The scope of HRC science covers many of the objectives of the AXAF mission as stated in the original Announcement of Opportunity and includes observations of the x-ray background, quasars, active galaxies, clusters of galaxies, galactic coronae, globular clusters, x-ray pulsars, compact objects, x-ray binaries and stellar coronae. Specifically, the scientific objectives we choose to investigate are:
Our observing program is limited by the available observing time and there are innumerable observational opportunities available for members of the astronomical community. Our observational targets as part of our program represent only a beginning to the scientific projects described. Extensive opportunities remain for general observers to participate in all the areas described above. Below we describe several individual targets of interest as well as summarize several broad areas of investigation for which the HRC is well-suited. In several of the scientific areas, the excellent spatial resolution, high time resolution, large field of view, and soft x-ray response make the HRC unique.
Studies of nearby galaxies can be carried out effectively with the HRC. These include determination of the luminosity function, time variability distribution and,insofar as possible, identification of galactic sources for which the high spatial and temporal resolution of the HRC is required. For example, single 10000 second exposures of M31 would cover large angular regions (32' x 32') providing excellent positional determinations (< 1") over the entire field to alimiting luminosity of 2 x 10^35 erg/s. More importantly, temporal variability of all the sources in the field could be investigated to the ultimate detector time resolution of 16 microsecond allowing searches for bursters, pulsars, QSO's, and other types of variability.
The HRC is ideal for studying possible extended emission around quasars. For example, hot gas either around the object itself or trapped in the potential of a group would be detectable by the HRC and could be studied with the LETGS.
The HRC is also well suited for detailed mapping of supernova remnants and for measuring the expansion rate of young SNRs, such as Cas A, over the lifetime of AXAF. Other unique SNR include Tycho and the Crab for detailed studies of spatial structure and pulsar searches or limits on the DC pulsar emission. Grating observations of SNR dominated by thermal emission - Tycho, Vela, Cygnus loop - provide powerful plasma diagnostics.
Eta Carina can be studied with direct imaging and with the low energy grating. Grating observations can yield elemental abundances of the material ejected and provide clues to the nature of the central object and the outburst.
Examples in the galaxy cluster area include detailed studies of nearby clusters, systematic measurements of cluster gas temperatures, and determination of the prevalence of gaseous galactic coronae as a function of cluster gas density. Very few nearby clusters, groups, or early-type galaxies are included in our proposal and many are well known objects which merit detailed analyses.
The scientific observations discussed above are only a small subset of the studies which the HRC makes possible. Wherever the highest spatial resolution and sensitivity are required the HRC will be the instrument of choice. While by no means exhaustive, the list below illustrates the wide range of these observations:
Planets: Detailed structure and variability of the aurorae of Jupiter and other planets; surface fluorescence mapping of the moon at 2 km resolution.
Interstellar medium: Size distributions of the dust grains towards galactic x-ray sources; ionization state and abundances of the hot phase of the interstellar medium through grating spectroscopy of galactic x-ray sources. The same techniques can limit the properties of any intergalactic dust and gas.
Stars: Monitor spectra and variability of T Tauri Stars in crowded fields (e.g. rho Oph). X-ray studies of evolved stars (giants and supergiants).
Supernova Remnants and Pulsars: Time resolved spectra of the Crab pulsar- what is the inter-pulse spectrum?; motions of the Crab 'wisps'; expansion of Cas A and motion of the knots; detailed study of the very soft, LMC supernova remnant sample; structure of synchrotron nebulae around radio pulsars and limits on pulsed x-ray emission.
Galaxies: Identify O-stars in M31 and the local group; resolve the bulge sources in nearby galaxies and study the distributions; attempt to understand the "super-Eddington" spiral-arm sources in nearby galaxies; search for pulsations in extragalactic compact binaries.
Radio Galaxies: Study emission mechanisms of the radio/optical/x-ray jets; confinement of radio lobes and jets and their interaction with intracluster medium.
Clusters of Galaxies: Cooling flows onto central galaxies; comparison with flows onto dominant poor group members and with isolated elliptical galaxies; detailed studies of nearby rich clusters and groups.
SAO has had substantial experience in working with and helping general observers through the Einstein Guest Observer Program and the ROSAT Program. We have found this experience to be mutually rewarding, and we are committed to assist AXAF observers who wish to use the HRC.
