Special Call for Archival Research on the NS RX J 185636-375:
Accepted Proposals

PI: Frederik Paerels  
Proposal Title: The Mass and Radius of a Neutron Star: 
                Chandra LETGS Observations of RX J1856.5-3754

Abstract: 
 
    We propose to make a comprehensive analysis of the full Chandra
    dataset of observations of the isolated neutron star RX J1856.5-3754. Our
    preliminary analysis of the first 50 ks of data indicates the presence of
    absorption features in the LETG spectrum; with 500 ks of data we will
    characterize these features precisely, search for related features to confirm
    atomic identifications, and, potentially, measure both the mass and radius of
    this neutron star to ~10 % precision. Such a measurement would have immediate
    implications for the equation of state of bulk matter at greater than nuclear
    densities -- a regime where no other experimental constraints on -->
    -- theory exist or can be expected.

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PI: Roger Romani
Proposal Title: Neutron Star Atmospherics: 
                Towards the Mass and Radius of the Nearest Isolated Neutron Star
 
Abstract: 
 
    Identification of neutron star surface spectral features would
    strongly impact compact object physics and determine the high density EOS.
    RXJ185635-3754 provides the best hope of such measurement, as colors indicate
    strong opacity. However, existing data limits line EWs to values well below
    those of simple models. After pioneering the basic models, we have recently
    modeled rotational effects, surface re-heating and magnetic line shifts. These
    will be treated in the proposed work; they can account for the EW decrease, aid
    in line identification and are likely crucial to interpretation of the LETG
    spectrum. With our sophisticated atmosphere models and codes for
    (phase-resolved) spectral fitting, we will extract the best possible M and R
    constraints, whether or not lines are detected.

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PI: Frederick Walter    
Proposal Title: The Atmosphere and Interior of the Isolated Neutron Star RX J185635-3754

Abstract: 
 
    We request funding to analyze the spectrum of the isolated neutron
    star RX J185635-3754. Our analysis of the multiwavelength spectral energy
    distribution indicates that the surface composition is heavy elements, and not
    Hydrogen. We find a tight contraint on the gravitational redshift, suggesting
    that the star is more compact than most realistic equations of state allow. The
    short CHANDRA LETG GTO spectrum has marginal S/N for detecting the expected
    absorption lines; the deep DDT exposure will permit us to determine the surface
    composition, gravitational redshift, and possibly the surface magnetic field
    strength. We will use the X-ray spectrum in concert with the full
    multi-wavelength spectral energy distribution to assess the surface temperature
    structure.

Last modified: 05/02/03

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