Chandra's First Decade of Discovery

Session 9 : Compact Objects

Chandra's Contribution Toward “Grand Unification”: Unravelling the Surprising Diversity in Neutron Stars

Victoria Kaspi, McGill University

The last decade has shown us that the observational properties of neutron stars, particularly those in their youth, are remarkably and surprisingly diverse. From magnetars to RRATs, from radio pulsars to the so-called “isolated neutron stars”, an enormous puzzle in this field is why we see so many different observational manifestations of what one naively might have thought to be a relatively simple object. In this talk I will review the field, trying to rationalize the many different current “types” of neutron stars, while of course highlighting the many important contributions made by Chandra toward solving this puzzle.

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Discovering X-ray Bright Neutron Stars for Current and Next-Generation Observatories

Derek Fox, Pennsylvania State University
R. E. Rutledge (McGill University), A. S. H. Shevchuk (U. Arizona), R. E. Letcavage (U.C. Irvine)

I will discuss our ongoing program of Swift, Chandra, and XMM-Newton observations aimed at discovering new X-ray bright neutron stars suitable for detailed study with current and next-generation X-ray observatories. This program recently yielded the eighth known isolated neutron star (INS), the first to be discovered in six years,and the highest-temperature INS known: 1RXS J141256.0+792204 or “Calvera.” Our program begins by using statistical techniques of cross-correlation to select objects from the ROSAT Bright Source Catalog that are unlikely to have off-band counterparts. Short Swift observations provide arcsecond X-ray positions and simultaneous UV/optical imaging to confirm the absence of bright counterparts. In this way, we have filtered an initial target list of almost 200 bright X-ray sources down to 36 candidate neutron stars now requiring sub-arcsecond X-ray positions and deep optical imaging for final confirmation; completion of our current programs with Chandra and the Gemini telescopes has the potential to double or triple the number of INSs known. As a demonstration of the interesting science that can result from study of these objects, I will present the results of our recent extended 30 ksec Chandra + ACIS (1/8 subarray)observation of Calvera.

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Modeling the Dynamical and Radiative Evolution of a Pulsar Wind Nebula inside a Supernova Remnant

Joseph Gelfand, New York University
Patrick Slane (CfA), Weiqun Zhang (NYU)

A pulsar wind nebula inside a supernova remnant offers a unique insight into the properties of neutron stars, pulsar winds, and the progenitor supernova. However, this is complicated by the rapid and complicated evolution such a pulsar wind nebulae undergoes. In this talk, I will present a model for the dynamical and radiative evolution of a pulsar wind nebulae inside a remnant which can extract the desired information from observations, and demonstrate its success in reproducing the total radio to X-ray spectrum of the Crab Nebula.

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Chandra Observations of the Vela Pulsar Wind Nebula

George Pavlov, Pennsylvania State University
Oleg Kargaltsev (University of Florida)

The nearby Vela pulsar wind nebula (PWN) provides a unique opportunity to study relativistic pulsar winds and their interaction with the ambient medium. First Chandra observations of the Vela PWN in 2000-2002 have shown the puzzling crossbow morphology of the bright inner PWN elements as well as the fainter bent outer jets and the large-scale diffuse emission. The entire Vela PWN turned out to be remarkably variable on a time scale of weeks, showing mildly relativistic motions of its elements.We will present first results of eight 40 ks Chandra ACIS observations of the Vela PWN in July-August 2009, taken with about one week intervals. These observations will provide a sequence of images optimized for studying the PWN variability. Very deep combined images will elucidate the large-scale structure and the complicated topology of the PWN. Spatially resolved spectroscopy will provide the spectra of the inner PWN elements with an arcsecond resolution, and it will allow us to trace the spectral evolution of the anisotropic outflows up to large distances from the pulsar.

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A Carbon Atmosphere for the Cassiopeia A Neutron Star

Craig Heinke, University of Alberta
Wynn Ho (University of Southampton)

The nature of the central compact objects in supernova remnants, showing thermal spectra but no radio pulsations, is a major mystery of the Chandra era. The youngest known CCO in Cassiopeia A is perhaps the most mysterious, as spectral fits with single-component models have given emitting areas too small for neutron star radii, while a hot spot should produce pulsations that have not yet been detected. We have produced a variety of light-element atmosphere models for neutron stars, and found that only unmagnetized carbon atmospheres provide both acceptable fits to the Cas A CCO spectrum (T~1.5e6 K, R~12 km) and radius constraints consistent with modern NS models. Our result has ramifications for the evolution of NS surfaces, NS thermal evolution, and constraints on NS interior structure.

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