Pannuti, Thomas G. and Rho, Jeonghee and Borkowski, Kazimierz J. and Cameron, P. Brian (2010) Mixed-morphology supernova remnants in x-rays: isothermal plasma in HB21 and probable oxygen-rich ejecta in CTB 1. Astronomical Journal, 140 (6). pp. 1787-1805. ISSN 0004-6256 http://resolver.caltech.edu/CaltechAUTHORS:20110106-115308139
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We present an analysis of X-ray observations of the Galactic supernova remnants (SNRs) HB21 (G89.0+4.7) and CTB 1 (G116.9+0.2), two well-known members of the class of mixed-morphology (MM) SNRs. Our analysis draws upon observations of both SNRs made with the Advanced Satellite for Cosmology and Astrophysics (ASCA): we have also used an archived Chandra observation of CTB 1 as part of this effort. We find a marked contrast between the X-ray properties of HB21 and CTB 1: in the case of HB21, the extracted spectra of the northwest and southeast regions of the X-ray-emitting plasma associated with the SNR can be fit with a single thermal model with marginally enhanced silicon and sulfur abundances. For both of these regions, the derived column density and temperature are N_H ~ 0.3 × 10^(22) cm^(−2) and kT ~ 0.7 keV, respectively. No significant spatial differences in temperature or elemental abundances between the two regions are detected and the X-ray-emitting plasma for both regions is close to ionization equilibrium. Our Chandra spectral analysis of CTB 1 reveals that this source is likely an oxygen-rich SNR with enhanced abundances of oxygen and neon: this result is quite surprising for an evolved SNR like CTB 1. The high angular resolution Chandra observation of CTB 1 reveals spectral variations across this SNR: in particular, we have detected localized hard emission with an angular extent of ~1'. The extracted ASCA spectra for both the southwest and northeastern regions of CTB 1 cannot be fit with a single thermal component and instead an additional component is required to account for the presence of excess emission seen at higher energies. Based on our fits to the extracted ASCA spectra, we derive a column density NH ~ 0.6 × 10^(22) cm^(−2) and a temperature for the soft thermal component of kT_(soft) ~ 0.28 keV for both regions. The hard emission from the southwest region may be modeled with either a thermal component with a temperature kT_(hard) ~ 3 keV or by a power-law component with a photon index Γ ~ 2–3; for the northeast region, the hard emission may be modeled with a power-law component with a photon index Γ = 1.4. The detection of center-filled ejecta-dominated X-ray emission from HB21 and CTB 1 as well as other MM SNRs suggests a new scenario for the origin of the contrasting X-ray and radio morphologies of this class of sources. Lastly, we have analyzed the properties of the discrete hard X-ray source 1WGA J0001.4+6229 which is seen in projection just inside the northeastern shell of CTB 1. Our extracted ASCA GIS spectra of this source are best fit using a power-law model with a photon index Γ = 2.2^(+0.5)_(−1.2): this slope is typical for featureless power-law continua produced by rotation-powered pulsars. This source may be a neutron star associated with CTB 1. We find marginal evidence for X-ray pulsations from this source with a period of 47.6154 ms. A deep radio observation of this source failed to reveal any pulsations.
|Additional Information:||© 2010 American Astronomical Society. Received 2006 February 2; accepted 2010 September 15; published 2010 November 3. We thank the referee for many useful comments which helped improve the overall quality of the manuscript. We acknowledge useful discussions with Steven Reynolds regarding the nature of the hard X-ray emission seen toward CTB 1. T.G.P. thanks Ken Ebisawa and Koji Mukai for their assistance with analyzing the ASCA data, Keith Arnaud for suggestions during the spectral fitting process and Ilana Harrus for her assistance with making the mosaicked X-ray images of HB21 and CTB 1. T.G.P. also thanks Daniel Harris, Samantha Stevenson, and Nicholas Lee for helpful suggestions regarding the reduction of the Chandra observations of CTB 1. We also thank Robert Fesen for kindly sharing his optical images of CTB 1 with us, Bryan Jacoby for assistance with the GBT observations, and Eric Gotthelf for his contributions in searching for pulsed X-ray emission from 1WGA J00001.4+6229. This research has made use of NASA’s Astrophysics Data System and data obtained through the High Energy Astrophysics Science Archive Research Center Online Service, provided by the NASA/Goddard Space Flight Center. The research presented in this paper has used data from the Canadian Galactic Plane Survey, a Canadian project with international partners, supported by the Natural Sciences and Engineering Resources Council.|
|Subject Keywords:||ISM: individual objects (SNR 089.0+04.7, SNR 116.9+00.2, 1WGA J0001.4+6229) – ISM: supernova remnants – X-rays: ISM|
|Classification Code:||PACS: 98.38.Mz; 98.70.Dk; 98.70.Qy; 95.30.Qd; 95.85.Nv|
|Official Citation:||Thomas G. Pannuti et al. 2010 The Astronomical Journal 140 1787 doi: 10.1088/0004-6256/140/6/1787|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Benjamin Perez|
|Deposited On:||06 Jan 2011 22:41|
|Last Modified:||26 Dec 2012 12:49|
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