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Title: An XMM-Newton study of the mixed-morphology supernova remnant W28 (G6.4–0.1)

Abstract

We have performed an XMM-Newton imaging and spectroscopic study of supernova remnant (SNR) W28, a prototype mixed-morphology or thermal composite SNR believed to be interacting with a molecular cloud. The observed hot X-ray emitting plasma is characterized by low metal abundances, showing no evidence of ejecta. The X-rays arising from the deformed northeastern shell consist of a thermal component with a temperature of ∼0.3 keV plus a hard component of either thermal (temperature ∼0.6 keV) or non-thermal (photon index = 0.9-2.4) origin. The X-ray emission in the SNR interior is blobby and the corresponding spectra are best described as the emission from a cold (∼0.4 keV) plasma in non-equilibrium ionization with an ionization timescale of ∼4.3 × 10{sup 11} cm{sup –3} s plus a hot (∼0.8 keV) gas in collisional ionization equilibrium. Applying the two-temperature model to the smaller central regions, we find non-uniform interstellar absorption, temperature, and density distribution, which indicates that the remnant is evolving in a non-uniform environment with denser material in the east and north. The cloudlet evaporation mechanism can essentially explain the properties of the X-ray emission in the center, and thermal conduction may also play a role for length scales comparable to the remnantmore » radius. A recombining plasma model with an electron temperature of ∼0.6 keV is also feasible for describing the hot central gas with the recombination age of the gas estimated at ∼2.9 × 10{sup 4} yr.« less

Authors:
; ; ;  [1]; ;  [2]
  1. School of Astronomy and Space Science, Nanjing University, Nanjing 210093 (China)
  2. Department of Physics and Astronomy, University of Manitoba, Winnipeg R3T 2N2 (Canada)
Publication Date:
OSTI Identifier:
22365340
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 791; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ABSORPTION; ABUNDANCE; DENSITY; DISTRIBUTION; ELECTRON TEMPERATURE; EMISSION; EQUILIBRIUM; EVAPORATION; HARD COMPONENT; IONIZATION; KEV RANGE; METALS; PHOTONS; PLASMA; RECOMBINATION; SPECTRA; SUPERNOVA REMNANTS; THERMAL CONDUCTION; X RADIATION

Citation Formats

Zhou, Ping, Chen, Yang, Zhang, Xiao, Jiang, Bing, Safi-Harb, Samar, and Ferrand, Gilles. An XMM-Newton study of the mixed-morphology supernova remnant W28 (G6.4–0.1). United States: N. p., 2014. Web. doi:10.1088/0004-637X/791/2/87.
Zhou, Ping, Chen, Yang, Zhang, Xiao, Jiang, Bing, Safi-Harb, Samar, & Ferrand, Gilles. An XMM-Newton study of the mixed-morphology supernova remnant W28 (G6.4–0.1). United States. doi:10.1088/0004-637X/791/2/87.
Zhou, Ping, Chen, Yang, Zhang, Xiao, Jiang, Bing, Safi-Harb, Samar, and Ferrand, Gilles. Wed . "An XMM-Newton study of the mixed-morphology supernova remnant W28 (G6.4–0.1)". United States. doi:10.1088/0004-637X/791/2/87.
@article{osti_22365340,
title = {An XMM-Newton study of the mixed-morphology supernova remnant W28 (G6.4–0.1)},
author = {Zhou, Ping and Chen, Yang and Zhang, Xiao and Jiang, Bing and Safi-Harb, Samar and Ferrand, Gilles},
abstractNote = {We have performed an XMM-Newton imaging and spectroscopic study of supernova remnant (SNR) W28, a prototype mixed-morphology or thermal composite SNR believed to be interacting with a molecular cloud. The observed hot X-ray emitting plasma is characterized by low metal abundances, showing no evidence of ejecta. The X-rays arising from the deformed northeastern shell consist of a thermal component with a temperature of ∼0.3 keV plus a hard component of either thermal (temperature ∼0.6 keV) or non-thermal (photon index = 0.9-2.4) origin. The X-ray emission in the SNR interior is blobby and the corresponding spectra are best described as the emission from a cold (∼0.4 keV) plasma in non-equilibrium ionization with an ionization timescale of ∼4.3 × 10{sup 11} cm{sup –3} s plus a hot (∼0.8 keV) gas in collisional ionization equilibrium. Applying the two-temperature model to the smaller central regions, we find non-uniform interstellar absorption, temperature, and density distribution, which indicates that the remnant is evolving in a non-uniform environment with denser material in the east and north. The cloudlet evaporation mechanism can essentially explain the properties of the X-ray emission in the center, and thermal conduction may also play a role for length scales comparable to the remnant radius. A recombining plasma model with an electron temperature of ∼0.6 keV is also feasible for describing the hot central gas with the recombination age of the gas estimated at ∼2.9 × 10{sup 4} yr.},
doi = {10.1088/0004-637X/791/2/87},
journal = {Astrophysical Journal},
number = 2,
volume = 791,
place = {United States},
year = {Wed Aug 20 00:00:00 EDT 2014},
month = {Wed Aug 20 00:00:00 EDT 2014}
}
  • We present a joint analysis of optical emission-line and X-ray observations of the archetypical Galactic mixed-morphology supernova remnant (MMSNR) W28 (G6.4–0.1). MMSNRs comprise a class of sources whose shell-like radio morphology contrasts with a filled center in X-rays; the origin of these contrasting morphologies remains uncertain. Our CTIO images reveal enhanced [S ii] emission relative to H α along the northern and eastern rims of W28. Hydroxyl (OH) masers are detected along these same rims, supporting prior studies suggesting that W28 is interacting with molecular clouds at these locations, as observed for several other MMSNRs. Our ROSAT HRI mosaic ofmore » W28 provides almost complete coverage of the supernova remnant (SNR). The X-ray and radio emission is generally anti-correlated, except for the luminous northeastern rim, which is prominent in both bands. Our Chandra observation sampled the X-ray-luminous central diffuse emission. Spectra extracted from the bright central peak and from nearby annular regions are best fit with two overionized recombining plasma models. We also find that while the X-ray emission from the central peak is dominated by swept-up material, that from the surrounding regions shows evidence for oxygen-rich ejecta, suggesting that W28 was produced by a massive progenitor. We also analyze the X-ray properties of two X-ray sources (CXOU J175857.55−233400.3 and 3XMM J180058.5–232735) projected into the interior of W28 and conclude that neither is a neutron star associated with the SNR. The former is likely to be a foreground cataclysmic variable or a quiescent low-mass X-ray-binary, while the latter is likely to be a coronally active main-sequence star.« less
  • We present a spatial and spectral X-ray analysis of the Galactic supernova remnant (SNR) G352.7–0.1 using archival data from observations made with the XMM-Newton X-ray Observatory and the Chandra X-ray Observatory. Prior X-ray observations of this SNR had revealed a thermal center-filled morphology that contrasts with a shell-like radio morphology, thus establishing G352.7–0.1 as a member of the class of Galactic SNRs known as mixed-morphology SNRs (MMSNRs). Our study confirms that the X-ray emission comes from the SNR interior and must be ejecta dominated. Spectra obtained with XMM-Newton may be fit satisfactorily with a single thermal component (namely a non-equilibriummore » ionization component with enhanced abundances of silicon and sulfur). In contrast, spectra extracted by Chandra from certain regions of the SNR cannot always be fit by a single thermal component. For those regions, a second thermal component with solar abundances or two thermal components with different temperatures and thawed silicon and sulfur abundances (respectively) can generate a statistically acceptable fit. We argue that the former scenario is more physically plausible: on the basis of parameters of our spectral fits, we calculate physical parameters including X-ray emitting mass (∼45 M {sub ☉} for solar abundances). We find no evidence for overionization in the X-ray emitting plasma associated with the SNR: this phenomenon has been seen in other MMSNRs. We have conducted a search for a neutron star within the SNR by using a hard (2-10 keV) Chandra image but could not identify a firm candidate. We also present (for the first time) the detection of infrared emission from this SNR as detected at 24 μm by the MIPS on board Spitzer. Finally, we discuss the properties of G352.7–0.1 in the context of other ejecta-dominated MMSNRs.« less
  • We present an X-ray imaging and spectroscopic study of the molecular cloud interacting mixed-morphology supernova remnant G346.6–0.2 using XMM-Newton . The X-ray spectrum of the remnant is well described by a recombining plasma that most likely arises from adiabatic cooling and has subsolar abundances of Mg, Si, and S. Our fits also suggest the presence of either an additional power-law component with a photon index of ∼2 or an additional thermal component with a temperature of ∼2.0 keV. We investigate the possible origin of this component and suggest that it could arise from either the Galactic ridge X-ray emission, anmore » unidentified pulsar wind nebula, or X-ray synchrotron emission from high-energy particles accelerated at the shock. However, deeper, high-resolution observations of this object are needed to shed light on the presence and origin of this feature. Based on its morphology, its Galactic latitude, the density of the surrounding environment, and its association with a dense molecular cloud, G346.6–0.2 most likely arises from a massive progenitor that underwent core collapse.« less
  • We present detailed analysis of two gamma-ray sources, 1FGL J1801.3-2322c and 1FGL J1800.5-2359c, that have been found toward the supernova remnant (SNR) W28 with the Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope. 1FGL J1801.3-2322c is found to be an extended source within the boundary of SNR W28, and to extensively overlap with the TeV gamma-ray source HESS J1801-233, which is associated with a dense molecular cloud interacting with the SNR. The gamma-ray spectrum measured with the LAT from 0.2 to 100 GeV can be described by a broken power-law function with a break at {approx}1 GeVmore » and photon indices of 2.09 {+-} 0.08 (stat) {+-} 0.28 (sys) below the break and 2.74 {+-} 0.06 (stat) {+-} 0.09 (sys) above the break. Given the clear association between HESS J1801-233 and the shocked molecular cloud and a smoothly connected spectrum in the GeV-TeV band, we consider the origin of the gamma-ray emission in both GeV and TeV ranges to be the interaction between particles accelerated in the SNR and the molecular cloud. The decay of neutral pions produced in interactions between accelerated hadrons and dense molecular gas provides a reasonable explanation for the broadband gamma-ray spectrum. 1FGL J1800.5-2359c, located outside the southern boundary of SNR W28, cannot be resolved. An upper limit on the size of the gamma-ray emission was estimated to be {approx}16' using events above {approx}2 GeV under the assumption of a circular shape with uniform surface brightness. It appears to coincide with the TeV source HESS J1800-240B, which is considered to be associated with a dense molecular cloud that contains the ultra compact H II region W28A2 (G5.89-0.39). We found no significant gamma-ray emission in the LAT energy band at the positions of TeV sources HESS J1800-230A and HESS J1800-230C. The LAT data for HESS J1800-230A combined with the TeV data points indicate a spectral break between 10 GeV and 100 GeV.« less
  • Here, we present detailed analysis of two gamma-ray sources, 1FGL J1801.3–2322c and 1FGL J1800.5–2359c, that have been found toward the supernova remnant (SNR) W28 with the Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope. 1FGL J1801.3–2322c is found to be an extended source within the boundary of SNR W28, and to extensively overlap with the TeV gamma-ray source HESS J1801–233, which is associated with a dense molecular cloud interacting with the SNR. The gamma-ray spectrum measured with the LAT from 0.2 to 100 GeV can be described by a broken power-law function with a break at ~1more » GeV and photon indices of 2.09 ± 0.08 (stat) ± 0.28 (sys) below the break and 2.74 ± 0.06 (stat) ± 0.09 (sys) above the break. Given the clear association between HESS J1801–233 and the shocked molecular cloud and a smoothly connected spectrum in the GeV-TeV band, we consider the origin of the gamma-ray emission in both GeV and TeV ranges to be the interaction between particles accelerated in the SNR and the molecular cloud. The decay of neutral pions produced in interactions between accelerated hadrons and dense molecular gas provides a reasonable explanation for the broadband gamma-ray spectrum. 1FGL J1800.5–2359c, located outside the southern boundary of SNR W28, cannot be resolved. An upper limit on the size of the gamma-ray emission was estimated to be ~16' using events above ~2 GeV under the assumption of a circular shape with uniform surface brightness. It appears to coincide with the TeV source HESS J1800–240B, which is considered to be associated with a dense molecular cloud that contains the ultra compact H II region W28A2 (G5.89–0.39). In conclusion, we found no significant gamma-ray emission in the LAT energy band at the positions of TeV sources HESS J1800–230A and HESS J1800–230C. The LAT data for HESS J1800–230A combined with the TeV data points indicate a spectral break between 10 GeV and 100 GeV.« less