A Broadband X‐Ray Study of Supernova Remnant 3C 397

Abstract

We present a broadband imaging and spectral study of the radio-bright supernova remnant (SNR) 3C 397 with ROSAT , ASCA, and RXT E. A bright X-ray spot seen in the HRI image hints at the presence of a pulsar-powered component and gives this SNR a composite X-ray morphology. Combined ROSAT and ASCA imaging shows that the remnant is highly asymmetric, with its X-ray emission peaking at the western lobe. The hard-band images obtained with the ASCA Gas Imaging Spectrometer show that much of the hard X-ray emission arises from the western lobe, associated with the SNR shell, with little hard X-ray emission associated with the central hot spot. The spectrum from 3C 397 is heavily absorbed and dominated by thermal emission with emission lines evident from Mg, Si, S, Ar and Fe. Single-component models fail to describe the X-ray spectrum, and at least two components are required : a soft component characterized by a low temperature and a large ionization timescale, and a hard component required to account for the Fe-K emission line and characterized by a much lower ionization timescale. We use a set of nonequilibrium ionization (NEI) models (Borkowski et al., in preparation), and Ðnd that the Ðtted parameters are robust. The temperatures from the soft and hard components are D0.2 keV and D1.6 keV respectively. The corresponding ionization timescales being the pren 0 t (n 0 shock hydrogen density) are D6 ] 1012 cm~3 s and D6 ] 1010 cm~3 s, respectively. The large of n 0 t the soft component suggests it is approaching ionization equilibrium ; thus it can be Ðt equally well with a collisional equilibrium ionization model. The spectrum obtained with the Proportional Counter Array (PCA) of RXT E is contaminated by emission from the Galactic ridge, with only D15% of the count rate originating from 3C 397 in the 5È15 keV range. The PCA spectrum allowed us to conÐrm the thermal nature of the hard X-ray emission. A third component originating from a pulsar-driven component is possible, but the contamination of the source signal by the Galactic ridge did not allow us to determine its parameters or Ðnd pulsations from any hidden pulsar. We discuss the X-ray spectrum in the light of two scenarios : a young ejecta-dominated remnant of a core-collapse SN, and a middle-aged SNR expanding in a dense ISM. In the Ðrst scenario, the hot component arises from the SNR shell, and the soft component from an ejecta-dominated component. 3C 397 would be a young SNR (a few thousand years old), but intermediate in dynamical age between the young historical shells (like Tycho or Kepler), and those that are well into the Sedov phase of evolution (like Vela). In the second scenario, the soft component represents the blast wave propagating in a dense medium, and the hard component is associated with hot gas encountering a fast shock, or arising from thermal conduction. In this latter scenario, the SNR would be Dtwice as old, and transitioning into the radiative phase. The current picture we present in this paper is marginally consistent with thi...

ChandraObservations and Models of the Mixed‐Morphology Supernova Remnant W44: Global Trends

“…Subsequently, Shelton et al (1995Shelton et al ( , 1999 and Harrus et al (1997) used hydrodynamic codes to show that the lack of a bright edge for W44 was more likely to be because the remnant had evolved beyond the adiabatic phase and into the radiative phase, in which the periphery has cooled (also see Cox et al 1999). This interpretation is consistent with the radio continuum evidence for shell formation and has been suggested for other centrally bright remnants as well (i.e., 3C 397, Safi-Harb et al 2000;3C 391, Chen & Slane 2001;IC 443, Kawasaki et al 2002;N206 in the Large Magellanic Cloud, Williams et al 1999;0045-734 and 0057-7226 in the Small Magellanic Cloud, Yokogawa et al 2002). While this evolutionary explanation could easily explain why thermal composite remnants lack X-ray-bright shells, it does not additionally explain the bright emission from the center.…”

ChandraSpatially Resolved Spectroscopic Study and Multiwavelength Imaging of the Supernova Remnant 3C 397 (G41.1−0.3)

“…Our fits to the hard band only yield an integrated flux of 1:1 ; 10 À13 ergs cm À2 s À1 , which at a distance of 10 kpc translates to L X (4 6 keV) 1:3 ; 10 33 ergs s À1 . This upper limit is consistent with the limit determined in the 5-15 keV range using the combined ASCA and RXTE spectrum (Safi-Harb et al 2000).…”

“…ROSAT observations of 3C 397 with the PSPC (Rho 1995;Rho & Petre 1998;Dyer & Reynolds 1999;Chen et al 1999;Safi-Harb et al 2000) reveal 2A5 ; 4A5 diffuse emission, with central emission and an enhancement along the western edge. Most intriguing in the ROSAT image is a central hot spot suggestive of a putative compact object or a small plerion; however, it is not correlated with any radio enhancement.…”

“…The combined ROSAT, ASCA, and RXTE study of the SNR (Safi-Harb et al 2000) showed that the overall SNR spectrum is heavily absorbed (N H ¼ 3:1 þ0:2 À0:3 ; 10 22 cm À2 ), complex, and dominated by thermal emission from Mg, Si, S, Ar, and Fe. A two-component thermal model provided an adequate fit: the soft component was characterized by a low temperature (kT $ 0:2 keV) and a large ionization timescale ($6 ; 10 12 cm À3 s), and the hard component required to account for the Fe K emission line was characterized by a high temperature (kT $ 2 keV) and much lower ionization timescale ($6 ; 10 10 cm À3 s).…”

TeV gamma-ray observations of SS-433 and a survey of the surrounding field with the HEGRA IACT-System

“…With a suitable model, this could then be used to constrain the post-shocked B field under the synchrotron/inverse-Compton scenario, similar to that discussed earlier for the SS-433 e3 region. 3C 397, studied at length by Safi-Harb et al (2000), is a composite SNR with centre-filled X-ray morphology and shell radio morphology. It is in fact one of the brightest SNR at radio energies.…”