Jasmina Lazendic

A high-resolution study of nonthermal radio and X-ray emission from supernova remnant G347.3-0.5

G347.3-0.5 is one of three shell-type supernova remnants (SNRs) in the Galaxy whose X-ray spectrum is dominated by nonthermal emission. This puts G347.3-0.5 in the small but growing class of SNRs for which the X-ray emission reveals directly the presence of extremely energetic electrons accelerated by the SNR shock. We have obtained new high-resolution X-ray and radio data on G347.3-0.5 using the Chandra X-Ray Observatory and the Australia Telescope Compact Array (ATCA), respectively. The bright northwestern peak of the SNR seen in ROSAT and ASCA images is resolved with Chandra into bright filaments and fainter diffuse emission. These features show good correspondence with the radio morphological structure, providing strong evidence that the same population of electrons is responsible for the synchrotron emission in both bands in this part of the remnant. Spectral index information from both observations is presented. We found significant difference in photon index value between bright and faint regions of the SNR shell. Spectral properties of these regions support the notion that efficient particle acceleration is occurring in the bright SNR filaments. We report the detection of linear radio polarization toward the SNR, which is most ordered at the northwestern shell where particle acceleration is presumably occurring. Using our new Chandra and ATCA data, we model the broadband emission from G347.3-0.5 with the synchrotron and inverse Compton mechanisms and discuss the conditions under which this is a plausible scenario.

ENHANCED ABUNDANCES IN THREE LARGE-DIAMETER MIXED-MORPHOLOGY SUPERNOVA REMNANTS

We present an X-ray study of three mixed-morphology (MM) supernova remnants (SNRs)—HB 21, CTB 1, and HB 3—using archival ASCA and ROSAT data. These data are complemented by archival Chandra X-Ray Observatory data for CTB 1 and XMM-Newton X-Ray Observatory data for HB 3. The spectra from HB 21 and HB 3 are well described with a single-temperature thermal plasma in ionization equilibrium, while a two-temperature thermal plasma is found in CTB 1. We found enhanced abundances in all three SNRs. The elemental abundance of Mg is clearly enhanced in CTB 1, while HB 21 has enhanced abundances of Si and S. The situation is not as clear in HB 3—the plasma in this SNR either has significantly enhanced abundances of O, Ne, and Mg, or has marginally enhanced abundances of Mg and underabundant Fe. We discuss the plausibility of mixed-morphology SNR models for the three SNRs, and the presence of enhanced abundances. We revise a list of MM SNRs and their properties, compare the three SNRs studied here with other members of this class, and discuss the presence of enhanced elemental abundances in MM SNRs. We also report the ASCA detection of a compact source in the southern part of HB 3. The source spectrum is consistent with a power law with a photon index of ~2.7, and an unabsorbed X-ray flux of ~10-12 ergs cm-2 s-1 in the 0.5-10.0 keV band. The column density toward this source differs from that toward the SNR, and it is therefore unlikely that they are related.

Chandra Detection of Ejecta in the Small-Diameter Supernova Remnant G349.7+0.2

We present high-resolution X-ray observations of the small-diameter supernova remnant (SNR) G349.7+0.2 with Chandra. The overall SNR spectrum can be described by two spectral components. The soft component is in ionization equilibrium and has a temperature of ?0.8?keV; the hard spectral component has a temperature of ?1.4?keV, an ionization timescale of ?5 ? 1011?cm-3 s, and enhanced abundances of Si. The spatially resolved spectral modeling shows that S may also be enhanced, at least in some regions. The enhanced abundances clearly point to the presence of an ejecta component in this remnant. Using the available H I and CO data toward G349.7+0.2 we derive a column density of ?7 ? 1022?cm-2 along the line of sight to the SNR, which is consistent with our X-ray data. The X-ray morphology of G349.7+0.2 is strikingly similar to that at radio wavelengths?an irregular shell with a brighter eastern side?which is consistent with expansion in a medium with a large-scale density gradient. The remnant is known to be interacting with a molecular cloud (from the presence of OH (1720?MHz) masers), but this interaction is probably limited to the central portion of the SNR, as seen in SNR IC?443. We found that H I clouds are present in the SNR region, which supports the notion that G349.7+0.2 belongs to a class of remnants evolving in the intercloud medium (such are IC?443 and W44), which is also responsible for the remnants morphology. G349.7+0.2 does not have the mixed-morphology found for other maser-emitting SNRs studied to date in X-rays, but its morphology can be explained by a projection model for mixed-morphology SNRs. We have identified a point source close to the center of the SNR with a luminosity of LX(0.5-10.0 keV) ~ (0.2-2.3) ? 1034?d22?ergs s-1, which is consistent with that of the compact central objects found in a few other Galactic SNRs.

X-ray Observations of the Compact Central Object in Supernova Remnant G347.3-0.5

We present Chandra, XMM-Newton, and Rossi X-Ray Timing Explorer observations of 1WGA J1713.4-3949, a compact source at the center of the Galactic supernova remnant (SNR) G347.3-0.5. The X-ray spectrum of the source is well fitted by the sum of a blackbody component with a temperature of ~0.4 keV plus a power-law component with a photon index of ~4. We found no pulsations down to 4% in the 0.01-0.16 Hz range nor down to 25% in the 0.01-128 Hz range. This source resembles other compact central objects in SNRs, and we suggest that 1WGA J1713.4-3949 is the associated neutron star for G347.3-0.5. We also measured the properties of the adjacent radio pulsar PSR J1713-3945 with a 392 ms period, and we show that it is not associated with 1WGA J1713.4-3949 nor, most probably, is it associated with SNR G347.3-0.5.

An ASCA Study of the High-Luminosity Supernova Remnant G349.7+0.2

We present ASCA observations of supernova remnant (SNR) G349.7+0.2. The remnant has irregular shell morphology and is interacting with a molecular cloud, evident from the presence of OH (1720 MHz) masers and shocked molecular gas. The X-ray morphology is consistent with that at radio wavelengths, with a distinct enhancement in the south. The X-ray emission from the SNR is well described by a model of a thermal plasma that has yet to reach ionization equilibrium. The hydrogen column of ~6.0 × 1022 cm-2 is consistent with the large distance to the remnant of ~22 kpc estimated from the maser velocities. We derive an X-ray luminosity of LX(0.5-10.0 keV) = 1.8 × 1037d ergs s-1, which makes G349.7+0.2 one of the most X-ray luminous shell-type SNRs known in the Galaxy. The age of the remnant is estimated to be ~2800 yr. The ambient density and pressure conditions appear similar to those inferred for luminous compact SNRs found in starburst regions of other galaxies and provide support for the notion that these may be the result of SNR evolution in the vicinity of dense molecular clouds.

An Optical and X-Ray Examination of Two Radio Supernova Remnant Candidates in 30 Doradus

The giant H II region 30 Doradus is known for its violent internal motions and bright diffuse X-ray emission, suggesting the existence of supernova remnants (SNRs), but no nonthermal radio emission has been detected. Recently, Lazendic et al. compared the Hα/Hβ and radio/Hα ratios and suggested two small radio sources to be nonthermal and thus SNR candidates; however, no optical or X-ray counterparts were detected. We have used high-resolution optical images and high-dispersion spectra to examine the morphological, spectral, and kinematic properties of these two SNR candidates and still find no optical evidence supporting their identification as SNRs. We have also determined the X-ray luminosities of these SNR candidates and find them 1-3 orders of magnitude lower than those commonly seen in young SNRs. High extinction can obscure optical and X-ray signatures of an SNR, but would prohibit the use of a high radio/Hα ratio to identify nonthermal radio emission. We suggest that the SNR candidate MCRX J053831.8-690620 is associated with a young star-forming region; while the radio emission originates from the obscured star-forming region, the observed optical emission is dominated by the foreground. We suggest that the SNR candidate MCRX J053838.8-690730 is associated with a dust/molecular cloud, which obscures some optical emission but not the radio emission.