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ABSTRACT: We report observations of the remnant of Supernova 1987A with the High Resolution Camera (HRC) onboard the Chandra X-ray Observatory. A direct image from the HRC resolves the annular structure of the X-ray remnant, confirming the morphology previously inferred by deconvolution of lower resolution data from the Advanced CCD Imaging Spectrometer. Detailed spatial modeling shows that the a thin ring plus a thin shell gives statistically the best description of the overall remnant structure, and suggests an outer radius 0.96" +/- 0.05" +/- 0.03" for the X-ray-emitting region, with the two uncertainties corresponding to the statistical and systematic errors, respectively. This is very similar to the radius determined by a similar modeling technique for the radio shell at a comparable epoch, in contrast to previous claims that the remnant is 10-15% smaller at X-rays than in the radio band. The HRC observations put a flux limit of 0.010 cts/s (99% confidence level, 0.08-10 keV range) on any compact source at the remnant center. Assuming the same foreground neutral hydrogen column density as towards the remnant, this allows us to rule out an unobscured neutron star with surface temperature T^\infty > 2.5MK observed at infinity, a bright pulsar wind nebula or a magnetar. Comment: 6 pages, 3 figures, accepted by ApJL, some figures have been scaled down in resolution
10/2009;
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ABSTRACT: X-ray emission from the enigmatic Rotating RAdio Transients (RRATs) offers a vital clue to understanding these objects and how they relate to the greater neutron star population. An X-ray counterpart to J1819-1458 is known, and its properties are similar to those of other middle-aged (0.1 Myr) neutron stars. We have searched for X-ray emission with Chandra/ACIS at the positions of two RRATs with arcsecond (or better) localisation, J0847-4316 and J1846-0257. Despite deep searches (especially for J1847-0257) we did not detect any emission with 0.3-8 keV count-rate limits of 1 counts/ks and 0.068 counts/ks, respectively, at 3sigma confidence. Assuming thermal emission similar to that seen from J1819-1458 (a blackbody with radius of approximately 20 km), we derive effective temperature limits of 77 eV and 91 eV for the nominal values of the distances and column densities to both sources, although both of those quantities are highly uncertain and correlated. If we instead fix the temperature of the emission (a blackbody with kT=0.14 keV), we derive unabsorbed luminosity limits in the 0.3-8 keV range of 1e32 erg/s and 3e32 erg/s. These limits are considerably below the luminosity of J1819-1458 (4e33 erg/s), suggesting that RRATs J0847-4316 and J1846-0257 have cooled beyond the point of visibility (plausible given the differences in characteristic age). However, as we have not detected X-ray emission, it may also be that the emission from RRATs J0847-4316 and J1846-0257 has a different character from that of J1819-1458. The two non-detections may prove a counterpoint to J1819-1458, but more detections are certainly needed before we can begin to derive general X-ray emission properties for the RRAT populations. Comment: 7 pages, 2 figures, 1 table, accepted by MNRAS
08/2009;
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ABSTRACT: We report on the discovery of extended X-ray emission around the high magnetic field Rotating Radio Transient J1819-1458. Using a 30ks Chandra ACIS-S observation, we found significant evidence for extended X-ray emission with a peculiar shape: a compact region out to 5.5", and more diffuse emission extending out to ~13" from the source. The most plausible interpretation is a nebula somehow powered by the pulsar, although the small number of counts prevents a conclusive answer on the nature of this emission. RRAT J1819-1458's spin-down energy loss rate (Edot~3x10^{32} erg/s) is much lower than that of other pulsars with observed spin-down powered pulsar wind nebulae (PWNe), and implies a rather high X-ray efficiency of eta_{X} = L_(pwn; 0.5-8keV)/Edot~0.2 at converting spin-down power into the PWN X-ray emission. This suggests the need of an additional source of energy rather than the spin-down power alone, such as the high magnetic energy of this source. Furthermore, this Chandra observation allowed us to refine the positional accuracy of RRAT J1819-1458 to a radius of ~0.3", and confirms the presence of X-ray pulsations and the ~1keV absorption line, previously observed in the X-ray emission of this source. Comment: 5 pages, 3 figures; ApJ Letter accepted
06/2009;
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ABSTRACT: We present an analysis of data from both the Röntgen Satellite (ROSAT) and the Advanced Satellite for Cosmology and Astrophysics (ASCA) of the supernova remnant G18.95-1.1. We find that the X-ray emission from G18.95-1.1 is predominantly thermal, heavily absorbed with a column density around 1022 atoms cm-2, and can be best described by an nonequilibrium ionization (NEI) model with a temperature around 0.9 keV and an ionization timescale of 1.1 × 1010 cm-3 s-1. We find only marginal evidence for nonsolar abundances. Comparisons between 21 cm H I absorption data and derived parameters from our spectral analysis strongly suggest a relatively nearby remnant (a distance of about 2 kpc). Above 4 keV, we identify a small region of emission located at the tip of the central, flat-spectrum barlike feature in the radio image. We examine two possibilities for this emission region: a temperature variation within the remnant or a pulsar wind nebula (PWN). The current data do not allow us to distinguish between these possible explanations. In the scenario where this high-energy emission region corresponds to a PWN, our analysis suggests a rotational loss rate for the unseen pulsar of about 7 × 1035 ergs s-1 and a ratio Lr/LX of about 3.6 for the entire PWN, slightly above the maximum ratio (3.4 for Vela) measured in known PWNe.
The Astrophysical Journal 12/2008; 603(1):152. · 6.02 Impact Factor
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ABSTRACT: 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.
The Astrophysical Journal 12/2008; 602(1):271. · 6.02 Impact Factor
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ABSTRACT: A Chandra X-ray observation has detected an unresolved source at the center of the supernova remnant Kes 79. The best single-model fit to the source spectrum is a blackbody with an X-ray luminosity of LX(0.3-8.0 keV) = 7 × 1033 ergs s-1. There is no evidence for a surrounding pulsar wind nebula. There are no cataloged counterparts at other wavelengths, but the absorption is high. The source properties are similar to the central source in Cas A even though the Kes 79 remnant is considerably older.
The Astrophysical Journal 12/2008; 584(1):414. · 6.02 Impact Factor
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ABSTRACT: We attempt to measure the proper motions of two magnetars - the soft gamma-ray repeater SGR 1900+14 and the anomalous X-ray pulsar 1E 2259+586 - using two epochs of Chandra observations separated by ~5 yr. We perform extensive tests using these data, archival data, and simulations to verify the accuracy of our measurements and understand their limitations. We find 90% upper limits on the proper motions of 54 mas/yr (SGR 1900+14) and 65 mas/yr (1E 2259+586), with the limits largely determined by the accuracy with which we could register the two epochs of data and by the inherent uncertainties on two-point proper motions. We translate the proper motions limits into limits on the transverse velocity using distances, and find v_perp < 1300 km/s (SGR 1900+14, for a distance of 5 kpc) and v_perp < 930 km/s (1E 2259+586, for a distance of 3 kpc) at 90% confidence; the range of possible distances for these objects makes a wide range of velocities possible, but it seems that the magnetars do not have uniformly high space velocities of > 3000 km/s. Unfortunately, our proper motions also cannot significantly constrain the previously proposed origins of these objects in nearby supernova remnants or star clusters, limited as much by our ignorance of ages as by our proper motions. Comment: 12 pages, 9 figures. Accepted for publication in AJ
10/2008;
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ABSTRACT: We report on the discovery of fast-moving X-ray--emitting ejecta knots in the Galactic Oxygen-rich supernova remnant Puppis A from XMM-Newton observations. We find an X-ray knotty feature positionally coincident with an O-rich fast-moving optical filament with blue-shifted line emission located in the northeast of Puppis A. We extract spectra from northern and southern regions of the feature. Applying a one-component non-equilibrium ionization model for the two spectra, we find high metal abundances relative to the solar values in both spectra. This fact clearly shows that the feature originates from metal-rich ejecta. In addition, we find that line emission in the two regions is blue-shifted. The Doppler velocities derived in the two regions are different with each other, suggesting that the knotty feature consists of two knots that are close to each other along the line of sight. Since fast-moving O-rich optical knots/filaments are believed to be recoiled metal-rich ejecta, expelled to the opposite direction against the high-velocity central compact object, we propose that the ejecta knots disclosed here are also part of the recoiled material. Comment: 16 pages, 3 figures
05/2008;
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ABSTRACT: We present the results of detailed spatial and spectral analysis of the pulsar wind nebula (PWN) in supernova remnant Kes 75 (G29.7-0.3) using a deep exposure with Chandra X-ray observatory. The PWN shows a complex morphology with clear axisymmetric structure. We identified a one-sided jet and two bright clumps aligned with the overall nebular elongation, and an arc-like feature perpendicular to the jet direction. Further spatial modeling with a torus and jet model indicates a position angle $207\arcdeg\pm8 \arcdeg$ for the PWN symmetry axis. We interpret the arc as an equatorial torus or wisp and the clumps could be shock interaction between the jets and the surrounding medium. The lack of any observable counter jet implies a flow velocity larger than 0.4c. Comparing to an archival observation 6 years earlier, some small-scale features in the PWN demonstrate strong variability: the flux of the inner jet doubles and the peak of the northern clump broadens and shifts 2" outward. In addition, the pulsar flux increases by 6 times, showing substantial spectral softening from $\Gamma$=1.1 to 1.9 and an emerging thermal component which was not observed in the first epoch. The changes in the pulsar spectrum are likely related to the magnetar-like bursts of the pulsar that occurred 7 days before the Chandra observation, as recently reported from RXTE observations. Comment: Accepted by ApJ, 8 figures, some of them have been scaled down in resolution
04/2008;
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ABSTRACT: We present an XMM-Newton observation of the long-overlooked radio source G350.1-0.3. The X-ray spectrum of G350.1-0.3 can be fit by a shocked plasma with two components: a high-temperature (1.5 keV) region with a low ionization time scale and enhanced abundances, plus a cooler (0.36 keV) component in ionization equilibrium and with solar abundances. The X-ray spectrum and the presence of non-thermal, polarized, radio emission together demonstrate that G350.1-0.3 is a young, luminous supernova remnant (SNR), for which archival HI and 12-CO data indicate a distance of 4.5 kpc. The diameter of the source then implies an age of only ~900 years. The SNR's distorted appearance, small size and the presence of 12-CO emission along the SNR's eastern edge all indicate that the source is interacting with a complicated distribution of dense ambient material. An unresolved X-ray source, XMMU J172054.5-372652, is detected a few arcminutes west of the brightest SNR emission. The thermal X-ray spectrum and lack of any multi-wavelength counterpart suggest that this source is a neutron star associated with G350.1-0.3, most likely a "central compact object", as seen coincident with other young SNRs such as Cassiopeia A. Comment: 6 pages, uses emulateapj. One B/W figure, one color figure. Minor text changes and update to Fig 2 following referee's report. ApJ Letters, in press
04/2008;
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ABSTRACT: We present constraints on the number of Galactic magnetars, which we have established by searching for sources with periodic variability in 506 archival Chandra observations and 441 archival XMM-Newton observations of the Galactic plane (|b|<5 degree). Our search revealed four sources with periodic variability on time scales of 200-5000 s, all of which are probably accreting white dwarfs. We identify 7 of 12 known Galactic magnetars, but find no new examples with periods between 5 and 20 s. We convert this non-detection into limits on the total number of Galactic magnetars by computing the fraction of the young Galactic stellar population that was included in our survey. We find that easily-detectable magnetars, modeled after persistent anomalous X-ray pulsars, could have been identified in 5% of the Galactic spiral arms by mass. If we assume there are 3 previously-known examples within our random survey, then there are 59 (+92,-32) in the Galaxy. Transient magnetars in quiescence could have been identified throughout 0.4% of the spiral arms, and the lack of new examples implies that <540 exist in the Galaxy (90% confidence). Similar constraints are found by considering the detectability of transient magnetars in outburst by current and past X-ray missions. For assumed lifetimes of 1e4 yr, we find that the birth rate of magnetars could range between 0.003 and 0.06 per year. Therefore, the birth rate of magnetars is at least 10% of that for normal radio pulsars. The magnetar birth rate could exceed that of radio pulsars, unless the lifetimes of transient magnetars are >1e5 yr. Obtaining better constraints will require wide-field X-ray or radio searches for transient X-ray pulsars similar to XTE J1810--197, AX J1845.0--0250, CXOU J164710.2--455216, and 1E 1547.0-5408. Comment: 16 pages, 10 figures, one with a bit of color. submitted to ApJ
11/2007;
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ABSTRACT: We present the second in a series of results in which we have searched for undiscovered neutron stars in supernova remnants (SNRs). This paper deals with the largest six SNRs in our sample, too large for Chandra or XMM-Newton to cover in a single pointing. These SNRs are nearby, with typical distances of <1 kpc. We therefore used the ROSAT Bright Source Catalog and past observations in the literature to identify X-ray point sources in and near the SNRs. Out of 54 sources, we were immediately able to identify optical/IR counterparts to 41 from existing data. We obtained Chandra snap-shot images of the remaining 13 sources. Of these, 10 were point sources with readily identified counterparts, two were extended, and one was not detected in the Chandra observation but is likely a flare star. One of the extended sources may be a pulsar wind nebula, but if so it is probably not associated with the nearby SNR. We are then left with no identified neutron stars in these six SNRs down to luminosity limits of \~1e32 ergs/s. These limits are generally less than the luminosities of typical neutron stars of the same ages, but are compatible with some lower-luminosity sources such as the neutron stars in the SNRs CTA 1 and IC 443. Comment: 32 pages, 30 figures; uses emulateapj.cls and hyperref.sty. Accepted for publication in ApJS
02/2006;
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ABSTRACT: We present a deep observation with the Chandra X-ray Observatory of the neutron star bow shock G189.22+2.90 in the supernova remnant (SNR) IC 443. Our data confirm the cometary morphology and central point source seen previously, but also reveal considerable new structure. Specifically, we find that the X-ray nebula consists of two distinct components: a "tongue" of bright emission close to the neutron star, enveloped by a larger, fainter "tail". We interpret the tongue and tail as delineating the termination shock and the post-shock flow, respectively, as previously identified also in the pulsar bow shock G359.23-0.82 ("the Mouse"). However, for G189.22+2.90 the tongue is much less elongated than for the Mouse, while the tail is much broader. These differences are consistent with the low Mach number, M >~ 2, expected for a neutron star moving through the hot gas in a SNR's interior, supporting the case for a physical association between G189.22+2.90 and IC 443. We resolve the stand-off distance between the star and the head of the bow shock, which allows us to estimate a space velocity for the neutron star of ~230 km/s, independent of distance. We detect thermal emission from the neutron star surface at a temperature of 102 +/- 22 eV, which is consistent with the age of SNR IC 443 for standard neutron star cooling models. We also identify two compact knots of hard emission located 1-2 arcsec north and south of the neutron star.
02/2006;
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ABSTRACT: We have discovered the pulsar associated with the supernova remnant G21.5-0.9. PSR J1833-1034, with spin period P = 61.8 ms and dispersion measure 169 pc/cc, is very faint, with pulse-averaged flux density of approximately 70 microJy at a frequency of 1.4 GHz, and was first detected in a deep search with the Parkes telescope. Subsequent observations with Parkes and the Green Bank Telescope have confirmed this detection, and yield a period derivative dP/dt = 2.02e-13. These spin parameters imply a characteristic age tau_c = 4.8 kyr and a spin-down luminosity dE/dt = 3.3e37 ergs/s, the latter value exceeded only by the Crab pulsar among the rotation-powered pulsars known in our Galaxy. The pulsar has an unusually steep radio spectrum in the 0.8-2.0 GHz range, with power law index ~3.0, and a narrow single-peaked pulse profile with full-width at half maximum of 0.04P. We have analyzed 350 ks of archival Chandra X-ray Observatory High Resolution Camera (HRC) data, and find a point-like source of luminosity approximately 3e-5dE/dt, offset from the center of an elliptical region of size ~7"x5" and luminosity approximately 1e-3dE/dt within which likely lies the pulsar wind termination shock. We have searched for X-ray pulsations in a 30 ks HRC observation without success, deriving a pulsed fraction upper limit for a sinusoidal pulse shape of about 70% of the pulsar flux. We revisit the distance to G21.5-0.9 based on HI and CO observations, arguing that it is 4.7+-0.4 kpc. We use existing X-ray and radio observations of the pulsar wind nebula, along with the measured properties of its engine and a recent detection of the supernova remnant shell, to argue that G21.5-0.9 and PSR J1833-1034 are much younger than tau_c, and likely their true age is ~<1000 yr. In that case, the initial spin period of the pulsar was >~55 ms. Comment: To appear in ApJ (submitted 2005 May 22; accepted 2005 September 26). 3 figures, 11 pages using emulateapj.cls. Independent discovery of the pulsar reported by Gupta et al. (astro-ph/0508257)
09/2005;
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American Astronomical Society Meeting Abstracts; 12/2004
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ABSTRACT: We present high-resolution X-ray observations of the small-diameter supernova remnant (SNR) G349.7+0.2 with the Chandra X-ray Observatory. 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 ~5x10^{11} 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. 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 HI 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, Chevalier 1999), which is also responsible for the remnant's 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)x10^{34} d_{22} erg/s, which is consistent with that of the compact central objects found in a few other Galactic SNRs. Comment: 12 pages, 8 figures, accepted for publication in ApJ, typos fixed
09/2004;
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ABSTRACT: We present the analysis of the X-ray Multi-Mirror Mission (XMM-Newton) European Photon Imaging Camera (EPIC) data of the Galactic supernova remnant (SNR) CTB 109 (G109.1-1.0). CTB 109 is associated with the anomalous X-ray pulsar (AXP) 1E 2259+586 and has an unusual semi-circular morphology in both the X-ray and the radio, and an extended X-ray bright interior region known as the `Lobe'. The deep EPIC mosaic image of the remnant shows no emission towards the west where a giant molecular cloud complex is located. No morphological connection between the Lobe and the AXP is found. We find remarkably little spectral variation across the remnant given the large intensity variations. All spectra of the shell and the Lobe are well fitted by a single-temperature non-equilibrium ionization model for a collisional plasma with solar abundances (kT = 0.5 - 0.7 keV, tau = n_e t = 1 - 4 x 10^11 s cm^-3, N_H = 5 - 7 x 10^21 cm^-2). There is no indication of nonthermal emission in the Lobe or the shell. We conclude that the Lobe originated from an interaction of the SNR shock wave with an interstellar cloud. Applying the Sedov solution for the undisturbed eastern part of the SNR, and assuming full equilibration between the electrons and ions behind the shock front, the SNR shock velocity is derived as v_s = 720 +/- 60 km s^-1, the remnant age as t = (8.8 +/- 0.9) x 10^3 d_3 yr, the initial energy as E_0 = (7.4 +/- 2.9) x 10^50 d_3^2.5 ergs, and the pre-shock density of the nuclei in the ambient medium as n_0 = (0.16 +/- 0.02) d_3^-0.5 cm^-3, at an assumed distance of D = 3.0 d_3 kpc. Assuming CTB 109 and 1E 2259+586 are associated, these values constrain the age and the environment of the progenitor of the SNR and the pulsar. Comment: Accepted for publication in ApJ. 9 figures. Figs. 1 + 2 are in color (fig1.jpg, fig2.jpg)
08/2004;
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ABSTRACT: Less than half of the SNRs within 5 kpc have identified central sources, and only three are identified as the remnants of Type Ia SNe. Here, we report a systematic effort to search for compact central sources in the remaining 23 SNRs of this distance limited sample. In this first paper we report Chandra observations of four SNRs. We have undertaken a systematic optical/IR identification program of the X-ray sources detected in the field of each SNR. Foreground and background sources have identifiable IR/optical counterparts, while the counterparts of neutron stars (or black holes) are expected to be very faint. We are able to account for all the well-detected X-ray sources and thus able to state with some confidence that there are no associated central sources down to a level of one tenth of that of the Cas A central source, L_X <~ 10e31 ergs/s. We compare our limits with cooling curves for neutron stars and find that any putative neutron stars in these SNRs must be cooling faster than expected for traditional 1.35 Mo neutron stars and that any putative pulsar must have low spin-down luminosities, Edot <~ 1e34 ergs/s. However, our limits are unable to constrain the presence or absence of more unusual options, such as relatively more massive neutron stars, neutron stars with exotic interiors, or quiescent black holes. In subsequent papers, we will report on the X-ray and optical/IR observations of the remaining members of the 5-kpc sample. Comment: 52 pages, 37 figures. Accepted for publication by ApJS. Uses emulateapj5.sty, onecolfloat5.sty
03/2004;
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American Astronomical Society Meeting Abstracts; 12/2003
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ABSTRACT: G347.3-0.5 is one of three shell-type supernova remnants 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 towards 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 broad-band emission from G347.3-0.5 with the synchrotron and inverse Compton mechanisms and discuss the conditions under which this is a plausible scenario.
11/2003;
