Remnant Center Research Articles

SRG/eROSITA and XMM-Newton observations of Vela Jr

Context. The Vela supernova remnant (SNR) complex is a region containing at least three SNRs: Vela, Puppis A, and Vela Jr. With the launch of the spectro-imaging X-ray telescope eROSITA on board the Spectrum-Röntgen-Gamma (SRG) mission, it became possible to observe the one degree wide Vela Jr in its entirety. Although several previous pointed Chandra and XMM-Newton observations are available, it is only the second time after the ROSAT all-sky survey that the whole remnant was observed in X-rays with homogeneous sensitivity. Aims. Vela Jr is one of the few remnants emitting in the TeV band, making it an important object in shock acceleration studies. However, the age and distance determination using X-ray emission is largely hampered by the presence of the Vela SNR along the same line. With the eROSITA data set our aim is to characterize the emission of Vela Jr and distinguish it from Vela emission, and also to characterize the spectral emission of the inner remnant. Methods. We processed the eROSITA data dividing the whole remnant into seven different regions. In addition, images of the whole remnant were employed to pinpoint the position of the geometric center and constrain the proper motion of the CCO. We also employed archival XMM-Newton pointed observations of the NW rim to determine the cutoff energy of the electrons and the expansion velocity. Results. We find the magnetic field can vary between 2 µG and 16 µG in the NW rim. We also find that the remnant spectrum is uniformly featureless in most regions, except for two inner regions where an extra thermal model component improves the fit. We obtain new coordinates for the geometric remnant center, resulting in a separation of only 35.2 ± 15.8″ from the position of the CCO. As a result, we reinforce the association between the CCO and a proposed faint optical–IR counterpart.

Type Ia Supernova Models: Asymmetric Remnants and Supernova Remnant G1.9+0.3

Abstract The youngest Galactic supernova remnant, G1.9+0.3, probably the result of a Type Ia supernova, shows surprising anomalies in the distribution of its ejecta in space and velocity. In particular, high-velocity shocked iron is seen in several locations far from the remnant center, in some cases beyond prominent silicon and sulfur emission. These asymmetries strongly suggest a highly asymmetric explosion. We present high-resolution hydrodynamic simulations in two and three dimensions of the evolution from ages of 100 s to hundreds of years of two asymmetric Type Ia models, expanding into a uniform medium. At the age of G1.9+0.3 (about 100 yr), our 2D model shows almost no iron shocked to become visible in X-rays. Only in a much higher-density environment could significant iron be shocked, at which time the model's expansion speed is completely inconsistent with the observations of G1.9+0.3. Our 3D model, evolving the most asymmetric of a suite of Type Ia supernova models from Seitenzahl et al. (2013), shows some features resembling G1.9+0.3. We characterize its evolution with images of composition in three classes: C and O, intermediate-mass elements (IMEs), and iron-group elements (IGEs). From ages of 13 to 1800 yr, we follow the evolution of the highly asymmetric initial remnant as the explosion asymmetries decrease in relative strength, to be replaced by asymmetries due to evolutionary hydrodynamic instabilities. At an age of about 100 yr, our 3D model has comparable shocked masses of C+O, IMEs, and IGEs, with about 0.03 M ⊙ each. Evolutionary changes appear to be rapid enough that continued monitoring with the Chandra X-ray Observatory may show significant variations.

Candidate isolated neutron stars in the 4XMM-DR10 catalogue of X-ray sources

ABSTRACT Most isolated neutron stars have been discovered thanks to the detection of their pulsed non-thermal emission, at wavelengths spanning from radio to gamma-rays. However, if the beamed non-thermal radiation does not intercept our line of sight or it is too faint or absent, isolated neutron stars can also be detected through their thermal emission, which peaks in the soft X-ray band and is emitted nearly isotropically. In the past 30 yr, several thermally emitting isolated neutron stars have been discovered thanks to X-ray all-sky surveys, observations targeted at the centre of supernova remnants, or as serendipitous X-ray sources. Distinctive properties of these relatively rare X-ray sources are very soft spectra and high ratios of X-ray to optical flux. The recently released 4XMM-DR10 catalogue contains more than half a million X-ray sources detected with the XMM–Newton telescope in the 0.2–10 keV range in observations carried out from 2000 to 2019. Based on a study of the spectral properties of these sources and on cross-correlations with catalogues of possible counterparts, we have carried out a search of isolated neutron stars, finding four potential candidates. The spectral and long-term variability analysis of these candidates, using Chandra and Swift-XRT data, allowed us to point out the most interesting sources deserving further multiwavelength investigations.

Large-field CO (1–0) observations toward the Galactic historical supernova remnants: a large cavity aroundTycho’s supernova remnant

The investigation of the interaction between the supernova remnants (SNRs) and interstellar gas is not only necessary to improve our knowledge of SNRs, but also to understand the nature of the progenitor systems. As a part of the Milky Way Imaging Scroll Painting CO line survey (MWISP), we study the interstellar gas surrounding the Galactic historical SNRs, using the PMO 13.7-meter telescope. In this work, we present large-field (3$^\circ$$\times$2$^\circ$) and high-sensitivity CO(1-0) molecular line observations toward Tycho's SNR. The CO observations reveal, from the outside in, large molecular clouds, stream-like structures, and an inner rim around Tycho's SNR. We derived the basic properties (column density, mass, and kinematics) of these objects based on the CO observations. The large molecular clouds individually show an arc toward the remnant center, outlining a large cavity with radii of $\sim$0.3$^\circ$$\times$0.6$^\circ$ (or 13 pc $\times$27 pc at a distance of 2.5 kpc) around the remnant. The CO line broadenings and asymmetries detected in the surrounding clouds, the observed expansion of the cavity, in concert with enhanced $^{12}$CO(2-1)/(1-0) intensity ratio detected in previous studies, suggest the interaction of the large cavity with a wind in the region. After excluding the scenario of a large bubble produced by bright massive stars, we suggest that the large cavity could be explained by accretion wind from the progenitor system of Tycho's supernova. Nevertheless, the possibility of the random distribution of a large cavity around Tycho's SNR cannot be ruled out thus far. Further observations are needed to confirm the physical association of the large cavity with Tycho's SNR.

Study of the progenitor of the magnetar 1E 2259+586 through Suzaku observations of the associated supernova remnant CTB 109

Abstract We present a study of the progenitor of the magnetar 1E 2259+586, from Suzaku observations of the associated supernova remnant CTB 109. The Suzaku spectra, either spatially integrated or spatially resolved, were successfully described by a two-component plasma model, which reconfirms a previous Chandra result on the northwestern part of this remnant (Sasaki et al. 2013, A&A, 552, A45). The hotter component, with a temperature of ∼0.7 keV, can be identified as the stellar ejecta heated by reverse shock, because its contribution increases towards the remnant center. The cooler one, with a temperature of ∼0.25 keV, can be identified as the shocked interstellar matter. The abundances of Ne, Mg, Si, and S of the hotter component support these identifications. The total masses of the cooler and hotter components are estimated to be 220 ± 40 M⊙ and 42 ± 11 M⊙, respectively. The remnant is considered to be adiabatically expanding as in the Sedov–Taylor phase. The explosion energy, estimated to be 1.0 × 1051 erg by a canonical Sedov model, is typical of a core-collapse supernova explosion. Assuming that the hotter component includes the ejecta as well as the matter lost by the progenitor star via stellar winds, 1E 2259+586 is inferred to have originated from a very massive star.

Spectroscopic mapping of the physical properties of supernova remnant N 49

Context. Physical conditions inside a supernova remnant can vary significantly between different positions. However, typical observational data of supernova remnants are integrated data or contemplate specific portions of the remnant. Aims. We study the spatial variation in the physical properties of the N 49 supernova remnant based on a spectroscopic mapping of the whole nebula. Methods. Long-slit spectra were obtained with the slit (~4′ × 1.03″) aligned along the east-west direction from 29 different positions spaced by 2″ in declination. A total of 3248 1D spectra were extracted from sections of 2″ of the 2D spectra. More than 60 emission lines in the range 3550 A to 8920 A were measured in these spectra. Maps of the fluxes and of intensity ratios of these emission lines were built with a spatial resolution of 2″ × 2″. Results. An electron density map has been obtained using the [S ii] λ 6716 / λ 6731 line ratio. Values vary from ~500 cm -3 at the northeast region to more than 3500 cm -3 at the southeast border. We calculated the electron temperature using line ratio sensors for the ions S + , O ++ , O + , and N + . Values are about 3.6 × 10 4 K for the O ++ sensor and about 1.1 × 10 4 K for other sensors. The H α /H β ratio map presents a ring structure with higher values that may result from collisional excitation of hydrogen. We detected an area with high values of [N ii] λ 6583/H α extending from the remnant center to its northeastern border, which may be indicating an overabundance of nitrogen in the area due to contamination by the progenitor star. We found a radial dependence in many line intensity ratio maps. We observed an increase toward the remnant borders of the intensity ratio of any two lines in which the numerator comes before in the sequence [O iii] λ 5007, [O iii] λ 4363, [Ar iii] λ 7136, [Ne iii] λ 3869, [O ii] λ 7325, [O ii] λ 3727, He ii λ 4686, H β λ 4861, [N ii] λ 6583, He i λ 6678, [S ii] λ 6731, [S ii] λ 6716, [O i] λ 6300, [Ca ii] λ 7291, Ca ii λ 3934, and [N i] λ 5199.

THE 2D DISTRIBUTION OF IRON-RICH EJECTA IN THE REMNANT OF SN 1885 IN M31

We present Hubble Space Telescope (HST) ultraviolet Fe I and Fe II images of the remnant of Supernova 1885 (S And) which is observed in absorption against the bulge of the Andromeda galaxy, M31. We compare these Fe I and Fe II absorption line images to previous HST absorption images of S And, of which the highest quality and theoretically cleanest is Ca II H & K. Because the remnant is still in free expansion, these images provide a 2D look at the distribution of iron synthesized in this probable Type Ia explosion, thus providing insights and constraints for theoretical SN Ia models. The Fe I images show extended absorption offset to the east from the remnant's center as defined by Ca II images and is likely an ionization effect due to self-shielding. More significant is the remnant's apparent Fe II distribution which consists of four streams or plumes of Fe-rich material seen in absorption that extend from remnant center out to about 10,000 km/s. This is in contrast to the remnant's Ca II absorption, which is concentrated in a clumpy, roughly spherical shell at 1000 to 5000 km/s but which extends out to 12,500 km/s. The observed distributions of Ca and Fe rich ejecta in the SN 1885 remnant are consistent with delayed detonation white dwarf models. The largely spherical symmetry of the Ca-rich layer argues against a highly anisotropic explosion as might result from a violent merger of two white dwarfs.

Spatial, Dietary and Temporal Niche Dimensions in Ecological Segregation of Two Sympatric, Congeneric Marsupial Species

Didelphis aurita and D. albiventris are widely distributed in South America, with a range of sympatry in the limit of their distribution, particularly in Araucaria mixed ombrophilous forest in the southern Atlantic Forest. We investigated the spatial, feeding, and time use between these morphologically similar species in a remnant of Araucaria forest in southern Brazil for one year. We tested the hypothesis that these species when in sympatry segregate each other in space use, diet, and/or activity time. We expect that they segregate between each other primarily in the dimension of space use, as occurs for Australian congeneric marsupials. We used a mark-capture-release protocol for obtaining data. We analysed the spatial segregation by measuring the distance of captures in relation to the remnant centre, stream and edges. There were significant differences in the use of space, as adult females of D. aurita used mainly the remnant interior and stream sides, and D. albiventris females its edges or open areas. The consumption of feeding resources, particularly fruits, was different mainly between females and during the breeding season. However, there was no difference in the activity time between species. We believe that the territorial behaviour of D. aurita females had a crucial role in this spatial segregation with D. albiventris females, leading to a diet differentiation, particularly for fruits which were highly available inside the remnant. Interspecific competition between females is thought to be the main reason maintaining D. albiventris females far from the richest parts of the remnant. The mechanism behind this ecological segregation is discussed, and an ecological niche shift when both species are in sympatry is suggested, rather than the ghost of competition past.

On the Progenitor of SNR 0509-67.5

AbstractWe have used three independent methods to determine an accurate and precise geometric center of SNR 0509-67.5, at RA=05:09:31.208, DEC=−67:31:17.48 (J2000). This supernova, which occurred approximately 400 years ago in the Large Magellanic Cloud, was confirmed to be a Type Ia by Rest et al. (2005), Rest et al. (2008) based on spectra of a light echo from the eruption. If this supernova had a single-degenerate progenitor system, we would see the “leftover” companion star within a certain distance of the remnant's center. Accounting for an offset due to enhanced ISM in the west-southwest quadrant of the remnant, we find the eruption position to be at RA=05:09:30.976, DEC=−67:31:17.90; the error circle which should contain any possible ex-companion star has a radius of 1.60″ for 99.73% (3-sigma) containment. This accounts for the proper motion of the stars, the possibility of kicks from the supernova, and asymmetries in the explosion and remnant expansion. We find no possible ex-companion stars within this ellipse, to a limiting magnitude of V=26.9: there are no red giants, which precludes symbiotic progenitors, no subgiants, which when combined with the lack of red giants precludes recurrent nova progenitors, and no main sequence stars with mass greater than 1.16 solar masses (V brighter than 22.7 mag), which precludes persistent supersoft X-ray source progenitors. Indeed, all published SD models are eliminated, so we conclude that this particular Type Ia supernova had a double-degenerate progenitor.

Evolution of a buried magnetic field in the central compact object neutron stars

The central compact objects are a newly-emerging class of young neutron stars near the centre of supernova remnants. From X-ray timing and spectral measurements, their magnetic fields are determined to be ~ 10^10-10^11 G, which is significantly lower than that found on most pulsars. Using the latest electrical and thermal conductivity calculations, we solve the induction equation to determine the evolution of a buried crustal or core magnetic field. We apply this model of a buried field to explain the youth and low observed magnetic field of the central compact objects. We obtain constraints on their birth magnetic field and depth of submergence (or accreted mass). Measurement of a change in the observed magnetic field strength would discriminate between the crustal and core fields and could yield uniquely the birth magnetic field and submergence depth. If we consider the central compact objects as a single neutron star viewed at different epochs, then we constrain the magnetic field at birth to be ~ (6-9)x10^11 G. A buried magnetic field can also explain their location in an underpopulated region of the spin period-period derivative plane for pulsars.

SEARCHING FOR COMPACT OBJECTS IN SNRs G27.8+0.6 AND G28.8+1.5

We analyzed XMM-Newton observations of two center-filled supernova remnants, G27.8+0.6 and G28.8+1.5, to search for pulsars/pulsar wind nebulae (PWNe) and other types of neutron stars associated with these remnants. We discovered a PWN candidate within the extent of the centrally-peaked radio emission of G27.8+0.6. The X-ray morphology of the PWN candidate and its position with respect to the host supernova remnant suggest that the alleged pulsar might be moving away from the supernova remnant's center with a transverse velocity of around 100-200 km/s. The majority of the detected X-ray point sources in both fields are classified as main-sequence stars, based on their bright optical counterparts and relatively soft X-ray spectra. The remaining medium-hard and hard sources are most probably either AGNs or cataclysmic variables, although we cannot completely rule out the possibility that some of these sources are neutron stars.

HIGH-RESOLUTION X-RAY IMAGING OF SUPERNOVA REMNANT 1987A

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.

SUBARU HIGH-RESOLUTION SPECTROSCOPY OF STAR G IN THE TYCHO SUPERNOVA REMNANT

It is widely believed that Type Ia supernovae (SN Ia) originate in binary systems where a white dwarf accretes material from a companion star until its mass approaches the Chandrasekhar mass and carbon is ignited in the white dwarf's core. This scenario predicts that the donor star should survive the supernova explosion, providing an opportunity to understand the progenitors of Type Ia supernovae.In this paper we argue that rotation is a generic signature expected of most non-giant donor stars that is easily measurable. \citep{2004Natur.431.1069R} examined stars in the center of the remnant of SN 1572 (Tycho's SN) and showed evidence that a subgiant star (Star G by their naming convention) near the remnant's centre was the system's donor star. We present high-resolution (R \simeq 40000) spectra taken with the High Dispersion Spectrograph on Subaru of this candidate donor star and measure the star's radial velocity as $79\pm 2$ \kms with respect to the LSR and put an upper limit on the star's rotation of 7.5 \kms. In addition, by comparing images that were taken in 1970 and 2004, we measure the proper motion of Star G to be $\mu_l = -1.6 \pm 2.1$ \masyr and $\mu_b = -2.7 \pm 1.6$ \masyr. We demonstrate that all of the measured properties of Star G presented in this paper are consistent with those of a star in the direction of Tycho's SN that is not associated with the supernova event. However, we discuss an unlikely, but still viable scenario for Star G to be the donor star, and suggest further observations that might be able to confirm or refute it.

NEAR-INFRARED [Fe II] AND H2LINE OBSERVATIONS OF THE SUPERNOVA REMNANT 3C 396: PROBING THE PRESUPERNOVA CIRCUMSTELLAR MATERIALS

We present the results of near-infrared [Fe II] and H2 line imaging and spectroscopic observations of the supernova remnant 3C 396 using the Palomar 5 m Hale telescope. We detect long, filamentary [Fe II] emission delineating the inner edge of the radio emission in the western boundary of the remnant in imaging observations, together with a bright [Fe II] emission clump close to the remnant center. There appears to be faint, diffuse [Fe II] emission between the central clump and the western filamentary emission. The spectroscopic observations determine the expansion velocity of the central clump to be ~56 km/s. This is far smaller than the expansion velocity of 3C 396 obtained from X-ray observations, implying the inhomogeneity of the ambient medium. The electron number density of the [Fe II] emission gas is < 2,000 cm-3. The H2 line emission, on the other hand, lies slightly outside the filamentary [Fe II] emission in the western boundary, and forms a rather straight filament. We suggest that the [Fe II] emission represents dense clumps in the wind material from the red supergiant phase of a Type IIL/b progenitor of 3C 396 which have been swept up by the supernova remnant shocks. The H2 emission may represent either the boundary of a wind bubble produced during the main-sequence phase of the progenitor or molecular clumps left over inside the bubble. We propose that the near-infrared [Fe II] and H2 emission observed in several supernova remnants of Type IIL/b SNe likely has the same origin.

Exploring the X-ray emission properties of the supernova remnant G67.7+1.8 and its central X-ray sources

We have studied the supernova remnant G67.7+1.8 with the Chandra X-ray observatory. The remnant’s X-ray morphology correlates well with the double-arc structure seen at radio wavelength. The X-ray spectra of the northern and southern rim of G67.7+1.8 exhibit emission line features of highly ionized metals, which suggests that most of the observed X-rays originate in a thermal plasma. We find magnesium , silicon, and sulphur overabundant relative to the solar values. Gaussian emission lines at ∼4 keV and ∼7 keV are detected. The ∼4 keV line is consistent with K-emission lines from 44 Ca and/or 44 Sc whereas the ∼7 keV line feature may arise from unresolved Fe-K lines. Chandra’s sub-arcsecond angular resolution allowed us to detect four faint point sources located within ∼1.5 arcmin of the geometrical remnant center. Among these objects, CXOU195424.75+312824.9 and CXOU195429.82+312834.1 do not have optical counterparts, leaving them as candidates for a possible compact stellar remnant.

A Catalog of Outer Ejecta Knots in the Cassiopeia A Supernova Remnant

Hubble Space Telescope images of the core-collapse supernova remnant Cassiopeia A are used to identify high-velocity knots of ejecta located outside the remnant's main emission shell of expanding debris. These ejecta fragments are found near or ahead of the remnant's forward shock front and mostly lie from 12000 to 30000 in radial distance from the remnant's center of expansion. Filter flux ratios when correlated with published spectra show that these knots can be divided into three emission classes: (1) knots dominated by [N II] lambda lambda 6548, 6583 emissions, ( 2) knots dominated by [O II] kk7319, 7330 emissions, and (3) knots displaying filter flux ratios suggestive of [ S II], [ O II], and [Ar III] lambda 7135 emission line strengths similar to the fast-moving knots'' (FMKs) found in the remnant's bright main shell. Of 1825 knots identified, 444 are strong [N II] emission knots, 192 are strong [O II] emission knots, and 1189 are FMK-like knots. In terms of location around the remnant, 972, 207, and 646 knots are found in the remnant's northeast jet, southwest jet, and non-jet regions, respectively. Assuming a distance of 3.4 kpc, derived knot transverse velocities based on proper motion measurements spanning a 9 month interval indicate maximum transverse expansion velocities for these three knot classes of 14,500, 13,500, and 11,500 km s(-1), respectively. We present a catalog of these outlying ejecta clumps comprising finding charts, epoch 2004.2 knot positions, proper motions, photometric filter fluxes, and estimated knot emission type, along with cross-references to previous knot identifications and data. This compilation represents a nearly tenfold increase in the number of outlying, high-velocity ejecta knots identified around the Cassiopeia A remnant.

Genetic diversity and geographic pattern of wild lotus (Nelumbo nucifera) in Heilongjiang Province

Based on 47 accessions from Ussuri River Valley, Songhua River Valley and Heilong River Valley together with 2 accessions from Russia and 27 accessions of cultivated lotus from other provinces in China, genetic diversity of wild lotus (Nelumbo nucifera) were revealed using RAPD and ISSR markers. Twenty RAPD primers generated 113 loci, of which 71.68% were polymorphic across all samples. The expected heterozygosity was 0.1583. The percentage of polymorphic loci and expected heterozygosity in the wild lotus were 50.44% and 0.1241, respectively. The parameters of the cultivated lotus were slightly higher, 53.98% and 0.1651 correspondingly. Sixteen ISSR primers produced 90 loci. The percentages of polymorphic loci and expected heterozygosity were 41.11% and 0.0851 at species level, 28.89% and 0.0661 for the wild lotus, and 32.22% and 0.0963 for the cultivated lotus. AMOVA analysis of the wild lotus showed that a small number of variances exist among the 3 river valleys (21.68% for RAPD with Gst=0.1312 and 15.11% for ISSR with Gst=0.1352). The molecular variances of both the wild and the cultivated lotuses came predominantly from within the 3 river valleys and the cultivated samples (73.25% for RAPD and 81.11% for ISSR). Variance components from the wild and the cultivated lotus accounted for 19.17% for RAPD and 13.17% for ISSR, and variations among the valleys and the culta seemed the least important (7.585 for RAPD and 5.725 for ISSR). Neighbor-joining analysis demonstrated that considerable differentiation happened between the wild and the cultivated lotus. The wild lotus at middle reaches of the Songhua River Valley seemed to be the centre of remnants, from which it spread to the Ussuri River Valley and the Heilong River Valley. The very limited genetic diversity suggests that the wild lotus has experienced severe bottleneck effect, founder effect and rebirth effect. Considering its long evolutionary history, scarcity of genetic variations and importance in wetland ecosystems, we appeal to take lawful measures to protect the wild lotus. For conservation purpose, special attention should be paid to the lotus at the middle reaches of the Songhua River Valley.

The Expansion of G11.2-0.3, a Radio Composite Supernova Remnant

We compare recent observations of the supernova remnant G11.2-0.3 taken with the VLA during 2001-02 with images from VLA archives (1984-85) to detect and measure the amount of expansion that has occurred during 17 years. The bright, circular outer shell shows a mean expansion of (0.71 +/- 0.15)% and (0.50 +/- 0.17)%, from 20- and 6-cm data, respectively, which corresponds to a rate of 0.057' +/- 0.012'/yr at 20 cm and 0.040' +/- 0.013'/yr at 6 cm. From this result, we estimate the age of the remnant to be roughly between 960 and 3400 years old, according to theoretical models of supernova evolution. This is highly inconsistent with the 24000 yr characteristic age of PSR J1811-1925, located at the remnant's center, but, rather, is consistent with the time since the historical supernova observed in 386 AD. We also predict that G11.2-0.3 is currently in a pre-Sedov evolutionary state, and set constraints on the distance to the remnant based on Chandra X-ray spectral results.

Detection of the High-Energy Cosmic Rays from the Monogem Ring

The MAKET-ANI detector reveals significant excess of extensive air showers with arrival directions pointed to the Monogem ring, a supernova remnant located at a distance of ≈300 pc from the Sun with ≈100 kyr old radio pulsar PSR B0656+14 near the center. The chances that this excess is due to the fluctuations of an isotropic flux is 2 per million. For the search of the cosmic-ray source, we use the MAKET-ANI detector data from years 1997 to 2003. The best signal bin coordinates, right ascension 75, declination 14° (750+14), significantly deviate from the ring morphological center, shifted in the direction of the most intensive X-ray emission from the supernova remnant's limb, now located 66 pc from the supernova remnant center and 27 pc from the candidate source.

ITAL]HUBBLE SPACE TELESCOPE[/ITAL][ITAL]Hubble Space Telescope[/ITAL] WFPC2 Imaging of Cassiopeia A

The young galactic supernova remnant Cassiopeia A was imaged with Wide Field Planetary Camera 2 (WFPC2) aboard the Hubble Space Telescope through filters selected to capture the complete velocity range of the remnant's main shell in several emission lines. The primary lines detected, along with the specific WFPC2 filters used, were [O III] λλ4959, 5007 (F450W), [N II] λ6583 (F658N), [S II] λλ6716, 6731 + [O II] λλ7319, 7330 + [O I] λλ6300, 6364 (F675W), and [S III] λλ9069, 9532 (F850LP). About three-quarters of the remnant's 4' diameter main shell was imaged with all four filters in three WFPC2 pointings, with most remaining shell regions imaged in just the F675W filter via three additional pointings. Considerable detail is observed in the reverse-shocked ejecta with typical knot scale lengths of 02–04 (1–2 × 1016 cm). Both bright and faint emission features appear highly clumped with little in the way of a smooth, diffuse emission component detected. Strong differences in [S III] and [O III] line intensities, indicating chemical abundance differences, are also seen, particularly in knots located along the bright northern limb and near the base of the northeastern jet. A line of curved overlapping filaments in the remnant's northwestern rim appears to mark the location of the remnant's reverse shock front in this region. The morphology of some finger-like ejecta structures elsewhere suggest cases in which the reverse shock front is encountering the remnant's clumped ejecta. Large velocity shears (≃1000 km s-1), possibly associated with the formation of these Rayleigh-Taylor–like features, are found in the line profiles of several emission lines (e.g., [S III] λλ9069, 9532 and [Cl II] λ8679) in ground-based, optical spectra of knots near the remnant's center. The [N II] images of the remnant's circumstellar knots (QSFs) reveal them to be 01–06 thick knots and filaments, often with diffuse edges facing away from the center of expansion. Three-color composite images of the whole remnant and certain sections, along with individual filter enlargements of selected regions of the bright optical shell, are presented and discussed.