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Register a new userA Nucleosynthetic Origin for the Southwestern Fe-rich Structure in Keplers Supernova Remnant
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{it Chandra} X-ray observations of Keplers supernova remnant indicate the existence of a high speed Fe-rich ejecta structure in the southwestern region. We report strong K-shell emission from Fe-peak elements (Cr, Mn, Fe, Ni), as well as Ca, in this Fe-rich structure, implying that those elements could be produced in the inner area of the exploding white dwarf. We found Ca/Fe, Cr/Fe, Mn/Fe and Ni/Fe mass ratios of 1.0--4.1%, 1.0--4.6%, 1--11% and 2--30%, respectively. In order to constrain the burning regime that could produce this structure, we compared these observed mass ratios with those in 18 one-dimensional Type Ia nucleosynthesis models (including both near-$M_{rm Ch}$ and sub-$M_{rm Ch}$ explosion models). The observed mass ratios agree well with those around the middle layer of incomplete Si-burning in Type Ia nucleosynthesis models with a peak temperature of $sim$(5.0--5.3)$times$10$^{9}$ K and a high metallicity, Z $>$ 0.0225. Based on our results, we infer the necessity for some mechanism to produce protruding Fe-rich clumps dominated by incomplete Si-burning products during the explosion. We also discuss the future perspectives of X-ray observations of Fe-rich structures in other Type Ia supernova remnants.
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Supernova 1604 is the last Galactic supernova for which historical records exist. Johannes Keplers name is attached to it, as he published a detailed account of the observations made by himself and European colleagues. Supernova 1604 was very likely a Type Ia supernova, which exploded 350 pc to 750 pc above the Galactic plane. Its supernova remnant, known as Keplers supernova remnant, shows clear evidence for interaction with nitrogen-rich material in the north/northwest part of the remnant, which, given the height above the Galactic plane, must find its origin in mass loss from the supernova progenitor system. The combination of a Type Ia supernova and the presence of circumstellar material makes Keplers supernova remnant a unique object to study the origin of Type Ia supernovae. The evidence suggests that the progenitor binary system of supernova 1604 consisted of a carbon- oxygen white dwarf and an evolved companion star, which most likely was in the (post) asymptotic giant branch of its evolution. A problem with this scenario is that the companion star must have survived the explosion, but no trace of its existence has yet been found, despite a deep search. 1 Introduction; 2 The supernova remnant, its distance and multiwavelength properties; 2.1 Position, distance estimates and SN1604 as a runaway system; 2.2 X-ray imaging spectroscopy and SN1604 as a Type Ia supernova 2.3 The circumstellar medium as studied in the optical and infrared; 3 The dynamics of Keplers SNR; 3.1 Velocity measurements; 3.2 Hydrodynamical simulations; 4 The progenitor system of SN 1604; 4.1 Elevated circumstellar nitrogen abundances, silicates and a single degenerate scenario for SN1604; 4.2 Problems with a single degenerate Type Ia scenario for SN 1604; 4.3 Was SN 1604 a core-degenerate Type Ia explosion?; 4.4 What can we learn from the historical light curve of SN 1604? ; 5 Conclusions
We present a detailed radio, X-ray and optical study of a newly discovered Large Magellanic Cloud (LMC) supernova remnant (SNR) which we denote MCSNR J0508-6902. Observations from the Australian Telescope Compact Array (ATCA) and the $textit{XMM-Newton}$ X-ray observatory are complemented by deep H$alpha$ images and Anglo Australian Telescope AAOmega spectroscopic data to study the SNR shell and its shock-ionisation. Archival data at other wavelengths are also examined. The remnant follows a filled-in shell type morphology in the radio-continuum and has a size of $sim$74 pc $times$ 57 pc at the LMC distance. The X-ray emission exhibits a faint soft shell morphology with Fe-rich gas in its interior $-$ indicative of a Type Ia origin. The remnant appears to be mostly dissipated at higher radio-continuum frequencies leaving only the south-eastern limb fully detectable while in the optical it is the western side of the SNR shell that is clearly detected. The best-fit temperature to the shell X-ray emission ($kT = 0.41^{+0.05}_{-0.06}$ keV) is consistent with other large LMC SNRs. We determined an O/Fe ratio of $<21$ and an Fe mass of 0.5-1.8$~M_{odot}$ in the interior of the remnant, both of which are consistent with the Type Ia scenario. We find an equipartition magnetic field for the remnant of $sim$28 $mu$G, a value typical of older SNRs and consistent with other analyses which also infer an older remnant.
We report measurements of proper motion, radial velocity, and elemental composition for 14 X-ray knots in Keplers supernova remnant (SNR) using Chandra data. The highest speed knots show both large proper motions (0.11-0.14 /yr) and high radial velocities (v ~ 8,700--10,020 km/s) with estimated space velocities comparable to the typical Si velocity (~10,000 km/s) seen in SN Ia near maximum light. High speed ejecta knots appear only in specific locations and are morphologically and kinematically distinct from the rest of the ejecta. The proper motions of five knots extrapolate back over the age of Keplers SNR to a consistent central position that agrees well with previous determinations, but is less subject to systematic errors. These five knots are expanding at close to the free expansion rate (expansion indices of 0.75 <~ m <~ 1.0), which we argue indicates either that they were formed in the explosion with a high density contrast (more than 100 times the ambient density) or that they have propagated through relatively low density (n_H < 0.1 cm^-3) regions in the ambient medium. X-ray spectral analysis shows that the undecelerated knots have high Si and S abundances, a lower Fe abundance and very low O abundance, pointing to an origin in the partial Si-burning zone, which occurs in the outer layer of the exploding white dwarf for SN Ia models. Other knots show slower speeds and expansion indices consistent with decelerated ejecta knots or features in the ambient medium overrun by the forward shock. Our new accurate location for the explosion site has well-defined positional uncertainties allowing for a great reduction in the area to be searched for faint surviving donor stars under non-traditional single-degenerate SN Ia scenarios; because of the lack of bright stars in the search area the traditional scenario remains ruled out.
Overionized recombining plasmas (RPs) have been discovered from a dozen of mixed- morphology (MM) supernova remnants (SNRs). However their formation process is still under debate. As pointed out by many previous studies, spatial variations of plasma temperature and ionization state provide clues to understand the physical origin of RPs. We report on a spatially resolved X-ray spectroscopy of W28, which is one of the largest MM SNRs found in our Galaxy. Two observations with Suzaku XIS cover the center of W28 to the northeastern rim where the shock is interacting with molecular clouds. The X-ray spectra in the inner regions are well reproduced by a combination of two-RP model with different temperatures and ionization states, whereas that in northeastern rim is explained with a single-RP model. Our discovery of the RP in the northeastern rim suggests an effect of thermal conduction between the cloud and hot plasma, which may be the production process of the RP. The X-ray spectrum of the north- eastern rim also shows an excess emission of the Fe I K{alpha} line. The most probable process to explain the line would be inner shell ionization of Fe in the molecular cloud by cosmic-ray particles accelerated in W28.
The guest star of AD 1181 is the only historical supernova of the last millennium that is without a definite counterpart. The previously proposed association with supernova remnant 3C58 is in strong doubt because of the inferred age of this remnant. Here we report a new identification of SN 1181 with our codiscovery of the hottest known Wolf Rayet star of the Oxygen sequence (dubbed Parkers star) and its surrounding nebula Pa 30. Our spectroscopy of the nebula shows a fast shock with extreme velocities of approx. 1,100kms. The derived expansion age of the nebula implies an explosive event approx 1,000 years ago which agrees with the 1181 AD event. The on sky location also fits the historical Chinese and Japanese reports of SN 1181 to 3.5degrees. Pa 30 and Parkers star have previously been proposed to be the result of a double-degenerate merger, leading to a rare Type Iax supernova. The likely historical magnitude and the distance suggest the event was subluminous for normal supernova. This agrees with the proposed Type Iax association which would also be the first of its kind in the Galaxy. Taken together, the age, location, event magnitude and duration elevate Pa 30 to prime position as the counterpart of SN 1181. This source is the only Type Iax supernova where detailed studies of the remnant star and nebula are possible. It provides strong observational support for the double degenerate merger scenario for Type Iax supernovae.
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