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Register a new userProbing the Innermost Ejecta Layers in SNR Kes 75: Implications for the Supernova Progenitor
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Supernova remnants (SNRs) that contain pulsar wind nebulae (PWNe) are characterized by distinct evolutionary stages. In very young systems, the PWN drives a shock into the innermost supernova (SN) material, giving rise to low-excitation lines and an infrared (IR) continuum from heated dust grains. These observational signatures make it possible to cleanly measure the properties of the deepest SN ejecta layers that can, in turn, provide constraints on the SN progenitor. We present Herschel Space Observatory far-IR observations of the PWN in the Galactic SNR Kes 75, containing the youngest known pulsar that exhibited magnetar-like activity. We detect highly-broadened oxygen and carbon line emission that arises from the SN ejecta encountered by the PWN. We also detect a small amount (a few thousandths of a solar mass) of shock-heated dust that spatially coincides with the ejecta material and was likely formed in the SN explosion. We use hydrodynamical models to simulate the evolution of Kes 75 and find that the PWN has so far swept up 0.05-0.1 solar masses of SN ejecta. Using explosion and nucleosynthesis models for different progenitor masses in combination with shock models, we compare the predicted far-IR emission with the observed line intensities and find that lower mass and explosion energy SN progenitors with mildly mixed ejecta profiles and comparable abundance fractions of carbon and oxygen are favored over higher mass ones. We conclude that Kes 75 likely resulted from an 8-12 solar-mass progenitor, providing further evidence that lower energy explosions of such progenitors can give rise to magnetars.
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PSR J1846-0258 is a radio-quiet rotation-powered pulsar at the center of Supernova remnant Kes 75. It is the youngest pulsar (~723 year) of all known pulsars and slows down very predictably since its discovery in 2000. Till June 7, 2006 very stable behavior has been displayed both in the temporal and spectral domains with pulsed emission detectable by INTEGRAL IBIS ISGRI and RXTE HEXTE up to ~150 keV. Then, a dramatic brightening was detected of the pulsar during June 7-12, 2006 Chandra observations of Kes 75. This radiative event, lasting for ~55 days, was accompanied by a huge timing glitch, reported on for the first in present work. Moreover, several short magnetar-like bursts were discovered. In this work not only the time-averaged pre-outburst X-ray/soft gamma-ray characteristics are discussed in detail, but also the spectral evolution during the outburst and its relaxation phase are addressed using RXTE PCA and HEXTE and INTEGRAL IBIS ISGRI data.
We report new Chandra X-ray observations of the shell supernova remnant (SNR) Kes 75 (G29.7-0.3) containing a pulsar and pulsar-wind nebula (PWN). Expansion of the PWN is apparent across the four epochs, 2000, 2006, 2009, and 2016. We find an expansion rate between 2000 and 2016 of the NW edge of the PWN of 0.249% +/- 0.023% yr^{-1}, for an expansion age R/(dR/dt) of 400 +/- 40 years and an expansion velocity of about 1000 km s^{-1}. We suggest that the PWN is expanding into an asymmetric nickel bubble in a conventional Type IIP supernova. Some acceleration of the PWN expansion is likely, giving a true age of 480 +/- 50 years. The pulsars birth luminosity was larger than the current value by a factor of 3 -- 8, while the initial period was within a factor of 2 of its current value. We confirm directly that Kes 75 contains the youngest known PWN, and hence youngest known pulsar. The pulsar PSR J1846-0258 has a spindown-inferred magnetic field of 5 x 10^{13} G; in 2006 it emitted five magnetar-like short X-ray bursts, but its spindown luminosity has not changed significantly. However, the flux of the PWN has decreased by about 10% between 2009 and 2016, almost entirely in the northern half. A bright knot has declined by 30% since 2006. During this time, the photon indices of the power-law models did not change. This flux change is too rapid to be due to normal PWN evolution in one-zone models.
The supernova remnant (SNR) Kes 75/PSR J1846-0258 association can be regarded as certain due to the accurate location of young PSR J1846-0258 at the center of Kes 75 and the detected bright radio/X-ray synchrotron nebula surrounding the pulsar. We provide a new distance estimate to the SNR/pulsar system by analyzing the HI and $^{13}$CO maps, the HI emission and absorption spectra, and the $^{13}$CO emission spectrum of Kes 75. No absorption features at negative velocities strongly argue against the widely-used large distance of 19 to 21 kpc for Kes 75, and show that Kes 75 is within the Solar circle, i.e. a distance $d<$13.2 kpc. Kes 75 is likely at distance of 5.1 to 7.5 kpc because the highest HI absorption velocity is at 95 km/s and no absorption is associated with a nearby HI emission peak at 102 km/s in the direction of Kes 75. This distance to Kes 75 gives a reasonable luminosity of PSR J1846-0258 and its PWN, and also leads to a much smaller radius for Kes 75. So the age of the SNR is consistent with the spin-down age of PSR J1846-0258, confirming this pulsar as the second-youngest in the Galaxy.
The Vela supernova remnant (SNR) shows several ejecta fragments protruding beyond the forward shock (shrapnel). Recent studies have revealed high Si abundance in two shrapnel (A and G), located in opposite directions with respect to the SNR center. This suggests the possible existence of a Si-rich jet-counterjet structure. We analyzed an XMM-Newton observation of a bright clump, behind shrapnel G, which lies along the direction connecting A and G. The aim is to study the physical and chemical properties of this clump to ascertain whether it is part of this putative jet-like structure. We produced background-corrected and adaptively-smoothed count-rate images and median photon energy maps, and performed a spatially resolved spectral analysis. We identified two structures with different physical properties. The first one is remarkably elongated along the direction connecting A and G. Its X-ray spectrum is much softer than that of the other two shrapnel, to the point of hindering the determination of the Si abundance, however its physical and chemical properties are consistent with those of shrapnel A and G. The second structure, running along the southeast-northwest direction, has a higher temperature and appears like a thin filament. By analyzing the ROSAT data, we have found that this filament is part of a very large and coherent structure that we identified in the western rim of the shell. We obtained a thorough description of the tail of Shrapnel G. In addition we discovered a coherent and very extended feature that we interpret as a signature of an earlier interaction of the remnant with the stellar wind of its progenitor star. The peculiar Ne/O ratio we found in the wind residual may be suggestive of a Wolf-Rayet progenitor for Vela SNR, though further analysis is required to address this point.
With presently known input physics and computer simulations in 1D, a self-consistent treatment of core collapse supernovae does not yet lead to successful explosions, while 2D models show some promise. Thus, there are strong indications that the delayed neutrino mechanism works combined with a multi-D convection treatment for unstable layers. On the other hand there is a need to provide correct nucleosynthesis abundances for the progressing field of galactic evolution and observations of low metallicity stars. The innermost ejecta is directly affected by the explosion mechanism, i.e. most strongly the yields of Fe-group nuclei for which an induced piston or thermal bomb treatment will not provide the correct yields because the effect of neutrino interactions is not included. We apply parameterized variations to the neutrino scattering cross sections and alternatively, parameterized variations are applied to the neutrino absorption cross sections on nucleons in the ``gain region. We find that both measures lead to similar results, causing explosions and a Ye>0.5 in the innermost ejected layers, due to the combined effect of a short weak interaction time scale and a negligible electron degeneracy, unveiling the proton-neutron mass difference. We include all weak interactions (electron and positron capture, beta-decay, neutrino and antineutrino capture on nuclei, and neutrino and antineutrino capture on nucleons) and present first nucleosynthesis results for these innermost ejected layers to discuss how they improve predictions for Fe-group nuclei. The proton-rich environment results in enhanced abundances of 45Sc, 49Ti, and 64Zn as requested by chemical evolution studies and observations of low metallicity stars as well as appreciable production of nuclei in the mass range up to A=80.
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