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Register a new userHigh Resolution Spectroscopy of Two Oxygen-Rich SNRs with the Chandra HETG
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The HETG can be used to obtain spatially resolved spectra of moderately extended sources. We present preliminary results for two well studied, oxygen rich supernova remnants in the Magellanic clouds, E0102-72 and N132D. The dispersed spectrum of E0102-72 shows images of the remnant in the light of individual emission lines from H-like and He-like ions of O, Mg, Ne and He-like Si with no evidence of Fe. The diameters of the images for various ions, measured in the cross-dispersion direction, increase monotonically with the ionization age for the given ion. This shows in detail the progression of the reverse shock through the expanding stellar ejecta. We see clear evidence for asymmetric Doppler shifts across E0102-72 of ~2000 km/s. These can be modelled approximately by a partially-filled, expanding shell inclined to the line of sight. The dispersed spectrum of N132D is more affected by spatial/spectral overlap but also shows monochromatic images in several strong lines. Preliminary spectra have been extracted for several bright knots. Some regions of oxygen-rich material, presumably stellar ejecta, are clearly identified. Additional details on E0102-72 are presented by Flanagan et al. and Davis et al. in these proceedings, and further analysis is in progress.
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As one of the best-characterized stellar-mass black holes, with good measurements of its mass, distance and inclination, V404 Cyg is the ideal candidate to study Eddington-limited accretion episodes. After a long quiescent period, V404 Cyg underwent a new outburst in June 2015. We obtained two Chandra HETG exposures of 20 ksec and 25 ksec. Many strong emission lines are observed; the ratio of Si He-like triplet lines gives an estimate for the formation region distance of $4times10^{11}$ cm, while the higher ionization Fe XXV He-like triplet gives an estimate of $7times10^9$ cm. A narrow Fe K$alpha$ line is detected with an equivalent width greater than 1 keV in many epochs, signaling that we do not directly observe the central engine. Obscuration of the central engine and strong narrow emission lines signal that the outer disk may be illuminated, and its structure may help to drive the strong variability observed in V404 Cyg. In the highest flux phases, strong P-Cygni profiles consistent with a strong disk wind are observed. The kinetic power of this wind may be extremely high.
We report our measurements of the bulk radial velocity from a sample of small, metal-rich ejecta knots in Keplers Supernova Remnant (SNR). We measure the Doppler shift of the He-like Si K$alpha$ line center energy in the spectra of these knots based on our $Chandra$ High-Energy Transmission Grating Spectrometer (HETGS) observation to estimate their radial velocities. We estimate high radial velocities of up to $sim$ 8,000 km s$^{-1}$ for some of these ejecta knots. We also measure proper motions for our sample based on the archival $Chandra$ Advanced CCD Imaging Spectrometer (ACIS) data taken in 2000, 2006, and 2014. Our measured radial velocities and proper motions indicate that some of these ejecta knots are almost freely-expanding after $sim$ 400 years since the explosion. The fastest moving knots show proper motions up to $sim$ 0.2 arcseconds per year. Assuming that these high velocity ejecta knots are traveling ahead of the forward shock of the SNR, we estimate the distance to Keplers SNR $d$ $sim$ 4.4 to 7.5 kpc. We find that the ejecta knots in our sample have an average space velocity of $ v_{s} sim$ 4,600 km s$^{-1}$ (at a distance of 6 kpc). We note that 8 out of the 15 ejecta knots from our sample show a statistically significant (at the 90$%$ confidence level) redshifted spectrum, compared to only two with a blueshifted spectrum. This may suggest an asymmetry in the ejecta distribution in Keplers SNR along the line of sight, however a larger sample size is required to confirm this result.
We present high spatial resolution X-ray spectroscopy of supernova remnant G292.0+1.8 with the {sl Chandra} observations. The X-ray emitting region of this remnant was divided into 25 $times$ 25 pixels with a scale of 20$arcsec$ $times$ 20$arcsec$ each. Spectra of 324 pixels were created and fitted with an absorbed one component non-equilibrium ionization model. With the spectral analysis results we obtained maps of absorbing column density, temperature, ionization age, and the abundances for O, Ne, Mg, Si, S, and Fe. The abundances of O, Ne and Mg show tight correlations between each other in the range of about two orders of magnitude, suggesting them all from explosive C/Ne burning. Meanwhile, the abundances of Si and S are also well correlated, indicating them to be the ashes of explosive explosive O-burning or incomplete Si-burbing. The Fe emission lines are not prominent among the whole remnant, and its abundance are significantly deduced, indicating that the reverse shock may have not propagated to the Fe-rich ejecta. Based on relative abundances of O, Ne, Mg, Si and Fe to Si, we suggest a progenitor mass of $25-30 M_{odot}$ for this remnant.
Based on observations with the $Chandra$ X-ray Observatory, we present the latest spectral evolution of the X-ray remnant of SN 1987A (SNR 1987A). We present a high-resolution spectroscopic analysis using our new deep ($sim$312 ks) $Chandra$ HETG observation taken in March 2018, as well as archival $Chandra$ gratings spectroscopic data taken in 2004, 2007, and 2011 with similarly deep exposures ($sim$170 - 350 ks). We perform detailed spectral model fits to quantify changing plasma conditions over the last 14 years. Recent changes in electron temperatures and volume emission measures suggest that the shocks moving through the inner ring have started interacting with less dense circumstellar material, probably beyond the inner ring. We find significant changes in the X-ray line flux ratios (among H- and He-like Si and Mg ions) in 2018, consistent with changes in the thermal conditions of the X-ray emitting plasma that we infer based on the broadband spectral analysis. Post-shock electron temperatures suggested by line flux ratios are in the range $sim$0.8 - 2.5 keV as of 2018. We do not yet observe any evidence of substantial abundance enhancement, suggesting that the X-ray emission component from the reverse-shocked metal-rich ejecta is not yet significant in the observed X-ray spectrum.
We measure chemical abundances for over 20 elements of 15 N-rich field stars with high resolution ($R sim 30000$) optical spectra. We find that Na, Mg, Al, Si, and Ca abundances of our N-rich field stars are mostly consistent with those of stars from globular clusters (GCs). Seven stars are estimated to have [Al/Fe$]>0.5$, which is not found in most GC first generation stars. On the other hand, $alpha$ element abundances (especially Ti) could show distinguishable differences between in situ stars and accreted stars. We discover that one interesting star, with consistently low [Mg/Fe], [Si/Fe], [Ca/Fe], [Ti/Fe], [Sc/Fe], [V/Fe], and [Co/Fe], show similar kinematic and [Ba/Eu] as other stars from the dissolved dwarf galaxy $Gaia$-Sausage-Enceladus. The $alpha$-element abundances and the iron-peak element abundances of the N-rich field stars with metallicities $-1.25 le {rm [Fe/H]} le -0.95$ show consistent values with Milky Way field stars rather than stars from dwarf galaxies, indicating that they were formed in situ. In addition, the neutron capture elements of N-rich field stars show that most of them could be enriched by asymptotic giant branch (AGB) stars with masses around $3 - 5, M_{odot}$.
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