X-Ray Observations of Nova Sco 2023: Spectroscopic Evidence of Charge Exchange
The supersoft source phase of a nova eruption, observed a few days after the outburst, usually displays an absorbed X-ray thermal continuum with absorption features, emitted by the white dwarf atmosphere. However, the X-ray spectra of many novae in this phase display additional emission lines that l...
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2025-01-01
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| Online Access: | https://doi.org/10.3847/1538-4357/adf1a3 |
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| author | Sharon Mitrani Ehud Behar Marina Orio Jack Worley |
| author_facet | Sharon Mitrani Ehud Behar Marina Orio Jack Worley |
| author_sort | Sharon Mitrani |
| collection | DOAJ |
| description | The supersoft source phase of a nova eruption, observed a few days after the outburst, usually displays an absorbed X-ray thermal continuum with absorption features, emitted by the white dwarf atmosphere. However, the X-ray spectra of many novae in this phase display additional emission lines that likely originate from shocks in the novae ejecta. When the shocked plasma interacts with cold gas, narrow radiative recombination continua (RRCs) and charge exchange (CX) emission are observed. We present the analysis of high-resolution Chandra Low Energy Transmission Grating X-ray grating spectra of Nova Sco 2023, observed 128 and 183 days after the optical peak in 2023 August and October. At both epochs, the absorbed X-ray thermal continuum is well described by a nonlocal thermal equilibrium atmosphere model with a temperature T ≃ 750,000 K ( kT ≃ 65 eV). On day 128, the atmosphere is found to be outflowing at v ≃ −3500 km s ^−1 . On day 183, the atmosphere brightened by a factor of ∼2 and slowed down to v ≃ −1500 km s ^−1 . The discrete emission features of the spectrum consist of the C ^+5 , N ^+5 , and N ^+6 RRCs, indicating a cold electron temperature of kT _e ≃ 1 eV on day 128 and kT _e ≃ 20 eV on day 183. The observed line series of H-like and He-like C ^+5 , N ^+5 , N ^+6 , and O ^+6 show enhanced intensities of high- n (principal quantum number) transitions, consistent with a CX model of hot ions at kT ∼ 100 eV. The velocity shift of the CX lines remained at v ∼ ±3000 km s ^−1 , which can be explained by a bipolar outflow. After Nova Ret 2020 (YZ Ret), Nova Sco 2023 is yet another nova in which we have found exquisite evidence of CX in astrophysical ionized plasma. |
| format | Article |
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| institution | DOAJ |
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| language | English |
| publishDate | 2025-01-01 |
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| series | The Astrophysical Journal |
| spelling | doaj-art-c5314bfdcdea4fd99707a0230745f3342025-08-20T03:02:46ZengIOP PublishingThe Astrophysical Journal1538-43572025-01-01989216610.3847/1538-4357/adf1a3X-Ray Observations of Nova Sco 2023: Spectroscopic Evidence of Charge ExchangeSharon Mitrani0https://orcid.org/0000-0001-6798-5447Ehud Behar1https://orcid.org/0000-0001-9735-4873Marina Orio2https://orcid.org/0000-0003-1563-9803Jack Worley3Department of Physics, Technion , Haifa 32000, Israel ; sharonm@campus.technion.ac.ilDepartment of Physics, Technion , Haifa 32000, Israel ; sharonm@campus.technion.ac.ilDepartment of Astronomy, University of Wisconsin , 475 N. Charter Str., Madison, WI 53706, USA; INAF-Padova , vicolo Osservatorio 5, I-35122 Padova, ItalyDepartment of Astronomy, University of Wisconsin , 475 N. Charter Str., Madison, WI 53706, USAThe supersoft source phase of a nova eruption, observed a few days after the outburst, usually displays an absorbed X-ray thermal continuum with absorption features, emitted by the white dwarf atmosphere. However, the X-ray spectra of many novae in this phase display additional emission lines that likely originate from shocks in the novae ejecta. When the shocked plasma interacts with cold gas, narrow radiative recombination continua (RRCs) and charge exchange (CX) emission are observed. We present the analysis of high-resolution Chandra Low Energy Transmission Grating X-ray grating spectra of Nova Sco 2023, observed 128 and 183 days after the optical peak in 2023 August and October. At both epochs, the absorbed X-ray thermal continuum is well described by a nonlocal thermal equilibrium atmosphere model with a temperature T ≃ 750,000 K ( kT ≃ 65 eV). On day 128, the atmosphere is found to be outflowing at v ≃ −3500 km s ^−1 . On day 183, the atmosphere brightened by a factor of ∼2 and slowed down to v ≃ −1500 km s ^−1 . The discrete emission features of the spectrum consist of the C ^+5 , N ^+5 , and N ^+6 RRCs, indicating a cold electron temperature of kT _e ≃ 1 eV on day 128 and kT _e ≃ 20 eV on day 183. The observed line series of H-like and He-like C ^+5 , N ^+5 , N ^+6 , and O ^+6 show enhanced intensities of high- n (principal quantum number) transitions, consistent with a CX model of hot ions at kT ∼ 100 eV. The velocity shift of the CX lines remained at v ∼ ±3000 km s ^−1 , which can be explained by a bipolar outflow. After Nova Ret 2020 (YZ Ret), Nova Sco 2023 is yet another nova in which we have found exquisite evidence of CX in astrophysical ionized plasma.https://doi.org/10.3847/1538-4357/adf1a3NovaeCharge exchange recombinationSpectroscopyX-ray novaeX-ray astronomySpectral line identification |
| spellingShingle | Sharon Mitrani Ehud Behar Marina Orio Jack Worley X-Ray Observations of Nova Sco 2023: Spectroscopic Evidence of Charge Exchange The Astrophysical Journal Novae Charge exchange recombination Spectroscopy X-ray novae X-ray astronomy Spectral line identification |
| title | X-Ray Observations of Nova Sco 2023: Spectroscopic Evidence of Charge Exchange |
| title_full | X-Ray Observations of Nova Sco 2023: Spectroscopic Evidence of Charge Exchange |
| title_fullStr | X-Ray Observations of Nova Sco 2023: Spectroscopic Evidence of Charge Exchange |
| title_full_unstemmed | X-Ray Observations of Nova Sco 2023: Spectroscopic Evidence of Charge Exchange |
| title_short | X-Ray Observations of Nova Sco 2023: Spectroscopic Evidence of Charge Exchange |
| title_sort | x ray observations of nova sco 2023 spectroscopic evidence of charge exchange |
| topic | Novae Charge exchange recombination Spectroscopy X-ray novae X-ray astronomy Spectral line identification |
| url | https://doi.org/10.3847/1538-4357/adf1a3 |
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