On the Origin of Spectral Features Observed during Thermonuclear X-Ray Bursts and in the Aftermath Emission of a Long Burst from 4U 1820–30
We study 15 thermonuclear X-ray bursts from 4U 1820–30 observed with the Neutron Star Interior Composition Explorer (NICER). We find evidence of a narrow emission line at 1.0 keV and three absorption lines at 1.7, 3.0, and 3.75 keV, primarily around the photospheric radius expansion phase of most bu...
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2025-01-01
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| Online Access: | https://doi.org/10.3847/1538-4357/adcc24 |
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| author | Gaurava K. Jaisawal Jérôme Chenevez Tod E. Strohmayer Hendrik Schatz J. J. M. in ’t Zand Tolga Güver Diego Altamirano Zaven Arzoumanian Keith C. Gendreau |
| author_facet | Gaurava K. Jaisawal Jérôme Chenevez Tod E. Strohmayer Hendrik Schatz J. J. M. in ’t Zand Tolga Güver Diego Altamirano Zaven Arzoumanian Keith C. Gendreau |
| author_sort | Gaurava K. Jaisawal |
| collection | DOAJ |
| description | We study 15 thermonuclear X-ray bursts from 4U 1820–30 observed with the Neutron Star Interior Composition Explorer (NICER). We find evidence of a narrow emission line at 1.0 keV and three absorption lines at 1.7, 3.0, and 3.75 keV, primarily around the photospheric radius expansion phase of most bursts. The 1.0 keV emission line remains constant, while the absorption features, attributed to wind-ejected species, are stable but show slight energy shifts, likely due to combined effects of Doppler and gravitational redshifts. We also examine with NICER the “aftermath” of a long X-ray burst (a candidate superburst observed by MAXI) on 2021 August 23 and 24. The aftermath emission recovers within half a day from a flux depression. During this recovery phase, we detect two emission lines at 0.7 and 1 keV, along with three absorption lines whose energies decrease to 1.57, 2.64, and 3.64 keV. Given the nature of the helium white dwarf companion, these absorption lines during the aftermath may originate from an accretion flow, but only if the accretion environment is significantly contaminated by nuclear ashes from the superburst. This provides evidence of temporary metal enhancement in the accreted material due to strong wind loss. Moreover, we suggest that the absorption features observed during the short X-ray bursts and in the superburst aftermath share a common origin in heavy nuclear ashes enriched with elements like Si, Ar, Ca, or Ti, either from the burst wind or from an accretion flow contaminated by the burst wind. |
| format | Article |
| id | doaj-art-d317e8a064794ea78eb0f8d550e42b20 |
| institution | DOAJ |
| issn | 1538-4357 |
| language | English |
| publishDate | 2025-01-01 |
| publisher | IOP Publishing |
| record_format | Article |
| series | The Astrophysical Journal |
| spelling | doaj-art-d317e8a064794ea78eb0f8d550e42b202025-08-20T03:19:24ZengIOP PublishingThe Astrophysical Journal1538-43572025-01-0198611610.3847/1538-4357/adcc24On the Origin of Spectral Features Observed during Thermonuclear X-Ray Bursts and in the Aftermath Emission of a Long Burst from 4U 1820–30Gaurava K. Jaisawal0https://orcid.org/0000-0002-6789-2723Jérôme Chenevez1https://orcid.org/0000-0002-4397-8370Tod E. Strohmayer2https://orcid.org/0000-0001-7681-5845Hendrik Schatz3https://orcid.org/0000-0003-1674-4859J. J. M. in ’t Zand4https://orcid.org/0000-0002-4363-1756Tolga Güver5https://orcid.org/0000-0002-3531-9842Diego Altamirano6https://orcid.org/0000-0002-3422-0074Zaven Arzoumanian7https://orcid.org/0009-0008-6187-8753Keith C. Gendreau8https://orcid.org/0000-0001-7115-2819DTU Space, Technical University of Denmark , Elektrovej 327-328, DK-2800 Lyngby, Denmark ; gaurava@space.dtu.dkDTU Space, Technical University of Denmark , Elektrovej 327-328, DK-2800 Lyngby, Denmark ; gaurava@space.dtu.dkAstrophysics Science Division and Joint Space-Science Institute , NASA’s Goddard Space Flight Center, Greenbelt, MD 20771, USADepartment of Physics and Astronomy, Michigan State University , East Lansing, MI 48824, USA; Facility for Rare Isotope Beams, Michigan State University , East Lansing, MI 48824, USA; Joint Institute for Nuclear Astrophysics - Center for the Evolution of the Elements (JINA-CEE) , USASRON Netherlands Institute for Space Research , Sorbonnelaan 2, 3584 CA Utrecht, The NetherlandsIstanbul University , Science Faculty, Department of Astronomy and Space Sciences, Beyazıt, 34119, İstanbul, Türkiye; Istanbul University Observatory Research and Application Center , Istanbul University 34119, İstanbul, TürkiyeSchool of Physics and Astronomy, University of Southampton , Southampton SO17 1BJ, UKAstrophysics Science Division, NASA’s Goddard Space Flight Center , Greenbelt, MD 20771, USAAstrophysics Science Division, NASA’s Goddard Space Flight Center , Greenbelt, MD 20771, USAWe study 15 thermonuclear X-ray bursts from 4U 1820–30 observed with the Neutron Star Interior Composition Explorer (NICER). We find evidence of a narrow emission line at 1.0 keV and three absorption lines at 1.7, 3.0, and 3.75 keV, primarily around the photospheric radius expansion phase of most bursts. The 1.0 keV emission line remains constant, while the absorption features, attributed to wind-ejected species, are stable but show slight energy shifts, likely due to combined effects of Doppler and gravitational redshifts. We also examine with NICER the “aftermath” of a long X-ray burst (a candidate superburst observed by MAXI) on 2021 August 23 and 24. The aftermath emission recovers within half a day from a flux depression. During this recovery phase, we detect two emission lines at 0.7 and 1 keV, along with three absorption lines whose energies decrease to 1.57, 2.64, and 3.64 keV. Given the nature of the helium white dwarf companion, these absorption lines during the aftermath may originate from an accretion flow, but only if the accretion environment is significantly contaminated by nuclear ashes from the superburst. This provides evidence of temporary metal enhancement in the accreted material due to strong wind loss. Moreover, we suggest that the absorption features observed during the short X-ray bursts and in the superburst aftermath share a common origin in heavy nuclear ashes enriched with elements like Si, Ar, Ca, or Ti, either from the burst wind or from an accretion flow contaminated by the burst wind.https://doi.org/10.3847/1538-4357/adcc24AccretionX-ray burstsLow-mass x-ray binary starsX-ray binary stars |
| spellingShingle | Gaurava K. Jaisawal Jérôme Chenevez Tod E. Strohmayer Hendrik Schatz J. J. M. in ’t Zand Tolga Güver Diego Altamirano Zaven Arzoumanian Keith C. Gendreau On the Origin of Spectral Features Observed during Thermonuclear X-Ray Bursts and in the Aftermath Emission of a Long Burst from 4U 1820–30 The Astrophysical Journal Accretion X-ray bursts Low-mass x-ray binary stars X-ray binary stars |
| title | On the Origin of Spectral Features Observed during Thermonuclear X-Ray Bursts and in the Aftermath Emission of a Long Burst from 4U 1820–30 |
| title_full | On the Origin of Spectral Features Observed during Thermonuclear X-Ray Bursts and in the Aftermath Emission of a Long Burst from 4U 1820–30 |
| title_fullStr | On the Origin of Spectral Features Observed during Thermonuclear X-Ray Bursts and in the Aftermath Emission of a Long Burst from 4U 1820–30 |
| title_full_unstemmed | On the Origin of Spectral Features Observed during Thermonuclear X-Ray Bursts and in the Aftermath Emission of a Long Burst from 4U 1820–30 |
| title_short | On the Origin of Spectral Features Observed during Thermonuclear X-Ray Bursts and in the Aftermath Emission of a Long Burst from 4U 1820–30 |
| title_sort | on the origin of spectral features observed during thermonuclear x ray bursts and in the aftermath emission of a long burst from 4u 1820 30 |
| topic | Accretion X-ray bursts Low-mass x-ray binary stars X-ray binary stars |
| url | https://doi.org/10.3847/1538-4357/adcc24 |
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