Do Central Compact Objects have Carbon Atmospheres?
Only three of the dozen central compact objects (CCOs) in supernova remnants (SNRs) show thermal X-ray pulsations due to nonuniform surface temperature (hot spots). The absence of X-ray pulsations from several unpulsed CCOs has motivated suggestions that they have uniform-temperature carbon atmosphe...
| Main Authors: | , |
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| Format: | Article |
| Language: | English |
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IOP Publishing
2023-01-01
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| Series: | The Astrophysical Journal |
| Subjects: | |
| Online Access: | https://doi.org/10.3847/1538-4357/acaf55 |
| _version_ | 1797695784744910848 |
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| author | J. A. J. Alford J. P. Halpern |
| author_facet | J. A. J. Alford J. P. Halpern |
| author_sort | J. A. J. Alford |
| collection | DOAJ |
| description | Only three of the dozen central compact objects (CCOs) in supernova remnants (SNRs) show thermal X-ray pulsations due to nonuniform surface temperature (hot spots). The absence of X-ray pulsations from several unpulsed CCOs has motivated suggestions that they have uniform-temperature carbon atmospheres (UTCAs), which adequately fit their spectra with appropriate neutron star (NS) surface areas. This is in contrast to the two-temperature blackbody or hydrogen atmospheres that also fit well. Here we investigate the applicability of UTCAs to CCOs. We show the following: (i) The phase-averaged spectra of the three pulsed CCOs can also be fitted with a UTCA of the appropriate NS area, despite pulsed CCOs manifestly having nonuniform surface temperature. A good spectral fit is therefore not strong support for the UTCA model of unpulsed CCOs. (ii) An improved spectrum of one unpulsed CCO, previously analyzed with a UTCA, does not allow an acceptable fit. (iii) For two unpulsed CCOs, the UTCA does not allow a distance compatible with the SNR distance. These results imply that, in general, CCOs must have hot, localized regions on the NS surface. We derive new X-ray pulse modulation upper limits on the unpulsed CCOs, and constrain their hot spot sizes and locations. We develop an alternative model that accounts for both the pulsed and unpulsed CCOs: a range of angles between hot spot and rotation axes consistent with an exponential distribution with scale factor λ ∼ 20°. We discuss the physical mechanisms that could produce such small angles and small hot spots. |
| first_indexed | 2024-03-12T03:17:13Z |
| format | Article |
| id | doaj.art-a21ec81a0bef408dafd96b2eab15d2a2 |
| institution | Directory Open Access Journal |
| issn | 1538-4357 |
| language | English |
| last_indexed | 2024-03-12T03:17:13Z |
| publishDate | 2023-01-01 |
| publisher | IOP Publishing |
| record_format | Article |
| series | The Astrophysical Journal |
| spelling | doaj.art-a21ec81a0bef408dafd96b2eab15d2a22023-09-03T14:08:30ZengIOP PublishingThe Astrophysical Journal1538-43572023-01-0194413610.3847/1538-4357/acaf55Do Central Compact Objects have Carbon Atmospheres?J. A. J. Alford0https://orcid.org/0000-0002-2312-8539J. P. Halpern1https://orcid.org/0000-0003-4814-2377Columbia Astrophysics Laboratory, Columbia University , 550 West 120th Street, New York NY, 10027, USA ; jason@astro.columbia.eduColumbia Astrophysics Laboratory, Columbia University , 550 West 120th Street, New York NY, 10027, USA ; jason@astro.columbia.eduOnly three of the dozen central compact objects (CCOs) in supernova remnants (SNRs) show thermal X-ray pulsations due to nonuniform surface temperature (hot spots). The absence of X-ray pulsations from several unpulsed CCOs has motivated suggestions that they have uniform-temperature carbon atmospheres (UTCAs), which adequately fit their spectra with appropriate neutron star (NS) surface areas. This is in contrast to the two-temperature blackbody or hydrogen atmospheres that also fit well. Here we investigate the applicability of UTCAs to CCOs. We show the following: (i) The phase-averaged spectra of the three pulsed CCOs can also be fitted with a UTCA of the appropriate NS area, despite pulsed CCOs manifestly having nonuniform surface temperature. A good spectral fit is therefore not strong support for the UTCA model of unpulsed CCOs. (ii) An improved spectrum of one unpulsed CCO, previously analyzed with a UTCA, does not allow an acceptable fit. (iii) For two unpulsed CCOs, the UTCA does not allow a distance compatible with the SNR distance. These results imply that, in general, CCOs must have hot, localized regions on the NS surface. We derive new X-ray pulse modulation upper limits on the unpulsed CCOs, and constrain their hot spot sizes and locations. We develop an alternative model that accounts for both the pulsed and unpulsed CCOs: a range of angles between hot spot and rotation axes consistent with an exponential distribution with scale factor λ ∼ 20°. We discuss the physical mechanisms that could produce such small angles and small hot spots.https://doi.org/10.3847/1538-4357/acaf55X-ray sourcesNeutron starsSupernova remnants |
| spellingShingle | J. A. J. Alford J. P. Halpern Do Central Compact Objects have Carbon Atmospheres? The Astrophysical Journal X-ray sources Neutron stars Supernova remnants |
| title | Do Central Compact Objects have Carbon Atmospheres? |
| title_full | Do Central Compact Objects have Carbon Atmospheres? |
| title_fullStr | Do Central Compact Objects have Carbon Atmospheres? |
| title_full_unstemmed | Do Central Compact Objects have Carbon Atmospheres? |
| title_short | Do Central Compact Objects have Carbon Atmospheres? |
| title_sort | do central compact objects have carbon atmospheres |
| topic | X-ray sources Neutron stars Supernova remnants |
| url | https://doi.org/10.3847/1538-4357/acaf55 |
| work_keys_str_mv | AT jajalford docentralcompactobjectshavecarbonatmospheres AT jphalpern docentralcompactobjectshavecarbonatmospheres |