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Title: | Timing Analysis of the 2022 Outburst of SAX J1808.4-3658: Hints of Orbital Decay | Authors: | ILLIANO, GIULIA PAPITTO, ALESSANDRO SANNA, ANDREA Bult, Peter AMBROSINO, Filippo MIRAVAL ZANON, ARIANNA Coti Zelati, Francesco STELLA, Luigi Altamirano, Diego Baglio, Maria Cristina BOZZO , ENRICO BURDERI, LUCIANO DE MARTINO, Domitilla DI MARCO, ALESSANDRO Di Salvo, Tiziana Ferrigno, Carlo Loktev, Vladislav MARINO, ALESSIO Ng, Mason PILIA, Maura Poutanen, Juri Salmi, Tuomo |
Issue Date: | 2023 | Journal: | THE ASTROPHYSICAL JOURNAL LETTERS | Number: | 942 | Issue: | 2 | First Page: | L40 | Abstract: | We present a pulse timing analysis of NICER observations of the accreting millisecond X-ray pulsar SAX J1808.4−3658 during the outburst that started on 2022 August 19. Similar to previous outbursts, after decaying from a peak luminosity of ≃1 × 1036 erg s−1 in about a week, the pulsar entered a ∼1 month long reflaring stage. Comparison of the average pulsar spin frequency during the outburst with those previously measured confirmed the long-term spin derivative of ${\dot{\nu }}_{\mathrm{SD}}=-(1.15\,\pm \,0.06)\times \,{10}^{-15}$ Hz s−1, compatible with the spin-down torque of a ≈1026 G cm3 rotating magnetic dipole. For the first time in the last twenty years, the orbital phase evolution shows evidence for a decrease of the orbital period. The long-term behavior of the orbit is dominated by an ∼11 s modulation of the orbital phase epoch consistent with a ∼21 yr period. We discuss the observed evolution in terms of a coupling between the orbit and variations in the mass quadrupole of the companion star. | URI: | http://hdl.handle.net/20.500.12386/33970 | URL: | https://iopscience.iop.org/article/10.3847/2041-8213/acad81/pdf | ISSN: | 2041-8205 | DOI: | 10.3847/2041-8213/acad81 | Bibcode ADS: | 2023ApJ...942L..40I | Fulltext: | open |
Appears in Collections: | 1.01 Articoli in rivista |
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2023_ApJL_942_L40.pdf | Pdf editoriale | 768.89 kB | Adobe PDF | View/Open |
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