Timing Analysis of the 2022 Outburst of the Accreting Millisecond X-Ray Pulsar SAX J1808.4-3658: Hints of an Orbital Shrinking
| Autor: | Giulia Illiano, Alessandro Papitto, Andrea Sanna, Peter Bult, Filippo Ambrosino, Arianna Miraval Zanon, Francesco Coti Zelati, Luigi Stella, Diego Altamirano, Maria Cristina Baglio, Enrico Bozzo, Luciano Burderi, Domitilla de Martino, Alessandro Di Marco, Tiziana di Salvo, Carlo Ferrigno, Vladislav Loktev, Alessio Marino, Mason Ng, Maura Pilia, Juri Poutanen, Tuomo Salmi |
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| Jazyk: | angličtina |
| Rok vydání: | 2023 |
| Předmět: | |
| Zdroj: | The Astrophysical Journal Letters, Vol 942, Iss 2, p L40 (2023) |
| Druh dokumentu: | article |
| ISSN: | 2041-8213 2041-8205 |
| DOI: | 10.3847/2041-8213/acad81 |
| Popis: | 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 × 10 ^36 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 ≈10 ^26 G cm ^3 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. |
| Databáze: | Directory of Open Access Journals |
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