The Astrophysical Journal Letters (Jan 2023)
Timing Analysis of the 2022 Outburst of the Accreting Millisecond X-Ray Pulsar SAX J1808.4-3658: Hints of an Orbital Shrinking
- 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
Affiliations
- Giulia Illiano
- ORCiD
- INAF-Osservatorio Astronomico di Roma , Via Frascati 33, I-00078, Monteporzio Catone (RM), Italy ; [email protected]; Tor Vergata University of Rome , Via della Ricerca Scientifica 1, I-00133 Roma, Italy
- Alessandro Papitto
- ORCiD
- INAF-Osservatorio Astronomico di Roma , Via Frascati 33, I-00078, Monteporzio Catone (RM), Italy ; [email protected]
- Andrea Sanna
- ORCiD
- Dipartimento di Fisica, Università degli Studi di Cagliari , SP Monserrato-Sestu km 0.7, I-09042 Monserrato, Italy
- Peter Bult
- ORCiD
- Department of Astronomy, University of Maryland , College Park, MD 20742, USA; Astrophysics Science Division, NASA Goddard Space Flight Center , Greenbelt, MD 20771, USA
- Filippo Ambrosino
- ORCiD
- INAF-Osservatorio Astronomico di Roma , Via Frascati 33, I-00078, Monteporzio Catone (RM), Italy ; [email protected]; INAF-Istituto di Astrofisica e Planetologia Spaziali , Via Fosso del Cavaliere 100, I-00133 Rome, Italy; Sapienza Università di Roma , Piazzale Aldo Moro 5, I-00185 Rome, Italy
- Arianna Miraval Zanon
- ORCiD
- INAF-Osservatorio Astronomico di Roma , Via Frascati 33, I-00078, Monteporzio Catone (RM), Italy ; [email protected]
- Francesco Coti Zelati
- ORCiD
- Institute of Space Sciences (ICE, CSIC) , Campus UAB, Carrer de Can Magrans s/n, E-08193 Barcelona, Spain; Institut d’Estudis Espacials de Catalunya (IEEC) , Carrer Gran Capità 2-4, E-08034 Barcelona, Spain; INAF, Osservatorio Astronomico di Brera , Via E. Bianchi 46, I-23807, Merate (LC), Italy
- Luigi Stella
- ORCiD
- INAF-Osservatorio Astronomico di Roma , Via Frascati 33, I-00078, Monteporzio Catone (RM), Italy ; [email protected]
- Diego Altamirano
- ORCiD
- Physics & Astronomy, University of Southampton , Southampton, Hampshire SO17 1BJ, UK
- Maria Cristina Baglio
- ORCiD
- INAF, Osservatorio Astronomico di Brera , Via E. Bianchi 46, I-23807, Merate (LC), Italy; Center for Astro, Particle, and Planetary Physics, New York University Abu Dhabi , P.O. Box 129188, Abu Dhabi, 100190, UAE
- Enrico Bozzo
- ORCiD
- ISDC, University of Geneva , Chemin d’Ecogia 16, CH-1290 Versoix, Switzerland
- Luciano Burderi
- ORCiD
- Dipartimento di Fisica, Università degli Studi di Cagliari , SP Monserrato-Sestu km 0.7, I-09042 Monserrato, Italy
- Domitilla de Martino
- ORCiD
- INAF–Osservatorio Astronomico di Capodimonte , Salita Moiariello 16, I-80131 Napoli, Italy
- Alessandro Di Marco
- ORCiD
- INAF-Istituto di Astrofisica e Planetologia Spaziali , Via Fosso del Cavaliere 100, I-00133 Rome, Italy
- Tiziana di Salvo
- ORCiD
- Università degli Studi di Palermo , Dipartimento di Fisica e Chimica, via Archirafi 36, I-90123 Palermo, Italy
- Carlo Ferrigno
- ORCiD
- ISDC, University of Geneva , Chemin d’Ecogia 16, CH-1290 Versoix, Switzerland
- Vladislav Loktev
- ORCiD
- Department of Physics and Astronomy, FI-20014 University of Turku , Finland
- Alessio Marino
- ORCiD
- Institute of Space Sciences (ICE, CSIC) , Campus UAB, Carrer de Can Magrans s/n, E-08193 Barcelona, Spain; Institut d’Estudis Espacials de Catalunya (IEEC) , Carrer Gran Capità 2-4, E-08034 Barcelona, Spain; INAF/IASF Palermo , via Ugo La Malfa 153, I-90146 Palermo, Italy
- Mason Ng
- ORCiD
- MIT Kavli Institute for Astrophysics and Space Research , Massachusetts Institute of Technology, Cambridge, MA 02139, USA
- Maura Pilia
- ORCiD
- INAF–Osservatorio Astronomico di Cagliarivia della Scienza 5I-09047 , Selargius, Italy
- Juri Poutanen
- ORCiD
- Department of Physics and Astronomy, FI-20014 University of Turku , Finland
- Tuomo Salmi
- ORCiD
- Anton Pannekoek Institute for Astronomy, University of Amsterdam , Science Park 904, 1090GE Amsterdam, the Netherlands
- DOI
- https://doi.org/10.3847/2041-8213/acad81
- Journal volume & issue
-
Vol. 942,
no. 2
p. 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 × 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.
Keywords