Utilizing the Neutron Star Inside Composition Explorer (NICER) onboard the Worldwide Area Station (ISS), a global staff of astronomers has inspected the latest outburst of an accreting millisecond X-ray pulsar often called SAX J1808.4−3658. Outcomes of the research, printed December 19 on the preprint server arXiv, shed extra mild on the character of this supply.
X-ray pulsars exhibit strict periodic variations in X-ray depth, which may be as brief as a fraction of a second. Accreting millisecond X-ray pulsars (AMXPs) are a peculiar kind of X-ray pulsars wherein brief spin durations are brought on by long-lasting mass switch from a low-mass companion star by means of an accretion disk onto a slow-rotating neutron star.
Astronomers understand AMXPs as astrophysical laboratories that might be essential in advancing our data about thermonuclear burst processes. Nonetheless, AMXPs are comparatively uncommon and thus far just a few dozen objects of this kind have been recognized utilizing NICER and different space observatories.
SAX J1808.4−3658 (or SAX J1808 for brief) was found in 1996 with the X-ray satellite BeppoSAX throughout an X-ray outburst. Two years later, when X-ray pulsations had been detected from this supply, it was categorized as the primary accreting millisecond X-ray pulsar. The item, situated some 11,400 mild years away, consists of a neutron star in an orbit with a brown dwarf companion (with a mass of about 0.05 solar plenty). The orbital interval of the system was measured to be round 2.01 hours.
SAX J1808 has undergone ten roughly month-long outbursts with a 2–3 years recurrence interval, since its discovery. Lately, on August 19, 2022, one other outburst of this pulsar began, which was observed by the Monitor of All-sky X-ray Picture (MAXI) instrument onboard the ISS. A gaggle of astronomers, led by Giulia Illiano of Rome Observatory in Italy, started to observe SAX J1808 shortly after the outburst commenced, hoping to get extra insights into the properties of this pulsar.
Throughout the latest outburst, SAX J1808 after decaying from a peak luminosity of roughly one undecillion erg/s in a couple of week, it entered in an about one month-long reflaring stage. Related conduct was seen additionally in earlier outbursts.
By analyzing the present outburst, the astronomers confirmed that the spin frequency of SAX J1808 decreased at a median fee of −0.001 pHz/s, as was prompt by earlier research. This result’s in line with vitality losses anticipated from a 100 YG cm3 rotating magnetic dipole.
The research discovered that for the primary time within the final twenty years, the orbital phase evolution confirmed proof that the orbit of SAX J1808 has contracted for the reason that final epoch. The astronomers famous that the long-term conduct of the orbit may be described by an 11-second modulation with a 21-year interval.
The brand new outburst of SAX J1808 is anticipated to happen in 2025. The authors of the paper underlined that observations of this upcoming outburst will likely be essential with a purpose to affirm their findings relating to the orbital evolution of this pulsar.
Extra data:
Giulia Illiano et al, Timing evaluation of the 2022 outburst of the accreting millisecond X-ray pulsar SAX J1808.4−3658: hints of an orbital shrinking, arXiv (2022). DOI: 10.48550/arxiv.2212.09778
Journal data:
arXiv
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Analysis investigates the most recent outburst of pulsar SAX J1808.4−3658 (2022, December 27)
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