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Title: | In-depth study of long-term variability in the X-ray emission of the Be/X-ray binary system AX J0049.4-7323 | Authors: | Ducci, Lorenzo ROMANO, Patrizia Malacaria, C. Ji, L. Bozzo, Enrico Santangelo, Andrea |
Issue Date: | 2018 | Journal: | ASTRONOMY & ASTROPHYSICS | Number: | 614 | Abstract: | AX J0049.4-7323 is a Be/X-ray binary in the Small Magellanic Cloud hosting a 750 s pulsar which has been observed over the last 17 years by several X-ray telescopes. Despite numerous observations, little is known about its X-ray behaviour. Therefore, we coherently analysed archival Swift, Chandra, XMM-Newton, RXTE, and INTEGRAL data, and we compared them with already published ASCA data, to study its X-ray long-term spectral and flux variability. AX J0049.4-7323 shows a high X-ray variability, spanning more than three orders of magnitudes, from L ≈ 1.6 × 10<SUP>37</SUP> erg s<SUP>-1</SUP> (0.3-8 keV, d = 62 kpc) down to L ≈ 8 × 10<SUP>33</SUP> erg s<SUP>-1</SUP>. RXTE, Chandra, Swift, and ASCA observed, in addition to the expected enhancement of X-ray luminosity at periastron, flux variations by a factor of 270 with peak luminosities of ≈2.1 × 10<SUP>36</SUP> erg s<SUP>-1</SUP> far from periastron. These properties are difficult to reconcile with the typical long-term variability of Be/XRBs, traditionally interpreted in terms of type I and type II outbursts. The study of AX J0049.4-7323 is complemented with a spectral analysis of Swift, Chandra, and XMM-Newton data which showed a softening trend when the emission becomes fainter, and an analysis of optical/UV data collected by the UVOT telescope on board Swift. In addition, we measured a secular spin-up rate of Ṗ = (-3.00 ± 0.12) × 10<SUP>-3</SUP> s day<SUP>-1</SUP>, which suggests that the pulsar has not yet achieved its equilibrium period. Assuming spherical accretion, we estimated an upper limit for the magnetic field strength of the pulsar of ≈3 × 10<SUP>12</SUP> G. | URI: | http://hdl.handle.net/20.500.12386/28545 | URL: | https://www.aanda.org/articles/aa/abs/2018/06/aa31922-17/aa31922-17.html | ISSN: | 0004-6361 | DOI: | 10.1051/0004-6361/201731922 | Bibcode ADS: | 2018A&A...614A..34D | Fulltext: | open |
Appears in Collections: | 1.01 Articoli in rivista |
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