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Extreme quiescent variability of the transient neutron star low-mass X-ray binary EXO 1745-248 in Terzan 5
- Source :
- Monthly Notices of the Royal Astronomical Society, Monthly Notices of the Royal Astronomical Society, 479(2), 2777-2788. Oxford University Press
- Publication Year :
- 2018
- Publisher :
- Oxford University Press, 2018.
-
Abstract
- EXO 1745-248 is a transient neutron-star low-mass X-ray binary that resides in the globular cluster Terzan 5. We studied the transient during its quiescent state using 18 Chandra observations of the cluster acquired between 2003 and 2016. We found an extremely variable source, with a luminosity variation in the 0.5-10 keV energy range of $\sim3$ orders of magnitude (between $3\times10^{31}$ erg s$^{-1}$ and $2\times10^{34}$ erg s$^{-1}$) on timescales from years down to only a few days. Using an absorbed power-law model to fit its quiescent spectra, we obtained a typical photon index of $\sim1.4$, indicating that the source is even harder than during outburst and much harder than typical quiescent neutron stars if their quiescent X-ray spectra are also described by a single power-law model. This indicates that EXO 1745-248 is very hard throughout the entire observed X-ray luminosity range. At the highest luminosity, the spectrum fits better when an additional (soft) component is added to the model. All these quiescent properties are likely related to strong variability in the low-level accretion rate in the system. However, its extreme variable behavior is strikingly different from the one observed for other neutron star transients that are thought to still accrete in quiescence. We compare our results to these systems. We also discuss similarities and differences between our target and the transitional millisecond pulsar IGR J18245-2452, which also has hard spectra and strong variability during quiescence.<br />Accepted for publication in MNRAS
- Subjects :
- Astrophysics::High Energy Astrophysical Phenomena
X-ray binary
FOS: Physical sciences
Astrophysics
Astrophysics::Cosmology and Extragalactic Astrophysics
01 natural sciences
Spectral line
Luminosity
Millisecond pulsar
0103 physical sciences
Astrophysics::Solar and Stellar Astrophysics
010303 astronomy & astrophysics
Solar and Stellar Astrophysics (astro-ph.SR)
Astrophysics::Galaxy Astrophysics
High Energy Astrophysical Phenomena (astro-ph.HE)
Physics
010308 nuclear & particles physics
Astronomy
Astronomy and Astrophysics
Neutron star
Astrophysics - Solar and Stellar Astrophysics
Orders of magnitude (time)
Space and Planetary Science
Globular cluster
Astrophysics - High Energy Astrophysical Phenomena
Low Mass
Subjects
Details
- Language :
- English
- ISSN :
- 13652966 and 00358711
- Volume :
- 479
- Issue :
- 2
- Database :
- OpenAIRE
- Journal :
- Monthly Notices of the Royal Astronomical Society
- Accession number :
- edsair.doi.dedup.....53254b7f68890c03ae3bb36e1cff808d