Browsing by Subject "X-rays: individual"
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Item IGR J14257−6117, a magnetic accreting white dwarf with a very strong strong X-ray orbital modulation(Oxford University Press, 2018-04-28) Bernardini, F.; de Martino, D.; Mukai, K.; Falanga, M.IGR J14257−6117 is an unclassified source in the hard X-ray catalogues. Optical follow-ups suggest it could be a Cataclysmic Variable (CV) of the magnetic type. We present the first high signal-to-noise (S/N) X-ray observation performed by XMM–Newton at 0.3–10 keV, complemented with 10–80 keV coverage by Swift/BAT, aimed at revealing the source nature. We detected for the first time a fast periodic variability at 509.5 s and a longer periodic variability at 4.05 h, ascribed to the white dwarf (WD) spin and binary orbital periods, respectively. These unambiguously identify IGR J14257−6117 as a magnetic CV of the intermediate polar (IP) type. The energy-resolved light curves at both periods reveal amplitudes decreasing with increasing energy, with the orbital modulation reaching ∼100 per cent in the softest band. The energy spectrum shows optically thin thermal emission with an excess at the iron complex, absorbed by two dense media (NH ∼ 10²²⁻²³ cm⁻²), partially covering the X-ray source. These are likely localized in the magnetically confined accretion flow above the WD surface and at the disc rim, producing the energy-dependent spin and orbital variabilities, respectively. IGR J14257−6117 joins the group of strongest orbitally modulated IPs now counting four systems. Drawing similarities with low-mass X-ray binaries displaying orbital dips, these IPs should be seen at large orbital inclinations allowing azimuthally extended absorbing material fixed in the binary frame to intercept the line of sight. For IGR J14257−6117, we estimate 50⁰ < i < 70⁰. Whether also the mass accretion rate plays a role in the large orbital modulations in IPs cannot be established with the present data.Item The true nature of Swift J0746.3-1608: a possible Intermediate Polar showing accretion state changes(2018-12-21) Bernardini, F.; de Martino, D.; Mukai, K.; Falanga, M.Optical and X-ray observations suggested that the 9.38 h binary, SWIFT J0746.3- 1608 could be a Cataclysmic Variable of the magnetic or nova-like type, or a low mass X-ray binary. Its optical, UV, and X-ray light curves are strongly variable over years. We report on a recent XMM-Newton observation (28 April 2018), when the source had recovered from a deep low state that likely begun mid-late 2011. We detect for the first time a signal at about 38 min that we interpret as the rotation of the accreting white dwarf primary. Its amplitude decreases with increasing energy, indicating localised photoelectric absorption from cold material. The X-ray spectrum shows optically thin thermal emission with excess at the iron complex, absorbed by a dense medium partially covering the X-ray source. Based on these features, we propose that SWIFT J0746.3-1608 is a magnetic CV of the Intermediate Polar (IP) type. The long-term light curves at different wavelengths show high and low states, a rare phenomenon in the IP subclass and observed so far in only three other systems. The long orbital period, the peculiar long term variability, and its proposed magnetic nature, makes SWIFT J0746.3-1608 an interesting evolutionary test case.