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The phenomenology of anomalous X-ray pulsars is usually interpreted within the paradigm of very highly magnetized neutron stars, also known as magnetars. According to this paradigm, the persistent emission of anomalous X-ray pulsars (AXPs) is powered by the decay of the magnetic field. However, an alternative scenario in which the persistent emission is explained through accretion is also discussed in literature. In particular AXP 4U 0142+61has been suggested to be either an accreting neutron star or a white dwarf. Here we rule out this scenario based on the the observed X-ray variability properties of the source. We directly compare the observed power spectra of 4U 0142+61 and of two other magnetars, 1RXS J170849.0$-$400910 and 1E 1841-045 with that of the X-ray pulsar 1A 0535+262, and of the intermediate polar GK Persei. In addition, we include a bright young radio pulsar PSR B1509-58 into comparison. We show that, unlike accreting sources, no aperiodic variability within the expected frequency range is observed in the power density spectrum of the magnetars and the radio pulsar. Considering that strong variability is an established features of all accreting systems from young stellar objects to super-massive black holes, and absence of the variability reports from other magnetars, we conclude that our results indicates also that magnetars in general are not powered by accretion.
We study simultaneous X-ray and optical observations of three intermediate polars EX Hya, V1223 Sgr and TV Col with the aim to understand the propagation of matter in their accretion flows. We show that in all cases the power spectra of flux variabil
These notes resulted from a series of lectures at the IAC winter school. They are designed to help students, especially those just starting in subject, to get hold of the fundamental tools used to study accretion powered sources. As such, the referen
We report the discovery of a luminous ultra-soft X-ray excess in a radio-loud narrow-line Seyfert1 galaxy, RXJ1633+4718, from archival ROSAT observations. The thermal temperature of this emission, when fitted with a blackbody, is as low as 32.5(+8.0,
Magnetars are young and highly magnetized neutron stars which display a wide array of X-ray activity including short bursts, large outbursts, giant flares and quasi-periodic oscillations, often coupled with interesting timing behavior including enhan
We consider the current observed ensemble of pulsing ultraluminous X-ray sources (PULXs). We show that all of their observed properties (luminosity, spin period, and spinup rate) are consistent with emission from magnetic neutron stars with fields in