Search results for " X-Rays: Binaries"
showing 10 items of 61 documents
Suzaku broad-band spectrum of 4U 1705-44: probing the reflection component in the hard state
2015
Iron emission lines at 6.4-6.97 keV, identified with Kalpha radiative transitions, are among the strongest discrete features in the X-ray band. These are one of the most powerful probes to infer the properties of the plasma in the innermost part of the accretion disk around a compact object. In this paper we present a recent Suzaku observation, 100-ks effective exposure, of the atoll source and X-ray burster 4U 1705-44, where we clearly detect signatures of a reflection component which is distorted by the high-velocity motion in the accretion disk. The reflection component consists of a broad iron line at about 6.4 keV and a Compton bump at high X-ray energies, around 20 keV. All these feat…
Searching for pulsed emission from XTE J0929-314 at high radio frequencies
2009
The aim of this work is to search for radio signals in the quiescent phase of accreting millisecond X-ray pulsars, in this way giving an ultimate proof of the recycling model, thereby unambiguously establishing that accreting millisecond X-ray pulsars are the progenitors of radio millisecond pulsars. To overcome the possible free-free absorption caused by matter surrounding accreting millisecond X-ray pulsars in their quiescence phase, we performed the observations at high frequencies. Making use of particularly precise orbital and spin parameters obtained from X-ray observations, we carried out a deep search for radio-pulsed emission from the accreting millisecond X-ray pulsar XTE J0929-31…
On Low Mass X-ray Binaries and Millisecond Pulsar
2013
The detection, in 1998, of the first Accreting Millisecond Pulsar, started an exciting season of continuing discoveries in the fashinating field of compact binary systems harbouring a neutron star. Indeed, in these last three lustres, thanks to the extraordinary performances of astronomical detectors, on ground as well as on board of satellites, mainly in the Radio, Optical, X-ray, and Gamma-ray bands, astrophysicists had the opportunity to thoroughly investigate the so-called Recycling Scenario: the evolutionary path leading to the formation of a Millisecond Radio Pulsar. The most intriguing phase is certainly the spin-up stage during which, because of the accretion of matter and angular m…
The pulse profile and spin evolution of the accreting pulsar in Terzan 5, IGR J17480-2446, during its 2010 outburst
2012
(abridged) We analyse the spectral and pulse properties of the 11 Hz transient accreting pulsar, IGR J17480-2446, in the globular cluster Terzan 5, considering all the available RXTE, Swift and INTEGRAL observations performed between October and November, 2010. By measuring the pulse phase evolution we conclude that the NS spun up at an average rate of =1.48(2)E-12 Hz/s, compatible with the accretion of the Keplerian angular momentum of matter at the inner disc boundary. Similar to other accreting pulsars, the stability of the pulse phases determined by using the second harmonic component is higher than that of the phases based on the fundamental frequency. Under the assumption that the sec…
Broadband spectral analysis of MXB 1659-298 in its soft and hard state
2019
The X-ray transient eclipsing source MXB 1659-298 went in outburst in 1999 and 2015, respectively, during which it was observed by XMM-Newton, NuSTAR and Swift. Using these observations we studied the broadband spectrum of the source to constrain the continuum components and to verify the presence of a reflection component. We analysed the soft and hard state of the source, finding that the soft state can be modelled with a thermal component associated with the inner accretion disc plus a Comptonised component. A smeared reflection component and the presence of an ionised absorber are also requested in the best-fit model. On the other hand, the direct continuum emission in the hard state ca…
NuSTARandXMM–Newtonbroad-band spectrum of SAX J1808.4–3658 during its latest outburst in 2015
2018
The first discovered accreting millisecond pulsar, SAX J1808.4-3658, went into X-ray outburst in April 2015. We triggered a 100 ks XMM-Newton ToO, taken at the peak of the outburst, and a 55 ks NuSTAR ToO, performed four days apart. We report here the results of a detailed spectral analysis of both the XMM-Newton and NuSTAR spectra. While the XMM-Newton spectrum appears much softer than in previous observations, the NuSTAR spectrum confirms the results obtained with XMM-Newton during the 2008 outburst. We find clear evidence of a broad iron line that we interpret as produced by reflection from the inner accretion disk. For the first time, we use a self-consistent reflection model to fit the…
Spin up and phase fluctuations in the timing of the accreting millisecond pulsar XTE J1807-294
2007
We performed a timing analysis of the 2003 outburst of the accreting X-ray millisecond pulsar XTE J1807-294 observed by RXTE. Using recently refined orbital parameters we report for the first time a precise estimate of the spin frequency and of the spin frequency derivative. The phase delays of the pulse profile show a strong erratic behavior superposed to what appears as a global spin-up trend. The erratic behavior of the pulse phases is strongly related to rapid variations of the light curve, making it very difficult to fit these phase delays with a simple law. As in previous cases, we have therefore analyzed separately the phase delays of the first harmonic and of the second harmonic of …
Secular spin-down of the AMP XTE J1751-305
2011
Context. Of the 13 known accreting millisecond pulsars, only a few showed more than one outburst during the RXTE era. XTE J1751-305 showed, after the main outburst in 2002, other three dim outbursts. We report on the timing analysis of the latest one, occurred on October 8, 2009 and serendipitously observed from its very beginning by RXTE. Aims. The detection of the pulsation during more than one outburst permits to obtain a better constraint of the orbital parameters and their evolution as well as to track the secular spin frequency evolution of the source. Methods. Using the RXTE data of the last outburst of the AMP XTE J1751-305, we performed a timing analysis to improve the orbital para…
Discovery of 105 Hz coherent pulsations in the ultracompact binary IGR J16597-3704
2018
We report the discovery of X-ray pulsations at 105.2 Hz (9.5 ms) from the transient X-ray binary IGR J16597-3704 using NuSTAR and Swift. The source was discovered by INTEGRAL in the globular cluster NGC 6256 at a distance of 9.1 kpc. The X-ray pulsations show a clear Doppler modulation implying an orbital period of ~46 minutes and a projected semi-major axis of ~5 lt-ms, which makes IGR J16597-3704 an ultra-compact X-ray binary system. We estimated a minimum companion mass of 0.0065 solar masses, assuming a neutron star mass of 1.4 solar masses, and an inclination angle of <75 degrees (suggested by the absence of eclipses or dips in its light-curve). The broad-band energy spectrum of the…
An XMM-Newton and INTEGRAL view on the hard state of EXO 1745-248 during its 2015 outburst
2017
CONTEXT - Transient low-mass X-ray binaries (LMXBs) often show outbursts lasting typically a few-weeks and characterized by a high X-ray luminosity ($L_{x} \approx 10^{36}-10^{38}$ erg/sec), while for most of the time they are found in X-ray quiescence ($L_X\approx10^{31} -10^{33}$ erg/sec). EXO 1745-248 is one of them. AIMS - The broad-band coverage, and the sensitivity of instrument on board of {\xmm} and {\igr}, offers the opportunity to characterize the hard X-ray spectrum during {\exo} outburst. METHODS - In this paper we report on quasi-simultaneous {\xmm} and {\igr} observations of the X-ray transient {\exo} located in the globular cluster Terzan 5, performed ten days after the begin…