NuSTAR DISCOVERY OF A CYCLOTRON LINE IN THE ACCRETING X-RAY PULSAR IGR J16393-4643
A. BodagheeJohn A. TomsickFrancesca M. FornasiniRoman KrivonosDaniel SternKaya MoriFarid RahouiSteven E. BoggsFinn E. ChristensenWilliam W. CraigCharles J. HaileyFiona A. HarrisonWilliam W. Zhang
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ABSTRACT The high-mass X-ray binary and accreting X-ray pulsar IGR J16393-4643 was observed by the Nuclear Spectroscope Telescope Array in the 3–79 keV energy band for a net exposure time of 50 ks. We present the results of this observation which enabled the discovery of a cyclotron resonant scattering feature with a centroid energy of keV. This allowed us to measure the magnetic field strength of the neutron star for the first time: B = (2.5 ± 0.1) × 10 12 G. The known pulsation period is now observed at 904.0 ± 0.1 s. Since 2006, the neutron star has undergone a long-term spin-up trend at a rate of s s −1 (−0.6 s per year, or a frequency derivative of Hz s −1 ). In the power density spectrum, a break appears at the pulse frequency which separates the zero slope at low frequency from the steeper slope at high frequency. This addition of angular momentum to the neutron star could be due to the accretion of a quasi-spherical wind, or it could be caused by the transient appearance of a prograde accretion disk that is nearly in corotation with the neutron star whose magnetospheric radius is around 2 × 10 8 cm.Keywords:
X-ray binary
X-ray pulsar
Compact star
Vela
Vela
Glitch
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Vela
X-ray pulsar
Rotational energy
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The prospects of observing a pulsed neutron flux at very high energies from pulsars are discussed. Most likely candidates are the Vela pulsar at 2 × 10 16 eV and the Crab Pulsar at 10 17 eV.
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X-ray pulsar
Crab Pulsar
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X-ray binaries are binary stellar systems containing a compact object and a normal companion star which are gravitationally bound and rotate about a common center of mass. The compact object accretes matter from the companion star. The accreted matter may have a high angular momentum and hence follow a Keplarian orbit about the compact object. It slowly spirals inward as its angular momentum is redistributed via viscous forces and forms an accreting disk before being finally accreted onto the compact object. The compact object that is accreting matter may either be a neutron star or a black hole. X-ray binaries can be broadly classified into two classes depending on the mass of the companion star. Low Mass X-ray Binaries (LMXBs) have companion star masses and accrete mass via Roche lobe overflow of the companion star. High Mass X-ray Binaries (HMXBs) have companion star masses and in these systems the compact object accretes matter from the high velocity stellar winds of the companion star.
For the work and results that are presented in the thesis we have studied the orbital evolution, apsidal motion and long term flux variations in High mass X-ray binaries which have a neutron star compact object with very high magnetic field of the order of B ~ 1012 G. Due to the high magnetic field, the accretion disk is disrupted at the Alfven radius where the magnetic field pressure equals the ram pressure of the infalling matter. From that boundary, the flow of the infalling matter will be guided by the magnetic field lines. The infalling matter will follow these lines, finally falling onto the magnetic poles with velocity nearly equal to the free fall velocity and form an accretion column over the magnetic poles. A hot spot is formed at both the magnetic poles and high energy photons are emitted from these regions. Inverse Compton scattering of these photons by high energy electrons in the accretion column can produce hard X-rays. If the optical depth of the accretion column is low, the radiation comes along the magnetic axis forming a pencil beam whereas if the optical depth is high, radiation escapes tangential to the accretion column forming a fan beam. Since the neutron star is rotating about its rotation axis, the radiation beam directed along magnetic axis non-aligned with the rotation axis will sweep across the sky. Whenever this beam of rotating radiation is aligned with the line of sight, a pulse of X-ray radiation is detected. Hence these systems are also called X-ray Binary Pulsars (XBP). These pulses are emitted at equal intervals of time, where the time between the emission of two pulses is the spin period of the neutron star. But since the neutron star is in a binary orbit, the arrival time of pulses as recorded by an observer will be delayed or advanced due to the motion of the neutron star. When the neutron star is moving towards the observer, the pulses arrive faster and when the neutron star is moving away from the observer, the pulses are delayed. These delays or advances of the arrival time of pulses…
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X-ray binary
X-ray burster
X-ray pulsar
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Of all pulsars known Vela has been one of the most productive in terms in understanding pulsars and their characteristics. We present the latest results derived from Australian telescopes. These include a more accurate pulsar distance, a more precise pulsar local space velocity, a new model of the spin up and the association of a radio nebula with the X-ray pulsar wind nebula.
Vela
Pulsar wind nebula
Pulsar planet
X-ray pulsar
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Of all pulsars known Vela has been one of the most productive in terms in understanding pulsars and their characteristics. We present the latest results derived from Australian telescopes. These include a more accurate pulsar distance, a more precise pulsar local space velocity, a new model of the spin up and the association of a radio nebula with the X-ray pulsar wind nebula.
Vela
Pulsar wind nebula
Pulsar planet
X-ray pulsar
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A pulsar-monitoring programme has been running at Hartebeesthoek Radio Astronomy Observatory over the last three years, at 2.32 and (during the last year) at 1.67 GHz. Twenty pulsars are observed once or twice a fortnight, and PSRs 1641-45 and 0833-45 (the Vela pulsar) daily.
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Discontinuity (linguistics)
Radio Astronomy
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Of all pulsars known, Vela has been one of the most productive in terms in understanding pulsars and their characteristics. We present the latest results derived from Australian telescopes. These include a more accurate pulsar distance, a more precise pulsar local space velocity, a new model of spin-up at a glitch, and the association of a radio nebula with the X-ray pulsar wind nebula.
Vela
Glitch
Pulsar planet
Pulsar wind nebula
X-ray pulsar
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Vela
X-ray pulsar
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A total of 71 glitches (Δν/ν≥10−9) have been reported to date in 30 pulsars. 13 of these glitches come from the Vela pulsar, whose glitches are mostly of magnitude Δν/ν∼10−6. Only about 40 per cent of the total glitches are of this magnitude. While glitches of this size have been observed from pulsars aged 104–107 yr, 80 per cent of them come from the youthful pulsars, aged 104–105 yr. For pulsars older than 104 yr, the glitch activity is found to be proportional to the logarithm of the spin-down rate, Based on this relationship, we identify six other pulsars that are most likely to yield frequent large glitches. Since these pulsars are of comparable ages to the Vela pulsar, real-time glitch detection on them and studies of their subsequent recovery would play a vital role in improving understanding of the neutron star interior and the pulsar glitch mechanisms.
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Vela
X-ray pulsar
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