Confirmation of two cyclotron lines in Vela X-1

Kreykenbohm, I.; Coburn, W.; Wilms, J.; Kretschmar, P.; Staubert, R.; Heindl, W. A.; Rothschild, R. E.

doi:10.1051/0004-6361:20021181

Cited by 97 publications

(128 citation statements)

References 37 publications

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“…However, the low false alarm probabilities may make the detection of the line stable against even crude mistakes in the computation of the significance (Kreykenbohm 2004). Therefore, taking into account these caveats, we can conclude that the the first harmonic CRSF is detected with high significance in the spectrum of this source.…”

Section: Combined Rxte and Integral Analysismentioning

confidence: 93%

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The first cyclotron harmonic of 4U 1538–52

Roca

Torrejón²,

Kreykenbohm

et al. 2009

A&A

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Context. Cyclotron resonant scattering features are an essential tool for studying the magnetic field of neutron stars. The fundamental line provides a measure of the field strength, while the harmonic lines provide information about the structure and configuration of the magnetic field. Until now only a handful of sources are known to display more than one cyclotron line and only two of them have shown a series of harmonics. Aims. The aim of this work is to see the first harmonic cyclotron line, confirming the fundamental line at ∼22 keV, thus increasing the number of sources with detected harmonic cyclotron lines. Methods. To investigate the presence of absorption or emission lines in the spectra, we have combined RXTE and INTEGRAL spectra. We modeled the 3-100 keV continuum emission with a power law with an exponential cut off and look for the second absorption feature. Results. We show evidence of an unknown cyclotron line at ∼47 keV (the first harmonic) in the phase-averaged X-ray spectra of 4U 1538−52. This line is detected by several telescopes at different epochs, even though the S/N of each individual spectrum is low. Conclusions. We conclude that the line-like absorption is a real feature, and the most straightforward interpretation is that it is the first harmonic, thus making 4U 1538−52 the fifth X-ray pulsar with more than one cyclotron line.

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Section: Combined Rxte and Integral Analysismentioning

confidence: 93%

“…However, because of response problems above ∼20 keV and the Xenon-K edge around 30 keV, we restricted the use of the PCA to the energy range from 3 keV to 20 keV (see also Kreykenbohm et al 2002). Systematic uncertainties are taken into account by the standard spectral analysis.…”

Section: Rxte Datamentioning

confidence: 99%

The first cyclotron harmonic of 4U 1538–52

Roca

Torrejón²,

Kreykenbohm

et al. 2009

A&A

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“…Later observations failed to detect this low energy feature, revealing only one absorption line at 53 ∼ 55 keV (Orlandini et al 1998;La Barbera et al 2003;Kreykenbohm et al 2008). Kretschmar et al (1997), with HEXE, Kreykenbohm et al (2002) with RXTE, Schanne et al (2007) with INTEGRAL, and Maitra & Paul (2013) and Odaka et al (2013) with Suzaku confirmed the presence of both features, with energies varying between ∼ 23 keV and ∼ 27 keV and between ∼ 45 keV and ∼ 54 keV, respectively. The low energy feature, interpreted as the fundamental CRSF, is considerably weaker than its second harmonic.…”

Section: Introductionmentioning

confidence: 96%

TheSwift-BAT monitoring reveals a long-term decay of the cyclotron line energy in Vela X-1

Parola¹,

Cusumano²,

Segreto³

et al. 2016

Mon. Not. R. Astron. Soc.

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We study the behaviour of the cyclotron resonant scattering feature (CRSF) of the high mass X-ray binary Vela X-1 using the long-term hard X-ray monitoring performed by the Burst Alert Telescope (BAT) on board Swift. High statistics, intensity selected spectra were built along 11 years of BAT survey. While the fundamental line is not revealed, the second harmonic of the CRSF can be clearly detected in all the spectra, at an energy varying between ∼ 53 keV and ∼ 58 keV, directly correlated with the luminosity. We have further investigated the evolution of the CRSF in time, by studying the intensity selected spectra built along four 33-month time intervals along the survey. For the first time we find in this source a secular variation in the CRSF energy: independent of the source luminosity, the CRSF second harmonic energy decreases by ∼ 0.36 keV/year between the first and the third time interval, corresponding to an apparent decay of the magnetic field of ∼ 3 × 10 10 G/year. The intensitycyclotron energy pattern is consistent between the third and the last time intervals. A possible interpretation for this decay could be the settling of an accreted mound that produces either a distortion of the poloidal magnetic field on the polar cap or a geometrical displacement of the line forming region. This hypothesis seems supported by the correspondance between the rate of the line shift per unit accreted mass and the mass accreted on the polar cap per unit area in Vela X-1 and Her X-1, respectively.

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“…We derived these values by fitting a two power law model simultaneously to a spectrum of a public RXTE observation of the Crab. See Wilms et al (1999) and Kreykenbohm et al (2002) for a more detailed discussion of this procedure. 1 (Kreykenbohm et al 2002).…”

Section: Introductionmentioning

confidence: 99%

“…See Wilms et al (1999) and Kreykenbohm et al (2002) for a more detailed discussion of this procedure. 1 (Kreykenbohm et al 2002). Due to the improved calibration of the Proportional Counter Array (PCA), the systematic uncertainties associated with the PCA differ with respect to our earlier work (compare Table 1 and Kreykenbohm et al 2002, Table 1).…”

Section: Introductionmentioning

confidence: 99%

The variable cyclotron line of GX 301–2

Kreykenbohm

Wilms

Coburn

et al. 2004

Nuclear Physics B - Proceedings Supplements

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Abstract. We present pulse phase resolved spectra of the hypergiant high mass X-ray binary GX 301−2. We observed the source in 2001 October with RXTE continuously for a total on-source time of almost 200 ksec. We model the continuum with both, a heavily absorbed partial covering model and a reflection model. In either case we find that the well known cyclotron resonant scattering feature (CRSF) at ∼35 keV is -although present at all pulse phases -strongly variable over the pulse: the line position varies by 25% from 30 keV in the fall of the secondary pulse to 38 keV in the fall of the main pulse where it is deepest. The line variability implies that we are seeing regions of magnetic field strength varying between 3.4 × 10 12 G and 4.2 × 10 12 G.

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Confirmation of two cyclotron lines in Vela X-1

Cited by 97 publications

References 37 publications

The first cyclotron harmonic of 4U 1538–52

The first cyclotron harmonic of 4U 1538–52

TheSwift-BAT monitoring reveals a long-term decay of the cyclotron line energy in Vela X-1

The variable cyclotron line of GX 301–2

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