2007A&A...465L..25S


Query : 2007A&A...465L..25S

2007A&A...465L..25S - Astronomy and Astrophysics, volume 465, L25-28 (2007/4-2)

Discovery of a flux-related change of the cyclotron line energy in Hercules X-1.

STAUBERT R., SHAKURA N.I., POSTNOV K., WILMS J., ROTHSCHILD R.E., COBURN W., RODINA L. and KLOCHKOV D.

Abstract (from CDS):

We present the results of ten years of repeated measurements of the Cyclotron Resonance Scattering Feature (CRSF) in the spectrum of the binary X-ray pulsar Her X-1 and report the discovery of a positive correlation of the centroid energy of this absorption feature in pulse phase averaged spectra with source luminosity. Our results are based on a uniform analysis of observations by the RXTE satellite from 1996 to 2005, using sufficiently long observations of 12 individual 35-day Main-On states of the source. The mean centroid energy Ec of the CRSF in pulse phase averaged spectra of Her X-1 during this time is around 40keV, with significant variations from one Main-On state to the next. We find that the centroid energy of the CRSF in Her X-1 changes by ∼5% in energy for a factor of 2 in luminosity. The correlation is positive, contrary to what is observed in some high luminosity transient pulsars. Our finding is the first significant measurement of a positive correlation between Ec and luminosity in any X-ray pulsar. We suggest that this behaviour is expected in the case of sub-Eddington accretion and present a calculation of a quantitative estimate, which is very consistent with the effect observed in Her X-1. We urge that Her X-1 is regularly monitored further and that other X-ray pulsars are investigated for a similar behaviour.

Abstract Copyright:

Journal keyword(s): accretion, accretion disks - binaries: eclipsing - stars: neutron - X-rays: binaries - X-rays: stars

CDS comments: In reflist 1998PASJ.43.501M is a misprint for 1991PASJ.43.501M

Simbad objects: 6

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Number of rows : 6
N Identifier Otype ICRS (J2000)
RA
ICRS (J2000)
DEC
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2023
#notes
1 V* V635 Cas HXB 01 18 31.9704955824 +63 44 33.072603144 17.05 16.64 15.19 14.34 13.22 B0.2Ve 709 0
2 V* BQ Cam HXB 03 34 59.9116110096 +53 10 23.296879776   17.16 15.42 14.26 13.04 O8.5Ve 449 1
3 HD 245770 HXB 05 38 54.5748918624 +26 18 56.836952784 9.30 9.84 9.39 8.77 8.30 O9/B0III/Ve 944 0
4 V* BP Cru HXB 12 26 37.5605188992 -62 46 13.261044684   12.70 10.66     B1.5Iaeq 657 0
5 V* HZ Her LXB 16 57 49.8110126616 +35 20 32.486555472 11.90 14.89 13.63 13.88   B3/6ep 2019 0
6 V* V490 Cep HXB 21 39 30.6903047304 +56 59 10.421969280   15.2       B1.5Ve 155 1

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2023.02.01-20:02:42

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