X-ray observations of the accreting pulsars Her X-1 and EXO 2030+375 [Elektronische Ressource] / vorgelegt von Dmitry Klochkov

Sujets

• Astronomie

Informations

• Publié par: eberhard_karls_universitat_tubingen
• Publié le: 01 janvier 2007
• Nombre de lectures: 10
• Langue: English
• Poids de l'ouvrage: 2 Mo

Extrait

X-ray observations
of the accreting pulsars
Her X-1 and EXO 2030+375
Dissertation
zur Erlangung des Grades eines Doktors
der Naturwissenschaften
der Fakulta¨t fu¨r Mathematik und Physik
¨ ¨der Eberhard-Karls-Universitat zu Tubingen
vorgelegt von
Dmitry Klochkov
aus Nizhnekamsk, Russland
2007Tag der mu¨ndlichen Pru¨fung: 17. Dezember 2007
Dekan: Prof. Dr. N. Schopohl
1. Berichterstatter: Prof. Dr. R. Staubert, Tu¨bingen
2. Berichterstatter: Prof. Dr. K. Werner, Tu¨bingen
iiAbstract
The dissertation presents the analysis and interpretation of the multi-instrument X-
ray observations of two accreting binary pulsars Her X-1 and EXO 2030+375 performed
with the X-ray observatories INTEGRAL, RXTE, and Swift.
The intermediate mass X-ray binary system Her X-1/HZ Her was repeatedly ob-
served with RXTE since its launch in 1996. The All Sky Monitor (ASM) aboard the
satellite provided almost uninterrupted monitoring of the 2–12 keV flux of the pulsar. In
July–August 2005 Her X-1 was observed by the INTEGRAL observatory which covered a
substantial part of a main-on state of the system. Using these observations along with the
historical data we studied the secular changing of the orbital period of the system; searched
for the long-term correlations between the 35 d precessional period of the accretion disk,
the 1.24 s pulsation period, and the X-ray luminosity of the source; explored the pulse-
averaged and pulse-resolved X-ray spectra of the source; modeled the observed behavior
of anomalous dips and post-eclipse recoveries. The following main results were obtained.
A new orbital ephemeris of the system was constructed. The value of the secular decrease
of its orbital period was improved. The long-term correlations between the 35 d preces-
sional period of the accretion disk and 1.24 s pulsation period as well as between the X-ray
luminosity of the source and the 1.24 s period were confirmed. A positive correlation of the
cyclotron line energy with the X-ray luminosity of the source was revealed. The observed
behavior of anomalous dips and post-eclipse recoveries was reproduced using a numerical
model. Spectral changes during X-ray dips were modeled with a partial covering spec-
tral model, assuming that the observed radiation contains both absorbed and non-absorbed
contributions. The energy, width, and the depth of the cyclotron line as well as the spec-
tral continuum parameters were found to vary significantly with pulse phase. To explain
iiimost of the observed properties of the system a model was used which includes a precess-
ing twisted accretion disk, a freely precessing neutron star, and an accretion stream which
moves out of the system’s orbital plane.
EXO 2030+375 belongs to the class of Be/X-ray binaries. In June–September
2006 the source entered into the second giant (type II) outburst since its discovery. During
the outburst the pulsar was observed with INTEGRAL and Swift. For the first time, the
broad band (3–200 keV) X-ray spectrum of the source during a giant outburst was studied.
X-ray pulse profiles were explored. The dependence of the spin-up rate on the X-ray lu-
minosity of the source was studied using different accretion torque models. The following
main results were obtained. We did not confirm the presence of the cyclotron line in the
spectrum of the source (reported previously on the basis of RXTE data). The X-ray pulse
profiles were found to be highly luminosity-dependent. The dependence of the spin-up rate
on the X-ray luminosity measured during the 2006 giant outburst was found to be different
from that observed during the 1985 giant outburst. This was interpreted as an indication of
a possible change of the configuration of the neutron star’s magnetosphere and/or accretion
disk between the two giant outbursts.
ivvContents
Abstract iii
1 Introduction 1
2 X-ray binaries 3
2.1 General picture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2.2 Origin and evolution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.2.1 Evolution of a single star . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.2.2 Roche approximation and mass transfer in a binary . . . . . . . . . . . . . 6
2.2.3 Evolution of HMXB . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
2.2.4 Evolution of LMXB . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
2.3 Accretion mechanism . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
2.3.1 Roche lobe overflow and disk accretion . . . . . . . . . . . . . . . . . . . 9
2.3.2 Accretion from the stellar wind . . . . . . . . . . . . . . . . . . . . . . . 10
2.4 Accreting pulsars . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
2.4.1 Accretion onto a magnetized neutron star . . . . . . . . . . . . . . . . . . 11
2.4.2 Accretion torques and spin period behavior . . . . . . . . . . . . . . . . . 12
2.4.3 X-ray spectrum . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
3 Her X-1/HZ Her: intermediate mass X-ray binary 14
3.1 System overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
3.2 Observational properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
3.2.1 35 d period . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
3.2.2 X-ray dips . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
3.2.3 X-ray pulse profiles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
3.2.4 Cyclotron line . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
3.3 Model and open questions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
4 RXTE observations of Her X-1 25
4.1 Rossi XTE: mission overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
4.1.1 Proportional counter array . . . . . . . . . . . . . . . . . . . . . . . . . . 25
4.1.2 HEXTE detectors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
4.1.3 All sky monitor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
4.2 Refining system orbital ephemeris . . . . . . . . . . . . . . . . . . . . . . . . . . 28
4.2.1 Phase-connection method . . . . . . . . . . . . . . . . . . . . . . . . . . 29
vi4.2.2 RXTE data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
4.2.3 Orbital ephemeris . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
4.3 Measuring parameters of individual 35 d cycles . . . . . . . . . . . . . . . . . . . 33
4.3.1 Preliminary processing . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
4.3.2 Turn-on times and (O− C) diagram . . . . . . . . . . . . . . . . . . . . . 35
4.3.3 Maximum main-on flux . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
4.3.4 Correlations between (O− C), maximum main-on flux, and the pulse period 38
4.3.5 Correlation between the CRSF energy and the maximum main-on flux . . . 45
4.4 Averaged ASM light curves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
4.4.1 Evidence for a change in the disk tilt during the 35 d cycle . . . . . . . . . 46
4.4.2 The model for reproducing the behavior of dips . . . . . . . . . . . . . . . 49
5 INTEGRAL observations of Her X-1 53
5.1 INTEGRAL observatory: mission overview . . . . . . . . . . . . . . . . . . . . . 53
5.1.1 IBIS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
5.1.2 SPI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
5.1.3 JEM-X . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
5.2 Observations and data reduction . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
5.2.1 Summary of observations . . . . . . . . . . . . . . . . . . . . . . . . . . 56
5.2.2 IBIS/ISGRI data processing . . . . . . . . . . . . . . . . . . . . . . . . . 57
5.2.3 SPI data processing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
5.2.4 JEM-X data processing . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
5.3 Timing analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60
5.3.1 Light curve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60
5.3.2 Pulse profiles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60
5.3.3 Pulse period behavior . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
5.4 Spectral analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
5.4.1 Pulse averaged spectrum. . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
5.4.2 X-ray dips . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68
5.4.3 Pulse-phase-resolved spectra . . . . . . . . . . . . . . . . . . . . . . . . . 70
6 EXO 2030+375: Be X-ray binary 75
6.1 System description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75
6.2 X-ray and optical monitoring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76
6.2.1 Pulse period and X-ray flux history . . . . . . . . . . . . . . . . . . . . . 76
6.2.2 Type I X-ray outbursts . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78
6.2.3 Optical/IR observations . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78
6.2.4 X-ray pulse profiles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
6.2.5 X-ray