194 research outputs found
Cyclotron lines in highly magnetized neutron stars
Cyclotron lines, also called cyclotron resonant scattering features (CRSF)
are spectral features, generally appearing in absorption, in the X-ray spectra
of objects containing highly magnetized neutron stars, allowing the direct
measurement of the magnetic field strength in these objects. Cyclotron features
are thought to be due to resonant scattering of photons by electrons in the
strong magnetic fields. The main content of this contribution focusses on
electron cyclotron lines as found in accreting X-ray binary pulsars (XRBP) with
magnetic fields on the order of several 1012 Gauss. Also, possible proton
cyclotron lines from single neutron stars with even stronger magnetic fields
are briefly discussed.With regard to electron cyclotron lines, we present an
updated list of XRBPs that show evidence of such absorption lines. The first
such line was discovered in a 1976 balloon observation of the accreting binary
pulsar Hercules X-1, it is considered to be the first direct measurement of the
magnetic field of a neutron star. As of today (mid 2018), we list 36 XRBPs
showing evidence of one ore more electron cyclotron absorption line(s). A few
have been measured only once and must be confirmed (several more objects are
listed as candidates). In addition to the Tables of objects, we summarize the
evidence of variability of the cyclotron line as a function of various
parameters (especially pulse phase, luminosity and time), and add a discussion
of the different observed phenomena and associated attempts of theoretical
modeling. We also discuss our understanding of the underlying physics of
accretion onto highly magnetized neutron stars. For proton cyclotron lines, we
present tables with seven neutron stars and discuss their nature and the
physics in these objects.Comment: 32 pages, 15 figures, 8 Tables, accepted by A&A 201
Discovery of a Third Harmonic Cyclotron Resonance Scattering Feature in the X-ray Spectrum of 4U 0115+63
We have discovered a third harmonic cyclotron resonance scattering feature
(CRSF) in observations of the recent outburst of 4U 0115+63 with the Rossi
X-ray Timing Explorer (RXTE). The spectrum in a narrow pulse phase range shows
CRSFs at 12.40+0.65/-0.35, 21.45+0.25/-0.38, and 33.56+0.70/-0.90 keV. With
centroid energy ratios to the fundamental of 1.73+/-0.08 and 2.71+/-0.13, the
CRSFs are not harmonically spaced. Strong variability of the continuum and
CRSFs with pulse phase indicate a complex emission geometry near the neutron
star polar cap. In addition, one RXTE observation, which spanned periastron
passage, revealed a strong 2 mHz quasi-periodic oscillation (QPO). This is
slower by two orders of magnitude than the beat-frequency QPO expected in this
system and slower by a factor of more than 5 compared with other QPOs seen in
accreting X-ray pulsars.Comment: To appear in The Astrophysical Journal Letters. 4 pages, 5 figures.
Uses "emulateapj.sty". Revised version includes new figures and additions to
the analysi
Near-infrared Observations of Be/X-ray Binary Pulsar A0535+262
We present results obtained from an extensive near-infrared spectroscopic and
photometric observations of the Be/X-ray binary A0535+262/HDE 245770 at
different phases of its ~111 day orbital period. This observation campaign is a
part of the monitoring programme of selective Be/X-ray binary systems aimed at
understanding the X-ray and near-IR properties at different orbital phases,
especially during the periastron passage of the neutron star. The near-IR
observations were carried out using the 1.2 m telescope at Mt. Abu IR
observatory. Though the source was relatively faint for spectroscopic
observations with 1.2 m telescope, we monitored the source during the 2011
February--March giant outburst to primarily investigate whether any drastic
changes in the near-IR JHK spectra take place at the periastron passage.
Changes of such a striking nature were expected to be detectable in our
spectra. Photometric observations of the Be star show a gradual and systematic
fading in the JHK light curves since the onset of the X-ray outburst that could
suggest a mild evacuation/truncation of the circumstellar disc of the Be
companion. Near-IR spectroscopy of the object shows that the JHK spectra are
dominated by the emission lines of hydrogen Brackett and Paschen series and HeI
lines at 1.0830, 1.7002 and 2.0585 micron. The presence of all hydrogen
emission lines in the JHK spectra, along with the absence of any significant
change in the continuum of the Be companion during X-ray quiescent and X-ray
outburst phases suggest that the near-IR line emitting regions of the disc are
not significantly affected during the X-ray outburst.Comment: 10 Pages, 5 Figures, Accepted for publication in Res. in Astronomy
and Astrophysic
Studies of orbital parameters and pulse profile of the accreting millisecond pulsar XTE J1807-294
The accreting millisecond pulsar XTE J1807-294 was observed by XMM-Newton on
March 22, 2003 after its discovery on February 21, 2003 by RXTE. The source was
detected in its bright phase with an observed average count rate of 33.3 cts/s
in the EPIC-pn camera in the 0.5-10 keV energy band (3.7 mCrab). Using the
earlier established best-fit orbital period of 40.0741+/-0.0005 minutes from
RXTE observations and considering a circular binary orbit as first
approximation, we derived a value of 4.8+/-0.1 lt-ms for the projected orbital
radius of the binary system and an epoch of the orbital phase of MJD
52720.67415(16). The barycentric mean spin period of the pulsar was derived as
5.2459427+/-0.0000004 ms. The pulsar's spin-pulse profile showed a prominent
(1.5 ms FWHM) pulse, with energy and orbital phase dependence in the amplitude
and shape. The measured pulsed fraction in four energy bands was found to be
3.1+/-0.2 % (0.5-3.0 keV), 5.4+/-0.4 % (3.0-6.0 keV), 5.1+/-0.7 % (6.0-10.0
keV) and 3.7+/-0.2 % (0.5-10.0 keV), respectively. Studies of spin-profiles
with orbital phase and energy showed significant increase in its pulsed
fraction during the second observed orbit of the neutron star, gradually
declining in the subsequent two orbits, which was associated with sudden but
marginal increase in mass accretion. From our investigations of orbital
parameters and estimation of other properties of this compact binary system, we
conclude that XTE J1807-294 is very likely a candidate for a millisecond radio
pulsar.Comment: 4 pages, 4 figures, Accepted for publication in Astronomy and
Astrophysics letter
The XMM-Newton view of the Crab
Aims. We discuss the current X-ray view of the Crab Nebula and Pulsar, summarising our analysis of observations of the source with the EPIC-pn camera on board the XMM-Newton observatory. Different modes of EPIC-pn were combined in order to yield a complete scenario of the spectral properties of the Crab resolved in space and time (pulse phase). In addition we give a description of the special
EPIC-pn Burst mode and guidance for data reduction in that mode.
Methods. We analysed spectra for the nebula and pulsar separately in the 0.6−12.0 keV energy band. All data were processed with the
SAS 6.0.0 XMM-Newton Scientific Analysis System package; models were fitted to the data with XSPEC 11. The high time resolution of EPIC-pn in its Burst mode (7 μs) was used for a phase resolved analysis of the pulsar spectrum, after determination of the period with epoch folding techniques. Data from the SmallWindow mode were processed and corrected for pile-up allowing for spectroscopy
simultaneously resolved in space and time.
Results. The spatial variation of the spectrum over the entire region of the Crab shows a gradual spectral softening from the inner pulsar region to the outer nebula region with a variation in photon index, Γ, from 2.0 to 2.4. Pulse phase resolved spectroscopy of the Crab Pulsar reveals a phase dependent modulation of the photon index in form of a significant hardening of the spectrum in the
inter-peak phase from Γ = 1.7 during the pulse peak to Γ = 1.5
The pre-outburst flare of the A 0535+26 August/September 2005 outburst
We study the spectral and temporal behavior of the High Mass X-ray Binary A
0535+26 during a `pre-outburst flare' which took place ~5 d before the peak of
a normal (type I) outburst in August/September 2005. We compare the studied
behavior with that observed during the outburst. We analyse RXTE observations
that monitored A 0535+26 during the outburst. We complete spectral and timing
analyses of the data. We study the evolution of the pulse period, present
energy-dependent pulse profiles both at the initial pre-outburst flare and
close to outburst maximum, and measure how the cyclotron resonance-scattering
feature (hereafter CRSF) evolves. We present three main results: a constant
period P=103.3960(5)s is measured until periastron passage, followed by a
spin-up with a decreasing period derivative of Pdot=(-1.69+/-0.04)x10^(-8)s/s
at MJD 53618, and P remains constant again at the end of the main outburst. The
spin-up provides evidence for the existence of an accretion disk during the
normal outburst. We measure a CRSF energy of Ecyc~50kev during the pre-outburst
flare, and Ecyc~46kev during the main outburst. The pulse shape, which varies
significantly during both pre-outburst flare and main outburst, evolves
strongly with photon energy.Comment: 4 pages, 4 figures, accepted for publication in A&A Letters. To be
published in parallel to Postnov et al. 200
The broad iron Kalpha line of Cygnus X-1 as seen by XMM-Newton in the EPIC-pn modified timing mode
We present the analysis of the broadened, flourescent iron Kalpha line in
simultaneous XMM-Newton and RXTE data from the black hole Cygnus X-1. The
XMM-Newton data were taken in a modified version of the timing mode of the
EPIC-pn camera. In this mode the lower energy threshold of the instrument is
increased to 2.8 keV to avoid telemetry drop outs due to the brightness of the
source, while at the same time preserving the signal-to-noise ratio in the Fe
Kalpha band. We find that the best-fit spectrum consists of the sum of an
exponentially cut off power-law and relativistically smeared, ionized
reflection. The shape of the broadened Fe Kalpha feature is due to strong
Compton broadening combined with relativistic broadening. Assuming a standard,
thin accretion disk, the black hole is close to rotating maximally.Comment: Astron. Astrophys., in pres
Accelerator experiments with soft protons and hyper-velocity dust particles: application to ongoing projects of future X-ray missions
We report on our activities, currently in progress, aimed at performing
accelerator experiments with soft protons and hyper-velocity dust particles.
They include tests of different types of X-ray detectors and related components
(such as filters) and measurements of scattering of soft protons and
hyper-velocity dust particles off X-ray mirror shells. These activities have
been identified as a goal in the context of a number of ongoing space projects
in order to assess the risk posed by environmental radiation and dust and
qualify the adopted instrumentation with respect to possible damage or
performance degradation. In this paper we focus on tests for the Silicon Drift
Detectors (SDDs) used aboard the LOFT space mission. We use the Van de Graaff
accelerators at the University of T\"ubingen and at the Max Planck Institute
for Nuclear Physics (MPIK) in Heidelberg, for soft proton and hyper-velocity
dust tests respectively. We present the experimental set-up adopted to perform
the tests, status of the activities and some very preliminary results achieved
at present time.Comment: Proceedings of SPIE, Vol. 8443, Paper No. 8443-24, 201
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