1,176 research outputs found
X-ray and optical observations of 1RXS J154814.5-452845: a new intermediate polar with soft X-ray emission
We report the identification of the ROSAT all-sky survey source 1RXS
J154814.5-452845as new intermediate polar and present the results from
follow-up optical and X-ray observations. The source shows pulsations with a
period of 693 s both in the optical and X-ray light curves and the detection of
a synodic frequency strongly suggests that this is the rotation period of the
white dwarf. Although the one day aliasing and the sparse optical data coverage
does not allow to unambiguously identify the orbital period, the most likely
values of 9.37 h and 6.72 h add 1RXS J154814.5-452845 to the intermediate
polars with the longest orbital periods known. The optical spectrum displays
features from the late type secondary and shows the presence of broad
absorption lines at \Hbet and higher order Balmer lines which may be a
signature of the white dwarf atmosphere, very similar to V 709 Cas. The average
X-ray spectra as obtained by the EPIC instruments on board XMM-Newton show hard
emission typical for this class of objects but also the presence of soft
blackbody-like emission similar to that seen from soft intermediate polars and
thought to arise from the white dwarf surface heated by the hard X-rays. The
best fit model comprises thermal emission from multi-temperature plasma in
collisional ionization equilibrium with a continuous temperature distribution
up to a maximum of 60 keV, an Fe fluorescence line at 6.4 keV and with
equivalent width of 260 eV and a blackbody component with kT of 86 eV. The hard
X-ray emission is absorbed by matter covering 47% of the X-ray source with an
equivalent hydrogen density of \ohcm{23}. The remaining hard emission is
absorbed by a much reduced column density of 1.5\hcm{21} as is the soft
blackbody emission. (truncated)Comment: 14 pages, Latex, with 19 figures, accepted for publication in
Astronomy and Astrophysic
The isolated neutron star X-ray pulsars RX J0420.0–5022 and RX J0806.4–4123 : new X-ray and optical observations
We report on the analysis of new X-ray data obtained with XMM-Newton and Chandra from two ROSAT-discovered X-ray dim isolated neutron stars (XDINs). RX J0806.4−4123 was observed with XMM-Newton in April 2003, 2.5 years after
the first observation. The EPIC-pn data confirm that this object is an X-ray pulsar with 11.371 s neutron star spin period. The X-ray spectrum is consistent with absorbed black-body emission with a temperature kT = 96 eV and N H = 4 × 10 19 cm −2 without significant changes between the two observations. Four XMM-Newton observations of RX
J0420.0−5022 between December 2002 and July 2003 did not confirm the 22.7 s pulsations originally indicated in ROSAT data, but clearly reveal a 3.453 s period. A fit to the X-ray spectrum using an absorbed black-body model yields kT = 45 eV, the lowest value found from the small group of XDINs and N H = 1.0 × 10 20 cm −2. Including a broad absorption line improves the quality of the spectral fits considerably for both objects and may indicate the presence of absorption features similar to those reported from RBS1223, RX J1605.3+3249 and RX J0720.4−3125. For both targets we derive accurate X-ray positions from the Chandra data and present an optical counterpart candidate for RX J0420.0−5022 with B = 26.6 ± 0.3 mag from VLT imaging
An Improved Heat Kernel Expansion from Worldline Path Integrals
The one--loop effective action for the case of a massive scalar loop in the
background of both a scalar potential and an abelian or non--abelian gauge
field is written in a one--dimensional path integral representation. From this
the inverse mass expansion is obtained by Wick contractions using a suitable
Green function, which allows the computation of higher order coefficients. For
the scalar case, explicit results are presented up to order O(T**8) in the
proper time expansion. The relation to previous work is clarified.Comment: 13 pages, Plain TEX, no figure
Once-ionized helium in superstrong magnetic fields
It is generally believed that magnetic fields of some neutron stars, the
so-called magnetars, are enormously strong, up to 10^{14} - 10^{15} G. Recent
investigations have shown that the atmospheres of magnetars are possibly
composed of helium. We calculate the structure and bound-bound radiative
transitions of the He^+ ion in superstrong fields, including the effects caused
by the coupling of the ion's internal degrees of freedom to its center-of-mass
motion. We show that He^+ in superstrong magnetic fields can produce spectral
lines with energies of up to about 3 keV, and it may be responsible for
absorption features detected recently in the soft X-ray spectra of several
radio-quiet isolated neutron stars. Quantization of the ion's motion across a
magnetic field results in a fine structure of spectral lines, with a typical
spacing of tens electron-volts in magnetar-scale fields. It also gives rise to
ion cyclotron transitions, whose energies and oscillator strengths depend on
the state of the bound ion.Comment: 12 pages, including 3 figures. Submitted to ApJ Letters (revised
version
Multi-wavelength properties of IGR J05007-7047 (LXP 38.55) and identification as a Be X-ray binary pulsar in the LMC
We report on the results of a 40 d multi-wavelength monitoring of the
Be X-ray binary system IGR J05007-7047 (LXP 38.55). During that period the
system was monitored in the X-rays using the Swift telescope and in the optical
with multiple instruments. When the X-ray luminosity exceeded erg/s
we triggered an XMM-Newton ToO observation. Timing analysis of the photon
events collected during the XMM-Newton observation reveals coherent X-ray
pulsations with a period of 38.551(3) s (1 {\sigma}), making it the 17
known high-mass X-ray binary pulsar in the LMC. During the outburst, the X-ray
spectrum is fitted best with a model composed of an absorbed power law () plus a high-temperature black-body (kT 2 keV) component. By
analysing 12 yr of available OGLE optical data we derived a 30.776(5) d
optical period, confirming the previously reported X-ray period of the system
as its orbital period. During our X-ray monitoring the system showed limited
optical variability while its IR flux varied in phase with the X-ray
luminosity, which implies the presence of a disk-like component adding cooler
light to the spectral energy distribution of the system.Comment: 11 pages, 11 figures, Accepted for publication in MNRA
Identification of two new HMXBs in the LMC: a 2013 s pulsar and a probable SFXT
We report on the X-ray and optical properties of two high-mass X-ray binary
systems located in the Large Magellanic Cloud (LMC). Based on the obtained
optical spectra, we classify the massive companion as a supergiant star in both
systems. Timing analysis of the X-ray events collected by XMM-Newton revealed
the presence of coherent pulsations (spin period 2013 s) for XMMU
J053108.3-690923 and fast flaring behaviour for XMMU J053320.8-684122. The
X-ray spectra of both systems can be modelled sufficiently well by an absorbed
power-law, yielding hard spectra and high intrinsic absorption from the
environment of the systems. Due to their combined X-ray and optical properties
we classify both systems as SgXRBs: the 19 confirmed X-ray pulsar
and a probable supergiant fast X-ray transient in the LMC, the second such
candidate outside our Galaxy.Comment: 12 pages, 10 figures, accepted for publication in MNRA
A Probable Optical Counterpart for the Isolated Neutron Star RX J1308.6+2127
Using a very deep observation with HST/STIS, we have searched for an optical
counterpart to the nearby radio-quiet isolated neutron star RX J1308.6+2127
(RBS 1223). We have identified a single object in the 90% Chandra error circle
that we believe to be the optical counterpart. This object has
mag, which translates approximately to an unabsorbed
flux of ergs/s/cm^2/A at 5150 A or an
X-ray-to-optical flux ratio of . This flux is a factor of
above the extrapolation of the black-body fit to the X-ray
spectrum, consistent with the optical spectra of other isolated neutron stars.
Without color information we cannot conclude that this source is indeed the
counterpart of RX J1308.6+2127. If not, then the counterpart must have
mag, corresponding to a flux that is barely consistent with
the extrapolation of the black-body fit to the X-ray spectrum.Comment: 4 pages, 2 figures. Uses emulateapj5.sty, onecolfloat5.sty. Accepted
by ApJ Letter
Timing and spectral studies of the transient X-ray pulsar EXO 053109-6609.2 with ASCA and Beppo-SAX
We report timing and spectral properties of the transient Be X-ray pulsar EXO
053109--6609.2 studied using observations made with the ASCA and BeppoSAX
observatories. Though there must have been at least one spin-down episode of
the pulsar since its discovery, the new pulse period measurements show a
monotonic spin-up trend since 1996. The pulse profile is found to have marginal
energy dependence. There is also evidence for strong luminosity dependence of
the pulse profile, a single peaked profile at low luminosity that changes to a
double peaked profile at high luminosity. This suggests a change in the
accretion pattern at certain luminosity level. The X-ray spectrum is found to
consist of a simple power-law with photon index in the range of 0.4--0.8. At
high intensity level the spectrum also shows presence of weak iron emission
line.Comment: 12 pages, 8 figures, Accepted for publication in Ap
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