2,932 research outputs found
Swift J053041.9-665426, a new Be/X-ray binary pulsar in the Large Magellanic Cloud
We observed the newly discovered X-ray source Swift J053041.9-665426 in the
X-ray and optical regime to confirm its proposed nature as a high mass X-ray
binary. We obtained XMM-Newton and Swift X-ray data, along with optical
observations with the ESO Faint Object Spectrograph, to investigate the
spectral and temporal characteristics of Swift J053041.9-665426. The XMM-Newton
data show coherent X-ray pulsations with a period of 28.77521(10) s (1 sigma).
The X-ray spectrum can be modelled by an absorbed power law with photon index
within the range 0.76 to 0.87. The addition of a black body component increases
the quality of the fit but also leads to strong dependences of the photon
index, black-body temperature and absorption column density. We identified the
only optical counterpart within the error circle of XMM-Newton at an angular
distance of ~0.8 arcsec, which is 2MASS J05304215-6654303. We performed optical
spectroscopy from which we classify the companion as a B0-1.5Ve star. The X-ray
pulsations and long-term variability, as well as the properties of the optical
counterpart, confirm that Swift J053041.9-665426 is a new Be/X-ray binary
pulsar in the Large Magellanic Cloud.Comment: 10 pages, 8 figures, accepted for publication in A&
Probabilistic Spatial and Temporal Resilience Landscapes for the Congo Basin
Recent research by Hirota et al. (2011) introduced the concept of resilience landscapes for tropical forests and savannahs. Basically, the approach statistically relates the probability of current forest/savannah occurrence with the concept of tipping points, at which the ecosystem has no other choice except to switch from on stable state (e.g., forest) to its alternative stable state (e.g., savannah) or vice versa.
This work will use a biogeochemical modelling approach to establish such probabilistic resilience landscapes for the Congo Basin rainforest biome. In a first step, the occurrence of tipping points will be related to climate features like annual precipitation, dry season length, occurrence of startiform non-precipitating cloud cover and the inter-annual variation in precipitation. In the second, spatial resilience landscapes for the Congo Basin will be provided using present climate conditions. Their relation to current forest/savannah distribution will be assessed and evident congruencies and discrepancies will be discussed. In a third step, the concept of temporal resilience landscapes will be developed along the patch-level life cycle dynamics of the Congo Basin rainforest biome. In a final step, the implications of results for ecosystem management decision will be assessed and possible implications on policy and land-use decisions will be presented
Discovery of pulsations from the Be/X-ray binary RX J0101.3-7211 in the SMC by XMM-Newton
We report pulsations in the X-ray flux of RX J0101.3-7211 in the Small
Magellanic Cloud (SMC) with a period of 455+/-2 s in XMM-Newton EPIC-PN data.
The X-ray spectrum can be described by a power-law with a photon index of
0.6+/-0.1. Timing analysis of ROSAT PSPC and HRI archival data confirms the
pulsations and indicates a period increase of ~5 s since 1993. RX J0101.3-7211
varied in brightness during the ROSAT observations with timescales of years
with a maximum unabsorbed flux of 6 x 10^-13 erg cm^-2 s^-1 (0.1 - 2.4 keV).
The flux during the XMM-Newton observation in the ROSAT band was lower than
during the faintest ROSAT detection. The unabsorbed luminosity derived from the
EPIC-PN spectrum is 2 x 10^35 erg s^-1 (0.2 - 10.0 keV) assuming a distance of
60 kpc. Optical spectra of the proposed counterpart taken at the 2.3 m
telescope of MSSSO in Australia in August 2000 show strong Halpha emission and
indicate a Be star. The X-ray and optical data confirm RX J0101.3-7211 as a
Be/X-ray binary pulsar in the SMC.Comment: letter accepted by A&
Ferromagnetism or slow paramagnetic relaxation in Fe-doped LiN?
We report on isothermal magnetization, M\"ossbauer spectroscopy, and
magnetostriction as well as temperature-dependent alternating-current (ac)
susceptibility, specific heat, and thermal expansion of single crystalline and
polycrstalline Li(LiFe)N with and .
Magnetic hysteresis emerges at temperatures below K with
coercivity fields of up to T at K and magnetic
anisotropy energies of K (meV). The ac susceptibility is strongly
frequency dependent (--Hz) and reveals an effective energy
barrier for spin reversal of K. The relaxation times
follow Arrhenius behavior for K. For K, however, the
relaxation times of s are only weakly
temperature-dependent indicating the relevance of a quantum tunneling process
instead of thermal excitations. The magnetic entropy amounts to more than
J molK which significantly exceeds ln2, the
value expected for the entropy of a ground state doublet. Thermal expansion and
magnetostriction indicate a weak magneto-elastic coupling in accordance with
slow relaxation of the magnetization. The classification of
Li(LiFe)N as ferromagnet is stressed and contrasted with highly
anisotropic and slowly relaxing paramagnetic behavior.Comment: 12 pages, 10 figure
A new super-soft X-ray source in the Small Magellanic Cloud: Discovery of the first Be/white dwarf system in the SMC?
The Small Magellanic Cloud (SMC) hosts a large number of Be/X-ray binaries,
however no Be/white dwarf system is known so far, although population synthesis
calculations predict that they might be more frequent than Be/neutron star
systems. XMMUJ010147.5-715550 was found as a new faint super-soft X-ray source
(SSS) with a likely Be star optical counterpart. We investigate the nature of
this system and search for further high-absorbed candidates in the SMC. We
analysed the XMM-Newton X-ray spectrum and light curve, optical photometry, and
the I-band OGLE III light curve. The X-ray spectrum is well represented by
black-body and white dwarf atmosphere models with highly model-dependent
temperature between 20 and 100 eV. The likely optical counterpart AzV 281
showed low near infrared emission during X-ray activity, followed by a
brightening in the I-band afterwards. We find further candidates for
high-absorbed SSSs with a blue star as counterpart. We discuss
XMMUJ010147.5-715550 as the first candidate for a Be/white dwarf binary system
in the SMC.Comment: 6 pages, 4 figures, accepted by A&
J004457+4123 (Sharov 21): not a remarkable nova in M31 but a background quasar with a spectacular UV flare
We announce the discovery of a quasar behind the disk of M31, which was
previously classified as a remarkable nova in our neighbour galaxy. The paper
is primarily aimed at the outburst of J004457+4123 (Sharov 21), with the first
part focussed on the optical spectroscopy and the improvement in the
photometric database. Both the optical spectrum and the broad band spectral
energy distribution of Sharov 21 are shown to be very similar to that of
normal, radio-quiet type 1 quasars. We present photometric data covering more
than a century and resulting in a long-term light curve that is densely sampled
over the past five decades. The variability of the quasar is characterized by a
ground state with typical fluctuation amplitudes of ~0.2 mag around B~20.5,
superimposed by a singular flare of ~2 yr duration (observer frame) with the
maximum at 1992.81 where the UV flux has increased by a factor of ~20. The
total energy in the flare is at least three orders of magnitudes higher than
the radiated energy of the most luminous supernovae, provided that it comes
from an intrinsic process and the energy is radiated isotropically. The profile
of the flare light curve appears to be in agreement with the standard
predictions for a stellar tidal disruption event where a ~10 M_sun giant star
was shredded in the tidal field of a ~2...5 10^8 M_sun black hole. The short
fallback time derived from the light curve requires an ultra-close encounter
where the pericentre of the stellar orbit is deep within the tidal disruption
radius. Gravitational microlensing provides an alternative explanation, though
the probability of such a high amplification event is very low.Comment: Accepted for publication in Astronomy and Astrophysics, 14 pages, 11
figure
Diffusion of Mn interstitials in (Ga,Mn)As epitaxial layers
Magnetic properties of thin (Ga,Mn)As layers improve during annealing by
out-diffusion of interstitial Mn ions to a free surface. Out-diffused Mn atoms
participate in the growth of a Mn-rich surface layer and a saturation of this
layer causes an inhibition of the out-diffusion. We combine high-resolution
x-ray diffraction with x-ray absorption spectroscopy and a numerical solution
of the diffusion problem for the study of the out-diffusion of Mn interstitials
during a sequence of annealing steps. Our data demonstrate that the
out-diffusion of the interstitials is substantially affected by the internal
electric field caused by an inhomogeneous distribution of charges in the
(Ga,Mn)As layer.Comment: 11 pages, 5 figure
Massive Coronae of Galaxies
There is reason to suspect that about half of the baryons are in
pressure-supported plasma in the halos of normal galaxies, drawn in by gravity
along with about half of the dark matter. To be consistent with the
observations this baryonic component, the corona, would have to be hotter than
the kinetic temperature of the dark matter in the halo so as to produce
acceptable central electron densities. We ascribe this hotter plasma
temperature to the addition of entropy prior to and during assembly of the
system, in an analogy to cluster formation. The plasma cooling time would be
longer than the gravitational collapse time but, in the inner parts, shorter
than the Hubble time, making the corona thermally unstable to the formation of
a cloudy structure that may be in line with what is indicated by quasar
absorption line systems. The corona of an isolated spiral galaxy would be a
source of soft X-ray and recombination radiation, adding to the more commonly
discussed effects of stars and supernovae. In this picture the mass in the
corona is much larger than the mass in condensed baryons in a spiral galaxy.
The corona thus would be a substantial reservoir of diffuse baryons that are
settling and adding to the mass in interstellar matter and stars, so that star
formation in isolated spirals will continue well beyond the present epoch.Comment: 14 pages, 5 figure
Starburst in the Intragroup Medium of Stephan's Quintet
Based on new ISO mid-infrared observations and ground based and
near-infrared observations, we report the detection of a bright starburst in
the intragroup medium (IGM) of the famous compact group of galaxies Stephan's
Quintet (Source A in Fig.1). We demonstrate that this starburst is caused by a
collision between a high velocity (V 1000 km/sec) intruder galaxy
(NGC7318b) and the IGM of the group. While this is the only starburst known
today that is induced by a galaxy/cold-intergalactic-medium collision, it
provides new constraints to the theory for interaction-induced starbursts, and
may hint at a new mechanism for the star formation excess seen in more distant
clusters.Comment: 17 pages, 2 PS figures. Accepted by Ap
- …