1,248 research outputs found
The SMC X-ray transient XTE J0111.2-7317 : a Be/X-ray binary in a SNR?
We report observations which confirm the identity of the optical/IR
counterpart to the Rossi X-ray Timing Explorer transient source XTE
J0111.2-7317. The counterpart is suggested to be a B0-B2 star (luminosity class
III--V) showing an IR excess and strong Balmer emission lines. The distance
derived from reddening and systemic velocity measurements puts the source in
the SMC. Unusually, the source exhibits an extended asymetric H alpha
structure.Comment: 5 pages, 3 figs, accepted by MNRA
Sobre la posición sistemática del género Placogyropsis Alloiteau, 1957. (Scleractinia cretácica)
Utilizando varios topotipos de la especie tipo, se estudia el género Placogyropsis Alloiteau, 1957, inscrito por el propio Alloiteau en la familia Dendrogyriidae Alloiteau, 1952. Se sugiere que no pertenece a esta familia, sino a la familia Latomeandriidae y se propone una diagnosis del género
Sobre la posición sistemática del género Placogyropsis Alloiteau, 1957. (Scleractinia cretácica)
Utilizando varios topotipos de la especie tipo, se estudia el género Placogyropsis Alloiteau, 1957, inscrito por el propio Alloiteau en la familia Dendrogyriidae Alloiteau, 1952. Se sugiere que no pertenece a esta familia, sino a la familia Latomeandriidae y se propone una diagnosis del género
A 0535+26: Back in business
In May/June 2005, after 10 years of inactivity, the Be/X-ray binary system A
0535+26 underwent a major X-ray outburst. In this paper data are presented from
10 years of optical, IR and X-ray monitoring showing the behaviour of the
system during the quiescent epoch and the lead up to the new outburst. The
results show the system going through a period when the Be star in the system
had a minimal circumstellar disk and then a dramatic disk recovery leading,
presumably, to the latest flare up of X-ray emission. The data are interpreted
in terms of the state of the disk and its interaction with the neutron star
companion.Comment: Accepted for publication in MNRA
Bound-state dark matter with Majorana neutrinos
We propose a simple scenario in which dark matter (DM) emerges as a stable
neutral hadronic thermal relics, its stability following from an exact
symmetry. Neutrinos pick up radiatively induced
Majorana masses from the exchange of colored DM constituents. There is a common
origin for both dark matter and neutrino mass, with a lower bound for
neutrinoless double beta decay. Direct DM searches at nuclear recoil
experiments will test the proposal, which may also lead to other
phenomenological signals at future hadron collider and lepton flavour violation
experiments.Comment: 9 pages, 4 figures. arXiv admin note: text overlap with
arXiv:1803.0852
Orbital X-Ray Variability of the Microquasar LS 5039
The properties of the orbit and the donor star in the high mass X-ray binary
microquasar LS 5039 indicate that accretion processes should mainly occur via a
radiatively driven wind. In such a scenario, significant X-ray variability
would be expected due to the eccentricity of the orbit. The source has been
observed at X-rays by several missions, although with a poor coverage that
prevents to reach any conclusion about orbital variability. Therefore, we
conducted RossiXTE observations of the microquasar system LS 5039 covering a
full orbital period of 4 days. Individual observations are well fitted with an
absorbed power-law plus a Gaussian at 6.7 keV, to account for iron line
emission that is probably a diffuse background feature. In addition, we have
taken into account that the continuum is also affected by significant diffuse
background contamination. Our results show moderate power-law flux variations
on timescales of days, as well as the presence of miniflares on shorter
timescales. The new orbital ephemeris of the system recently obtained by
Casares et al. have allowed us to show, for the first time, that an increase of
emission is seen close to the periastron passage, as expected in an accretion
scenario. Moreover, the detected orbital variability is a factor of ~4 smaller
than the one expected by using a simple wind accretion model, and we suggest
that an accretion disk around the compact object could be responsible for this
discrepancy. On the other hand, significant changes in the photon index are
also observed clearly anti-correlated with the flux variations. We interpret
the overall X-ray spectral characteristics of LS 5039 in the context of X-ray
radiation produced by inverse Compton and/or synchrotron processes in the jet
of this microquasar.Comment: published in Astrophysical Journal, submission format (real number of
pages: 7, 4 figures
The Be/X-ray binary LS 992/RX J0812.4-3114: physical parameters and long-term variability
We present the first long-term optical and infrared study of the optical
counterpart to the source RX J0812.4-3114, an X-ray pulsar with a Be type
companion. During the period covered by the observations the profile of some
Balmer lines changed from absorption to emission and back again to absorption.
Contemporaneously, the infrared magnitudes varied by more than 0.8 mag. This
long-term variability is interpreted as the formation and subsequent
dissipation of the Be star's disc. The building up of the disc ended up in an
active X-ray state characterised by regular outbursts occurring at 80 day
intervals. The overall duration of the formation/dissipation of the disc is
found to be < 4.3 years. Optical spectroscopic and infrared photometric
observations were used to refine the spectral type of the primary (B0.2IV) and
to monitor the circumstellar envelope around the Be star. UBVRI and uvby\beta
photometric observations allowed the determination of the astrophysical
parameters of the optical companion.Comment: 7 pages, 3 figures, accepted for publication in A&
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