204 research outputs found
1RXS J180408.9-342058: an ultra compact X-ray binary candidate with a transient jet
We present a detailed NIR/optical/UV study of the transient low mass X-ray
binary 1RXS J180408.9-342058 performed during its 2015 outburst, aimed at
determining the nature of its companion star. We obtained three optical spectra
at the 2.1 m San Pedro Martir Observatory telescope (Mexico). We performed
optical and NIR photometric observations with both the REM telescope and the
New Technology Telescope (NTT) in La Silla. We obtained optical and UV
observations from the Swift archive. Finally, we performed optical polarimetry
of the source by using the EFOSC2 instrument mounted on the NTT. The optical
spectrum of the source is almost featureless since the hydrogen and He I
emissions lines, typically observed in LMXBs, are not detected. Similarly,
carbon and oxygen lines are neither observed. We marginally detect the He II
4686 AA emission line, suggesting the presence of helium in the accretion disc.
No significant optical polarisation level was observed. The lack of hydrogen
and He I emission lines in the spectrum implies that the companion is likely
not a main sequence star. Driven by the tentative detection of the He II 4686
AA emission line, we suggest that the system could harbour a helium white
dwarf. If this is the case, 1RXS J180408.9-342058 would be an ultra-compact
X-ray binary. By combining an estimate of the mass accretion rate together with
evolutionary tracks for a He white dwarf, we obtain a tentative orbital period
of ~ 40 min. On the other hand, we also built the NIR-optical-UV spectral
energy distribution (SED) of the source at two different epochs. One SED was
gathered when the source was in the soft X-ray state, and it is consistent with
the presence of a single thermal component. The second SED, obtained when the
source was in the hard X-ray state, shows a thermal component together with a
tail in the NIR, likely indicating the presence of a (transient) jet.Comment: 8 pages, 5 figures, 4 tables. Accepted for publication in Astronomy &
Astrophysics (Section 7
NuSTAR + XMM-Newton monitoring of the neutron star transient AX J1745.6-2901
AX J1745.6-2901 is a high-inclination (eclipsing) transient neutron star (NS)
Low Mass X-ray Binary (LMXB) showcasing intense ionised Fe K absorption. We
present here the analysis of 11 XMM-Newton and 15 NuSTAR new data-sets
(obtained between 2013-2016), therefore tripling the number of observations of
AX J1745.6-2901 in outburst. Thanks to simultaneous XMM-Newton and NuSTAR
spectra, we greatly improve on the fitting of the X-ray continuum. During the
soft state the emission can be described by a disk black body (
keV and inner disc radius km), plus hot ( keV)
black body radiation with a small emitting radius ( km)
likely associated with the boundary layer or NS surface, plus a faint
Comptonisation component. Imprinted on the spectra are clear absorption
features created by both neutral and ionised matter. Additionally, positive
residuals suggestive of an emission Fe K disc line and consistent with
relativistic ionised reflection are present during the soft state, while such
residuals are not significant during the hard state. The hard state spectra are
characterised by a hard () power law, showing no evidence
for a high energy cut off ( keV) and implying a small optical
depth (). The new observations confirm the previously witnessed trend
of exhibiting strong Fe K absorption in the soft state, that significantly
weakens during the hard state. Optical (GROND) and radio (GMRT) observations
suggest for AX J1745.6-2901 a standard broad band SED as typically observed in
accreting neutron stars.Comment: Accepted for publication in MNRA
Co-evaluation in a problem solving practice in a bioscience subject
La co-evaluación o evaluación entre pares es reconocida como una actividad que
estimula el papel activo del alumnado en el proceso de aprendizaje. Los estudiantes
tienen la oportunidad de revisar el trabajo de su compañeros de clase frente a su propia
evaluación lo que permite una reflexión sobre su proceso de aprendizaje. Como
resultado, son capaces de reorientar sus propias estrategias de apredizaje. En esta
comunicación se muestran los resultados de un ejercicio de co-evaluación llevado a
cabo con un grupo de 90 estudiantes del Grado en Biología de la Universidad de La
Laguna en el marco de un un curso general de Bioquímica con contenidos en cinética
enzimática. Aunque ninguno realizó antes co-evaluaciones, los resultados muestran
que las correcciones realizadas fueron correctas y consistentes con las de los profesoresCo-evaluation or evaluation between peers is gaining ground as a drive for the
active role of the student in the learning process. Students are given the opportunity
to review their classmate’s work, facing their own evaluation and thus reflecting of
their learning process. As a result they are able to reorient their own strategy. In
this communication we show the results of a co-evaluation exercise carried out
with a group of 90 students of a degree in Biology, within a general course of
biochemistry containing enzymology issues. Although none of them have done
co-evaluations before, results show that the corrections made were refined and
consistent with those made by teacher
Black hole mass and spin measurements through the Relativistic Precession Model: XTE J1859+226
The X-ray light curves of accreting black holes and neutron stars in binary
systems show various types of quasi-periodic oscillations (QPOs), the origin of
which is still debated. The Relativistic Precession Model identifies the QPO
frequencies with fundamental time scales from General Relativity, and has been
proposed as a possible explanation of certain types of such oscillations. Under
specific conditions (i.e., the detection of a particular QPOs triplet) such a
model can be used to obtain self-consistent measurements of the mass and spin
of the compact object. So far this has been possible only in the black hole
binary GRO J1655-40. In the RXTE/PCA data from the 1999-2000 outburst of the
black hole transient XTE J1859+226 we found a QPO triplet, and used the the
Relativistic Precession Model to obtain high-precision measurements of the
black hole mass and spin - M = (7.85+/-0.46) Msun, a* = 0.149+/-0.005 - the
former being consistent with the most recent dynamical mass determination from
optical measurements. Similarly to what has been already observed in other
black hole systems, the frequencies of the QPOs and broad-band noise components
match the general relativistic frequencies of particle motion close to the
compact object predicted by the model. Our findings confirm previous results
and further support the validity of the Relativistic Precession Model, which is
the only electromagnetic-measurement-based method that so far has consistently
yielded spins close to those from the gravitational waves produced by merging
binary black holes.Comment: 8 pages, 5 figures, accepted for publication in MNRA
Echo Tomography of Sco X-1 using Bowen Fluorescence Lines
We present preliminary results of a simultaneous X-ray/optical campaign of
the prototypical LMXB Sco X-1 at 1-10 Hz time resolution. Lightcurves of the
high excitation Bowen/HeII emission lines were obtained through narrow
interference filters with ULTRACAM, and these were cross-correlated with X-ray
lightcurves. We find evidence for correlated variability, in particular when
Sco X-1 enters the Flaring Branch. The Bowen/HeII lightcurves lag the X-ray
lightcurves with a light travel time which is consistent with reprocessing in
the companion star.Comment: Contribution presented at the conference "Interacting Binaries:
Accretion, Evolution and Outcomes", held in Cefalu, Sicily (Italy) in July
2004. To be published by AIP (American Institute of Physics), eds. L. A.
Antonelli, L. Burderi, F. D'Antona, T. Di Salvo, G.L. Israel, L. Piersanti,
O. Straniero, A. Tornambe. 6 pages, 5 figure
Evidence for a black hole in the historical X-ray transient A 1524-61 (=KY TrA)
We present VLT spectroscopy, high-resolution imaging and time-resolved
photometry of KY TrA, the optical counterpart to the X-ray binary A 1524-61. We
perform a refined astrometry of the field, yielding improved coordinates for KY
TrA and the field star interloper of similar optical brightness that we locate
arcsec SE. From the spectroscopy, we refine the radial velocity
semi-amplitude of the donor star to km s by employing
the correlation between this parameter and the full-width at half-maximum of
the H emission line. The -band light curve shows an ellipsoidal-like
modulation with a likely orbital period of d (
h). These numbers imply a mass function M. The
KY TrA de-reddened quiescent colour is consistent
with a donor star of spectral type K2 or later, in case of significant
accretion disc light contribution to the optical continuum. The colour allows
us to place a very conservative upper limit on the companion star mass, M, and, in turn, on the binary mass ratio, . By exploiting the correlation between the binary inclination and the
depth of the H line trough, we establish deg. All these
values lead to a compact object and donor mass of
M and M, respectively, thus confirming the
black hole nature of the accreting object. In addition, we estimate a distance
toward the system of kpc.Comment: 7 pages, 5 figure
First Results from Fermi GBM Earth Occultation Monitoring: Observations of Soft Gamma-Ray Sources Above 100 keV
The NaI and BGO detectors on the Gamma-ray Burst Monitor (GBM) on Fermi are
now being used for long-term monitoring of the hard X-ray/low energy gamma-ray
sky. Using the Earth occultation technique as demonstrated previously by the
BATSE instrument on the Compton Gamma-Ray Observatory, GBM can be used to
produce multiband light curves and spectra for known sources and transient
outbursts in the 8 keV to 1 MeV energy range with its NaI detectors and up to
40 MeV with its BGO detectors. Over 85% of the sky is viewed every orbit, and
the precession of the Fermi orbit allows the entire sky to be viewed every ~26
days with sensitivity exceeding that of BATSE at energies below ~25 keV and
above ~1.5 MeV. We briefly describe the technique and present preliminary
results using the NaI detectors after the first two years of observations at
energies above 100 keV. Eight sources are detected with a significance greater
than 7 sigma: the Crab, Cyg X-1, SWIFT J1753.5-0127, 1E 1740-29, Cen A, GRS
1915+105, and the transient sources XTE J1752-223 and GX 339-4. Two of the
sources, the Crab and Cyg X-1, have also been detected above 300 keV.Comment: 13 pages, 9 figures, submitted to Ap
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