707 research outputs found
The spectacular X-ray echo of a magnetar burst
The Anomalous X-ray Pulsar (AXP) 1E 1547.0-5408 reactivated in 2009 January
with the emission of dozens of short bursts. Follow-up observations with
Swift/XRT and XMM-Newton showed the presence of multiple expanding rings around
the position of the AXP. These rings are due to scattering, by different layers
of interstellar dust, of a very high fluence burst emitted by 1E 1547.0-5408 on
2009 January 22. Thanks to the exceptional brightness of the X-ray rings, we
could carry out a detailed study of their spatial and spectral time evolution
until 2009 February 4. This analysis gives the possibility to estimate the
distance of 1E 1547.0-5408. We also derived constraints on the properties of
the dust and of the burst responsible for this rare phenomenon.Comment: Proceedings of the conference X-Ray Astronomy 2009, Present Status,
multiwavelength approach and future perspectives, September 7 - 11, 2009,
Bologna, Ital
Three new X-ray emitting sdO stars discovered with Chandra
X-ray observations of sdO stars are a useful tool to investigate their
properties, but so far only two sdO stars were detected at X-rays. We observed
a complete flux-limited sample of 19 sdO stars with the Chandra HRC-I camera to
measure the count rate of the detected sources or to set a tight upper limit on
it for the undetected sources. We obtained a robust detection of BD+37 1977 and
Feige 34 and a marginal detection of BD+28 4211. The estimated luminosity of
BD+37 1977 is above 10^31 erg/s, which is high enough to suggest the possible
presence of an accreting compact companion. This possibility is unlikely for
all the other targets (both detected and undetected), since in their case L_X <
10^30 erg/s. On the other hand, for all 19 targets the estimated value of L_X
(or its upper limit) implies an X-ray/bolometric flux ratio that agrees with
log(L_X/L_bol) = -6.7 +/- 0.5, which is the range of values typical of
main-sequence and giant O stars. Therefore, for Feige 34 and BD+28 4211 the
observed X-ray flux is most probably due to intrinsic emission. The same is
possibile for the 16 undetected stars.Comment: 6 pages. Accepted for publication by Astronomy and Astrophysic
Follow-up observations of X-ray emitting hot subdwarf star: the He-rich sdO BD +37{\deg} 1977
We report on the results of the first XMM-Newton satellite observation of the
luminous and helium-rich O-type subdwarf BD +37{\deg} 1977 carried out in April
2014. X-ray emission is detected with a flux of about 4*10^(-14) erg/cm2/s
(0.2-1.5 keV), corresponding to a f_X/f_bol ratio about 10^(-7); the source
spectrum is very soft, and is well fit by the sum of two plasma components at
different temperatures. Both characteristics are in agreement with what is
observed in the main-sequence early-type stars, where the observed X-ray
emission is due to turbulence and shocks in the stellar wind. A smaller but
still significant stellar wind has been observed also in BD +37{\deg} 1977;
therefore, we suggest that also in this case the detected X-ray flux has the
same origin.Comment: 6 pages. Accepted for publication by Astronomy and Astrophysic
Spectral properties of the soft excess pulsar RX J0059.2-7138 during its 2013 outburst
We report on an X-ray observation of the Be X-ray Binary Pulsar RX
J0059.2-7138, performed by XMM-Newton in March 2014. The 19 ks long observation
was carried out about three months after the discovery of the latest outburst
from this Small Magellanic Cloud transient, when the source luminosity was Lx ~
10 erg/s. A spin period of P=2.762383(5) s was derived, corresponding to
an average spin-up of
s from the only previous period measurement, obtained more than 20
years earlier. The time-averaged continuum spectrum (0.2-12 keV) consisted of a
hard power-law (photon index ~0.44) with an exponential cut-off at a
phase-dependent energy (20-50 keV) plus a significant soft excess below about
0.5 keV. In addition, several features were observed in the spectrum: an
emission line at 6.6 keV from highly ionized iron, a broad feature at 0.9-1 keV
likely due to a blend of Fe L-shell lines, and narrow emission and absorption
lines consistent with transitions in highly ionized oxygen, nitrogen and iron
visible in the high resolution RGS data (0.4-2.1 keV). Given the different
ionization stages of the narrow line components, indicative of photoionization
from the luminous X-ray pulsar, we argue that the soft excess in RX
J0059.2-7138 is produced by reprocessing of the pulsar emission in the inner
regions of the accretion disc.Comment: Accepted for publication in Mon. Not. R. Astron. Soc. 9 pages, 5
figure
XMM-Newton and NuSTAR simultaneous X-ray observations of IGR J11215-5952
We report the results of an XMM-Newton and NuSTAR coordinated observation of
the Supergiant Fast X-ray Transient (SFXT) IGRJ11215-5952, performed on
February 14, 2016, during the expected peak of its brief outburst, which
repeats every about 165 days. Timing and spectral analysis were performed
simultaneously in the energy band 0.4-78 keV. A spin period of 187.0 +/- 0.4 s
was measured, consistent with previous observations performed in 2007. The
X-ray intensity shows a large variability (more than one order of magnitude) on
timescales longer than the spin period, with several luminous X-ray flares
which repeat every 2-2.5 ks, some of which simultaneously observed by both
satellites. The broad-band (0.4-78 keV) time-averaged spectrum was well
deconvolved with a double-component model (a blackbody plus a power-law with a
high energy cutoff) together with a weak iron line in emission at 6.4 keV
(equivalent width, EW, of 40+/-10 eV). Alternatively, a partial covering model
also resulted in an adequate description of the data. The source time-averaged
X-ray luminosity was 1E36 erg/s (0.1-100 keV; assuming 7 kpc). We discuss the
results of these observations in the framework of the different models proposed
to explain SFXTs, supporting a quasi-spherical settling accretion regime,
although alternative possibilities (e.g. centrifugal barrier) cannot be ruled
out.Comment: 13 pages, 11 figures, accepted for publication on The Astrophysical
Journa
A study of the long term variability of RX J1856.5-3754 with XMM-Newton
We report on a detailed spectral analysis of all the available XMM-Newton
data of RX J1856.5-3754, the brightest and most extensively observed nearby,
thermally emitting neutron star. Very small variations (~1-2%) in the
single-blackbody temperature are detected, but are probably due to an
instrumental effect, since they correlate with the position of the source on
the detector. Restricting the analysis to a homogeneous subset of observations,
with the source at the same detector position, we place strong limits on
possible spectral or flux variations from March 2005 to present-day. A slightly
higher temperature (kT~61.5 eV, compared to the average value kT~61 eV) was
instead measured in April 2002. If this difference is not of instrumental
origin, it implies a rate of variation of about 0.15 eV/yr between April 2002
and March 2005. The high-statistics spectrum from the selected observations is
well fit by the sum of two blackbody models, which extrapolate to an optical
flux level in agreement with the observed value.Comment: 4 pages, to appear in the proceedings of the ERPM conference, Zielona
Gora, April 201
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