744 research outputs found
Swift J1357.2-0933: the faintest black hole?
Swift J1357.2-0933 is the first confirmed very faint black hole X-ray
transient and has a short estimated orbital period of 2.8 hr. We observed Swift
J1357.2-0933 for ~50 ks with XMM-Newton in 2013 July during its quiescent
state. The source is clearly detected at a 0.5-10 keV unabsorbed flux of
~3x10^-15 erg cm-2 s-1. If the source is located at a distance of 1.5 kpc (as
suggested in the literature), this would imply a luminosity of ~8x10^29 erg
s-1, making it the faintest detected quiescent black hole LMXB. This would also
imply that there is no indication of a reversal in the quiescence X-ray
luminosity versus orbital period diagram down to 2.8 hr, as has been predicted
theoretically and recently supported by the detection of the 2.4 hr orbital
period black hole MAXI J1659-152 at a 0.5-10 keV X-ray luminosity of ~ 1.2 x
10^31 erg s-1. However, there is considerable uncertainty in the distance of
Swift J1357.2-0933 and it may be as distant as 6 kpc. In this case, its
quiescent luminosity would be Lx ~ 1.3 x 10^31 erg s-1, i.e., similar to MAXI
J1659-152 and hence it would support the existence of such a bifurcation
period. We also detected the source in optical at r' ~22.3 mag with the
Liverpool telescope, simultaneously to our X-ray observation. The X-ray/optical
luminosity ratio of Swift J1357.2-0933 agrees with the expected value for a
black hole at this range of quiescent X-ray luminosities.Comment: 5 pages, 3 figures, Accepted for publication in MNRA
Radiatively-Driven Outflows and Avoidance of Common-Envelope Evolution in Close Binaries
Recent work on Cygnus X-2 suggests that neutron-star or black-hole binaries
survive highly super-Eddington mass transfer rates without undergoing
common-envelope evolution. We suggest here that the accretion flows in such
cases are radiation pressure-dominated versions of the "ADIOS" picture proposed
by Blandford and Begelman (1999), in which almost all the mass is expelled from
large radii in the accretion disk. We estimate the maximum radius from which
mass loss is likely to occur, and show that common-envelope evolution is
probably avoided in any binary in which a main-sequence donor transfers mass on
a thermal timescale to a neutron star or black hole, even though the mass
transfer rate may reach values of 0.001 solar masses per year. This conclusion
probably applies also to donors expanding across the Hertzsprung gap, provided
that their envelopes are radiative. SS433 may be an example of a system in this
state.Comment: 4 pages, submitted to Astrophysical Journal Letters, 26 March 199
A Flare of AE Aquarii Observed with XMM-Newton
We present the results of analyzing the XMM-Newton data obtained in 2001
November 7 - 8. A flare is observed simultaneously in X-ray and UV together
with a quiescence. We find that during the flare event X-ray flux varies with
UV with no significant time lag, indicating a close correlation of flux
variation for X-ray and UV flares. An upper limit of the lag is estimated to be
\~1 min. From a timing analysis for X-ray data, we find that both pulsed and
unpulsed flux increase clearly as the flare advances in the entire energy band
0.15 - 10 keV. The net increase of pulsed flux to the quiescence is, however,
small and corresponds to about 3 - 4% of the increase in unpulsed flux,
confirming that a flux variation of flare in AE Aqr is dominated by unpulsed
X-rays. A spectral analysis reveals that the energy spectrum is similar to that
of the quiescence at the beginning of the flare, but the spectrum becomes
harder as the flare advances. Based on these results, we discuss the current
issues that need to be clarified, e.g., the possible flaring site and the mass
accretion problem of the white dwarf. We also discuss the flare properties
obtained in this study.Comment: 15 pages, 3 tables, 9 figures, accepted for publication in Ap
Implications of X-Ray Line Variations for 4U1822-371
4U 1822-371 is one of the proto-type accretion disk coronal sources with an
orbital period of about 5.6 hours. The binary is viewed almost edge-on at a
high inclination angle of 83 degrees, which makes it a unique candidate to
study binary orbital and accretion disk dynamics in high powered X-ray sources.
We observed the X-ray source in 4U 1822-371 with the Chandra High Energy
Transmission Grating Spectrometer (HETGS) for almost nine binary orbits. X-ray
eclipse times provide an update of the orbital ephemeris. We find that our
result follows the quadratic function implied by previous observations;
however, it suggests a flatter trend. Detailed line dynamics also confirm a
previous suggestion that the observed photo-ionized line emission originates
from a confined region in the outer edge of the accretion disk near the hot
spot. Line properties allow us to impose limits on the size of accretion disk,
the central corona, and the emission region. The photo-ionized plasma is
consistent with ionization parameters of log(xi) > 2, and when combined with
disk size and reasonable assumptions for the plasma density, this suggests
illuminating disk luminosities which are over an order of magnitude higher than
what is actually observed. That is, we do not directly observe the central
emitting X-ray source. The spectral continua are best fit by a flat power law
with a high energy cut-off and partial covering absorption (N_H ranging from
5.4-6.3x10^{22} cm^{-2}) with a covering fraction of about 50%. We discuss some
implications of our findings with respect to the photo-ionized line emission
for the basic properties of the X-ray source.Comment: Submitted to the Astrophysical Journa
The "K-Correction" for Irradiated Emission Lines in LMXBs: Evidence for a Massive Neutron Star in X1822-371 (V691 CrA)
We study the K-correction for the case of emission lines formed in the X-ray
illuminated atmosphere of a Roche lobe filling star. We compute the
K-correction as function of the mass ratio 'q' and the disc flaring angle
'alpha' using a compact binary code where the companion's Roche lobe is divided
into 10^5 resolution elements. We also study the effect of the inclination
angle in the results. We apply our model to the case of the neutron star
low-mass X-ray binary X1822-371 (V691 CrA), where a K-emission velocity
K_em=300 +-8 km/s has been measured by Casares et al. (2003). Our numerical
results, combined with previous determination of system parameters, yields
1.61Msun < M_NS < 2.32Msun and 0.44Msun < M_2 < 0.56Msun for the two binary
components(i. e. 0.24 < q < 0.27), which provide a compelling evidence for a
massive neutron star in this system. We also discuss the implications of these
masses into the evolutionary history of the binary.Comment: 6 pages, 5 figures. Accepted for publication in Ap
Impact of the orbital uncertainties on the timing of pulsars in binary systems
The detection of pulsations from an X-ray binary is an unambiguous signature
of the presence of a neutron star in the system. When the pulsations are missed
in the radio band, their detection at other wavelengths, like X-ray or
gamma-rays, requires orbital demodulation, since the length of the observations
are often comparable to, or longer than the system orbital period. The detailed
knowledge of the orbital parameters of binary systems plays a crucial role in
the detection of the spin period of pulsars, since any uncertainty in their
determination translates into a loss in the coherence of the signal during the
demodulation process. In this paper, we present an analytical study aimed at
unveiling how the uncertainties in the orbital parameters might impact on
periodicity searches. We find a correlation between the power of the signal in
the demodulated arrival time series and the uncertainty in each of the orbital
parameters. This correlation is also a function of the pulsar frequency. We
test our analytical results with numerical simulations, finding good agreement
between them. Finally, we apply our study to the cases of LS 5039 and LS I +61
303 and consider the current level of uncertainties in the orbital parameters
of these systems and their impact on a possible detection of a hosted pulsar.
We also discuss the possible appearance of a sideband ambiguity in real data.
The latter can occur when, due to the use of uncertain orbital parameters, the
power of a putative pulsar is distributed in frequencies lying nearby the
pulsar period. Even if the appearance of a sideband is already a signature of a
pulsar component, it may introduce an ambiguity in the determination of its
period. We present here a method to solve the sideband issue.Comment: Accepted 2012 September 08 by MNRAS. The paper contains 18 figures
and 5 table
A Black Hole of > 6 Solar Masses in the X-ray Nova XTE J1118+480
Observations of the quiescent X-ray nova XTE J1118+480 with the new 6.5-m MMT
have revealed that the velocity amplitude of the dwarf secondary is 698 +/- 14
km/s and the orbital period of the system is 0.17013 +/- 0.00010 d. The implied
value of the mass function, f(M) = 6.00 +/- 0.36 solar masses, provides a hard
lower limit on the mass of the compact primary that greatly exceeds the maximum
allowed mass of a neutron star. Thus we conclude that the compact primary is a
black hole. Among the eleven dynamically established black-hole X-ray novae,
the large mass function of XTE J1118+480 is rivaled only by that of V404 Cyg.
We estimate that the secondary supplies 34% +/- 8% of the total light at 5900A
and that its spectral type is in the range K5V to M1V. A double-humped I-band
light curve is probably due to ellipsoidal modulation, although this
interpretation is not entirely secure because of an unusual 12-minute offset
between the spectroscopic and photometric ephemerides. Assuming that the light
curve is ellipsoidal, we present a provisional analysis which indicates that
the inclination of the system is high and the mass of the black hole is
correspondingly modest. The broad Balmer emission lines (FWHM = 2300-2900 km/s)
also suggest a high inclination. For the range of spectral types given above,
we estimate a distance of 1.8 +/- 0.6 kpc.Comment: 4 pages, 2 figures, to appear in ApJ Letters; Minor changes to Fig 1
Recovery of the X-Ray Transient QX Nor (=X1608-52) in Outburst and Quiescence
We present optical and near-IR observations of QX Nor, the counterpart to the
recurrent soft X-ray transient X1608-52, after its reappearance following the
X-ray outburst in February 1996. The object has been seen only once before,
during an X-ray outburst in 1977. Data from 3-5 months after the outburst show
the counterpart at a mean magnitude of R=20.2 and variable on timescales of
days. A comparison with identical observations in 1995 implies that the object
has brightened by at least 1.8 mag in R following the X-ray outburst. We also
detected QX Nor in the IR in both quiescence and outburst. A faint source is
visible in the J but not the R band in May 1995. These first observations in
the quiescent state yield magnitudes and colors consistent with optical
emission from a low mass companion in the binary system, as is true in other
soft X-ray transients.Comment: 10 pages including 4 figures and 2 tables; Uses AASTeX 4.0; Accepted
for publication in The Astrophysical Journal, Volume 485, August 20, 199
Polarised infrared emission from X-ray binary jets
Near-infrared (NIR) and optical polarimetric observations of a selection of
X-ray binaries are presented. The targets were observed using the Very Large
Telescope and the United Kingdom Infrared Telescope. We detect a significant
level (3 sigma) of linear polarisation in four sources. The polarisation is
found to be intrinsic (at the > 3 sigma level) in two sources; GRO J1655-40 (~
4-7% in H and Ks-bands during an outburst) and Sco X-1 (~ 0.1-0.9% in H and K),
which is stronger at lower frequencies. This is likely to be the signature of
optically thin synchrotron emission from the collimated jets in these systems,
whose presence indicates a partially-ordered magnetic field is present at the
inner regions of the jets. In Sco X-1 the intrinsic polarisation is variable
(and sometimes absent) in the H and K-bands. In the J-band (i.e. at higher
frequencies) the polarisation is not significantly variable and is consistent
with an interstellar origin. The optical light from GX 339-4 is also polarised,
but at a level and position angle consistent with scattering by interstellar
dust. The other polarised source is SS 433, which has a low level (0.5-0.8%) of
J-band polarisation, likely due to local scattering. The NIR counterparts of
GRO J0422+32, XTE J1118+480, 4U 0614+09 and Aql X-1 (which were all in or near
quiescence) have a linear polarisation level of < 16% (3 sigma upper limit,
some are < 6%). We discuss how such observations may be used to constrain the
ordering of the magnetic field close to the base of the jet in such systems.Comment: Accepted to be published in MNRAS; 13 pages, 6 figure
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