756 research outputs found
Circinus X-1: survivor of a highly asymmetric supernova
We have analyzed the kinematical parameters of Cir X-1 to constrain the
nature of its companion star, the eccentricity of the binary and the
pre-supernova parameter space. We argue that the companion is most likely to be
a low-mass (< 2.0 M_sun) unevolved star and that the eccentricity of the orbit
is 0.94 +/- 0.04. We have evaluated the dynamical effects of the supernova
explosion and we find it must have been asymmetric. On average, we find that a
kick of 740 km/s is needed to account for the recently measured radial velocity
of +430 km/s (Johnston, Fender & Wu) for this extreme system. The corresponding
minimum kick velocity is 500 km/s. This is the largest kick needed to explain
the motion of any observed binary system. If Cir X-1 is associated with the
supernova remnant G321.9-0.3 then we find a limiting minimum age of this
remnant of 60000 yr. Furthermore, we predict that the companion star has lost
10% of its mass as a result of stripping and ablation from the impact of the
supernova shell shortly after the explosion.Comment: 6 pages, 3 figues, 2 tables, accepted for publication in MNRA
Time-resolved optical/near-IR polarimetry of V404 Cyg during its 2015 outburst
We present optical and near-IR linear polarimetry of V404 Cyg during its 2015
outburst and in quiescence. We obtained time resolved r'-band polarimetry when
the source was in outburst, near-IR polarimetry when the source was near
quiescence and multiple wave-band optical polarimetry later in quiescence. The
optical to near-IR linear polarization spectrum can be described by
interstellar dust and an intrinsic variable component. The intrinsic optical
polarization, detected during the rise of one of the brightest flares of the
outburst, is variable, peaking at 4.5 per cent and decaying to 3.5 per cent. We
present several arguments that favour a synchrotron jet origin to this variable
polarization, with the optical emission originating close to the jet base. The
polarization flare occurs during the initial rise of a major radio flare event
that peaks later, and is consistent with a classically evolving synchrotron
flare from an ejection event. We conclude that the optical polarization flare
represents a jet launching event; the birth of a major ejection. For this event
we measure a rather stable polarization position angle of -9 degrees E of N,
implying that the magnetic field near the base of the jet is approximately
perpendicular to the jet axis. This may be due to the compression of magnetic
field lines in shocks in the accelerated plasma, resulting in a partially
ordered transverse field that have now been seen during the 2015 outburst. We
also find that this ejection occurred at a similar stage in the repetitive
cycles of flares.Comment: 9 pages, 5 figures, accepted for publication by MNRA
A Comparison of Intermediate Mass Black Hole Candidate ULXs and Stellar-Mass Black Holes
Cool thermal emission components have recently been revealed in the X-ray
spectra of a small number of ultra-luminous X-ray (ULX) sources with L_X > 1
E+40 erg/s in nearby galaxies. These components can be well fitted with
accretion disk models, with temperatures approximately 5-10 times lower than
disk temperatures measured in stellar-mass Galactic black holes when observed
in their brightest states. Because disk temperature is expected to fall with
increasing black hole mass, and because the X-ray luminosity of these sources
exceeds the Eddington limit for 10 Msun black holes (L_Edd = 1.3 E+39 erg/s),
these sources are extremely promising intermediate-mass black hole candidates
(IMBHCs). In this Letter, we directly compare the inferred disk temperatures
and luminosities of these ULXs, with the disk temperatures and luminosities of
a number of Galactic black holes. The sample of stellar-mass black holes was
selected to include different orbital periods, companion types, inclinations,
and column densities. These ULXs and stellar-mass black holes occupy distinct
regions of a L_X -- kT diagram, suggesting these ULXs may harbor IMBHs. We
briefly discuss the important strengths and weaknesses of this interpretation.Comment: 4 pages, 2 color figures, uses emulateapj.sty and apjfonts.sty, subm.
to ApJ
The "universal" radio/X-ray flux correlation : the case study of the black hole GX 339-4
The existing radio and X-ray flux correlation for Galactic black holes in the
hard and quiescent states relies on a sample which is mostly dominated by two
sources (GX 339-4 and V404 Cyg) observed in a single outburst. In this paper,
we report on a series of radio and X-ray observations of the recurrent black
hole GX 339-4 with the Australia Telescope Compact Array, the Rossi X-ray
Timing Explorer and the Swift satellites. With our new long term campaign, we
now have a total of 88 quasi-simultaneous radio and X-ray observations of GX
339-4 during its hard state, covering a total of seven outbursts over a
15--year period. Our new measurements represent the largest sample for a
stellar mass black hole, without any bias from distance uncertainties, over the
largest flux variations and down to a level that could be close to quiescence,
making GX 339-4 the reference source for comparison with other accreting
sources (black holes, neutrons stars, white dwarfs and active galactic nuclei).
Our results demonstrate a very strong and stable coupling between radio and
X-ray emission, despite several outbursts of different nature and separated by
a period of quiescence. The radio and X-ray luminosity correlation of the form
L_X ~L_Rad^0.62 +/-0.01 confirms the non-linear coupling between the jet and
the inner accretion flow powers and better defines the standard correlation
track in the radio-X-ray diagram for stellar mass black holes. We further note
epochs of deviations from the fit that significantly exceed the measurement
uncertainties, especially during the formation and destruction of the compact
jets ...[abridged]. We incorporated our new data in a more global study of
black hole candidates strongly supporting a scale invariance in the
jet-accretion coupling of accreting black holes, and confirms the existence of
two populations of sources in the radio/X-ray diagram.Comment: Paper accepted in MNRAS. 18 pages, 9 figure
The large-scale jet-powered radio nebula of Circinus X-1
We present multi-epoch observations of the radio nebula around the neutron
star X-ray binary Circinus X-1 made at 1.4 and 2.5 GHz with the Australia
Telescope Compact Array between October 2000 and September 2004. The nebula can
be seen as a result of the interaction between the jet from the system and the
interstellar medium and it is likely that we are actually looking toward the
central X-ray binary system through the jet-powered radio lobe. The study of
the nebula thus offers a unique opportunity to estimate for the first time
using calorimetry the energetics of a jet from an object clearly identified as
a neutron star. An extensive discussion on the energetics of the complex is
presented: a first approach is based on the minimum energy estimation, while a
second one employs a self-similar model of the interaction between the jets and
the surrounding medium. The results suggest an age for the nebula of \leq 10^5
years and a corresponding time-averaged jet power \geq 10^{35} erg s^{-1}.
During periodic flaring episodes, the instantaneous jet power may reach values
of similar magnitude to the X-ray luminosity.Comment: Accepted to MNRA
The infrared/X-ray correlation of GX 339-4: Probing hard X-ray emission in accreting black holes
GX 339-4 has been one of the key sources for unravelling the accretion
ejection coupling in accreting stellar mass black holes. After a long period of
quiescence between 1999 and 2002, GX 339-4 underwent a series of 4 outbursts
that have been intensively observed by many ground based observatories [radio,
infrared(IR), optical] and satellites (X-rays). Here, we present results of
these broad-band observational campaigns, focusing on the optical-IR
(OIR)/X-ray flux correlations over the four outbursts. We found tight OIR/X-ray
correlations over four decades with the presence of a break in the IR/X-ray
correlation in the hard state. This correlation is the same for all four
outbursts. This can be interpreted in a consistent way by considering a
synchrotron self-Compton origin of the X-rays in which the break frequency
varies between the optically thick and thin regime of the jet spectrum. We also
highlight the similarities and differences between optical/X-ray and IR/X-ray
correlations which suggest a jet origin of the near-IR emission in the hard
state while the optical is more likely dominated by the blackbody emission of
the accretion disc in both hard and soft state. However we find a non
negligible contribution of 40 per cent of the jet emission in the V-band during
the hard state.
We finally concentrate on a soft-to-hard state transition during the decay of
the 2004 outburst by comparing the radio, IR, optical and hard X-rays light
curves. It appears that unusual delays between the peak of emission in the
different energy domains may provide some important constraints on jet
formation scenario.Comment: Accepted for publication in MNRAS, 12 pages, 8 figure
Radio / X-ray correlation in the low/hard state of GX 339--4
We present the results of a long-term study of the black hole candidate GX
339-4 using simultaneous radio (from the Australia Telescope Compact Array) and
X-ray (from the Rossi X-ray Timing Explorer and BeppoSAX) observations
performed between 1997 and 2000. We find strong evidence for a correlation
between these two emission regimes that extends over more than three decades in
X-ray flux, down to the quiescence level of GX 339-4. This is the strongest
evidence to date for such strong coupling between radio and X-ray emission. We
discuss these results in light of a jet model that can explain the radio/X-ray
correlation. This could indicate that a significant fraction of the X-ray flux
that is observed in the low-hard state of black hole candidates may be due to
optically thin synchrotron emission from the compact jet.Comment: 8 pages. Accepted for publication in Astronomy & Astrophysics, 200
Cygnus X-3 with ISO: investigating the wind
We observed the energetic binary Cygnus X-3 in both quiescent and flaring
states between 4 and 16 microns using the ISO satellite. We find that the
quiescent source shows the thermal free-free spectrum typical of a hot, fast
stellar wind, such as from a massive helium star. The quiescent mass-loss rate
due to a spherically symmetric, non-accelerating wind is found to be in the
range 0.4-2.9 x 10E-4 solar masses per year, consistent with other infrared and
radio observations, but considerably larger than the 10E-5 solar masses per
year deduced from both the orbital change and the X-ray column density. There
is rapid, large amplitude flaring at 4.5 and 11.5 microns at the same time as
enhanced radio and X-ray activity, with the infrared spectrum apparently
becoming flatter in the flaring state. We believe non-thermal processes are
operating, perhaps along with enhanced thermal emission.Comment: Accepted for publication in MNRAS, 11 pages, 6 figure
Limits on the quiescent radio emission from the black hole binaries GRO J1655-40 and XTE J1550-564
We present the results of radio observations of the black hole binaries GRO
J1655-40 and XTE J1550-564 in quiescence, with the upgraded Australia Telescope
Compact Array. Neither system was detected. Radio flux density upper limits (3
sigma) of 26 micro Jy (at 5.5 GHz), 47 micro Jy (at 9 GHz) for GRO J1655-40,
and 1.4 mJy (at 1.75 GHz), 27 micro Jy (at 5.5 GHz), 47 micro Jy (at 9 GHz) for
XTE J1550-564 were measured. In conjunction with quasi-simultaneous Chandra
X-ray observations (in the case of GRO J1655-40) and Faulkes Telescope optical
observations (XTE J1550-564) we find that these systems provide the first
evidence of relatively `radio quiet' black hole binaries at low luminosities;
indicating that the scatter observed in the hard state X-ray:radio correlation
at higher luminosities may also extend towards quiescent levels.Comment: Accepted for publication in MNRA
Classification of Multiwavelength Transients with Machine Learning
With the advent of powerful telescopes such as the Square Kilometer Array and
the Vera C. Rubin Observatory, we are entering an era of multiwavelength
transient astronomy that will lead to a dramatic increase in data volume.
Machine learning techniques are well suited to address this data challenge and
rapidly classify newly detected transients. We present a multiwavelength
classification algorithm consisting of three steps: (1) interpolation and
augmentation of the data using Gaussian processes; (2) feature extraction using
wavelets; and (3) classification with random forests. Augmentation provides
improved performance at test time by balancing the classes and adding diversity
into the training set. In the first application of machine learning to the
classification of real radio transient data, we apply our technique to the
Green Bank Interferometer and other radio light curves. We find we are able to
accurately classify most of the 11 classes of radio variables and transients
after just eight hours of observations, achieving an overall test accuracy of
78 percent. We fully investigate the impact of the small sample size of 82
publicly available light curves and use data augmentation techniques to
mitigate the effect. We also show that on a significantly larger simulated
representative training set that the algorithm achieves an overall accuracy of
97 percent, illustrating that the method is likely to provide excellent
performance on future surveys. Finally, we demonstrate the effectiveness of
simultaneous multiwavelength observations by showing how incorporating just one
optical data point into the analysis improves the accuracy of the worst
performing class by 19 percent.Comment: 16 pages, 12 figure
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