342 research outputs found
Physical properties of the gamma-ray binary LS 5039 through low and high frequency radio observations
We have studied in detail the 0.15-15 GHz radio spectrum of the gamma-ray
binary LS 5039 to look for a possible turnover and absorption mechanisms at low
frequencies, and to constrain the physical properties of its emission. We have
analysed two archival VLA monitorings, all the available archival GMRT data and
a coordinated quasi-simultaneous observational campaign conducted in 2013 with
GMRT and WSRT. The data show that the radio emission of LS 5039 is persistent
on day, week and year timescales, with a variability at all
frequencies, and no signature of orbital modulation. The obtained spectra
reveal a power-law shape with a curvature below 5 GHz and a turnover at
GHz, which can be reproduced by a one-zone model with synchrotron
self-absorption plus Razin effect. We obtain a coherent picture for a size of
the emitting region of , setting a magnetic field of
, an electron density of and a mass-loss rate of . These values imply a significant mixing of the stellar wind with the
relativistic plasma outflow from the compact companion. At particular epochs
the Razin effect is negligible, implying changes in the injection and the
electron density or magnetic field. The Razin effect is reported for first time
in a gamma-ray binary, giving further support to the young non-accreting pulsar
scenario.Comment: 16 pages, 9 figures, accepted for publication in MNRA
Towards the origin of the radio emission in AR Sco, the first radio-pulsing white dwarf binary
The binary system AR Sco contains an M star and the only known radio-pulsing
white dwarf. The system shows emission from radio to X-rays, likely dominated
by synchrotron radiation. The mechanism that produces most of this emission
remains unclear. Two competing scenarios have been proposed: Collimated
outflows, and direct interaction between the magnetospheres of the white dwarf
and the M star. The two proposed scenarios can be tested via very long baseline
interferometric radio observations. We conducted a radio observation with the
Australian Long Baseline Array (LBA) on 20 Oct 2016 at 8.5 GHz to study the
compactness of the radio emission. Simultaneous data with the Australian
Telescope Compact Array (ATCA) were also recorded for a direct comparison of
the obtained flux densities. AR Sco shows radio emission compact on
milliarcsecond angular scales (, or $4\
\mathrm{R_{\odot}}\approx 6.5\ \mathrm{mJy}$. A comparison with the simultaneous ATCA
data shows that no flux is resolved out on mas scales, implying that the radio
emission is produced in this compact region. Additionally, the obtained radio
light curves on hour timescales are consistent with the optical light curve.
The radio emission in AR Sco is likely produced in the magnetosphere of the M
star or the white dwarf, and we see no evidence for a radio outflow or
collimated jets significantly contributing to the radio emission.Comment: 4 pages, 2 figures, accepted for publication in A&
Refining the origins of the gamma-ray binary 1FGL J1018.6-5856
Gamma-ray binaries are systems composed of a massive star and a compact
object that exhibit emission from radio to very high energy gamma rays. They
are ideal laboratories to study particle acceleration and a variety of physical
processes that vary as a function of the orbital phase. We aim to study the
radio emission of the gamma-ray binary 1FGL J1018.6-5856 to constrain the
emitting region and determine the peculiar motion of the system within the
Galaxy to clarify its origin by analyzing an observation with the Australian
Long Baseline Array at 8.4~GHz. We combined these data with the optical Gaia
DR2 and UCAC4 catalogs to consolidate the astrometry information therein. 1FGL
J1018.6-5856 shows compact radio emission ( mas or au at
kpc distance), implying a brightness temperature of K, and confirming its nonthermal origin. We report consistent
results between the proper motion reported by Gaia DR2 and the positions
obtained from the Gaia, UCAC4, and LBA data. We also determined the distance to
1FGL J1018.6-5856 to be kpc. Together with the radial
velocity of the source we computed its three-dimensional proper and peculiar
motion within the Galaxy. We obtained a peculiar motion on its regional
standard of rest (RSR) frame of km s, with the
system moving away from the Galactic plane. In the simplest scenario of a
symmetric stellar core collapse we estimate a mass loss of M during the creation of the compact object. 1FGL
J1018.6-5856 exhibits compact radio emission similar to that detected in other
gamma-ray binaries. We provide the first accurate peculiar motion estimations
of the system and place it within the Galaxy. The obtained motion and distance
excludes its physical relation with the supernova remnant G284.3-1.8.Comment: 8 pages, 7 figures, Accepted for publication by A&
Discovering the colliding wind binary HD 93129A
HD 93129A is a binary system including an O2 If+ and probably an O3.5 V-star orbiting at a distance of about 140 AU (55 mas given the distance of 2.5 kpc), which potentially makes the system the most massive one in the Galaxy, ahead of eta-Carina. Its non-thermal radio emission was proposed to be originated by the collision between the winds of both stars. HST/FGS data have been reanalyzed to derive an accurate absolute position of the stars to compare them with the radio emission. The analysis of ATCA radio observations along several years reveals a power-lawspectrum with an increase on the radio flux density along time. We conducted an observation with the Australian Long Baseline Array (LBA) at 2.3 GHz in 2008 to resolve the radio source and its location within the stellar system. These radio data revealed a bow-shape extended emissionlocated between both stars, as expected in a wind collision region. The observed structure allows us to roughly estimate the mass-loss rate ratio for the two stars in the system, concluding that dM_b/dt = 0.7 dM_a/dt. The multiwavelength analysis points out that the detected radio emission is likely to be originated by one of the most massive collision wind binary in the Galaxy.Fil: Marcote, B.. Universidad de Barcelona; EspañaFil: Benaglia, Paula. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones CientÃficas. Instituto Argentino de RadioastronomÃa. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Centro CientÃfico Tecnológico Conicet - La Plata. Instituto Argentino de RadioastronomÃa; ArgentinaFil: Moldon, J.. Netherlands Institute for Radio Astronomy; PaÃses BajosFil: Nelan, E.. Space Telescope Science Institute; Estados UnidosFil: De Becker, M.. Université de Liège; BélgicaFil: Dougherty, S, M.. NRC Herzberg Astronomy And Astrophysics; CanadáFil: Koribalski, Bärbel. Australia Telescope National Facility; Australia12th European VLBI Network Symposium and Users MeetingCagliariItaliaIstituto di Radioastronomi
Orbital and superorbital variability of LS I +61 303 at low radio frequencies with GMRT and LOFAR
LS I +61 303 is a gamma-ray binary that exhibits an outburst at GHz
frequencies each orbital cycle of 26.5 d and a superorbital
modulation with a period of 4.6 yr. We have performed a detailed
study of the low-frequency radio emission of LS I +61 303 by analysing all the
archival GMRT data at 150, 235 and 610 MHz, and conducting regular LOFAR
observations within the Radio Sky Monitor (RSM) at 150 MHz. We have detected
the source for the first time at 150 MHz, which is also the first detection of
a gamma-ray binary at such a low frequency. We have obtained the light-curves
of the source at 150, 235 and 610 MHz, all of them showing orbital modulation.
The light-curves at 235 and 610 MHz also show the existence of superorbital
variability. A comparison with contemporaneous 15-GHz data shows remarkable
differences with these light-curves. At 15 GHz we see clear outbursts, whereas
at low frequencies we see variability with wide maxima. The light-curve at 235
MHz seems to be anticorrelated with the one at 610 MHz, implying a shift of
0.5 orbital phases in the maxima. We model the shifts between the maxima
at different frequencies as due to changes in the physical parameters of the
emitting region assuming either free-free absorption or synchrotron
self-absorption, obtaining expansion velocities for this region close to the
stellar wind velocity with both mechanisms.Comment: 12 pages, 10 figures, accepted for publication in MNRA
Detection of Bursts from FRB 121102 with the Effelsberg 100-m Radio Telescope at 5 GHz and the Role of Scintillation
FRB 121102, the only repeating fast radio burst (FRB) known to date, was
discovered at 1.4 GHz and shortly after the discovery of its repeating nature,
detected up to 2.4 GHz. Here we present three bursts detected with the 100-m
Effelsberg radio telescope at 4.85 GHz. All three bursts exhibited frequency
structure on broad and narrow frequency scales. Using an autocorrelation
function analysis, we measured a characteristic bandwidth of the small-scale
structure of 6.41.6 MHz, which is consistent with the diffractive
scintillation bandwidth for this line of sight through the Galactic
interstellar medium (ISM) predicted by the NE2001 model. These were the only
detections in a campaign totaling 22 hours in 10 observing epochs spanning five
months. The observed burst detection rate within this observation was
inconsistent with a Poisson process with a constant average occurrence rate;
three bursts arrived in the final 0.3 hr of a 2 hr observation on 2016 August
20. We therefore observed a change in the rate of detectable bursts during this
observation, and we argue that boosting by diffractive interstellar
scintillations may have played a role in the detectability. Understanding
whether changes in the detection rate of bursts from FRB 121102 observed at
other radio frequencies and epochs are also a product of propagation effects,
such as scintillation boosting by the Galactic ISM or plasma lensing in the
host galaxy, or an intrinsic property of the burst emission will require
further observations.Comment: Accepted to ApJ. Minor typos correcte
On the nature of FRB 150418:clues to its nature from European VLBI Network and e-MERLIN observations
We investigate the nature of the compact, and possibly variable nuclear radio
source in the centre of WISE J0716-19, the proposed host galaxy of fast radio
burst, FRB 150418. We observed WISE J0716-19 at 5.0 GHz with the European VLBI
Network four times between 2016 March 16 and June 2. At three epochs, we
simultaneously observed the source with e-MERLIN at the same frequency. We
detected a compact source in the EVN data in each epoch with a significance up
to ~8sigma. The four epochs yielded consistent results within their
uncertainties, for both peak surface intensity and positions. The mean values
for these quantities are I_peak = (115+-9) {\mu}Jy/beam and r.a. =
07:16:34.55496(7), dec. = -19:00:39.4754(8), respectively. The e-MERLIN data
provided ~3-5sigma detections, at a position consistent with those of the EVN
data. The presence of emission on angular scales intermediate between the EVN
and e-MERLIN is consistent with being null. The brightness temperature of the
EVN core is Tb~10^8.5K, close to the value required by Akiyama & Johnson (2016)
to explain the radio properties of WISE J0716-19 in terms of interstellar
induced short-term variability. Our observations provide direct, independent
evidence of the existence of a nuclear compact source in WISE J0716-19, a
physical scenario with no evident connection with FRB 150418. However, the EVN
data do not show indication of the variability observed with the VLA.Comment: 4 pages, accepted for publication in A&A Letters to the Edito
- …