364 research outputs found
Review on the multiwavelength emission of the gamma-ray binary LS I +61 303
Gamma-ray binaries are systems composed of a massive star and a compact
object that produce emission from radio to very high energy gamma-rays. LS I
+61 303 is one of the only six gamma-ray binaries discovered so far. It is
thought that gamma-ray binaries contain a young highly rotating neutron star as
compact object, and the emission is produced by the interaction between its
relativistic pulsar wind and the stellar wind, However, in the case of LS I +61
303 a microquasar scenario is still considered and results pointing to oppose
directions have been published during the last decades. Here we provide a
review about the state of the art of LS I +61 303, summarizing the observed
emission from radio to very high energy gamma-rays along all these years, and
we discuss the proposed scenarios that can explain such emission.Comment: 9 pages to be published in the proceedings of XII Multifrequency
Behaviour of High Energy Cosmic Sources Workshop, Palermo (Italy),
PoS(MULTIF2017)04
Localizations of Fast Radio Bursts on milliarcsecond scales
Fast Radio Bursts (FRBs) are transient sources that emit a single radio pulse
with a duration of only a few milliseconds. Since the discovery of the first
FRB in 2007, tens of similar events have been detected. However, their physical
origin remains unclear, and a number of scenarios even larger than the number
of known FRBs has been proposed during these years. The presence of repeating
bursts in FRB 121102 allowed us to perform a precise localization of the source
with the Very Large Array and the European VLBI Network (EVN). Optical
observations with Keck, Gemini and HST unveiled the host to be a
low-metallicity star-forming dwarf galaxy located at a redshift of 0.193. The
EVN results showed that the bursts are co-located (within a projected
separation of pc) to a compact and persistent radio source with a size
of pc inside a star-forming region. This environment resembles the ones
where superluminous supernovae (SLSNe) or long gamma-ray bursts are produced.
Although the nature of this persistent source and the origin of the bursts
remain unknown, scenarios considering a pulsar/magnetar energizing a young
SLSN, or a system with a pulsar/magnetar in the vicinity of a massive black
hole are the most plausible ones to date. More recent observations have shown
that the bursts from FRB 121102 are almost 100% linearly polarized at an
unexpectedly high and variable Faraday rotation measure, that has been observed
to date only in vicinities of massive black holes. The bursts are thus likely
produced from a neutron star in such environment, although the system can still
be explained by a young neutron star embedded in a highly magnetized nebula.
Upcoming interferometric searches are expected to report tens of these
localizations in the coming years, unveil if this source is representative of
the whole population or a particular case, and dramatically boosting the field
of FRBs.Comment: 11 pages, 3 figures, proceedings of the 14th European VLBI Network
Symposium & Users Meeting, held on 8-11 October 2018 in Granada, Spai
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&
First EVN measurements of the transient FIRST J141918.9+394036 on milliarcsecond scales
FIRST J141918.9+394036 has been reported as a slowly-evolving extragalactic radio transient (Law et al. 2018, arXiv:1808.08964), consistent with a fading orphan long gamma-ray burst (LGRB)
Resolving the decades-long transient FIRST J141918.9+394036: an orphan long gamma-ray burst or a young magnetar nebula?
Ofek (2017) identified FIRST J141918.9+394036 (hereafter FIRST J1419+3940) as
a radio source sharing similar properties and host galaxy type to the compact,
persistent radio source associated with the first known repeating fast radio
burst, FRB 121102. Law et al. (2018) showed that FIRST J1419+3940 is a
transient source decaying in brightness over the last few decades. One possible
interpretation is that FIRST J1419+3940 is a nearby analogue to FRB 121102 and
that the radio emission represents a young magnetar nebula (as several
scenarios assume for FRB 121102). Another interpretation is that FIRST
J1419+3940 is the afterglow of an `orphan' long gamma-ray burst (GRB). The
environment is similar to where most such events are produced. To distinguish
between these hypotheses, we conducted radio observations using the European
VLBI Network at 1.6 GHz to spatially resolve the emission and to search for
millisecond-duration radio bursts. We detect FIRST J1419+3940 as a compact
radio source with a flux density of (on 2018
September 18) and a source size of (i.e. given the angular diameter distance of ).
These results confirm that the radio emission is non-thermal and imply an
average expansion velocity of . Contemporaneous
high-time-resolution observations using the 100-m Effelsberg telescope detected
no millisecond-duration bursts of astrophysical origin. The source properties
and lack of short-duration bursts are consistent with a GRB jet expansion,
whereas they disfavor a magnetar birth nebula.Comment: 8 pages, 4 figures, accepted for publication in ApJ
High resolution radio imaging of the two Particle-Accelerating Colliding-Wind Binaries HD167971 and HD168112
The colliding-wind region in binary systems made of massive stars allows us
to investigate various aspects of shock physics, including particle
acceleration. Particle accelerators of this kind are tagged as
Particle-Accelerating Colliding-Wind Binaries, and are mainly identified thanks
to their synchrotron radio emission. Our objective is first to validate the
idea that obtaining snapshot high-resolution radio images of massive binaries
constitutes a relevant approach to unambiguously identify particle
accelerators. Second, we intend to exploit these images to characterize the
synchrotron emission of two specific targets, HD167971 and HD168112, known as
particle accelerators. We traced the radio emission from the two targets at 1.6
GHz with the European Very Long Baseline Interferometry Network, with an
angular resolution of a few milli-arcseconds. Our measurements allowed us to
obtain images for both targets. For HD167971, our observation occurs close to
apastron, at an orbital phase where the synchrotron emission is minimum. For
HD168112, we resolved for the very first time the synchrotron emission region.
The emission region appears slightly elongated, in agreement with expectation
for a colliding-wind region. In both cases the measured emission is
significantly stronger than the expected thermal emission from the stellar
winds, lending strong support for a non-thermal nature. Our study brings a
significant contribution to the still poorly addressed question of high angular
resolution radio imaging of colliding-wind binaries. We show that snapshot Very
Long Baseline Interferometry measurements constitute an efficient approach to
investigate these objects, with promising results in terms of identification of
additional particle accelerators, on top of being promising as well to reveal
long period binaries.Comment: 8 pages, 1 figure, accepted for publication in A&
Radio modelling of the brightest and most luminous non-thermal colliding-wind binary Apep
Stars and planetary system
Radio modelling of the brightest and most luminous non-thermal colliding-wind binary Apep
Stars and planetary system
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