387 research outputs found
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
4C 02.27: what is inside a double-double radio quasar?
Recently Jamrozy et al. (2009) identified 4C 02.27 (J0935+0204) as the first
possible example of a double-double radio source which is optically identified
with a quasar (i.e. not a galaxy), at the redshift of z=0.649. The overall
projected angular size of the radio source reaches about 1.5', with a prominent
"core" component in the centre. The two opposite pairs of radio lobes might
indicate two periods of episodic activity. We report on our short exploratory
1.6-GHz Very Long Baseline Interferometry (VLBI) observations of the innermost
radio structure of the quasar, conducted with the electronic European VLBI
Network (e-EVN) on 2009 September 30. These revealed a milliarcsecond-scale
compact source which is the base of the approaching one of the two symmetric
relativistic jets currently supplying the hot spots in the inner pair of the
arcsecond-scale radio lobes in 4C 02.27.Comment: 4 pages, 2 figures, to appear in the proceedings of the 10th European
VLBI Network Symposium (September 20-24, 2010, Manchester, UK). Proceedings
of Science (http://pos.sissa.it), PoS(10th EVN Symposium)07
Four hot DOGs in the microwave
Hot dust-obscured galaxies (hot DOGs) are a rare class of hyperluminous
infrared galaxies identified with the Wide-field Infrared Survey Explorer
(WISE) satellite. The majority of them is at high redshifts (z~2-3), at the
peak epoch of star formation in the Universe. Infrared, optical, radio, and
X-ray data suggest that hot DOGs contain heavily obscured, extremely luminous
active galactic nuclei (AGN). This class may represent a short phase in the
life of the galaxies, signifying the transition from starburst- to
AGN-dominated phases. Hot DOGs are typically radio-quiet, but some of them show
mJy-level emission in the radio (microwave) band. We observed four hot DOGs
using the technique of very long baseline interferometry (VLBI). The 1.7-GHz
observations with the European VLBI Network (EVN) revealed weak radio features
in all sources. The radio is free from dust obscuration and, at such high
redshifts, VLBI is sensitive only to compact structures that are characteristic
of AGN activity. In two cases (WISE J0757+5113, WISE J1603+2745), the flux
density of the VLBI-detected components is much smaller than the total flux
density, suggesting that ~70-90 per cent of the radio emission, while still
dominated by AGN, originates from angular scales larger than probed by the EVN.
The source WISE J1146+4129 appears a candidate compact symmetric object, and
WISE J1814+3412 shows a 5.1-kpc double structure, reminiscent of hot spots in a
medium-sized symmetric object. Our observations support that AGN residing in
hot DOGs may be genuine young radio sources where starburst and AGN activities
coexist.Comment: 8 pages, 4 tables, 1 figure; accepted for publication in the Monthly
Notices of the Royal Astronomical Societ
LLAGN and jet-scaling probed with the EVN
Accreting black holes on all mass scales (from stellar to supermassive)
appear to follow a nonlinear relation between X-ray luminosity, radio
luminosity and BH mass, indicating that similar physical processes drive the
central engines in X-ray binaries and active galactic nuclei (AGN). However, in
recent years an increasing number of BH systems have been identified that do
not fit into this scheme. These outliers may be the key to understand how BH
systems are powered by accretion. Here we present results from EVN observations
of a sample of low-luminosity AGN (LLAGN) with known mass that have unusually
high radio powers when compared with their X-ray luminosity.Comment: Presented at the 11th EVN Symposium, Bordeaux, France, 2012 October
9-12. Six pages, including a figure and a table. Final, accepted versio
The compact radio structure of the high-redshift blazar J1430+4204 before and after a major outburst
The high-redshift (z=4.72) blazar J1430+4204 produced an exceptional radio
outburst in 2006. We analyzed 15-GHz radio interferometric images obtained with
the Very Long Baseline Array (VLBA) before and after the outburst, to search
for possible structural changes on milli-arcsecond angular scales and to
determine physical parameters of the source.Comment: Proceedings of the 5th Workshop of Young Researchers in Astronomy and
Astrophysics, Budapest, 2009; to be published in J. Phys.: Conf. Series
(JPCS); 4 pages, 3 figure
Four hot DOGs eaten up with the EVN
Hot dust-obscured galaxies (hot DOGs) are a rare class of hyperluminous
infrared galaxies recently identified with the Wide-field Infrared Survey
Explorer (WISE) satellite. The majority of the ~1000-member all-sky population
should be at high redshifts (z~2-3), at the peak of star formation in the
history of the Universe. This class most likely represents a short phase during
galaxy merging and evolution, a transition from starburst- to AGN-dominated
phases. For the first time, we observed four hot DOGs with known mJy-level
radio emission using the European VLBI Network (EVN) at 1.7 GHz, in a hope to
find compact radio features characteristic to AGN activity. All four target
sources are detected at ~15-30 mas angular resolution, confirming the presence
of an active nucleus. The sources are spatially resolved, i.e. the flux density
of the VLBI-detected components is smaller than the total flux density,
suggesting that a fraction of the radio emission originates from larger-scale
(partly starburst-related) activity. Here we show the preliminary results of
our e-EVN observations made in 2014 February, and discuss WISE J1814+3412, an
object with kpc-scale symmetric radio structure, in more detail.Comment: 6 pages, 1 figure; appears in the proceedings of the 12th European
VLBI Network Symposium and Users Meeting (7-10 October 2014, Cagliari,
Italy), eds. A. Tarchi, M. Giroletti & L. Feretti. JREF Proceedings of
Science, PoS(EVN 2014)003,
http://pos.sissa.it/archive/conferences/230/003/EVN%202014_003.pd
- …