186 research outputs found
X-ray and Radio Follow-up Observations of High-Redshift Blazar Candidates in the Fermi-LAT Unassociated Source Population
We report on the results of X-ray and radio follow-up observations of two GeV
gamma-ray sources 2FGL J0923.5+1508 and 2FGL J1502.1+5548, selected as
candidates for high-redshift blazars from unassociated sources in the {\it
Fermi} Large Area Telescope Second Source Catalog. We utilize the Suzaku
satellite and the VLBI Exploration of Radio Astrometry (VERA) telescopes for
X-ray and radio observations, respectively. For 2FGL J0923.5+1508, a possible
radio counterpart NVSS J092357+150518 is found at 1.4 GHz from an existing
catalog, but we do not detect any X-ray emission from it and derive a flux
upper limit 1.37 10 erg cm
s. Radio observations at 6.7 GHz also result in an upper limit of
19 mJy, implying a steep radio spectrum that is not
expected for a blazar. On the other hand, we detect X-rays from NVSS
J150229+555204, the potential 1.4 GHz radio counterpart of 2FGL J1502.1+5548.
The X-ray spectrum can be fitted with an absorbed power-law model with a photon
index =1.8 and the unabsorbed flux is =4.3 10 erg cm s. Moreover,
we detect unresolved radio emission at 6.7 GHz with flux =30.1
mJy, indicating a compact, flat-spectrum radio source. If NVSS J150229+555204
is indeed associated with 2FGL J1502.1+5548, we find that its multiwavelength
spectrum is consistent with a blazar at redshift .Comment: 24 pages, 7 figures, 6 tables, accepted for publication in Ap
Radio and gamma-ray follow-up of the exceptionally high activity state of PKS 1510-089 in 2011
We investigate the radio and gamma-ray variability of the flat spectrum radio
quasar PKS 1510-089 in the time range between 2010 November and 2012 January.
In this period the source showed an intense activity, with two major gamma-ray
flares detected in 2011 July and October. During the latter episode both the
gamma-ray and the radio flux density reached their historical peak.
Multiwavelength analysis shows a rotation of about 380 deg of the optical
polarization angle close in time with the rapid and strong gamma-ray flare in
2011 July. An enhancement of the optical emission and an increase of the
fractional polarization both in the optical and in radio bands is observed
about three weeks later, close in time with another gamma-ray outburst. On the
other hand, after 2011 September a huge radio outburst has been detected, first
in the millimeter regime followed with some time delay at centimeter down to
decimeter wavelengths. This radio flare is characterized by a rising and a
decaying stage, in agreement with the formation of a shock and its evolution,
as a consequence of expansion and radiative cooling. If the gamma-ray flare
observed in 2011 October is related to this radio outburst, then this strongly
indicates that the region responsible for the gamma-ray variability is not
within the broad line, but a few parsecs downstream along the jet.Comment: 14 pages, 12 figures, accepted for publication in MNRA
An automated archival VLA transients survey
In this paper we present the results of a survey for radio transients using
data obtained from the Very Large Array archive. We have reduced, using a
pipeline procedure, 5037 observations of the most common pointings - i.e. the
calibrator fields. These fields typically contain a relatively bright point
source and are used to calibrate `target' observations: they are therefore
rarely imaged themselves. The observations used span a time range ~ 1984 - 2008
and consist of eight different pointings, three different frequencies (8.4, 4.8
and 1.4 GHz) and have a total observing time of 435 hours. We have searched for
transient and variable radio sources within these observations using components
from the prototype LOFAR transient detection system. In this paper we present
the methodology for reducing large volumes of Very Large Array data; and we
also present a brief overview of the prototype LOFAR transient detection
algorithms. No radio transients were detected in this survey, therefore we
place an upper limit on the snapshot rate of GHz frequency transients > 8.0 mJy
to rho less than or equal to 0.032 deg^-2 that have typical timescales 4.3 to
45.3 days. We compare and contrast our upper limit with the snapshot rates -
derived from either detections or non-detections of transient and variable
radio sources - reported in the literature. When compared with the current Log
N - Log S distribution formed from previous surveys, we show that our upper
limit is consistent with the observed population. Current and future radio
transient surveys will hopefully further constrain these statistics, and
potentially discover dominant transient source populations. In this paper we
also briefly explore the current transient commissioning observations with
LOFAR, and the impact they will make on the field.Comment: Accepted for publication in MNRA
Possible Detection of Apparent Superluminal inward motion in Markarian 421 after the Giant X-ray flare in February, 2010
We report on the VLBI follow-up observations using the Japanese VLBI Network
(JVN) array at 22 GHz for the largest X-ray flare of TeV blazar Mrk 421 that
occurred in mid-February, 2010. The total of five epochs of observations were
performed at intervals of about 20 days between March 7 and May 31, 2010. No
new-born component associated with the flare was seen directly in the total
intensity images obtained by our multi-epoch VLBI observations. However, one
jet component located at ~1 mas north-west from the core was able to be
identified, and its proper motion can be measured as -1.66+/-0.46 mas yr^-1,
which corresponds to an apparent velocity of -3.48+/-0.97 c. Here, this
negative velocity indicates that the jet component was apparently moving toward
the core. As the most plausible explanation, we discuss that the apparent
negative velocity was possibly caused by the ejection of a new component, which
could not be resolved with our observations. In this case, the obtained Doppler
factor of the new component is around 10 to 20, which is consistent with the
ones typically estimated by model fittings of spectral energy distribution for
this source.Comment: 9 pages, 6 figures, 3 tables, accepted for publication in Ap
A 22-year Southern Sky Survey for Transient and Variable Radio Sources using the Molonglo Observatory Synthesis Telescope
We describe a 22-year survey for variable and transient radio sources,
performed with archival images taken with the Molonglo Observatory Synthesis
Telescope (MOST). This survey covers 2775 \unit{deg^2} of the sky south of
at an observing frequency of 843 MHz, an angular
resolution of 45 \times 45 \csc | \delta| \unit{arcsec^2} and a sensitivity
of 5 \sigma \geq 14 \unit{mJy beam^{-1}}. We describe a technique to
compensate for image gain error, along with statistical techniques to check and
classify variability in a population of light curves, with applicability to any
image-based radio variability survey. Among radio light curves for almost 30000
sources, we present 53 highly variable sources and 15 transient sources. Only 3
of the transient sources, and none of the variable sources have been previously
identified as transient or variable. Many of our variable sources are suspected
scintillating Active Galactic Nuclei. We have identified three variable sources
and one transient source that are likely to be associated with star forming
galaxies at , but whose implied luminosity is higher than the
most luminous known radio supernova (SN1979C) by an order of magnitude. We also
find a class of variable and transient source with no optical counterparts.Comment: Accepted for publication in MNRAS. 34 pages, 30 figures, 7 table
GCRT J1742-3001: A New Radio Transient Towards the Galactic Center
We report the detection of a new transient radio source, GCRT J1742-3001,
located ~1 degree from the Galactic center. The source was detected ten times
from late 2006 to 2007 May in our 235 MHz transient monitoring program with the
Giant Metrewave Radio Telescope (GMRT). The radio emission brightened in about
one month, reaching a peak observed flux density of ~100 mJy on 2007 January
28, and decaying to ~50 mJy by 2007 May when our last monitoring observation
was made. Two additional faint, isolated 235 MHz detections were made in
mid-2006, also with the GMRT. GCRT J1742-3001 is unresolved at each epoch, with
typical resolutions of ~20 arcsec x 10 arcsec. No polarization information is
available from the observations. Based on nondetections in observations
obtained simultaneously at 610 MHz, we deduce that the spectrum of GCRT
J1742-3001 is very steep, with a spectral index less than about -2. Follow-up
radio observations in 2007 September at 330 MHz and 1.4 GHz, and in 2008
February at 235 MHz yielded no detections. No X-ray counterpart is detected in
a serendipitous observation obtained with the X-ray telescope aboard the Swift
satellite during the peak of the radio emission in early 2007. We consider the
possibilities that GCRT J1742-3001 is either a new member of an existing class
of radio transients, or is representative of a new class having no associated
X-ray emission.Comment: 19 pages, 3 figures, submitted to Ap
Upregulation of AEBP1 in endothelial cells promotes tumor angiogenesis in colorectal cancer
血管新生は大腸がんの重要な治療標的である.本論文では,大腸がんの腫瘍血管関連遺伝子を探索し,AEBP1(Adipocyte enhancer binding protein 1)の血管内皮細胞における高発現を同定し,AEBP1が腫瘍血管新生促進に働くことを明らかにした
The almost ubiquitous association of 6.7 GHz methanol masers with dust
We report the results of 870-m continuum observations, using the Large
APEX Bolometer Camera (LABOCA), towards 77 class-II, 6.7-GHz methanol masers
identified by the Methanol Multibeam (MMB) survey to map the thermal emission
from cool dust towards these objects. These data complement a study of 630
methanol masers associated with compact dense clumps identified from the
ATLASGAL survey. Compact dust emission is detected towards 70 sources, which
implies a dust-association rate of 99% for the full MMB catalogue. Evaluation
of the derived dust and maser properties leads us to conclude that the combined
sample represents a single population tracing the same phenomenon. We find
median clump masses of a few 10 M and that all but a handful of
sources satisfy the mass-size criterion required for massive star formation.
This study provides the strongest evidence of the almost ubiquitous association
of methanol masers with massive, star-forming clumps. The fraction of
methanol-maser associated clumps is a factor of ~2 lower in the outer Galaxy
than the inner Galaxy, possibly a result of the lower metallicity environment
of the former. We find no difference in the clump-mass and maser-luminosity
distributions of the inner and outer Galaxy. The maser-pumping and
clump-formation mechanisms are therefore likely to be relatively invariant to
Galactic location. Finally, we use the ratio of maser luminosity and clump mass
to investigate the hypothesis that the maser luminosity is a good indicator of
the evolutionary stage of the embedded source, however, we find no evidence to
support this.Comment: Accepted by MNRAS. 17 pages, 17 figures and 5 tables. The full
version of Figs. 3 and 5 are only available in electronic form of the journal
while the full versions of Tables 1, 2 and 4 will only be available through
CDS. A complete version of the paper is available on reques
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