88 research outputs found
A low-luminosity type-1 QSO sample; III. Optical spectroscopic properties and activity classification
We report on the optical spectroscopic analysis of a sample of 99
low-luminosity quasi-stellar objects (LLQSOs) at base the
Hamburg/ESO QSO survey (HES). The LLQSOs presented here offer the possibility
of studying the faint end of the QSO population at smaller cosmological
distances and, therefore, in greater detail. A small number of our LLQSO
present no broad component. Two sources show double broad components, whereas
six comply with the classic NLS1 requirements. As expected in NLR of broad line
AGNs, the [S{\sc{ii}}]based electron density values range between 100 and
1000 N/cm. Using the optical characteristics of Populations A and
B, we find that 50\% of our sources with H broad emission are consistent
with the radio-quiet sources definition. The remaining sources could be
interpreted as low-luminosity radio-loud quasar. The BPT-based classification
renders an AGN/Seyfert activity between 50 to 60\%. For the remaining sources,
the possible star burst contribution might control the LINER and HII
classification. Finally, we discuss the aperture effect as responsible for the
differences found between data sets, although variability in the BLR could play
a significant role as well.Comment: 22 pages; 5 tables; 17 figures; in press with A&
2FGL J0846.0+2820: A new neutron star binary with a giant secondary and variable -ray emission
We present optical photometric and spectroscopic observations of the likely
stellar counterpart to the unassociated \emph{Fermi}-Large Area Telescope (LAT)
-ray source 2FGL J0846.0+2820, selected for study based on positional
coincidences of optical variables with unassociated LAT sources. Using optical
spectroscopy from the SOAR telescope, we have identified a late-G giant in an
eccentric ( = 0.06) 8.133 day orbit with an invisible primary. Modeling the
spectroscopy and photometry together lead us to infer a heavy neutron star
primary of and a partially stripped giant secondary of . H emission is observed in some of the spectra, perhaps
consistent with the presence of a faint accretion disk. We find the
-ray flux of 2FGL J0846.0+2820 dropped substantially in mid-2009,
accompanied by an increased variation in the optical brightness, and since then
it has not been detected by \emph{Fermi}. The long period and giant secondary
are reminiscent of the -ray bright binary 1FGL J1417.7--4407, which
hosts a millisecond pulsar apparently in the final stages of the pulsar
recycling process. The discovery of 2FGL J0846.0+2820 suggests the
identification of a new subclass of millisecond pulsar binaries that are the
likely progenitors of typical field millisecond pulsars.Comment: 12 pages, 8 figures, 3 tables. Accepted for publication in Ap
X-ray and radio observations of central black holes in nearby low-mass early-type galaxies: Preliminary evidence for low Eddington fractions
We present new radio and X-ray observations of two nearby ( Mpc)
low-mass early-type galaxies with dynamically-confirmed central black holes:
NGC 5102 and NGC 205. NGC 5102 shows a weak nuclear X-ray source and has no
core radio emission. However, for the first time we demonstrate that it shows
luminous extended radio continuum emission in low-resolution, low-frequency ( GHz) data, consistent with jet lobes on scales pc formed from
past accretion and jet activity. By contrast, in new, extremely deep,
strictly-simultaneous Very Large Array and Chandra observations, no radio or
X-ray emission is detected from the black hole in NGC 205. We consider these
measurements and upper limits in the context of the few other low-mass
early-type galaxies with dynamically-confirmed black holes, and show that the
mean ratio of bolometric to Eddington luminosity in this sample is only
. These Eddington
ratios are lower than typical in a comparison sample of more massive early-type
galaxies, though this conclusion is quite tentative due to our small sample of
low-mass galaxies and potential biases in the comparison sample. This
preliminary result is in mild tension with previous work using less sensitive
observations of more distant galaxies, which predict higher X-ray luminosities
than we observe for low-mass galaxies. If it is confirmed that central black
holes in low-mass galaxies typically have low Eddington ratios, this presents a
challenge to measuring the occupation fraction of central black holes with
standard optical emission line, X-ray, or radio surveys.Comment: 13 pages, 4 figures, 3 tables. Accepted for publication in Ap
SAX J1810.8-2609: An Outbursting Neutron Star X-ray Binary with Persistent Spatially Coincident Radio Emission
Here we report on joint X-ray and radio monitoring of the neutron star
low-mass X-ray binary SAX J1810.8-2609. Our monitoring covered the entirety of
its ~5 month outburst in 2021, revealing a temporal correlation between its
radio and X-ray luminosity and X-ray spectral properties consistent with a
`hard-only' outburst. During the outburst, the best-fit radio position shows
significant variability, suggesting emission from multiple locations on the
sky. Furthermore, our 2023 follow-up observations revealed a persistent,
unresolved, steep spectrum radio source ~2 years after SAX J1810.8-2609
returned to X-ray quiescence. We investigated potential origins of the
persistent emission, which included an unrelated background source,
long-lasting jet ejection(s), and SAX J1810 as a transitional millisecond
pulsar. While the chance coincidence probability is low (<0.16%), an unrelated
background source remains the most likely scenario. SAX J1810.8-2609 goes into
outburst every ~5 years, so monitoring of the source during its next outburst
at higher sensitivities and improved spatial resolutions (e.g., with the Karl
G. Jansky Very Large Array or Square Kilometre Array) should be able to
identify two components (if the persistent emission originates from a
background source). If only one source is observed, this would be strong
evidence that the persistent emission is local SAX J1810.8-2609, and future
monitoring campaigns should focus on understanding the underlying physical
mechanisms, as no neutron star X-ray binary has shown a persistent radio signal
absent any simultaneous X-ray emission.Comment: 19 pages, 9 figure
Merger driven star-formation activity in Cl J1449+0856 at z=1.99 as seen by ALMA and JVLA
We use ALMA and JVLA observations of the galaxy cluster Cl J1449+0856 at z=1.99, in order to study how dust-obscured star-formation, ISM content and AGN activity are linked to environment and galaxy interactions during the crucial phase of high-z cluster assembly. We present detections of multiple transitions of 12CO, as well as dust continuum emission detections from 11 galaxies in the core of Cl J1449+0856. We measure the gas excitation properties, star-formation rates, gas consumption timescales and gas-to-stellar mass ratios for the galaxies.
We find evidence for a large fraction of galaxies with highly-excited molecular gas, contributing >50% to the total SFR in the cluster core. We compare these results with expectations for field galaxies, and conclude that environmental influences have strongly enhanced the fraction of excited galaxies in this cluster. We find a dearth of molecular gas in the galaxies' gas reservoirs, implying a high star-formation efficiency (SFE) in the cluster core, and find short gas depletion timescales Ï„<0.1-0.4 Gyrs for all galaxies. Interestingly, we do not see evidence for increased specific star-formation rates (sSFRs) in the cluster galaxies, despite their high SFEs and gas excitations. We find evidence for a large number of mergers in the cluster core, contributing a large fraction of the core's total star-formation compared with expectations in the field. We conclude that the environmental impact on the galaxy excitations is linked to the high rate of galaxy mergers, interactions and active galactic nuclei in the cluster core
Radio non-detection during nearly-simultaneous Swift/XRT observations of MAXI J0911-635/Swift J0911.9-6452 in NGC 2808
We report nearly-simultaneous radio and X-ray observations of the newly discovered X-ray transient MAXI J0911-635/Swift J0911.9-6452 in the globular cluster NGC 2808 (ATel #8872, #8884)
Search and identification of transient and variable radio sources using MeerKAT observations:a case study on the MAXI J1820+070 field
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