359 research outputs found
The Local Nanohertz Gravitational-Wave Landscape From Supermassive Black Hole Binaries
Supermassive black hole binaries (SMBHBs) in the 10 million to 10 billion
range form in galaxy mergers, and live in galactic nuclei with large
and poorly constrained concentrations of gas and stars. There are currently no
observations of merging SMBHBs--- it is in fact possible that they stall at
their final parsec of separation and never merge. While LIGO has detected high
frequency GWs, SMBHBs emit GWs in the nanohertz to millihertz band. This is
inaccessible to ground-based interferometers, but possible with Pulsar Timing
Arrays (PTAs). Using data from local galaxies in the 2 Micron All-Sky Survey,
together with galaxy merger rates from Illustris, we find that there are on
average sources emitting GWs in the PTA band, and binaries
which will never merge. Local unresolved SMBHBs can contribute to GW background
anisotropy at a level of , and if the GW background can be
successfully isolated, GWs from at least one local SMBHB can be detected in 10
years.Comment: submitted to Nature Astronomy (reformatted for arXiv
Metallicity Gradients at Large Galactocentric Radii Using the Near-infrared Calcium Triplet
We describe a new spectroscopic technique for measuring radial metallicity
gradients out to large galactocentric radii. We use the DEIMOS multi-object
spectrograph on the Keck telescope and the galaxy spectrum extraction technique
of Proctor et al. (2009). We also make use of the metallicity sensitive
near-infrared (NIR) Calcium triplet (CaT) features together with single stellar
population models to obtain metallicities. Our technique is applied as a pilot
study to a sample of three relatively nearby (<30 Mpc) intermediate-mass to
massive early-type galaxies. Results are compared with previous literature
inner region values and generally show good agreement. We also include a
comparison with profiles from dissipational disk-disk major merger simulations.
Based on our new extended metallicity gradients combined with other
observational evidence and theoretical predictions, we discuss possible
formation scenarios for the galaxies in our sample. The limitations of our new
technique are also discussed.Comment: 13 Pages, 9 Figures, 7 Tables, Accepted for publication in MNRA
Radiation properties of extreme nulling pulsar J1502-5653
We report on radiation properties of extreme nulling pulsar J1502-5653, by
analyzing the data acquired from the Parkes 64-m telescope at 1374 MHz. The
radio emission from this pulsar exhibits sequences of several tens to several
hundreds consecutive burst pulses, separated by null pulses, and the appearance
of the emission seems quasi-periodic. The null fraction from the data is
estimated to be 93.6%. No emission is detected in the integrated profile of all
null pulses. Systematic modulations of pulse intensity and phase are found at
the beginning of burst-pulse sequences just after null. The intensity usually
rises to a maximum for the first few pulses, then declines exponentially
afterwards, and becomes stable after few tens of pulse periods. The peak phase
appears at later longitudes for the first pulse, then drifts to earlier
longitudes rapidly, and then systematic drifting gradually vanishes while the
intensity becomes stable. In this pulsar, the intensity variation and phase
modulation of pulses are correlated in a short duration after the emission
starts following a null. Observed properties of the pulsar are compared with
other nulling pulsars published previously, and the possible explanation for
phase modulation is discussed.Comment: 5 pages, 7 figures. Accepted by MNRA
The Origin of Color Gradients in Early-Type Systems and Their Compactness at High-z
In this Letter, we present mean optical+NIR color gradient estimates for 5080
early-type galaxies (ETGs) in the grizYJHK wavebands of the Sloan Digital Sky
Survey (SDSS) plus UKIRT Infrared Deep Sky Survey (UKIDSS). The color gradient
is estimated as the logarithmic slope of the radial color profile in ETGs. With
such a large sample size, we study the variation of the mean color gradient as
a function of waveband with unprecedented accuracy. We find that (i) color
gradients are mainly due, on average, to a metallicity variation of about
-0.4dex per decade in galaxy radius; and (ii) a small, but significant,
positive age gradient is present, on average, in ETGs, with the inner stellar
population being slightly younger, by ~0.1dex per radial decade, than the outer
one. Also, we show that the presence of a positive mean age gradient in ETGs,
as found in the present study, implies their effective radius to be smaller at
high z, consistent with observations.Comment: 4 pages, 2 color figures, accepted for publication in the
Astrophysical Journal Letter
RRATs: New Discoveries, Timing Solutions & Musings
We describe observations of Rotating RAdio Transients (RRATs) that were
discovered in a re-analysis of the Parkes Multi-beam Pulsar Survey (PMPS). The
sources have now been monitored for sufficiently long to obtain seven new
coherent timing solutions, to make a total of 14 now known. Furthermore we
announce the discovery of 7 new transient sources, one of which may be
extragalactic in origin (with ) and would then be a second example of
the so-called `Lorimer burst'. The timing solutions allow us to infer neutron
star characteristics such as energy-loss rate, magnetic field strength and
evolutionary timescales, as well as facilitating multi-wavelength followup by
providing accurate astrometry. All of this enables us to consider the question
of whether or not RRATs are in any way special, i.e. a distinct and separate
population of neutron stars, as has been previously suggested. We see no reason
to consider 'RRAT' as anything other than a detection label, the subject of a
selection effect in the parameter space searched. However, single-pulse
searches can be utilised to great effect to identify pulsars difficult, or
impossible, to find by other means, in particular those with long-periods (half
of the PMPS RRATs have periods greater than 4 seconds), high-magnetic field
strengths ( G) and pulsars approaching the 'death valley'.
The detailed nulling properties of such pulsars are unknown but the mounting
evidence suggests a broad range of behaviour in the pulsar population. The
group of RRATs fit in to the picture where pulsar magnetospheres switch between
stable configurations.Comment: accepted for publication in MNRAS, 17 pages, 7 figures, 3 table
The PULSE@Parkes project: A new observing technique for long-term pulsar monitoring
The PULSE@Parkes project has been designed to monitor the rotation of radio
pulsars over time spans of days to years. The observations are obtained using
the Parkes 64-m and 12-m radio telescopes by Australian and international high
school students. These students learn the basis of radio astronomy and
undertake small projects with their observations. The data are fully calibrated
and obtained with the state-of-the-art pulsar hardware available at Parkes. The
final data sets are archived and are currently being used to carry out studies
of 1) pulsar glitches, 2) timing noise, 3) pulse profile stability over long
time scales and 4) the extreme nulling phenomenon. The data are also included
in other projects such as gamma-ray observatory support and for the Parkes
Pulsar Timing Array project. In this paper we describe the current status of
the project and present the first scientific results from the Parkes 12-m radio
telescope. We emphasise that this project offers a straightforward means to
enthuse high school students and the general public about radio astronomy while
obtaining scientifically valuable data sets.Comment: accepted for publication by PAS
Detection of fast radio transients with multiple stations: a case study using the Very Long Baseline Array
Recent investigations reveal an important new class of transient radio
phenomena that occur on sub-millisecond timescales. Often transient surveys'
data volumes are too large to archive exhaustively. Instead, an on-line
automatic system must excise impulsive interference and detect candidate events
in real-time. This work presents a case study using data from multiple
geographically distributed stations to perform simultaneous interference
excision and transient detection. We present several algorithms that
incorporate dedispersed data from multiple sites, and report experiments with a
commensal real-time transient detection system on the Very Long Baseline Array
(VLBA). We test the system using observations of pulsar B0329+54. The
multiple-station algorithms enhanced sensitivity for detection of individual
pulses. These strategies could improve detection performance for a future
generation of geographically distributed arrays such as the Australian Square
Kilometre Array Pathfinder and the Square Kilometre Array.Comment: 12 pages, 14 figures. Accepted for Ap
Calibration and assessment of electrochemical low-cost sensors in remote alpine harsh environments
This work presents results from an original open-source low-cost sensor (LCS) system developed to measure tropospheric O3 in a remote high altitude alpine site. Our study was conducted at the Col Margherita Observatory (2543 m above sea level), in the Italian Eastern Alps. The sensor system mounts three commercial low-cost O3/NO2 sensors that have been calibrated before field deployment against a laboratory standard (Thermo Scientific; 49i-PS), calibrated against the standard reference photometer no. 15 calibration scale of the World Meteorological Organization (WMO). Intra- and intercomparison between the sensors and a reference instrument (Thermo Scientific; 49c) have been conducted for 7 months from May to December 2018. The sensors required an individual calibration, both in laboratory and in the field. The sensor's dependence on the environmental meteorological variables has been considered and discussed. We showed that it is possible to reduce the bias of one LCS by using the average coefficient values of another LCS working in tandem, suggesting a way forward for the development of remote field calibration techniques. We showed that it is possible reconstruct the environmental ozone concentration during the loss of reference instrument data in situations caused by power outages. The evaluation of the analytical performances of this sensing system provides a limit of detection (LOD) <5 ppb (parts per billion), limit of quantification (LOQ) <17 ppb, linear dynamic range (LDR) up to 250 ppb, intra-Pearson correlation coefficient (PCC) up to 0.96, inter-PCC >0.8, bias >3.5 ppb and ±8.5 at 95 % confidence. This first implementation of a LCS system in an alpine remote location demonstrated how to obtain valuable data from a low-cost instrument in a remote environment, opening new perspectives for the adoption of low-cost sensor networks in atmospheric sciences
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