66 research outputs found
Unprecedented extreme high-frequency radio variability in early-stage active galactic nuclei
We report on the discovery of one of the most extreme cases of high-frequency
radio variability ever measured in active galactic nuclei (AGN), observed on
timescales of days and exhibiting variability amplitudes of three to four
orders of magnitude. These sources, all radio-weak narrow-line Seyfert 1 (NLS1)
galaxies, were discovered some years ago at Aalto University Mets\"ahovi Radio
Observatory (MRO) based on recurring flaring at 37 GHz, strongly indicating the
presence of relativistic jets. In subsequent observations with the Karl G.
Jansky Very Large Array (JVLA) at 1.6, 5.2, and 9.0~GHz no signs of jets were
seen. To determine the cause of their extraordinary behaviour, we observed them
with the JVLA at 10, 15, 22, 33, and 45 GHz, and with the Very Long Baseline
Array (VLBA) at 15 GHz. These observations were complemented with single-dish
monitoring at 37 GHz at MRO, and at 15 GHz at Owens Valley Radio Observatory
(OVRO). Intriguingly, all but one source either have a steep radio spectrum up
to 45 GHz, or were not detected at all. Based on the 37 GHz data the timescales
of the radio flares are a few days, and the derived variability brightness
temperatures and variability Doppler factors comparable to those seen in
blazars. We discuss alternative explanations for their extreme behaviour, but
so far no definite conclusions can be made. These sources exhibit radio
variability at a level rarely, if ever, seen in AGN. They might represent a new
type of jetted AGN, or a new variability phenomenon, and thus deserve our
continued attention.Comment: 31 pages, 37 figures, submitted to MNRA
CH radio emission from heiles cloud 2 as a tracer of molecular cloud evolution
A mapping observation of the -type doubling transition (3.3
GHz) of CH has been conducted toward Heiles Cloud 2 (HCL2) in the Taurus
molecular cloud complex to reveal its molecular cloud-scale distribution. The
observations were carried out with the Effelsberg 100 m telescope. The CH
emission is found to be extended over the whole region of HCL2. It is brighter
in the southeastern part, which encloses the TMC-1 cyanopolyyne peak than in
the northwestern part. Its distribution extends continuously from the peak of
the neutral carbon emission (CI peak) to the TMC-1 ridge, as if it were
connecting the distributions of the [C I] and CO emissions. Since CH is
an intermediate in gas-phase chemical reactions from C to CO, its emission
should trace the transition region. The above distribution of the CH emission
is consistent with this chemical behavior. Since the CH abundance is subject to
the chemical evolutionary effect, the CH column density in HCL2 no longer
follows a linear correlation wit the H column density reported for diffuse
and translucent clouds. More importantly, the CH line profile is found to be
composed of the narrow and broad components. Although the broad component is
dominant around the CI peak, the narrow component appears in the TMC-1 ridge
and dense core regions such as L1527 and TMC-1A. This trend seems to reflect a
narrowing of the line width during the formation of dense cores. These results
suggest that the 3.3 GHz CH line is a useful tool for tracing the chemical and
physical evolution of molecular clouds.Comment: 8 page
Discrimination as a One-Day Performance Critically Reviewing an Anti-racism Day at School
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Association of IceCube neutrinos with radio sources observed at Owens Valley and Metsahovi Radio Observatories
Context. Identifying the most likely sources for high-energy neutrino emission has been one of the main topics in high-energy astrophysics ever since the first observation of high-energy neutrinos by the IceCube Neutrino Observatory. Active galactic nuclei with relativistic jets, also known as blazars, have been considered to be one of the main candidates because of their ability to accelerate particles to high energies.Aims. We study the connection between radio emission and IceCube neutrino events using data from the Owens Valley Radio Observatory (OVRO) and Metsahovi Radio Observatory blazar monitoring programs.Methods. We identify sources in our radio monitoring sample that are positionally consistent with IceCube high-energy neutrino events. We estimate their mean flux density and variability amplitudes around the neutrino arrival time, and compare these with values from random samples to establish the significance of our results.Results. We find radio source associations within our samples with 15 high-energy neutrino events detected by IceCube. Nearly half of the associated sources are not detected in the gamma-ray energies, but their radio variability properties and Doppler boosting factors are similar to the gamma-ray detected objects in our sample, meaning that they could still be potential neutrino emitters. We find that the number of strongly flaring objects in our statistically complete OVRO samples is unlikely to be a random coincidence (at 2 sigma level).Conclusions. Based on our results, we conclude that although it is clear that not all neutrino events are associated with strong radio flaring blazars, observations of large-amplitude radio flares in a blazar at the same time as a neutrino event are unlikely to be a random coincidence
CH abundance gradient in TMC-1
We observed the 9-cm Lambda-doubling lines of CH along the dense filament of
TMC-1. The CH column densities were compared with the total H2 column densities
derived using the 2MASS NIR data and previously published SCUBA maps and with
OH column densities derived using previous observations with Effelsberg. We
also modelled the chemical evolution of TMC-1 adopting physical conditions
typical of dark clouds using the UMIST Database for Astrochemistry gas-phase
reaction network to aid the interpretation of the observed OH/CH abundance
ratios. The CH column density has a clear peak in the vicinity of the
cyanopolyyne maximum of TMC-1. The fractional CH abundance relative to H2
increases steadily from the northwestern end of the filament where it lies
around 1.0e-8, to the southeast where it reaches a value of 2.0e-8. The OH and
CH column densities are well correlated, and we obtained OH/CH abundance ratios
of ~ 16 - 20. These values are clearly larger than what has been measured
recently in diffuse interstellar gas and is likely to be related to C to CO
conversion at higher densities. The good correlation between CH and OH can be
explained by similar production and destruction pathways. We suggest that the
observed CH and OH abundance gradients are mainly due to enhanced abundances in
a low-density envelope which becomes more prominent in the southeastern part
and seems to continue beyond the dense filament. An extensive envelope probably
signifies an early stage of dynamical evolution, and conforms with the
detection of a large CH abundance in the southeastern part of the cloud. The
implied presence of other simple forms of carbon in the gas phase provides a
natural explanation for the observation of "early-type" molecules in this
region.Comment: 12 pages, 16 figure
Reconstructing the density and temperature structure of prestellar cores from <i>Herschel</i> data: a case study for B68 and L1689B
Utilizing multiwavelength dust emission maps acquired with Herschel, we reconstruct local volume density and dust temperature profiles for the prestellar cores B68 and L1689B using an inverse-Abel transform-based technique. We present intrinsic radial dust temperature profiles of starless cores directly from dust continuum emission maps disentangling the effect of temperature variations along the line of sight, which were previously limited to the radiative transfer calculations. The reconstructed dust temperature profiles show a significant drop in the core center, a flat inner part, and a rising outward trend until the background cloud temperature is reached. The central beam-averaged dust temperatures obtained for B68 and L1689B are 9.3 ± 0.5 K and 9.8 ± 0.5 K, respectively, which are lower than the temperatures of 11.3 K and 11.6 K obtained from direct SED fitting. The best mass estimates derived by integrating the volume density profiles of B68 and L1689B are 1.6 Mâ and 11 Mâ, respectively. Comparing our results for B68 with the near-infrared extinction studies, we find that the dust opacity law adopted by the HGBS project, Îșλ = 0.1 Ă (λ/300 ÎŒm)-2 cm2 g-1 agrees to within 50% with the dust extinction constraints
The Astropy Project: Building an inclusive, open-science project and status of the v2.0 core package
The Astropy project supports and fosters the development of open-source and openly-developed Python packages that provide commonly-needed functionality to the astronomical community. A key element of the Astropy project is the core package Astropy, which serves as the foundation for more specialized projects and packages. In this article, we provide an overview of the organization of the Astropy project and summarize key features in the core package as of the recent major release, version 2.0. We then describe the project infrastructure designed to facilitate and support development for a broader ecosystem of inter-operable packages. We conclude with a future outlook of planned new features and directions for the broader Astropy project
Performance and first measurements of the MAGIC stellar intensity interferometer
In recent years, a new generation of optical intensity interferometers has emerged, leveraging the existing infrastructure of Imaging Atmospheric Cherenkov Telescopes (IACTs). The MAGIC telescopes host the MAGIC-SII system (Stellar Intensity Interferometer), implemented to investigate the feasibility and potential of this technique on IACTs. After the first successful measurements in 2019, the system was upgraded and now features a real-time, dead-time-free, 4-channel, GPU-based correlator. These hardware modifications allow seamless transitions between MAGICâs standard very-high-energy gamma-ray observations and optical interferometry measurements within seconds. We establish the feasibility and potential of employing IACTs as competitive optical Intensity Interferometers with minimal hardware adjustments. The measurement of a total of 22 stellar diameters are reported, 9 corresponding to reference stars with previous comparable measurements, and 13 with no prior measurements. A prospective implementation involving telescopes from the forthcoming Cherenkov Telescope Array Observatoryâs Northern hemisphere array, such as the first prototype of its Large-Sized Telescopes, LST-1, is technically viable. This integration would significantly enhance the sensitivity of the current system and broaden the UV-plane coverage. This advancement would enable the system to achieve competitive sensitivity with the current generation of long-baseline optical interferometers over blue wavelengths
Constraints on axion-like particles with the Perseus Galaxy Cluster with MAGIC
Axion-like particles (ALPs) are pseudo-Nambu-Goldstone bosons that emerge in
various theories beyond the standard model. These particles can interact with
high-energy photons in external magnetic fields, influencing the observed
gamma-ray spectrum. This study analyzes 41.3 hrs of observational data from the
Perseus Galaxy Cluster collected with the MAGIC telescopes. We focused on the
spectra the radio galaxy in the center of the cluster: NGC 1275. By modeling
the magnetic field surrounding this target, we searched for spectral
indications of ALP presence. Despite finding no statistical evidence of ALP
signatures, we were able to exclude ALP models in the sub-micro electronvolt
range. Our analysis improved upon previous work by calculating the full
likelihood and statistical coverage for all considered models across the
parameter space. Consequently, we achieved the most stringent limits to date
for ALP masses around 50 neV, with cross sections down to GeV.Comment: 25 pages, 10 figures, accepted for publication in Physics of the Dark
Univers
Performance of the joint LST-1 and MAGIC observations evaluated with Crab Nebula data
Aims. Large-Sized Telescope 1 (LST-1), the prototype for the Large-Sized Telescope at the upcoming Cherenkov Telescope Array Observatory, is concluding its commissioning phase at the Observatorio del Roque de los Muchachos on the island of La Palma. The proximity of LST-1 to the two MAGIC (Major Atmospheric Gamma Imaging Cherenkov) telescopes makes it possible to carry out observations of the same gamma-ray events with both systems. Methods. We describe the joint LST-1+MAGIC analysis pipeline and used simultaneous Crab Nebula observations and Monte Carlo simulations to assess the performance of the three-telescope system. The addition of the LST-1 telescope allows for the recovery of events in which one of the MAGIC images is too dim to survive analysis quality cuts. Results. Thanks to the resulting increase in the collection area and stronger background rejection, we found a significant improvement in sensitivity, allowing for the detection of 30% weaker fluxes in the energy range between 200 GeV and 3 TeV. The spectrum of the Crab Nebula, reconstructed in the energy range between âŒ60 GeV and âŒ10 TeV, is in agreement with previous measurements
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