G51.04+0.07 and its environment: Identification of a new Galactic supernova remnant at low radio frequencies

We have identified a new supernova remnant (SNR), G51.04+0.07, using observations at 74 MHz from the Very Large Array Low-Frequency Sky Survey Redux (VLSSr). Earlier, higher frequency radio continuum, recombination line, and infrared data had correctly inferred the presence of nonthermal radio emission within a larger, complex environment including ionised nebulae and active star formation. However, our observations have allowed us to redefine at least one SNR as a relatively small source (7.05 × 30in size) located at the southern periphery of the originally defined SNR candidate G51.21+0.11. The integrated flux density of G51.04+0.07 at 74 MHz is 6.1 ± 0.8 Jy, while its radio continuum spectrum has a slope α = −0.52 ± 0.05 (Sν ∝ να), typical of a shell-type remnant. We also measured spatial variations in the spectral index between 74 and 1400 MHz across the source, ranging from a steeper spectrum (α = −0.50 ± 0.04) coincident with the brightest emission to a flatter component (α = −0.30 ± 0.07) in the surrounding fainter region. To probe the interstellar medium into which the redefined SNR is likely evolving, we have analysed the surrounding atomic and molecular gas using the 21 cm neutral hydrogen (HI) and 13CO(J = 1 − 0) emissions. We found that G51.04+0.07 is confined within an elongated HI cavity and that its radio emission is consistent with the remains of a stellar explosion that occurred ∼6300 yr ago at a distance of 7.7 ± 2.3 kpc. Kinematic data suggest that the newly discovered SNR lies in front of HII regions in the complex, consistent with the lack of a turnover in the low frequency continuum spectrum. The CO observations revealed molecular material that traces the central and northern parts of G51.04+0.07. The interaction between the cloud and the radio source is not conclusive and motivates further study. The relatively low flux density (∼1.5 Jy at 1400 MHz) of G51.04+0.07 is consistent with this and many similar SNRs lying hidden along complex lines of sight towards inner Galactic emission complexes. It would also not be surprising if the larger complex studied here hosted additional SNRs.Fil: Supán, Jorge Leonardo. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; ArgentinaFil: Castelletti, Gabriela Marta. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; ArgentinaFil: Peters, W. M.. Spece Sciences División. Naval Research Laboratory; Estados UnidosFil: Kassim, N. E.. Spece Sciences División. Naval Research Laboratory; Estados Unido

Radio and X-ray study of two multi-shell Supernova Remnants: Kes79 and G352.7-0.1

We investigate two multi-shell galactic supernova remnants (SNRs), Kes79 and G352.7-0.1, to understand the causes of such morphology. The research was carried out based on new and reprocessed archival VLA observations and XMM-Newton archival data. The surrounding was investigated based on data extracted from the HI Canadian Galactic Plane Survey, the 13^CO Galactic Ring Survey and the HI Southern Galactic Plane Survey. The present study revealed that the overall morphology of both SNRs is the result of the mass-loss history of their respective progenitor stars. Kes79 would be the product of the gravitational collapse of a massive O9 star evolving near a molecular cloud and within the precursor's wind-driven bubble, while G352.7-0.1 would be the result of interactions of the SNR with an asymmetric wind from the progenitor together with projection effects. No radio point source or pulsar wind nebula was found associated with the X-ray pulsar CXOU J185238.6+004020 in Kes79. The X-ray study of G352.7-0.1, on its hand, revealed that most of the thermal X-ray radiation completely fills in the interior of the remnant and originates in heated ejecta. Characteristic parameters, like radio flux, radio spectral index, age, distance, shock velocity, initial energy and luminosity, were estimated for both SNRs.Comment: 14 pages, 13 figures. Accepted to be published in Astronomy and Astrophysic

Feature-tailored spectroscopic analysis of the SNR Puppis A in X-rays

We introduce a distinct method to perform spatially-resolved spectral analysis of astronomical sources with highly structured X-ray emission. The method measures the surface brightness of neighbouring pixels to adaptively size and shape each region, thus the spectra from the bright and faint filamentary structures evident in the broadband images can be extracted. As a test case, we present the spectral analysis of the complete X-ray emitting plasma in the supernova remnant Puppis A observed with XMM-Newton and Chandra. Given the angular size of Puppis A, many pointings with different observational configurations have to be combined, presenting a challenge to any method of spatially-resolved spectroscopy. From the fit of a plane-parallel shocked plasma model we find that temperature, absorption column, ionization time scale, emission measure and elemental abundances of O, Ne, Mg, Si, S and Fe, are smoothly distributed in the remnant. Some regions with overabundances of O-Ne-Mg, previously characterized as ejecta material, were automatically selected by our method, proving the excellent response of the technique. This method is an advantageous tool for the exploitation of archival X-ray data.Comment: Accepted in Astronomy & Astrophysic

The most complete and detailed X-ray view of the SNR Puppis A

With the purpose of producing the first detailed full view of Puppis A in X-rays, we carried out new XMM-Newton observations covering the missing regions in the southern half of the supernova remnant (SNR) and combined them with existing XMM-Newton and Chandra data. The new images were produced in the 0.3-0.7, 0.7-1.0 and 1.0-8.0 energy bands. We investigated the SNR morphology in detail, carried out a multi-wavelength analysis and estimated the flux density and luminosity of the whole SNR. The complex structure observed across the remnant confirms that Puppis A evolves in an inhomogeneous, probably knotty interstellar medium. The southwestern corner includes filaments that perfectly correlate with radio features suggested to be associated with shock/cloud interaction. In the northern half of Puppis A the comparison with Spitzer infrared images shows an excellent correspondence between X-rays and 24 and 70 microns emission features, while to the south there are some matched and other unmatched features. X-ray flux densities of 12.6 X 10^-9, 6.2 X 10^-9, and 2.8 X 10^-9 erg cm^-2 s^-1 were derived for the 0.3-0.7, 0.7-1.0 and 1.0-8.0 keV bands, respectively. At the assumed distance of 2.2 kpc, the total X-ray luminosity between 0.3 and 8.0 keV is 1.2 X 10^37 erg s^-1. We also collected and updated the broad-band data of Puppis A between radio and GeV gamma-ray range, producing its spectral energy distribution. To provide constraints to the high-energy emission models, we re-analyzed radio data, estimating the energy content in accelerated particles to be Umin=4.8 X 10^49 erg and the magnetic field strength B=26 muG.Comment: Article accepted to be published in the Astronomy and Astrophysics Main Journa

Optimisation-based refinement of genesis indices for tropical cyclones

Tropical cyclone genesis indices are valuable tools for studying the relationship between large-scale environmental fields and the genesis of tropical cyclones, supporting the identification of future trends of cyclone genesis. However, their formulation is generally derived from simple statistical models (e.g., multiple linear regression) and are not optimised globally. In this paper, we present a simple framework for optimising genesis indexes given a user-specified trade-off between two performance metrics, which measure how well an index captures the spatial and interannual variability of tropical cyclone genesis. We apply the proposed framework to the popular Emanuel and Nolan Genesis Potential Index, yielding new, optimised formulas that correspond to different trade-offs between spatial and interannual variability. Result show that our refined indexes can improve the performance of the Emanuel and Nolan index up to 8% for spatial variability and 16%-22% for interannual variability; this improvement was found to be statistically significant (p < 0.01). Lastly, by analysing the formulas found, we give some insights into the role of the different inputs of the index in maximising one metric or the other

A new study towards PSR J1826-1334 and PSR J1826-1256 in the region of HESS J1825-137 and HESS J1826-130

Aims. The goal of this paper is to detect synchrotron emission from the relic electrons of the crushed pulsar wind nebula (PWN) HESS J1825-137 and to investigate the origin of the $\gamma$-ray emission from HESS J1826-130.\\ Methods. The study of HESS J1825-137 was carried out on the basis of new radio observations centred at the position of PSR J1826-1334 performed with the Karl G. Jansky Very Large Array at 1.4 GHz in configurations B and C. To investigate the nature of HESS J1826-130, we reprocessed unpublished archival data obtained with XMM-Newton.\\ Results. The new radio continuum image towards PSR J1826-1334 reveals a bright radio source, with the pulsar located in its centre, which suggests that this feature could be the radio counterpart of the compact component of the PWN detected at high energy. The new 1.4 GHz radio data do not reveal emission with an extension comparable with that observed in $\gamma$-rays for the HESS J1825-137 source. On the other hand, the XMM-Newton study of the region including PSR J1826-1256 reveals an elongated non-thermal X-ray emitting nebula with the pulsar located in the northern border and a tail towards the peak of the very high energy source. The spectrum is characterized by a power law with a photon index going from 1.6 around the pulsar to 2.7 in the borders of the nebula, a behaviour consistent with synchrotron cooling of electrons. From our X-ray analysis we propose that HESS J1826-130 is likely produced by the PWN powered by PSR J1826-1256 via the inverse Compton mechanism.Comment: 9 pages, 5 figures, 4 tables. Accepted for publication in the Astronomy & Astrophysics Journal. The quality of the images has been degrade

Arctic sea ice dynamics forecasting through interpretable machine learning

Machine Learning (ML) has become an increasingly popular tool to model the evolution of sea ice in the Arctic region. ML tools produce highly accurate and computationally efficient forecasts on specific tasks. Yet, they generally lack physical interpretability and do not support the understanding of system dynamics and interdependencies among target variables and driving factors. Here, we present a 2-step framework to model Arctic sea ice dynamics with the aim of balancing high performance and accuracy typical of ML and result interpretability. We first use time series clustering to obtain homogeneous subregions of sea ice spatiotemporal variability. Then, we run an advanced feature selection algorithm, called Wrapper for Quasi Equally Informative Subset Selection (W-QEISS), to process the sea ice time series barycentric of each cluster. W-QEISS identifies neural predictors (i.e., extreme learning machines) of the future evolution of the sea ice based on past values and returns the most relevant set of input variables to describe such evolution. Monthly output from the Pan-Arctic Ice-Ocean Modeling and Assimilation System (PIOMAS) from 1978 to 2020 is used for the entire Arctic region. Sea ice thickness represents the target of our analysis, while sea ice concentration, snow depth, sea surface temperature and salinity are considered as candidate drivers. Results show that autoregressive terms have a key role in the short term (with lag time 1 and 2 months) as well as the long term (i.e., in the previous year); salinity along the Siberian coast is frequently selected as a key driver, especially with a one-year lag; the effect of sea surface temperature is stronger in the clusters with thinner ice; snow depth is relevant only in the short term. The proposed framework is an efficient support tool to better understand the physical process driving the evolution of sea ice in the Arctic region