Revisiting the distance, environment and supernova properties of SNR G57.2+0.8 that hosts SGR 1935+2154

We have performed a multi-wavelength study of supernova remnant (SNR) G57.2+0.8 and its environment. The SNR hosts the magnetar SGR 1935+2154, which emitted an extremely bright ms-duration radio burst on 2020 Apr 28 (The Chime/Frb Collaboration et al. 2020; Bochenek et al. 2020). We used the 12CO and 13CO J=1-0 data from the Milky Way Image Scroll Painting (MWISP) CO line survey to search for molecular gas associated with G57.2+0.8, in order to constrain the physical parameters (e.g., the distance) of the SNR and its magnetar. We report that SNR G57.2+0.8 is likely impacting the molecular clouds (MCs) at the local standard of rest (LSR) velocity V_{LSR} ~ 30 km/s and excites a weak 1720 MHz OH maser with a peak flux density of 47 mJy/beam. The chance coincidence of a random OH spot falling in the SNR is <12%, and the OH-CO correspondence chance is 7% at the maser spot. This combines to give < 1% false probability of the OH maser, suggesting a real maser detection. The LSR velocity of the MCs places the SNR and magnetar at a kinematic distance of d=6.6 +/- 0.7 kpc. The nondetection of thermal X-ray emission from the SNR and the relatively dense environment suggests G57.2+0.8 be an evolved SNR with an age $t>1.6 \times 10^4$ (d/6.6 kpc) yr. The explosion energy of G57.2+0.8 is lower than $2 \times 10^{51}(n_0/10 cm^{-3})^{1.16} (d/~6.6 kpc)^{3.16}$ erg, which is not very energetic even assuming a high ambient density $n_0$ = 10 cm$^{-3}$. This reinforces the opinion that magnetars do not necessarily result from very energetic supernova explosions.Comment: 9 pages, 5 figures, accepted for publication in the Astrophysical Journa

A Novel Scheme for Accelerating Support Vector Clustering

Limited by two time-consuming steps, solving the optimization problem and labeling the data points with cluster labels, the support vector clustering (SVC) based algorithms, perform ineffectively in processing large datasets. This paper presents a novel scheme aimed at solving these two problems and accelerating the SVC. Firstly, an innovative definition of noise data points is proposed which can be applied in the design of noise elimination to reduce the size of a data set as well as to improve its separability without destroying the profile. Secondly, in the cluster labeling, a double centroids (DBC) labeling method, representing each cell of a cluster by the centroids of shape and density, is presented. This method is implemented towards accelerating this procedure and addressing the problem of labeling the original data set with irregular or imbalanced distribution. Compared with the state-of-the-art algorithms, the experimental results show that the proposed method significantly reduces the computational resources and improves the accuracy. Further analysis and experiments of semi-supervised cluster labeling confirm that the proposed DBC model is suitable for representing cells in clustering

Multi-wavelength study of the supernova remnant Kes 79 (G33.6+0.1): On its supernova properties and expansion into a molecular environment

Kes 79 (G33.6+0.1) is an aspherical thermal composite supernova remnant (SNR) observed across the electromagnetic spectrum and showing an unusual highly-structured morphology, in addition to harboring a central compact object (CCO). Using the CO J=1-0, J=2-1, and J=3-2 data, we provide the first direct evidence and new morphological evidence to support the physical interaction between the SNR and the molecular cloud at $V_LSR\sim 105$ km s$^{-1}$. We revisit the 380 ks XMM-Newton observations and perform a dedicated spatially resolved X-ray spectroscopic study with careful background subtraction. The overall X-ray-emitting gas is characterized by an under-ionized ($\tau_c \sim 6\times 10^{11}$ cm^${-3}$) cool ($kT_c \approx 0.20$ keV) plasma with solar abundances, plus an under-ionized ($\tau_h\sim 8\times 10^{10}$ cm$^{-3}$) hot ($kT_h\approx 0.80$ keV) plasma with elevated Ne, Mg, Si, S and Ar abundances. Kes 79 appears to have a double-hemisphere morphology viewed along the symmetric axis. Projection effect can explain the multiple shell structures and the thermal composite morphology. The X-ray filaments, spatially correlated with the 24 um IR filaments, are suggested to be due to the SNR shock interaction with dense gas, while the halo forms from SNR breaking out into a tenuous medium. The high-velocity, hot ($kT_h\sim 1.4$--1.6 keV) ejecta patch with high metal abundances, together with the non-uniform metal distribution across the SNR, indicating an asymmetric SN explosion of Kes 79. We refine the Sedov age to 4.4--6.7 kyr and the mean shock velocity to 730 km s$^{-1}$. Our multi-wavelength study suggests a progenitor mass of $\sim 15$--20 solar masses for the core-collapse explosion that formed Kes 79 and its CCO, PSR J1852+0040.Comment: 17 pages, 12 figures, 3 tables, published in Ap