Discovery of an old supernova remnant candidate through carbon monoxide line emission

Most old supernova remnants (SNRs) in the Milky Way have not yet been identified. Considering their large potential number and the sufficient momentum-energy transfer to the interstellar medium (ISM), they are a key part of our understanding of the overall role of SNRs in the ISM. Here we report our discovery of an expanding molecular shell identified by CO line observations, namely G16.11-0.51. It covers a known SNR, specifically G16.0-0.5, and is larger in size, i.e. 0.56 deg over 0.20 deg. Based on its spatial and kinematic structures, weak nonthermal radio-continuum emission, and derived physical properties, we suggest that it is an old SNR. At a systemic velocity of +41.3 km s^-1, the best estimated kinematic distance of G16.11-0.51 is ~3.2 kpc, implying its radius of about 15.6 pc. The age of G16.11-0.51 is estimated to be greater than ~10^5 yr, and, in a dense molecular environment, it has formed dense and thin shell layers. The kinetic energy of the expanding molecular gas of G16.11-0.51 is about 6.4x10^49 erg, accounting for approximately six percent of the initial SN explosion energy. Although old SNRs have essentially become cold and hard to detect, our discovery suggests that they can be found by searching for CO line emissions.Comment: 10 pages, 6 figures, 1 table, in production in Astronomy&Astrophyic

Pressure Balance and Energy Budget of the Nuclear Superbubble of NGC 3079

Superbubbles in the nuclear region of galaxies could be produced by the AGN or nuclear starburst via different driving forces. We report analysis of the multi-wavelength data of the kpc-scale nuclear superbubble in NGC 3079, in order to probe the mechanisms driving the expansion of the superbubble. Based on the Chandra X-ray observations, we derive the hot gas thermal pressure inside the bubble, which is about one order of magnitude higher than that of the warm ionized gas traced by optical lines. We derive a [C II]-based star formation rate of ${\rm SFR}\sim1.3\rm~M_\odot~{\rm yr}^{-1}$ from the nuclear region using the SOFIA/FIFI-LS observation. This SFR infers a radiation pressure toward the bubble shells much lower than the thermal pressure of the gases. The VLA radio image infers a magnetic pressure at the northeast cap above the superbubble less than the thermal pressure of the hot gas enclosed in the bubble, but has a clearly larger extension. The magnetic field may thus still help to reconcile the expansion of the bubble. The observed thermal energy of the hot gas enclosed in the bubble requires an energy injection rate of $\gtrsim10^{42}\rm~ergs~s^{-1}$ within the bubble's dynamical age, which is probably larger than the power provided by the current nuclear starburst and the parsec-scale jet. If this is true, stronger past AGN activity may provide an alternative energy source to drive the observed bubble expansion.Comment: 12 pages, 3 figures, 1 table, ApJ in pres

Detect anomalous quartic gauge couplings using isolation forest

The search of new physics~(NP) beyond the Standard Model is one of the most important tasks of high energy physics. A common characteristic of the NP signals is that they are usually few and kinematically different. We use a model independent strategy to study the phenomenology of NP by directly picking out and studying the kinematically unusual events. For this purpose, the isolation forest~(IF) algorithm is applied, which is found to be efficient in identifying the signal events of the anomalous quartic gauge couplings~(aQGCs). The IF algorithm can also be used to constraint the coefficients of aQGCs. As a machine learning algorithm, the IF algorithm shows a good prospect in the future studies of NP.Comment: 19 pages, 10 figure

Subspecies in Przewalski's gazelle Procapra przewalskii and its conservation implication

Przewalski's gazelle Procapra przewalskii is an endangered species endemic to China. A question remains about subspecific variation in this species. Skulls of Przewalski's gazelle collected from its current remnant ranges around the Qinghai Lake in combi

The Online Data Quality Monitoring System at BESIII

The online Data Quality Monitoring (DQM) plays an important role in the data taking process of HEP experiments. BESIII DQM samples data from online data flow, reconstructs them with offline reconstruction software, and automatically analyzes the reconstructed data with user-defined algorithms. The DQM software is a scalable distributed system. The monitored results are gathered and displayed in various formats, which provides the shifter with current run information that can be used to find problems early. This paper gives an overview of DQM system at BESIII.Comment: Already submit to Chinese Physics