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Register a new userThe kinematic distances of SNR G16.7+0.1 and G15.9+0.2 by analyzing HI absorption spectra
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We build HI absorption spectra towards Supernova Remnant (SNRs) G16.7+0.1 and G15.9+0.2 using the THOR survey data. With the absorption spectra, we give a new distance range of 7 to 16 kpc for G15.9+0.2. We also resolve the near/far-side distance ambiguity of G16,7+0.1 and confirm its kinematic distance of about 14 kpc. In addition, we analyze the CO (J=3-2) spectra towards G16.7+0.1 and find obvious CO emission at the 20 kms$^{-1}$ OH 1720 MHz maser site. This supports Reynoso and Mangum (2000)s suggestions that the velocity difference between the maser and southern molecular cloud is caused by the shock acceleration. We discuss the impact of the distances on other physical parameters of the two SNRs.
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G15.9+0.2 is a Galactic shell-type supernova remnant (SNR), which was detected in radio and has been confirmed in X-rays based on Chandra observations. An X-ray point source CXOUJ181852.0-150213 has been detected and suggested to be an associated neutron star. In a recent study, we have confirmed the source to be a central compact object (CCO). We have studied the SNR using high-resolution X-ray data taken with Chandra in combination with infrared (IR) data in order to understand its emission and to derive its physical parameters. This will also help to constrain, e.g., the age of the CCO and the environment in which it was born. The spectral analysis of the X-ray emission using the new Chandra data and the comparison to the IR data have shown that the SNR is relatively young with an age of a few thousand years and that its emission is dominated by that of shocked interstellar medium (ISM). However, the analysis of the spectrum of the bright eastern shell shows that there is an additional emission component with enhanced abundances of {alpha} elements and Fe, suggesting ejecta emission. The multi-wavelength emission is consistent with SNR G15.9+0.2 expanding in an ISM with a density gradient, while there is also colder material located in front of the SNR, which absorbs its thermal X-ray emission in the softer bands.
We present X-ray observations of PWN G16.73+0.08/SNR G16.7+0.1 using archival data of {it Chandra} ACIS. The X-ray emission peak location of this pulsar wind nebula is found to be offset by 24 arcsec from the centre of the 1.4-GHz emission of this nebula. The X-ray nebula is elongated in the direction from the X-ray peak to the 1.4-GHz emission centre. This offset suggests that G16.73+0.08 is an evolved pulsar wind nebula interacting with the supernova remnant reverse shock. We identify a point source, CXO J182058.16-142001.5, near the location of the X-ray peak. The spectrum of the X-ray nebula can be described by an absorbed power law of photon index $0.98^{+0.79}_{-0.71}$ and hydrogen column density $N_{rm H}=4.99^{+2.75}_{-2.28}times 10^{22}$ cm$^{-2}$. CXO J182058.16-142001.5 is likely a pulsar. We estimate its spin-down power to be about $2.6times 10 ^{36}$ erg s$^{-1}$. Assuming its age at 3000 and 10,000 years, its dipole magnetic field strength at the polar surface is estimated to be about $4.2 times 10^{13}$ G and $1.3 times 10^{13}$ G, respectively.
We have observed the Galactic supernova remnant G16.7+0.1 for 13 ks using the EPIC cameras aboard the XMM-Newton X-ray Observatory, producing the first detection of the SNR outside of the radio band. G16.7+0.1 is one of the faintest radio synchrotron nebulae yet detected, although the core-to-shell flux ratio at 6 cm is typical of composite SNRs. The distance to the object is unknown. Our image is seriously contaminated by single-reflection arcs from the X-ray binary GX17+2, which lies just outside the field of view. Nonetheless, the remnants synchrotron core is clearly detected. We report on the spectrum and intensity of the core emission as well as on our search for emission from the thermal shell, and describe the constraints these observations place on the SNRs distance, age, and central pulsar properties.
There are either a near kinematic distance of 5.5 kpc or a far distance of 8.8 kpc for a Galactic supernova remnant (SNR) G32.8$-$0.1 derived by using the rotation curve of the Galaxy. Here we make sure that the remnant distance is the farther one 8.8 kpc through solving a group of equations for the shell-type remnants separately at the adiabatic-phase and the radiative-phase. For SNR G346.6$-$0.2 we determine its distance also the farther one 11 kpc rather than the nearer one 5.5 kpc.
We measure the neutral atomic hydrogen (HI) gas content of field galaxies at intermediate redshifts of z ~ 0.1 and z ~ 0.2 using hydrogen 21-cm emission lines observed with the Westerbork Synthesis Radio Telescope (WSRT). In order to make high signal-to-noise ratio detections, an HI signal stacking technique is applied: HI emission spectra from multiple galaxies, optically selected by the CNOC2 redshift survey project, are co-added to measure the average HI mass of galaxies in the two redshift bins. We calculate the cosmic HI gas densities ({Omega}_{HI}) at the two redshift regimes and compare those with measurements at other redshifts to investigate the global evolution of the HI gas density over cosmic time. From a total of 59 galaxies at z ~ 0.1 we find {Omega}_{HI} = (0.33 $pm$ 0.05) ~ $times$ 10$^{-3}$, and at z ~ 0.2 we find {Omega}_{HI} = (0.34 $pm$ 0.09) ~ $times$ 10$^{-3}$, based on 96 galaxies. These measurements help bridge the gap between high-z damped Lyman-$alpha$ observations and blind 21-cm surveys at $z=$ 0. We find that our measurements of {Omega}_{HI} at z ~ 0.1 and 0.2 are consistent with the HI gas density at z ~ 0 and that all measurements of {Omega}_{HI} from 21-cm emission observations at $z la$ ~ 0.2 are in agreement with no evolution of the HI gas content in galaxies during the last 2.4 Gyr.
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