Distances of the TeV SNR complex CTB 37 towards the Galactic Bar

TL;DR

This study refines the distances to the CTB 37 supernova remnants using HI absorption measurements, revealing they are at different locations in the Galaxy and not associated with the historical supernova AD 393.

Contribution

The paper provides revised kinematic distances for the CTB 37 SNRs using HI absorption data, clarifying their positions relative to Galactic structures.

Findings

CTB 37A is at 6.3-9.5 kpc, closer than previously thought.

G348.5-0.0 is at ≤6.3 kpc, likely in front of the 3-kpc arm.

CTB 37B is at approximately 13.2 kpc, farther than earlier estimates.

Abstract

Three supernova remnants form the CTB 37 complex: CTB 37A (G348.5+0.1, associated with the TeV $\gamma$-ray source HESS J1714-385), CTB 37B (G348.7+0.3, associated with HESS J1713-381 and the magnetar CXOU J171405.7.381031), and G348.5-0.0. We use 21 cm HI absorption measurements to constrain the kinematic distances to these SNRs, which have not previously been determined well. We revise the kinematic distance for CTB 37A to be in the range 6.3 to 9.5 kpc (previously $\sim$11.3 kpc) because it is beyond the near 3-kpc arm and in front of the far side of the CO cloud at -145 km s$^{-1}$ towards $l$=348.5. G348.5-0.0 has a HI column density (N$_{HI}$ $\sim6.1\times10^{21}$ cm$^{-2}$) lower than CTB 37A ($\sim7.1\time10^{21}$ cm$^{-2}$). Also, G348.5-0.0 does not have the major absorption feature at -107 km s$^{-1}$ that CTB 37A shows. This is caused by the near 3-kpc arm, so G348.5-0.0 is at a distance of $\le$ 6.3 kpc. CTB 37B is at a distance of $\sim$13.2 kpc (previously 5 to 9 kpc) based on: 1) it has an absorption feature at -10$\pm$5 km s$^{-1}$ from the far 3-kpc arm, so CTB 37B is behind it; 2) there is absorption at -30 km s$^{-1}$ but not at -26 km s$^{-1}$, which yields the distance value; 3) the HI column density towards CTB 37B ($\sim8.3\times10^{21}$ cm$^{-2}$) is larger than CTB 37A. In summary, CTB 37A, CTB 37B and G348.5+0.0 are all at different distances and are only by chance nearby each other on the sky. In addition, we conclude that CTB 37 A and B are not associated with the historical Supernova AD 393.