- Gamma-ray emission uncovered to the west of the Vela SNR
- Investigations of this region in the X-ray uncover soft, diffuse X-ray emission overlapping with the gamma-ray position
- We now look across the light spectrum using Aladin (free for everyone and you don’t need to download anything. It’s truly amazing – See over a dozen sky maps across the light spectrum right now: https://aladin.u-strasbg.fr/AladinLite/)
Click the link above. I’ll show you how we found our optical counterpart. Type in “08 26 07 -45 00 00” verbatim, double check you have “DSS2” selected. Hit ENTER. Do you see a thin film of material move downwards from the crosshair in the center of the screen? Yeah – that’s our optical counterpart and you just found it using the gamma-ray emission’s coordinates.
Here’s what I found out.
Vela is about 10,000 years old descending from a Type II supernova which we have discussed before here. Because it is a type II supernova remnant, it houses a pulsar, the remnant of the star’s explosion which powers a pulsar wind nebula that is quite large. Vela as it turns out is the closest composite SNR to Earth which means there are tons of literature about the region. I read dozens of papers studying Vela from the radio to the gamma-ray. It became apparent that the pulsar wind nebula is huge and is seen brightly in all wavelengths and so is the pulsar. The remnant itself was only known to generate gamma-rays 1.2 degrees away from the pulsar or about 15 parseconds (50 light years) but in the opposite direction of where we found the new gamma-ray emission and we are still not really sure where the gamma-rays in this other region come from. It’s possible it could be another interaction site (which I’ll get to).
Because Vela is a Type II supernova remnant, this means the area surrounding the remnant is quite dense compared to other regions of space. As a refresher, let’s remind ourselves that Type II supernovae occur when a seriously massive star explodes. Massive stars have shorter lifespans than smaller stars because the larger the star is, the faster it burns its fuel. Once it runs out, it explodes. The largest stars have lives as short as a few million years old. For comparison, our star, the Sun, is very “average” in size and will not explode at end of life but will rather complete a few evolutionary stages before shedding it’s layers and retiring to the white dwarf stage – which will take our Sun a total of 10 billion years. So, when a massive star is born, it is born into a dense environment of stellar gas, a stellar nursery, if you will. The most massive stars die off and explode the quickest and thus never leave the dense region of stellar gasses, so when it explodes, the explosion is typically very asymmetrical and quite complicated due to the complexity of the region. As the initial blast wave plows into interstellar space, it will readily interact with material already here like gas, dust, molecular clouds and clumps, etc. Depending on how fast the initial blast wave is and how dense the material is, it interacts differently. If the shock wave is still hugely fast, it will sweep up this material, shock it, and move it with the blast wave itself. If it is has slowed down considerably, it will run into the material and slowly shock and heat it as the shock wave dissipates into the material. The timescales of these interactions depend on the density of the material.
This was the same paper I noticed our optical counterpart was being studied. Like, our exact optical filament, believed to be associated in some way to the mysterious gamma-ray emission, was being discussed and implicated in a theory in this paper, that was published over 20 years ago.
We found older X-ray maps from a previous mission, ROSAT (The Roentgen satellite, named after the scientist who discovered X-rays), that mapped the entire Vela region in the soft X-rays. You can see in the image, appended below, where our source lies with respect to the entire remnant. Let’s spend a few minutes dissecting the image for a more wholesome understanding, then we will loop back to the important piece of evidence here.
So, essentially the bright X-ray boundaries give you a little information about the 1) density of the surrounding medium and 2) speed of the shock there and 3) where the remnant ends and the surroundings begin.
In summary, we have an optical filament attached to both the X- and gamma-ray emission to the west, that is now also associated with a neutral hydrogen cloud and they share opposite curvature, and all of this coincides with a bright X-ray boundary.