IC 443: The Jellyfish Nebula...

Object: IC 443
Type: Supernova remnant
Constellation: Gemini
Distance: 5000 light years

Date: February 10th. 2019
Equipment: ATIK 460EX, Vixen 114mm f5.3 ED114 refractor, NEQ6 mount, guiding with Lodestar X2/PHD

Subframes: 16 x 600s H-alpha, 6 x 150s each for RGB (2x2 binned), no flats, hot pixel removal in Astroart (no main frame darks).

Discovered on September 25th, 1892 by German astrophotographer Max Wolf, IC 443 is a supernova remnant in the constellation Gemini, produced by a supernova explosion thought to have occurred between 3,000 and 30,000 years ago.  Physically, the nebula is about 70 light years across. Visually it appears to be approximately 50 arc-minutes across, an area of sky just under twice the apparent size of the full moon.  It is not readily seen in backyard telescopes.

The location of IC 443 is shown in the Stellarium sky chart below, just to the east of the third magnitude star Eta Geminorium (named Propus, the bright orange star to the right of the image).

Observations from the Chandra X-ray observatory show that the explosion that created the Jellyfish Nebula may have also formed a peculiar object located on the southern edge of the remnant, called CXOU J061705.3+222127, or J0617 for short. The object is likely a rapidly spinning neutron star, or pulsar, representing the end stage of a star with between 1.4 and 3 solar masses  

When a massive star runs out of thermonuclear fuel, it implodes, forming a dense stellar core called a neutron star.  The outer layers of the star collapse toward the neutron star then bounce outward in a supernova explosion.  

A spinning neutron star that produces a beam of radiation is called a pulsar.  The radiation sweeps by like a beacon of light from a lighthouse and can be detected as pulses of radio waves and other types of radiation.

The comet-like shape of the diffuse X-ray emission suggests motion towards the lower right of the image.  The structure is also evidenced at visible wavelengths, as highlighted in the hydrogen alpha image below:

The orientation of the “line” is about 50 degrees away from the direction expected if the pulsar was moving away from the centre of the supernova remnant in a straight line.

This misalignment has cast some doubt on the association of the pulsar with the supernova remnant. 

However, it is thought that this misalignment could also be explained by movement towards the left of material in the supernova remnant pushing J0617's cometary tail aside.



Seeing conditions and atmospheric clarity were excellent on this particular evening. I was able to grab 16 hydrogen alpha frames before the dreaded "meridian flip" (where the object crosses the east/west line, requiring the telescope to be spun round to prevent it hitting its own pier).  This is a pain and requires the telescope to be re-targetted, although fortunately my set-up usually gets the object back on the CCD chip after the flip, requiring only minor adjustments to re-frame the object on the CCD chip.

Given that the weather forecast was threatening clouds, I decided to grab the RGB frames rather than get more H-alpha data, although 16 subs isn't really enough to beat the background noise down.  My luck held, and I got the last of the blue subs just as a few clouds started to roll in at around midnight.

Colour processing was conducted using the same methods as I used for the Cave Nebula.