3 Attachment(s)
Object of the Week, March 16, 2025 – IC 443, the "Jellyfish Nebula"
IC 443 (Sh 2-248, LBN 844, VMT 9, CTB 20, SNR 189.1)
SNR in Gemini
RA: 06h 17m
DEC: +22° 34'
Size: ~40'x50'
Today we visit the second-brightest Supernova Remnant (SNR) in the winter sky - IC 443, the "Jellyfish Nebula". Fading in the evening but still high enough in the sky, the object is 2.5° SE of Messier 35 and directly east of the 3.3mag star eta Gem.
The photographic discovery started interesting and differently than the "normal" visual discoveries of Herschel and co.
Max Wolf took a plate in 1892 from the T-Aur Nova through a 2 1/4" small Hermagis objective at Königstuhl Observatory, Heidelberg and reported "Very extended and bright nebulous masses...". E.E. Barnard independently discovered IC 443 (beside IC 444) in 1894 also photographically through probably the 6" Cook refractor at Vanderbilt Observatory.
Because of its position, size and brightness, the SNR has already been very well investigated scientifically. But what important details are known and understandable for a non-physicists like most of us.
The AGE unfortunately is only roughly determined by factor 10 and range between 3000 and 30000 years. Lee et al. (2008) defines probably the most accurate age at 20000 years.
The DISTANCE is better known and numbers dated it to around 5600ly. Messier 35 is listed at 2800ly.
The CULPRIT for this event is also known. The neutron star is called CXOUJ061705.3+222127 (see APOD) and is positioned somewhat off the geometric center at the southern edge of the SNR. The movement and the direction of the jet does not fit to the theory of the real initiator of the SNR. New studies found a potent source of gamma rays near the middle. Could this be the main culprit?
The STRUCTURE is also investigated intensively in several wavelengths. Roughly explained, IC 443 is situated in the third SNR phase - the pressure-driven snowplow phase. The expanding gas is interacting with the Gemini OB1 Molecular Cloud. Because of the differences in the density of the cloud, the shell-like SNR looks very different, and the structures vary from ring-like structures in the southwest, and wall-like straight structures in the brighter northeast.
As the APPENDIX, we got a second SNR in the field - SNR G189-6+03.3. Starting from the brightest north-western arc, we see two faint shock-waves, which represents the northern edge of the SNR. This remnant is believed to be much older than IC 443 and listed at around 10000 years. In contrast, new studies (A&A, 680 (2023) A83) suspected the same progenitor for both remnants and a multiple supernova alone for IC 443.
Now, what is visible in the telescope? Even when the SNR is the second-brightest object in the winter sky, IC 443 remains a difficult nebula. A good start is searching for the brightest NE part, which is also bright in the [OIII]. When the conditions are good enough, this part is visible as a small line up to around 4-inch. When the conditions are soso, it could be difficult even in 16-inch. A very narrow filter can help. The much fainter SW part is visible up to around 6-inch. Remember, it is huge. Try different exit-pupils and magnifications can be the key to see the remnants.
picture: Jens Zippel, FSQ 85, Ha/[OIII]/RGB
(link to single narrowband results)
Attachment 5675
sketch: Uwe Glahn, 6" (east to the right), 36x, [OIII], NELM 6m5+
Attachment 5676
sketch: Uwe Glahn, 27", 172x, [OIII], NELM 6m5+
Attachment 5677
Give it a go and let us know!
