From Wikipedia a supernova has been observed in NGC 4636 in 1939. It was a type Ia too, and the maximum magnitude was estimated to be 11.9. Same type, same distance so out of local light absorption, the magnitude of this one of today must reach similar value, isn't it?
And then 14.9 two days after the discovery I wonder that this means maybe that we are days after the maximum?
The spectrum suggests it was discovered before maximum and I have had feedback from a professional team that it is currently brightening. (The problem with magnitude measurements is they might be based on different comparision stars)
There are a couple of reasons why it may not be the same brightness as 1939A
1. There may be a different amount of interstellar absorption in the host galaxy between it and us compared with SN 1939A . (I have not seen any estimates of extinction but from a quick look at the spectrum it does not look exceptionally high.
2. Not all Ia have exactly the same luminosity. (To use them as "standard candles" the luminosity has to be corrected slightly based on the shape of the light curve)
It "should" be a bright one but we will have to see
Edited by robin_astro, 17 January 2020 - 06:25 AM.