Saturday, February 10, 2024

A Tale of Two Supernovae ... Part 2

 Saturday Night Turned into Sunday Morning ...

Picking up where we left off in part 1, we removed the L-eXtreme filter from the imaging train because we planned on imaging a broadband target, and the dual-narrowband filter would detrimentally impact the results. Dual-narrowband filters are effective for emission nebulae like H2 regions, supernovae remnants, and planetary nebulae but are not recommended when imaging targets like galaxies, star clusters, and reflection nebulae. Since we changed the imaging train, we took a second set of flats to be used with this target. It was after midnight at this point, and we agreed to image to 1 am. We opened the roof and slewed the telescope to Virgo, which was rising above the eastern horizon. Our target was a recent supernova that had occurred in the Galaxy NGC 4216. The supernova was discovered on January 4, 2024 by Japanese astronomer Koichi Itagaki, who has discovered 170 supernovae! This supernova has a designation of, SN 2024gy. 

We imaged until the agreed upon time of 1 am. We ended up rejecting the last few subs (short for sub-exposure) as the image quality was degrading due to the poor transparency. Had to be some very high thin cloud or haze, even though the sky looked clear, guiding, focus, and image quality indicated we were losing the skies. We managed to collect 7 subs at 180 sec each. The supernova, the dust lanes in NGC 4216, and many smaller background galaxies were visible in the individual exposures. Here is the resulting image: 

SN 2024gy in NGC 4216 captured on 2/4/2024 from the BMO.

An annotated version of the image indicating the location of supernova SN 2024gy.

An animated GIF of SN 2024gy in NGC 4216


All pre and post processing was performed in PixInsight. Pre-processing: Blink & WBPP. Linear Post-processing: GraXpert, BXT (correct only), Color Calibration, BXT, NXT, & Histogram Transformation. Non-linear Post Processing: SXT. Stars: Curves (saturation) and SCNR. Starless: Curves (contrast & saturation), SCNR, LHE (3x's), Unsharp Mask, MMT, and PixelMath (to screen the stars back in).

Magnitude Estimate:

Disclaimer: I'm not an experienced variable star observer. There is a decent probability that the following methodology is flawed.

The BAA had our monthly meeting for February on 2/9/2024. After the meeting, I joined the Astrophotography breakout room, and we discussed estimating the magnitude of the supernova from the images we collected on 2/4/2024. This ended up as a fun activity for the small group of us left in the meeting. Since imaging supernova SN2023ixf in M101 in May of 2023, I've made an effort to try to learn how to estimate the magnitude of the supernova from my images. I recently joined the AAVSO and managed to cobble together and idea on how to estimate the magnitude of the supernova from stars with known magnitudes in the same field of view. The manner in which we captured images was optimized for "pretty pictures" not photometry, but the value we ended up with is pretty close to other reported values of the supernova from the same date. 

One of the other members generated a star chart from the AAVSO website. This chart depicted stars in the field of view, of which several were labeled with known magnitudes. It took some trial and error to the chart correct so it matched the field of view of our image. The first chart was off, we had used RA & Dec coordinates from Sky Safari. When we used RA & Dec coordinates from The Sky X, it finally matched the image. We think the difference may be the epoch used by each software (J2000 vs. Jnow). We visually estimated the brightness to be somewhere between 13 and 15th magnitude. Another member pulled a light curve from the AAVSO website. This light curve was compiled from member reports and indicated that the magnitude was around 13.5. We identified a star in the field with a known magnitude of 13.1. I took one of the calibrated and debayered individual sub exposures and extracted the RGB channels in PixInsight. The image was still linear, only a display or screen stretch was applied. Using the green channel, we measured the flux of the known star and the supernova using PixInsight's Dynamic PSF process. We put the resulting values into this formula:

Mag(supernova) = Mag (star) - 2.5Log(FluxSN/FluxStar)

We came up with a magnitude of 13.4 which closely matches reported values!!!! 

What is it?

SN 2024gy is a Type 1A Supernova in the Galaxy NGC 4216. It was discovered on 1/4/2024 by Japanese astronomer Koichi Itagaki. Type 1A supernovae occur when a White Dwarf syphons material from another star that it is in a binary pair with. Once the White Dwarf reaches 1.4 times the mass of the Sun, it goes Supernova. This type of Supernova is used as a standard candle and is important in determining the distance to objects in the universe.

Annotated image of the field of view.

How far is it?

It is located about 45 million light-years (ly) from Earth in the Constellation Virgo.

How to find it?

SN  2024gy is located in the Galaxy NGC 4216 which is located in the Constellation Virgo. Refer to the Finder Chart below. The tiny red rectangle in the center of the image marks the position of NGC 4216. It is very near M86, in the bowl of Virgo.

      Finder Chart for NGC 4216. 

      Image Details:

      Capture Date: 02/04/2024
      Location: Beaver Meadow Observatory (North Java, NY)
      Telescope: Celestron 14" Edge HD w/0.7x Reducer
      Camera: ZWO ASI2600MC Pro
      Filter: none
      Mount: Astro Physics AP-1200
      Exposure: 7 exposures at 180 sec / Gain 100 / Offset 50 / -10°C each for a total exposure of 21 minutes
      Software: NINA, PHD2, and PixInsight

      Clear Skies!

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