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Examples of Bullseyes
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| from FIELD GUIDE | |
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from FIELD GUIDE
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from FIELD GUIDE
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from FIELD GUIDE
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| from FIELD GUIDE |
According to FIELD GUIDE ("FIELD GUIDE" is found to the right in https://www.zooniverse.org/projects/dwright04/supernova-hunters/about/research),
"Bullseyes result from problems during image processing and should be labelled bogus.
Bullseyes occur when a bright object is not subtracted properly. If the detection is centred on a bright object in the left and centre images, and the detection in the righthand image has a "shadow" of dark pixels or appears very narrow it is likely a bullseye.
Sometimes when the weather is better than normal in Hawaii the new target images can be sharper than the high-quality reference image. In the example above, the sources in the target image (left) appear smaller. This means light from that star has been scattered very little by turbulence in the atmosphere. However, on average the conditions are not as good and the sources in the reference image appear less sharp. When we subtract the two images the source often looks like a very sharp source in the difference image. Sometimes there may be negative pixels (black areas) next to the source as in the second example below. These artefacts can be very difficult to distinguish from real detections and we need to judge the quality of the reference compared to the target."
See also "Examples of bullseye artefacts and Darryl's comments" (https://www.zooniverse.org/projects/dwright04/supernova-hunters/talk/479/2640094)
Example of "Real": Supernova on or near the center of a galaxy
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from FIELD GUIDE
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from FIELD GUIDE and https://star.pst.qub.ac.uk/ps1threepi/psdb/candidate/1022313190043101900/
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| from FIELD GUIDE |
See also "Examples of "real" objects including SN, Asteroids, Variable stars and AGN, and Darryl's comments" (https://www.zooniverse.org/projects/dwright04/supernova-hunters/talk/479/2640454)
Examples of "Real": AGN and QSO
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| from FIELD GUIDE: AGN |
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| from FIELD GUIDE: AGN |
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| from FIELD GUIDE: QSO |
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| from FIELD GUIDE: QSO |
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| from https://star.pst.qub.ac.uk/ps1threepi/psdb/candidate/1055958951520654600/: confirmed AGN: AT2017hup |
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| from https://star.pst.qub.ac.uk/ps1threepi/psdb/candidate/1224342870165908400/: confirmed AGN: AT 2018bcb |
According to FIELD GUIDE,
"Active Galactic Nuclei (AGNs) and Quasi-Stellar Objects (QSOs)
AGNs and QSOs are really the same thing. The changes in brightness are the result of accretion onto a supermassive black hole at the centre of a galaxy. The difference is that for AGN we can easily see the galactic structure as in the first two examples above. QSOs appear more like stars (quasi-stellar) because we can only see the centre of the galaxy - the rest of the galaxy is too faint to be detected (3rd and 4th examples)."
Darryl (a researcher)'s comment:
"AGNs can vary on timescales of seconds to years and as such we probably expect to detect any known AGNs in the field of observations. This is provided that the difference in brightness between the reference and the target image is large enough to pass our signal-to-noise cuts and that the AGN is brightening and not fading compared to the reference image. We cross-match detections against known AGN catalogues and many do pop up each night. However, it can be very difficult to tell whether the detection in the difference image is due to real AGN activity or a bullseye artefact for example. We also have a cut on the brightness of stars for this very reason, it can be almost impossible to tell if bright stars are displaying real variability or if it is due to the differing quality of the target and reference. The reason we don't reject known AGNs is that, as you say, they could be confused with supernovae or tidal disruption events close to the nucleus of the galaxy. Here's an example from our Pan-STARRS Survey for Transients (PSST) webpages:
https://star.pst.qub.ac.uk/ps1threepi/psdb/candidate/1022313190043101900/
This is a Type Ia supernova, but it looks just like what we expect from an AGN. Without waiting around for months to see how the like curve evolves, the easiest way to tell the difference is to get a spectrum." (https://www.zooniverse.org/projects/dwright04/supernova-hunters/talk/479/62864?comment=126567)
Examples of "Real": Variable Stars
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| from FIELD GUIDE |
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| from FIELD GUIDE |
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| from FIELD GUIDE |
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| from FIELD GUIDE |
According to FIELD GUIDE,
"Some variable stars undergo violent outbursts that are many times brighter than the star in its quiescent state and may not be detected in the reference image."
Examples of "Real": TDE
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| from https://star.pst.qub.ac.uk/ps1threepi/psdb/candidate/1075654531341543500/: AT2018zr |
"TDE" is a Tidal Disruption Event (https://en.wikipedia.org/wiki/Tidal_disruption_event).
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