Undiscovered #supernova candidate in the picture. 🙂

Hi, :slightly_smiling_face:

While wandering around in Legacy Survey I found a beautiful, undiscovered transient candidate. The green/aqua blob is visible in DECaLS DR5 and DR7, Legacy Survey 6&7 and DES DR1. Not visible in SDSS and PanSTARRS or HSC DR2.

There are three ‘single image cutouts’ 2015-11-06 in r-band (first seen) and two from 2015-11-07 in g and r-band.

I was able to open some DES DR1 fits.gz data (images and headers) in APT via the DES DR1 site. These images are from 2017-5-4. Could it be that this transient lasts 1,5 year? :thinking:

This candidate is not in NED, Simbad Search, the TNS or the RBS pages. It has given mags. in the DECaLS DR5, DR7 and Legacy Survey DR8 and DR9 catalog. The mags. from DR8 and DR9 are unlikely so maybe I have to calculate an apparent magnitude before reporting.

Ine :stars::dizzy:






cutout (1)


Hi Ine,

All the data shown in the “DECaLS DR5” layer for that location were taken as part of the DES program (DES proposal ID 2012B-0001), eg decals-dr5 data for RA,Dec (358.3822, 1.2269)

My guess might be that the DES DR1 images are COADDS with a date like when they were coadded, or something bad like that.

Our fit for it in DR7 (look at the DECaLS DR7 Model layer) is terrible, so I wouldn’t trust that catalog photometry.


Hi Dustin, :slightly_smiling_face:

To report it is common that you use the image data (fits file) of that image where the transient is first visible. In this case, that’s an image from 2015-11-06 in r-band. (a ‘single image exposure’ of the DECaLS exposures) That is, if that particular image is not damaged or is of poor quality.

Because I had to make sure there was no image from an earlier point in time in DES DR1 I had to view the headers of the DES images in APT. But these were fortunately from a later date. DES has no single exposures. And the images I was able to obtain from the DES website were indeed of poor quality.

So I certainly will not use the DES images to calculate an apparent magnitude. I will also compare my calculated, Apparent magnitude with the DECaLS DR7 catalog r-band magnitude.There shouldn’t be too much difference between the DECaLS DR7 catalog’s r-band magnitude and the calculated Apparent magnitude.

But first I have to find a suitable reference target (star) before I can determine the fluxes with APT and apply the equation. :slightly_smiling_face:

Thank you for your reply.

Kind regards from Ine :stars::dizzy:

The DECaLS DR7 catalog magnitude for that source will be an average of all the exposures, and most of the exposures do not contain the transient, so they will drag the flux down to zero.

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That’s why Richard Nowell and I usually calculate an Apparent magnitude because the catogus magnitudes are often incorrect or unrealistic.

Sometimes we use the given magnitudes of the SDSS skyserver DR14 when it concerns a transient in SDSS. Usually these transients are referred to as star or galaxy in the SDSS skyserver DR14 tool.

Ine :stars::dizzy:

B.t.w. this will be my 90th discovered #transient. :grinning::star_struck:
In the beginning Richard or Melina did report for me but now I can do it myself.

When I discovered my first supernova candidate, I fell completely in love with the supernova phenomenon. I am constantly hunting for supernovae in the Legacy Survey Sky browser. And when I find another one, I’ll be over the moon ha ha! :relaxed::star_struck: But of course they shouldn’t get too close…:wink:

Ine :stars::dizzy:

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Congratulations Ine!


Alright reported as AT2015dy. :slightly_smiling_face:


I calculated an Apparent magnitude of 19.52 with APT and a this reference star here: SDSS J235326.55+011322.7


Initially I chose a different reference star but this star was outside the fits file image. The calculated Apparent magnitude is and will always remain an estimate.

Mag. target=mag. reference-2.5*
log10( flux target/flux reference)
Mag. target=18.48-2.5*
Mag. target=19.5182816566
Apparent magnitude target=19.52

I also calculated an Absolute magnitude of -17.53

Ine :stars::dizzy: