Mon, 02/17/2020 - 17:10
Hello! I imaged DY HER last night. It is a short period vairable, so I was doing a time series.
There is a bright spot that appears in one of the images (DY HER1 V15) that I wonder is a cosmic ray hit. It only appears in the one image and threw off the photometry of DY HER for this image since it is next to the 114 comp.
It looks too perfectly circular. Perhaps something that went on with the pixels themselves for this exposure?
The three bright stars form an asymetric triangle. The bright spot appears next to the lower left hand star, which is comp 114. I've included DY HER1 V14 and DY HER2 V1 as well, which bracket the image in question. Thank you and best regards.
Mike
File Upload
DY HER1_120sec_V_0014_-10C_P.JPG86.65 KB
DY HER1_120sec_V_0015_-10C_P.JPG84.53 KB
DY HER2_120sec_V_0001_-10C_P.JPG109.34 KB
Hello! Sorry, I forgot to upload the B and I images that bracketed V15. The order in the sequence was B filter first, then V, then I. I've uploaded DY HER1 B15, V15, and I15. The exposures for the time series were all 2-minutes in length.
There appears to be a tiny spot at DY HER1 I15 at that spot. Perhaps a transient hot pixel, if there is such a thing? Best regards.
Mike
Mike, I looked at the pictures in MaximDL, especially the star profiles. On JPG's all the bright star-like objects are saturated at 256 , including the suspicious transient object. I would guess that it is an artifact. A transient star, especially if saturated, would cast a halo. The shoulder on this artifact has some slope, but an astronomical object I would expect a halo showing a more gradual return to background. I assume you have the raw FITS images so we can see all 16 bits.
Don
Thanks! Then is it transient saturated pixels for some reason that developed from the camera's electronics?
Mike
Hello! Here is the link to the FITS files, both raw and calibrated (P files). Best regards.
Mike
https://www.dropbox.com/sh/3e7kfs9cgozndfh/AABr9UhiJpfYojZfsS22tUexa?dl…
Michael, I have attached 2 3-D plots of the profiles that include the transient as well as the bright star next to it. On the autoscale plot of the raw FITS image, the transient saturates a single pixel. Scaling for the stars in the field the star profile is well-shaped. The single pixel transient also generates a halo about the same width as the star's FWHM. The single pixel bright transient indicates to me an internal electronic event. I don't know much about the physics of cosmic ray hits, they are usually squiggles appearing randomly. There is such a "squiggle" on the left edge of your image, but that "squiggle" is not at all saturated. Do you find the saturated transient in the other bands?
Don
Interesting. I mean if the point spread function of the transient is consistent with that of a star (looks like it to me, whether it happens to saturate a pixel or not), how are we to tell this is *not* an astrophysical transient? Would be informative to see the FWHM value and campare it to other stars, will do this later this evening.
The main evidence to me seems to be the absence of a signal in the frames bracketing the transient both in time and wavelength (have not checked this myself, I trust that someone has done that already). I simple don't know of any type of astrophysical transient that could rise and fade so quickly by what must be many magnitudes between the transient's magnitude estimate and the limiting magnitude , in a matter of around 2 minutes. If someone could tell me a type of transient that can do this, I would think this one deserves a deeper investigation :-) Gamma ray burst optical aferglows come to mind... perhaps???
Just to be sure, the date+timestamps in the FITS files are reasonably accurate??? (say within +/- 1 minute?)
Cheers
HB
OK
On the V_0015 image I see this transient source, at a sky position of RA 16:30:58.58 DEC 11 59 24.6 DEC 11 59 24.9
On the I_0015 image, I also see a faint source at exactly the same position. What I find striking is that the stars on the I image are somewhat more elongated (tracking drift), but so is the faint spot, and in a consistent direction.
I think someone with more experience than me should have a look at this.At the moment I see nothing in the pictures itself that would rule out an optical signal (as opposed to a sensor artefact),
CS
HB
EDIT: It would be interesting to know how many more images you have after this one in the timeseries. It would probably make sense to co-add those images to see if there is a detectable signal persisting for some time if you increase the SNR.
It looks like the object (point) is on both the V and I frame. Cosmic-rays would only be on a single frame. The I frame really looks like it could be a real object. I can think of a few options here, but would want to check them out. I have a lot of DY Her data over many years. It would be interesting to see if this has happened before. Or if there was a deeper exposure that showed something. It doesn't look like a transiting object like an asteroid, so it would be interesting to look for other frames covering this area.
To be sure that the I-band image is telling us anything useful, one would have to be sure that the sensor isn't showing residual bulk image (RBI) artefacts here. So if you have a very bright star in a frame (say 7 or 8 mag) and then take a dark frame immediatly afterwards, will there be traces of the bright star on the first dark frame? In that case, the signal on the I band image could just be a "ghost" image of whaever saturated the sensor on the previous V band image where we see this "transient". To me it looks a bit bright to be a "ghost", but this is easily tested.
The last time I saw something similar on one of my own images was a perfectly shaped "new" star on one frame....but there were two trails to the left and right ... from the position lights of an airplane and that "star" was an image of a strobe light on that airplane. So I was lucky to have a field wide enough to catch the trails from the plane's lights that are always on :-)
CS
HB
Thank you, all! I appreciate the feedback.
I've got about 32 images of 2-minute integrations in each B,V, and I filter - 7 after the images in question. I stacked those, but I did not see anything at the position of interest. Best regards.
Mike
Too bad, we might never learn what this was. I have not found any object at that position in any of the databases I checked, neither galactic nor extra-galactic. I haven't found a gamma ray burst being reported for that time either.
It's not crazy to think this was real, so called Fast Optical Transients are the subject of active research, e.g. https://arxiv.org/abs/1903.11083 , and I guess theoretically it could be something as "simple" as a gamma ray burst optical afterglow where the gamma ray beam missed Earth but the optical afterglow was detectable, even tho afterglows that are this bright are VERY rare AFAIK.
As for air traffic, sites like flightradar24.com keep historical records of flight movements and you would be able to check for aircraft near your observation site at the correct time.
Cheers
HB
Mike
Thank you!
Mike
I seek someone who could know an answer to my question: can this strike in the down-right corner on the left Image be from a Gammarayburst-Afterglow visual. This two pictures are only jpg-copies ( the right shows the positioning on CDS-Strassbourgh Portalsearcher). It is more to see on the Fits-Image. I did accitendly on an Onlineteleskop! (black Artefacts come from making the screenshoot in png). To see in the middle. If you are interessted, Thank you very much!!
That looks like a perfect example of a cosmic ray hit, that is not at all like a real optical light point-source.
An optical afterglow of a gamma ray burst would look just like a star: roundish and fluffy around the edges, not like a razor-sharp short trail like this one.
CS
HB
Thank you very much indeed!
John