AT2018cow - what is it

Affiliation

American Association of Variable Star Observers (AAVSO)

Wed, 07/11/2018 - 23:12

Today, 11 July 2018, AT2018cow is a new kind of variable that is a hot topic in the astronomical community. I was looking at the light curve, and though the visible bands are decreasing (V ~ 17) the IR appears to have risen, as, for example, we would have happen in the NS-NS collision. However, this time it has been acting differently, so perhaps it is a NS-BH merger. In any case, it would be very helpful to monitor the IR bands as well as the other bands of course, but the IR is brightening (looks like) and the visible getting fainter. Last observation in the LCG is a week ago, so it would be nice to get some more date. If indeed this is a BH-NS merger, this might continue to be bright in the infrared bands for a while.

Bikeman

Affiliation

American Association of Variable Star Observers (AAVSO)

Sat, 07/14/2018 - 23:09

I understand that a NS-NS

I understand that a NS-NS merger would be expeced to have a less luminious 'kilonova' EM counterpart, but we have only one definitive observation so far, so can we be sure? And unfortunately the LIGO gravitational wave detectors are being upgraded now and will resume science data taking only next year.

I wonder whether another mysterious event could be related to AT 2018cow: iPTF16asu , which was also somehow similar to a type Ic-BL supernova, but more luminous and faster evolving at the start than usual events of that type. I haven't scaled all the numbers from https://arxiv.org/pdf/1706.05018.pdf  (that event was roughly at a 10 times greater distance than AT3018cow ) but at first glance it seems in the same ballpark.

PaulKuin

Affiliation

American Association of Variable Star Observers (AAVSO)

Sun, 07/15/2018 - 14:46

AT2018cow - only data will tell

The truth is, we want as much data in the form of magnitudes, colours, spectra, even time-series to compare to other objects that we know better. Yes, the binary merger GW170817 (aka AT2017gfo) was the only one we saw so far, but we can also consider short-GRBs, which we know better after several years of chasing GRBs; we can compare to tidal disruption events when a star encounters a black hole, and supernovae. Theroretically, there might be hypernovae that are brighter. The puzzle will be to explain all we observe and link it to our existing knowledge, like how gravity works, nuclear processes, ionised plasma in electro-magnetic fields and such. To bring the heavens down to Earth, really.

I am starting to change my mind slowly on what the nature of the event is, but will talk about that in the future.