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Thread: I Am The Cow, Destroyer Of Worlds (or: AT2018cow is one hell of a mysterious object)

  1. #1
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    I Am The Cow, Destroyer Of Worlds (or: AT2018cow is one hell of a mysterious object)

    Please bear with me... Before I write anything serious, I just have to post this:

    https://mysteriousuniverse.org/2018/...redible-speed/

    The mind boggles, and the Woo woos.

    Okay!! It seems there is no thread yet on AT2018cow. This is an Astronomical Transient (AT) discovered by the ATLAS survey on Mauna Kea (which has nothing to do with the Keck telescopes, and there is no "Keck observatory"...) - see http://www.astronomerstelegram.org/?read=11727. Opening this link should also list all other ATels posted.

    The facts so far:

    - The transient had a very rapid rise time. The probably tightest constraint is a non-detection (I estimate to 17th mag) by ASAS-SN 1.5 days before the discovery observation. It rose by more than three magnitudes over that time, which is quite unusual, at least for SNe that are this luminous.

    - It is definitely associated with a face-on spiral galaxy with disturbed morphology at 60 Mpc (~ 200 Mly).

    - The early emission which became bright so rapidly is NOT your typical SN emission but a very hot (about 25000 K) blackbody, excepting the narrow absorption lines from interstellar matter in the host and our Milky Way, the early spectra were featureless.

    - Within some days, spectral features typical for a so-called broad-lined Type Ic SN (often associated with Gamma-Ray Burst [GRBs]) began to emerge, but the hot blackbody continues to dominate.

    - The source has been detected brightly both in X-rays and in mm/sub-mm (and faintly in radio). This is quite atypical for SNe, and indicates a component which emits synchrotron emission, which usually implies matter accelerated to (ultra)relativistic velocities - as typically seen in GRBs. Except no one has detected an actual GRB from this event.

    To summarize, this transient consists of three components. A (probably reasonably typical) broad-lined Type Ic SN, a relativistic synchrotron component (these two together form a "relativistic SN", a rare class of GRB-SN-like SNe without GRBs) - and then the very hot, extremely luminous, and seemingly hardly cooling blackbody emission, and THAT is the part which is unlike anything seen so far. There have been some GRB-SNe showing a similar (though less luminous) component at early times (SN 2006aj, for example) but this rose and decayed within about a day, and did not dominate the UV/optical emission as in this case.

    Bright minds are probably already conjecturing models, but for now, the transient community is observing, observing, observing.

    The SN, by the way, is not just luminous, but also bright in general, about 15th magnitude in the optical now, so amateurs with good scopes (20" or so) should be easily able to detect it.

  2. #2
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    Thanks for this. I'll keep an eye out for more details. Looks interesting.
    Forming opinions as we speak

  3. #3
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    I'm seeing more crackpot ideas on the internet claiming the AT2018COW as proof. Once again thanks Don Alexander for some facts before the nonsense arrived!
    Forming opinions as we speak

  4. #4
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    Doesn't post often, but when he does... No mentions of GW detections, are there none or possibly not published yet?
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  5. #5
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    Quote Originally Posted by slang View Post
    No mentions of GW detections, are there none or possibly not published yet?
    LIGO is down for upgrades to its equipment (will start observing again in 2019), so it couldn't detect any GW associated with this event. VIRGO may have been active; their website doesn't provide any obvious status report, unfortunately. I certainly haven't heard any news from VIRGO on this event.

  6. #6
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    The event—or object—is referred to as “The Cow,” which seems a distinctly boring name for a violent, galaxy destroying explosion of unknown origin. It was detected as far brighter than an average supernova, and moving at an anomalously fast speed. The team of astronomers working the ATLAS telescope at the Keck Observatory reported the event in the Astronomer’s Telegram, where it sparked international curiosity and where the automated naming and cataloging system of the Telegram listed the report as “AT2018cow.” This is why we shouldn’t let computers name things.
    I am constantly expecting deep space astronomy to turn up something like this; evidence of star-killer warfare, or a failed attempt to rip a wormhole into the next brane?
    Or just another rare event, like a collision between two supermassive stars?

  7. #7
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    The absence of gamma rays might not be so surprising-- they are typically beamed, perhaps moreso than the synchrotron emission and certainly moreso than the blackbody emission. Seems likely someone will suggest a fairly mundane model pretty soon! Though star killing certainly sounds more dramatic.

  8. #8
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    I turned the telescope over to some colleagues for a couple of hours to look at it about 10 nights back.

    "I haven't double-checked the guider parameters tonight"
    "No prob, we'll use short exposures, it's really bright"
    "Let's offset to check HOLY COW, IS THAT IT?"

    (I contend that would be a better origin for the name than the ATel designation permutations, anyway).

  9. #9
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    Quote Originally Posted by slang View Post
    Doesn't post often, but when he does... No mentions of GW detections, are there none or possibly not published yet?
    Thanks for the honors.

    As StupendousMan has stated, LIGO is down for upgrades. While I'm sure this source emitted gravitational waves upon explosion (as the is evidence it is some kin of core-collapse event), these were very likely undetectable at this distance (1.5 times the distance of GW 170817).

    In recent days, more peculiarities have been posted:

    - NuSTAR detected a hard X-ray spectral component which now seems to have disappeared, this could be a FOURTH emission component.

    - The spectral features of the Ic SN have pretty much disappeared again! The spectrum as of now has gotten really weird, not explicable by a single blackbody + SN emission.

    - Swift X-ray data have shown two bright flares which are not seen in the UV/optical data.

    - The source seems to be decaying in some UV/opt bands but has come to a standstill in others. This goes even beyond the expected chromatic evolution of a cooling blackbody.

    - multiple satellite missions now report... no detected GRB.

    If anything, the Cow has become even more puzzling.

    Quote Originally Posted by ngc3314 View Post
    (I contend that would be a better origin for the name than the ATel designation permutations, anyway).

    Actually, that's another error that is being propagated. The AT2018cow designation has been assigned by the TNS (Transient Name Server) at the time the discovery report was posted. It has nothing to do with ATel at all.
    Last edited by Don Alexander; 2018-Jul-09 at 08:24 PM.

  10. #10
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    To show how bright it is - here's an RGB (optical) composite from data at the Jacobus Kapteyn Telescope on La Palma early on July 6.
    Attached Images Attached Images

  11. #11
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    The Nordic Optical Telescope is now reporting the rise to prominence of a whole sequence of Helium emissions lines! It's rather unclear where these come from and whether they imply this is a Type Ib SN, not Type Ic...

    So far, no Type Ib has ever been associated with relativistic emission.

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