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Thread: Hot off the press: Potential Gamma-Ray Burst at 5 Mpc!!!

  1. #1
    Join Date
    Oct 2004
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    Exclamation Hot off the press: Potential Gamma-Ray Burst at 5 Mpc!!!



    This is the general feeling of quite a few transient astronomers right now.

    A few hours ago, the Swift satellite detected a rather faint GRB, named GRB 200729A based off the date, whose only claim to fame - but what a claim! - is that it is localized to an outer spiral arm of the nearby but dim spiral galaxy NGC 4242, a galaxy with some conflicting distance measurements, placing it somewhere between 5 and 10 Mpc. But no matter which number is correct, that makes it between about four to eight times closer than any other GRB, IF it is associated with the galaxy.

    It occurred not long before dusk in western Europe, and I scrambled to trigger several of our observing programs. No luck. One site had a thunderstorm, in the other case I was told the telescope is simply not operating this week...

    Luckily, we were able to get observations from La Palma which mysteriously show nothing. Not just no afterglow (which theoretically could be brilliant at this distance) but also no sign of a rising supernova. There does seem to be a lot of stuff (so-called "hydrogen column density") in the way, this may include dust which is obscuring the early emission, which is generally strong in the ultraviolet. Archival observations with the Spitzer Space telescope (RIP) may show a source there which could represent the GRB progenitor, which would be a MASSIVE result.

    And on the other hand, this could be a weirdly placed background event which is masquerading as the closest GRB ever.

    So all of this is very much in motion now, let's see what the coming hours and days bring.

    The exact source localization (as far as we have it right now) is:
    RA (J2000): 12h 17m 30.30s
    Dec (J2000): +45d 35' 41.1"
    with an uncertainty of 1.7 arcsec (radius, 90% confidence).


    Just in case anyone has some "amateur big glass" that can reach down to 20th magnitude and clear skies in the US. The galaxy is only visible at the beginning of the night.

  2. #2
    Join Date
    Oct 2004
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    No one interested?

    Anyway, this has turned out to very likely be a background event. HST imaging taken just two weeks prior to the GRB shows a red object in the XRT error circle which is likely a background galaxy. This source is also seen in Spitzer pre-imaging.

    This is very unlikely statistically but of course not impossible - so from now on it will likely be a poster child for this counter-example of GRBs being associated with the brightest galaxy at their position.

  3. #3
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    I'm interested, I just didn't have anything useful to add.
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  4. #4
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    Quote Originally Posted by Don Alexander View Post
    No one interested?
    I always perk up when I see you post This one wasn't different. Been away a bit, and was surprised to see so little follow up. I guess not every "hey, that's odd!" leads to something spectacular after all.
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  5. #5
    Join Date
    Jun 2006
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    Love Gamma Rays

    Quote Originally Posted by Don Alexander View Post
    No one interested?

    Anyway, this has turned out to very likely be a background event. HST imaging taken just two weeks prior to the GRB shows a red object in the XRT error circle which is likely a background galaxy. This source is also seen in Spitzer pre-imaging.

    This is very unlikely statistically but of course not impossible - so from now on it will likely be a poster child for this counter-example of GRBs being associated with the brightest galaxy at their position.
    You are already on my read list. At the moment, however, covid-19 tracking hs precedence.

    Reading yours now. Back in a few minutes, I hope.

  6. #6
    Join Date
    Jun 2006
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    4,842

    Glow In The Dark

    Background. Well, nice catch, anyhow.

    Regards, John M.

  7. #7
    Join Date
    Feb 2009
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    Which fraction of sky is covered by galaxies of Local Group other than Milky Way, and how many gamma ray bursts have happened?

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