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Thread: GRB 130427A - burst of the (quarter) century

  1. #1
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    Exclamation GRB 130427A - burst of the (quarter) century

    Hello, everyone, this fresh off the press, you read it here first™!!

    This morning, a GRB occurred, fittingly labeled GRB 130427A, which is turning out to be very, very extraordinary.

    It triggered the Swift satellite, which slewed to the GRB, finding an extremely luminous X-ray afterglow, at > 6,000 counts/s (uncorrected for pile-up, I expect the final value to go to about 10,000). This is among the highest ever measured, but still beneath some like 100621A which peaked at > 100,000 ct/s.

    The Swift BAT light curve over a broader time range (http://gcn.gsfc.nasa.gov/notices_s/s...20000msbx.jpeg) reveals a huge peak about 50 seconds before Swift actually triggered. Turns out Swift was slewing to a pre-planned target when the main activity occurred (triggering is turned off during slews), then triggered on the tail of the main peak, before another smaller peak at roughly 100 secs occurred, which is the one seen in X-rays.
    The main Swift peak, even in this raw view, exceeds 100,000 counts per second in BAT, which is higher than any GRB detected except for some SGR 1900+14 flares ("Storm episode" on 060329).

    The extreme fluence of this GRB was revealed in full by the SPI-ACS detector onboard INTEGRAL: http://www.isdc.unige.ch/integral/ib...-05802-39824-0

    The last time a GRB reached about 90k counts per 50 msec in SPI-ACS, it was GRB 110918A, which to this day holds the record as the highest peak luminosity ever measured for a GRB.

    And by now, the Swift BAT automatic refined analysis has appeared. Hidden in all these numbers and figures are a few astonishing facts.

    - The 15-350 keV fluence is measured to be 6.5E-4 erg/cm^2. To put this into perspective, the famous "naked-eye burst" 080319B, one of the most intense GRBs ever detected, had a fluence in the same window of 1.6E-4, so a factor 4 lower. The "broadband" fluence of 080319B (measured over a much broader spectral window up to many MeV) is about identical to this one's fluence in the narrow Swift energy window.
    - The peak count rate is close to 50 photons/s/detector. The current record holder for Swift, GRB 090424, reached about 11, which equated to ~ 77 photons/cm^2. So this one will likely have ~ 400 ph/s/det.
    - The spectrum in the Swift energy window is an absolutely straight power law with a slope of 1.2. This indicates that a) the peak energy of the spectrum lies above the Swift window and b) it lies significantly above the Swift window. So Sift is just seeing a relatively small fraction of the entire emission.

    All this leads me to predict a total fluence in a broadband window of > 1x10^-3 erg/cm^2 (remember, the Naked Eye-Burst had ~ 6 x 10^4, and even GRB 110918A had "only" ~ 8 x 10^-4), with something in the range of 2 - 3 x 10^-3 possible. The last time a GRB with such a fluence was detected was 25 years ago, GRB 881024. Only two other events (830801B and 840384) have fluences in the range of a few millierg/cm^2.

    Therefore GRB 130427A is likely the most energetic (observed) GRB of the last 25 years, and maybe among the top 3 GRBs EVER (well, ever since the late 1960s, of course).

    Of course, the location of this GRB was rapidly observed with ground-based telescopes, Several robots were on target within minutes, detecting a very bright afterglow at about 11th magnitude. This is actually "moderately unextraordinary", considering GRB 080319B reached mag 5.3. Spectroscopy with Gemini-North by Levan et al. reveals a redshift of 0.34, making this one of the closer GRBs known and explaining its extraordinary brightness. Continuing follow-up shows an afterglow which in the first hours is brighter than that of any Swift GRB, but still significantly fainter than that of the famous GRB 030329 which occurred at redshift 0.16.

    Some very "back of the envelope" calculations I have done show that the GRB and its afterglow are, intrinsically and compared to the whole sample we know, actually rather run-of-the-mill. If this GRB hat happened at a redshift of 2, it would have been good but nothing spectacular - only the low distance makes this such an incredible event.

    It lies at (J2000) RA = 11:32:32.84, Dec. = +27:41:56.2, for anyone with a good (> 30 cm) amateur telescope and a CCD. It is not, and never was, a naked-eye object, and was visible in binoculars only for some minutes.

    EDIT: Oh, two more things:

    - Sadly, this burst is not going to have very good Swift data. The satellite relies on field stars to lock its star tracker (similar to guiding for ground-based telescopes) and the field is very empty. Initial star tracker loss-of-lock caused an error in the aspect, and the reported X-ray position was 50 arcseconds (!) off the correct one.
    - In much better news, unlike GRB 110918A, this one was detected by the GBM instrument on Fermi (with the mindbogglingly ludicrous detection significance of 5014 sigma... :| ), and it seems to be in the field-of-view of the LAT instrument, which hopefully was also slewed to the GRB position. Therefore, this GRB may yield the best high-energy data set ever taken.
    Last edited by Don Alexander; 2013-Apr-27 at 03:01 PM.

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    Thanks Don Alexander for bring to us early something great that most media will miss.
    Forming opinions as we speak

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    Quote Originally Posted by antoniseb View Post
    Thanks Don Alexander for bring to us early something great that most media will miss.
    Antoniseb.yep...I'll second that.congrats don. Pete.

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    UPDATE:

    I am good at predicting, since pretty much all my predictions have come true.

    Swift BAT has measured the peak photon flux to be 310 photons/s/detector, so my 400 was a decent guesstimate.

    Fermi GBM has given us the broadband spectrum of the prompt GRB emission, finding a peak energy of 830 keV, far above the Swift energy band, a total fluence of 2 millierg/cm^2, which makes this the 3rd brightest GRB ever detected and the brightest in 29 years, it beats GRB 881024. In the broader energy range, the photon peak flux was 1050, which is the second highest value I've ever heard of (830801B had > 5000, it saturated everything).

    Fermi LAT not only detected it, but "detected it with a vengeance". Over 200 photons at energies > 100 MeV (largest number ever, though not by a large margin), and the most energetic photon reached 94 GeV, a significant record. This is more energy than the rest mass of the Z_0 boson, and close to the rest mass of the Higgs. Using special cuts which allow the detection of photons down to about 20 MeV, LAT detected thousands. This is the most significant LAT detection (of a GRB) in the five years of the mission, and will likely remain the most significant.

    The most recent optical detections, at 10 hours after the GRB, show it to be 16th magnitude in R, still within easy reach of good amateur telescopes (with CCDs, likely not visual).

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    Catching Swift mid-slew is unfortunate; but what a great find! Hopefully something close enough that the visual spectrum will correlate with...something.

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    The RAPTOR team has just reported that three of their ultra-wide-field monitoring telescopes imaged the GRB position during the entire gamma-ray emission. During the gigantic main peak, optical emission flashed, reaching a maximum of R = 7.4, in easy binocular range and the second brightest optical flash ever detected (after the naked-eye burst).

    Jerry, I don't quite get what you mean... the redshift is 0.34 and the host galaxy is so bright it is easily detectable in the SDSS.

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    Forwarded this to the SARA observers scheduled tonight - only to discover that the only scheduled observer is the consortium's resident GRB aficionado anyway! I plan to try the afterglow tomorrow night for fun as well.

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    Thanks for the heads up! I saw your post just as I was heading to the car for what was probably the last observation night until late August. We managed to get some BVR photometry done with the 45 cm Newton and a deeper LRGB image with the 41 cm RC. No results yet, we'll sleep first.

    /Patrik Holmstr÷m - Uppsala Amateur Astronomers
    Last edited by glappkaeft; 2013-Apr-28 at 02:32 AM.

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    The wide field LRGB image with the BVRI measurements is available at Astronet (Swedish astrophotography forum - it's too large for CQX's size rules). Short-short version is that the GRB (between ~23-00 UT) was mag 17-17.4 depending on filter.

    Now to figure out where to send the data...

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    Patrik, if you have good photometry (measured against SDSS stars, if possible), you can send a GCN Circular. If you do not have an account, you can contact me (PM me and we can exchange e-mails) and I can send it for you.

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    Quote Originally Posted by Don Alexander View Post
    ...the most energetic photon reached 94 GeV, a significant record. This is more energy than the rest mass of the Z_0 boson, and close to the rest mass of the Higgs.
    A record for a GRB or for any process? (I ask while thinking that a GRB is the most powerful process we can observe.)
    Et tu BAUT? Quantum mutatus ab illo.

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    A GRB.

    Of course, ground-based TeV telescopes (atmospheric Cherenkov or water tank) detect gamma-rays at significantly higher energies all the time. But then, they have integration times of many hours.

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    Quote Originally Posted by Don Alexander View Post
    Patrik, if you have good photometry (measured against SDSS stars, if possible), you can send a GCN Circular. If you do not have an account, you can contact me (PM me and we can exchange e-mails) and I can send it for you.
    Thanks, PM sent.

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    And answered with a lot of hopefully helpful suggestions.

    By the way, have you thought of actually submitting the image to APOD. I mean, it's a nice picture. It does not look special at first glance (just another star...) but this is the remnant of the brightest GRB in 30 years!!! And obviously in easy range of even amateur observers with good equipment. I think that would be a nice story to tell the public.

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    Quick look with SARA-N 1m around 0400 UT on 29 April, R mag about 18.5 based on raw counts. Still way brighter than the SDSS host galaxy magnitude.

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    Quote Originally Posted by Don Alexander View Post
    And answered with a lot of hopefully helpful suggestions.
    And thanks a million for the help! Actions like this really shows of the power of the internet.

    By the way, have you thought of actually submitting the image to APOD. I mean, it's a nice picture. It does not look special at first glance (just another star...) but this is the remnant of the brightest GRB in 30 years!!! And obviously in easy range of even amateur observers with good equipment. I think that would be a nice story to tell the public.
    I hadn't yet but I already had a APOD forum account (I submitted an image of light pillars in the past) and this is an excellent suggestion so now I have. Fingers crossed...

    Unfortunately followup observations from our observatory seems unlikely since our weather won't clear up until Thursday and by then the GRB will be to faint for our equipment to measure during the few reasonably dark hours (astronomical twilight ended the 21st).
    Last edited by glappkaeft; 2013-Apr-29 at 09:03 PM.

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    Thanks very much to Don Alexander for bringing this to our attention! I'm teaching a course on extragalactic astronomy this quarter, and I've written a short summary of the information so far for class tomorrow. Perhaps some other people might find it useful:

    http://spiff.rit.edu/classes/phys443...rb130427a.html

    If I've made mistakes, please let me know and I'll try to fix them.

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    Hey, StupendousMan, nice summary!

    I have a few corrections/tips.

    First, here is a plot of the INTEGRAL SPI/ACS light curve stretched to better show detail: http://grb.rssi.ru/GRB130427A/GRB130427A_SPI-ACS.png Also, please note the light curve is from the AntiCoincidence Shield (ACS) of the SPI instrument, NOT the SPI (SPectrometer onboard Integral) itself. To my best knowledge, this GRB was not in the field of view of any of INTEGRAL's "narrow-field" instruments.

    You might add that the extreme spikiness of the GRB is a typical sign of a very hard, high-luminosity event.

    You plot the Swift XRT light curve. Note that these are X-rays, not gamma-rays. You'll see an ultra-bright spike right at the beginning. If one rebins the light curve with 0.05s resolution and "dynamic binning off" ones sees it peaks at 300,000 counts/s, which, yes, is the brightest ever measured. But I highly doubt this feature is real, I think it's an artifact of data processing. Nonetheless, just after this peak, the X-ray light curve still has 20,000 count/s, and that is still the brightest ever measured (discounting such peaks found in a few other GRBs like 100621A, which they even wrote a press release about...).

    The dip in the hardness ratio is a common phenomenon. You'll see it pretty much corresponds to the steep part of the decay. That is so-called high-latitude emission, produced by a rather complicated relativistic process that occurs when the prompt emission "turns off". Such emission decays steeply while at the same time softening (reddening) rapidly. Then the actual X-ray afterglow takes over, and such emission is usually rather hard (blue). Everything after that steep-to-shallow break is afterglow, and it is expected to not spectrally evolve, so the hardness remains constant. Purely in terms of spectral and temporal evolution, this X-ray afterglow is actually very run-of-the-mill. It's just hugely bright.

    A heads-up on energetics. Konus-Wind has measured the fluence to be 2.68 milliergs/cm^2, making this one of the three brightest GRBs of all time and the brightest in 29 years. GRB 830801B is the brightest in terms of peak flux (> 5000 ct/s) of all time and saturated detectors, having at least 2 millierg/cm^2. GRB 840304 had 3 millierg/cm^2. So 130427A is a sure #3, and a possible #2. The peak flux measured by Konus-Wind, by the way, is still 30% lower than the ultraluminous GRB 110918A (which was at almost redshift 1, and therefore much more luminous at peak than this one).

    GRB 080319B reached mag 5.3 in R/V at peak, so more "5" than "6". One may also note that 130427A is at later times the second brightest optical afterglow ever detected, after GRB 030329.

    The redshift measurement did not depend on the host. A colleague of mine initially told me there was an SDSS galaxy at the position with a photometric redshift of 0.21 +/- 0.13, but that's a huge error margin. Interestingly, it's correct, but at the upper 1 sigma edge. The redshift was measured via multiple absorption features of the afterglow. Only the VLT/X-shooter spectrum has revealed multiple emission lines typical for starburst galaxies.

    Now, in a final newsflash, the Fermi LAT team have released a refined analysis circular which is... breathtaking!!! (http://gcn.gsfc.nasa.gov/gcn3/14508.gcn3) The three points to take away for the moment are:

    - The high-energy emission is temporally the very first signal seen, before the "low-energy" gamma-rays in GBM. AFAIK this is totally unprecedented, LAT usually lags by one or two seconds, or it is contemporaneous.
    - The LAT emission alone has a total fluence of 0.1 millierg/cm^2, this is as much as really bright "once every two months or so" GRBs have in TOTAL.
    - The LAT emission is detected out to about a day. For me, that's the jaw-dropper. GRB 940217 is a famous CGRO burst which got a Nature paper thanks to a second-orbit EGRET detection (so ~ 1 ... 2 hours after the GRB), this one goes roughly an order of magnitude longer.

    If this GRB were a puddle, I'd wallow in the awesomeness.
    Last edited by Don Alexander; 2013-Apr-29 at 11:34 PM.

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    So which is the Brightest ad ntrinsically most Luminous Gamma ray burst ever if this one is third most bright? And does this one beat GRB 080916C in total energy release?

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    But is this burst Intrinsically as luminous as GRB 110918A or as enegetic as 080916A? Or is it bright only because of its low redshift and less distance?

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    There's different ways of determining "brightness" of a GRB, with basically two subcategories each: peak vs. total, and observed vs. intrinsic.

    Observed:
    Peak:
    You can have peak flux, for which you need a spectrum. Unless you do a so-called bolometric expansion to a very broad energy range, this is detector-dependent. Peak flux is generally measured at the brightest point of the light curve, but can simply be fluence/duration.
    Peak photon flux is just the number of photons per cm▓ and s. It is strongly spectrum-dependent, a soft event will have a much higher photon flux than a hard event of the same peak flux, as you need more low-energy photons.

    Total:
    The fluence is the summed energy over the entire duration, again, you need a spectrum, and this is strongly detector-dependent.

    Intrinsic:
    Correcting for the distance, peak flux becomes luminosity, and fluence becomes the isotropic energy release.

    Peak flux: The highest peak flux and peak photon flux is GRB 830801B, with > 5000 ph/cm▓/s, I don't know an exact peak flux number. It saturated detectors. The extremely intense short GRB 031214 had a peak flux of 2E-3 erg/cm▓/s, at least according to the report back then. This seems to have been forgotten, as the Konus-Wind circular on GRB 110918A claims it has the highest measured peak flux of all KW GRBs. The peak flux if GRB 130427A is 30% lower than that of GRB 110918A

    Fluence: GRB 840304 has the highest measured fluence with 3E-3 erg/cm▓. GRB 130427A comes next with 2.68E-3 erg/cm▓. GRB 830801B has > 2E-3 erg/cm▓, but remember this saturated detectors, I expect it to be the highest of all, actually.

    Peak luminosity: There are indications 830801B was a VERY nearby GRB, though no one ever found a counterpart or measured a redshift. GRB 110918A remains the record-holder in this category, not only having a higher peak flux than 130427A, but also being significantly further away. I did a very rough calculation which indicates 110918A is about an order of magnitude more luminous than 130427A. 110918A has a peak luminosity of 4.4E54 erg/s, which is twice as high as the extreme high-redshift GRB 080607.

    Bolometric isotropic energy release: Both GRB 110918A and 130427A belong to the "emperor class" of GRBs with E_iso > 10^54 erg. The true record holders in this class of "brightness" are GRBs 080916C (as you mentioned) and GRB 090323, two high redshift Fermi LAT GRBs.

    130427A is a very impressive event even intrinsically, perhaps among the ten most powerful GRBs ever observed, and it was, of course, ridiculously close.

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    It will be interesting to see if the afterglow
    morphs into a common or garden supernova as has
    happened before and is predicted in a GCN notice
    I see. But featureless spectra do not help!

    Common or garden?...only joking

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    Quote Originally Posted by glappkaeft View Post
    The wide field LRGB image with the BVRI measurements is available at Astronet (Swedish astrophotography forum - it's too large for CQX's size rules). Short-short version is that the GRB (between ~23-00 UT) was mag 17-17.4 depending on filter.

    Now to figure out where to send the data...

    Hi- I'd love to use that photo on my blog. May I have permission to use it? Thanks!

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    Sure, I checked with the other guys. Go ahead!

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    Patrik, not in the mood to report your mags in a GCN?

    Anyway, Pete's question concerning the SN is indeed an interesting one. Since the exact "operating method" of a GRB central engine is still unknown, AND we do not really understand how SNe explode, it is entirely unclear what the link between the GRB properties and the SN properties should be. There seem to be some vague hints that SN energie somehow is correlated with the peak energy of GRBs, with X-ray Flashes producing SNe of lower energy than cosmological GRBs. The thing is, most GRBs associated well with SNe are either the clearly subluminous XRF variety, or at least relatively soft, not too bright "X-Ray Rich" GRBs - e.g., GRB 030329.

    This is the first ever extremely energetic and very hard GRB at low redshift that has been located, so you can bet we will be all over this one.

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    Quote Originally Posted by glappkaeft View Post
    Sure, I checked with the other guys. Go ahead!
    Yay! Thanks!

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    Whoa! *marks calendar - Day-of-the-BA*

    Don A, is there any specific speculation yet about the cause of this big bad boom? I'm partial to TDE's (they're so cool), but I guess if it fit that profile you'd have mentioned it already.
    ETA: nevermind, missed your last post.
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    Quote Originally Posted by Don Alexander View Post
    Patrik, not in the mood to report your mags in a GCN?
    It's number one on the to do list but we have been delayed by work (or in my case a persistent visit of the flu) and the Swedish Valborg and 1st of May holidays.

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    Man, the skies are angry these days...

    On the 2nd of May, we had another intense, extremely spiky GRB: http://www.isdc.unige.ch/integral/ib...02-39824-0.png
    This one was not initially localized by Swift, but well-detected by Fermi GBM and especially LAT, which allowed for a localization which was tight enough to have Swift observe the field, finding the X-ray afterglow. Optical observations revealed only a very marginal source in the error circle, though, classifying the GRB as dark and highly extinguished. I hope one day someone will get a redshift by observing the host, though.
    4th of May, we get a really bright short GRB: http://www.isdc.unige.ch/integral/ib...-05802-39824-0
    Again, not localized by Swift. Was detected by GBM and in the LAT Field of View, but no LAT GCN has been issued. I guess we will lose this one...

    And just a few hours ago, Swift detected the next monster!! http://www.isdc.unige.ch/integral/ib...-05802-39824-0
    This time, Swift performed flawlessly, but it seems we "lost" Fermi, likely it was simply on the other side of the Earth. That's a real pity. The GRB has a very bright optical afterglow (okay, not comparable to 27A), and the Gemini North measured its redshift to be 2.27, which is a very "normal" GRB redshift, except this one is very bright!! I've done a quick "back-of-the-envelope" plot with the SPI/ACS data and find:

    - 05A is ~ SEVEN times more luminous at peak than 27A, and close to GRB 110918A
    - It seems 05A exceeds all of the recent bright GRBs in terms of isotropic energy release, especially having about twice the value of the naked-eye burst 080319B, and several times that of 110918A and 130427A. It might be in the range of the record-holders 080916C and 090323.

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    Wow, has there been a sudden change in our ability to detect these things, or is this a normal coincidence of several very energetic GRBs being detected in such a short time?
    Forming opinions as we speak

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