Eyes and ears wide open for Einstein's richest laboratory
Rumors of detection of gravitational waves from a binary neutron-star merger with potential electromagnetic offsprings
According to New Scientist, there's a good chance LIGO is about to announce the discovery of gravitational waves from {a} neutron stars {merger} by the end of the week. LIGO itself is neither confirming or denying any discovery, but astronomer J. Craig Wheeler of the University of Texas at Austin posted a tweet hinting at a neutron star discovery.
Simultaneously, the Hubble telescope has been spending time observing a pair of neutron stars in the galaxy NGC 4993, about 130 million light years away. If LIGO did detect a collision, it would explain why valuable telescope time was being used to watch an otherwise unremarkable set of stars.
Either way, we won't know for sure until Friday. LIGO spokesperson David Shoemaker told New Scientist, "A very exciting O2 {second} observing run {of advanced detectors} is drawing to a close August 25. We look forward to posting a top-level update at that time." So we'll just have to wait until then to find out.
By Avery Thompson Aug 23, 2017
If you look at the (public) Chandra {X-ray Observatory} short-term schedule,
http://cxc.harvard.edu/target_lists/stscheds/ you see that it has also pointed on the 19th August for 25ks (at NGC4993) at SGRB170817A*, a triggered Target-of-Opportunity for X-ray counterpart of a Gravitational Wave event.
From the (entirely public) obsid details at
http://cda.cfa.harvard.edu/chaser/startViewer.do?menuItem=details&obsid=18955 you can see that
(a) a requirement for the trigger to be activated was both a GW discovery AND a positive EM counterpart identification by the Dark Energy Camera
(b) the obsid has a count rate of 11Hz and there are 300k X-ray photons in the observation (which sounds like a HUGE count rate for an X-ray telescope)
It looks very real.
Joseph Conlon August 23, 2017 at 5:38 pm//*update : GRB170817A was detected by the space gamma telescope Fermi//
Since ESO VLT was observing it for a GRB follow-up team over the weekend it looks like it was coincident in time with a GRB source and that gave the position on the outskirts of ngc4993. If you want the exact coord you can look in ESO archive! GRB interpreted as neutron star- neutron star collision. All unconfirmed but…
Tom Shanks August 23, 2017 at 7:57 pm
To appreciate what the gravitational waveform may look like this time (how different it should be from a binary black hole merger) have a look at this article. The most recent review article (to my knowledge) on the binary neutron-star mergers can be found here.
One can go to bed now, dreaming about how future LIGO and VIRGO spectral gravitational wave data may inform us about the structure of neutron stars and the equation of state of matter at nuclear density...
//update
Promises from some educated estimates
The discovery {in April 2003} of a binary system with the characteristics of J0737−3039 {a millisecond pulsar with a spin period of 22.7 ms included in a double-neutron star system with an orbital period of 2.4 hrs} implies a significant increase of the estimates of the double neutron stars (DNSs) Galactic coalescence rate R (Burgay et al. 2003, Kalogera et al. 2004) and, in turn, of the gravitational waves detection rate for ground based observatories ...
... J0737−3039A and B will coalesce due to the emission of gravitational waves in a merger time τm ≈ 85 Myr, a timescale that is a factor 3.5 shorter than that for {the first detected binary pulsar} PSR B1913+16 (Taylor, Fowler & McCulloch 1979). In addition, the estimated distance for J0737−3039 system (∼ 600 pc with an intrinsic uncertainty of about 50% from the dispersion measure, ∼ 1 kpc from X-ray absorption) is an order of magnitude less than that of PSR B1913+16. These properties have a substantial effect on the prediction of the rate of merging events in the Galaxy.
... ground based gravitational wave detectors such as LIGO, VIRGO or GEO should be able to detect a burst of gravitational waves produced in a DNS merger event once every few years instead than once in few decades, with important consequences for the gravitational wave community.
M. Burgay, N. D'Amico, A. Possenti, R.N. Manchester, A.G. Lyne, B.C. Joshi, M.A. McLaughlin, M. Kramer, J.M. Sarkissian, F. Camilo, V. Kalogera, C. Kim, D.R. Lorimer(Submitted on 11 May 2004)
Using Hubble Space Telescope optical and near-IR observations we identify a fading near-IR source with MH ≈ −15.2 mag and V −H & 1.9 mag at 9.4 days post-burst. The observed emission is at least 25 times brighter than expected from an extrapolation of the fading afterglow, as measured from our Magellan observations and from multi-band Gemini data (Cucchiara et al. 2013b). A kilonova model with Mej ≈ 0.03 − 0.08 M⊙ (for vej = 0.1 − 0.3c) provides a good match to both the absolute magnitude in the near-IR and the red optical/near-IR color, making GRB 130603B the first short burst with evidence for rprocess rich ejecta, a clear signature of compact object mergers. The inferred ejecta mass is in good agreement with the results of numerical simulations for a wide range of compact object binaries (Goriely et al. 2011; Piran et al. 2013). In addition, the faint optical/near-IR emission rules out an association with a Type Ic supernova typical of those that accompany long GRBs, or even non-GRB Type Ib/c supernovae, demonstrating that the progenitor of GRB 130603B was not a massive star.
In addition to providing strong evidence for compact object mergers as the progenitors of short GRBs, the detection of a kilonova has additional key implications. First, the inferred ejecta mass coupled with the (albeit poorly known) rate of compact object mergers, suggests that such mergers are likely to be the primary site for the r-process (Lattimer & Schramm 1976; Lattimer et al. 1977; Korobkin et al. 2013). Second, the observed H-band brightness and the inferred ejecta mass indicate that for a typical NS-NS merger detected at the Advanced LIGO/Virgo range of 200 Mpc, the optical I-band magnitude will be ∼ 23.5 − 24.5 in the first week, while Jband will reach a peak of ∼ 21.5 mag. Given the current lack of wide-field near-IR imagers capable of covering the typical Advanced LIGO/Virgo localization regions ... to this depth, this indicates that searches in the reddest optical filters (izy) with wide-field imagers on large telescopes (e.g., Pan-STARRS, DECam, Subaru, LSST) will provide the most promising route to the electromagnetic counterparts of gravitational wave sources. GRB 130603B is likely to become the benchmark for these searches.
(Submitted on 17 Jun 2013 (v1), last revised 3 Aug 2013 (this version, v2))
The gold mine of multimessenger astronomy
Since GWs are weakly interacting, any waves produced will traverse the universe without being scattered or absorbed; this gives another unique opportunity for scientists to see new phenomena in our universe. In this article we discuss how LIGO and Virgo are searching for GW signals in coincidence with EM events. This is an example of multimessenger astronomy. Searches are conducted for GWs at times of observed EM events (the external trigger strategy)... Since GW data from LIGO and Virgo is non-stationary 19,20, finding a GW signal candidate in coincidence with an EM transient will increase confidence that the signal is astrophysically produced, and not a spurious noise event.
There are a number of possible sources for an EM signal accompanying a GW. Long GRBs are likely associated with massive star collapse 22, producing γ-rays then subsequent x-ray and optical afterglows. A double neutron star (NS) or NS/blackhole merger could be the source of short GRBs 23 (with prompt γ-rays and maybe weak, isotropic afterglows). Other interesting phenomena include soft gamma repeater (SGR) flares; these are highly magnetized (10^15G) neutron stars that emit γ-ray flares sporadically 29.
In addition, many astrophysical events will produce detectable high and low energy neutrinos; neutrino events will be another important multimessenger area. LIGO and Virgo are currently working with IceCube 24,25 and ANTARES 26,27 in the search for GW signals at the time these neutrino observatories register events. It is suspected that high energy neutrinos could be emitted from long GRBs 22, short GRBs 23, low-luminosity GRBs 28, or even choked GRBs 30. Core collapse supernovae have prompt low energy neutrino emission (along with delayed optical signals). In the future, with the advanced detectors, it will be fruitful to search for GWs in coincidence with low energy neutrinos from supernovae 31.
Multimessenger observations could help to address and perhaps resolve a number of open questions in astrophysics 32. For example:
* What is the speed of GWs? (subluminal or superluminal?)* Can GW detectors provide an early warning to EM observers? (to allow the detection of early light curves.)* What is the precise origin of SGR flares? (what is the mechanism for GW and EM emission and how are they correlated?)* What happens in a core collapse supernova before the light and neutrinos escape? * Are there electromagnetically hidden populations of GRBs?* What GRB progenitor models can we confirm or reject?
(Submitted on 30 May 2011)
//a later update (August 25)
Here is the proposal 15382 of the Hubble Space Telescope program created on Tuesday, August 22, 2017 11:00:39 AM EST
ABSTRACT
OBSERVING DESCRIPTION1 orbit UV spectrum of LIGO BNS optical counterpart. Using STIS + G230L for wide wavelength coverage.
Comments
Post a Comment
Cher-ère lecteur-trice, le blogueur espère que ce billet vous a sinon interessé-e du moins interpellé-e donc, si le coeur vous en dit, osez partager avec les autres internautes comme moi vos commentaires éclairés !
Dear reader, the blogger hopes you have been interested by his post or have noticed something (ir)relevant, then if you are in the mood, do not hesitate to share with other internauts like me your enlightened opinion !