dcc.ligo.org/LIGO-P150914/public
Observation of Gravitational waves from a binary black hole merger
On Sept. 14, 2015 at 9:50:45 UTC the two detectors of the LIGO simultaneously observed a transient gravitational wave signal. The signal sweeps upwards in frequency from 35 to 250 Hz with a peak gravitational-wave strain of 1e-21. It matches the waveform predicted by GR for the inspired and merger of pair of BHs and the bringdown of the resulting single BH. The signal was observed with a matched-filter S/N ratio of 24 and a false alarm rate estimated two be less than1 event per 203000 years, equivalent to a significance greater than 5.1 sigma. The source lies at a luminosity distance of 410+160-180 Mpc corresponding to a redshift z=0.09+0.03-0.04. In the source frame, the initial BH masses are 36+5-4 Msun and 29±4 Msun, and the final BH mass is 62±4 Msun, with 3.0±0.5 Msun c^2 radiated in gravitational waves. All uncertainties define 90% credible intervals. These observations demonstrate the existence of binary stellar-mass BH systems. This is the first direct detection of GWs and the first observation of a binary BH merger.
1602.03512
Extragalactic background light: measurements and applications
Cooray
A review: measurements of extragalactic background light (EBL) intensity from gamma-rays to radio in the EM spectrum over 20 decades in wavelength. CMB: best measured spectrum. COB (optical), centered at 1 microns: impacted by the large zodiacal light associated with interplanetary dust in the inner solar system. Best measurements of COB come from an indirect technique involves gamma-ray spectra of bright blasars with an absorption feature resulting from pair-production off of COB photons. The CIB (infrared): peaking at ~100 microns, established an energetically important background with an intensity comparable to the optical background. This discovery paved the path for large aperture far-IR and sub-millimeter observations resulting in the discovery of dusty, star bursting galaxies. Their role in galaxy formation and evolution remains an active area of research. The extreme UV background remains mostly unexplored and will be a challenge to measure due to the high Galactic background and absorption of extragalactic photons by the IGM at these EUV/soft X-ray energies. Also summarize the understanding of the spatial anisotropies and angular power spectra of intensity fluctuations. Motivate a precise direct measurement of the COB between 0.1 and 5 microns using a small aperture telescope observing either from the outer SS, at distances 5 AU or more, or out of the ecliptic plane. Other future applications include improving the understanding of the background at TeV energies and spectral distortions of CMB and CIB.
1602.03842
The rate of binary black hole mergers inferred from advanced LIGO observations surrounding GW150914
Abbott et al
Report on the constraints the LIGO observations place on the rate of BBH coalescences. Considering only GW150914, assuming that allBBHs in the universe have the same masses and spins as this event, imposing false alarm threshold for 1 per 100 years, and assuming that the BBH merger rage is constant in the comoving frame, infer a 90% credible range of 2-53 /Gpc^3/yr (comoving frame). Incorporating all triggers that pass the search threshold while accounting for the uncertainty in the astrophysical origin of each trigger, estimate a higher range, ranging from 6-400 /Gpc^3/yr depending on assumptions about the BBH mass distribution. All together, the various rate estimates fall in the conservative range 2-400 /Gpc^3/yr.
1602.03846
Astrophysical implications of the binary black-hole merger GW150914
The LIGO scientific collaboration, the Virgo Collaboration
The discovery of GW150914 with advanced LIGO provides the first observational evidence for the existence of binary BH systems that inspiral and merge within the age of the Universe. Such BH mergers have been predicted in 2 main type of formation models, involving isolated binaries in galactic fields or dynamical interactions in young and old dense stellar environments. The measured masses robustly demonstrate that relatively "heavy" BHs (<~25 Msun) can form in nature. This discovery implies relatively weak massive-star winds and the the formation of GW150914 in an environment with metallicity lower than ~1/2 of the solar value. The rate of binary BH mergers inferred from the observation of GW150914 is consistent with the higher end of rate predictions (>1/Gpc^3/yr) from both types of formation models. The low measured redshift (z~0.1) of GW150914 and the low inferred metallicity of the stellar progenitor imply either binary BH formation in a low-mass galaxy in the local universe and a prompt merger, or formation at high redshift with a time delay between formation and merger of several Gyr. This discovery motivates further studies of binary-BH formation astrophysics. It also has implications for future detections and studies by Advanced LIGO and Advanced Virgo, and GW detectors in space.
1602.03868
Swift follow-up of the Gravitational wave source GW150914
Evans, et al
No new X-ray, optical, UV or hard X-ray sources were detected in the observations, which were focussed on nearby galaxies in the GW error region; discuss the implications of this.
1601.03718
A new route towards merging massive black holes
Merchant, Langer, Podsiadlowski, Tauris, Moria
Recent advances in GW astronomy make the direct detection of GW from the merger of two stellar-mass compact objects a realistic prospect. Evolutionary scenarios towards mergers of double compact objects generally invoke common-envelope evolution which is poorly understood, leading to large uncertainties in merger rates. Explore he alternative scenario of massive over contact binary (MOB) evolution, which involves two very massive stars in a very tight binary which remain fully mixed due to their tidally induced high spin. Use the public stellar-evolution code MESA to systematically study this channel by means of detailed simulations. Find that, at low metallicity, MOBs produce double-BH (BH+BH) systems that will merge within a Hubble time with mass ratios close to one, in two mass ranges, ~25-60 Msun and >~130 Msun, with pair instability supernovae (PISNe) being produced in-between. The models are also able to reproduce counterparts of various stages in the MOB scenario in the local Universe, providing direct support for it. Map the initial parameter space that produces BH+BH mergers, determine the expected chirp mass distribution, merger times, Kerr parameters and predict event rates. Typically find that for Z~Zsun/10, there is one BH+BH merger for ~1000 core-collapse SNe. The advanced LIGO (aLIGO) detection rate is more uncertain and depends on the metallicity evolution. Deriving upper and lower limits from a local and a global approximation for the metallicity distribution of massive stars, estimate aLIGO detection rates (at design limit) of ~19-550/yr for BH+BH mergers below the PISN gap and of ~2.1-370/yr above the PISN gap. Even with conservative assumptions, find that aLIGO should soon detect BH+BH mergers from the MOB scenario and that these could be the dominant source for aLIGO detections.
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