PoS(MULTIF2019)020 https://pos.sissa.it/ ∗ † [email protected] Speaker. Corresponding author The recent discovery of gravitationaling waves systems has are opened very common asion in new spans astrophysics window the and in whole are astronomy. electromagnetic multifreqeuncy spectrum.messenger sources, Accret- sources, Accreting since since systems their they in emis- can astronomy emit areand gravitational also waves because via multi- of a their variety of intrinsical physicalwave binary mechanisms emission nature. of This accreting paper systemsnuclei, presents at showing a that all review the scales, emission of occurs from the over gravitational cataclysmic the whole variables gravitational to spectrum. active galactic † ∗ Copyright owned by the author(s) under the terms of the Creative Commons c Multifrequency Behaviour of High Energy Cosmic3-8 Sources June - 2019 XIII - MULTIF2019 Palermo, Italy Attribution-NonCommercial-NoDerivatives 4.0 International License (CC BY-NC-ND 4.0). Rosa Poggiani Università di Pisa and Istituto NazionaleE-mail: di Fisica Nucleare, Sezione di Pisa Gravitational waves from accreting systems PoS(MULTIF2019)020 ], 9 ], [ 8 ], [ 7 Rosa Poggiani ], [ covers several 6 1 ], [ 4 ], [ 3 ]. 75 ]. Space based interferometers are 63 ]. The emission in this region relies on ]. The very low frequency region below 56 74 ], [ 55 1 ] and TianQin [ ]. 22 53 ][ 62 ], [ 52 ], [ 65 The gravitational wave spectrum; credits: http://gwplotter.com/ Figure 1: ]. The standard model of accretion has been proposed by [ 47 Hz includes the emission of supermassive binaries, the astrophysical stochastic background Accreting systems appear in the list of binaries discussed above. Accretion appears at all In this paper, the gravitational wave emission from accreting sources will be discussed from The recent observations of gravitational waves from binary black hole mergers and a binary 5 ]. The spectrum of gravitational waves from different sources reported in Fig. − 15 scales in astrophysics, from young stellarall objects masses to [ white dwarfs to neutron stars to black holes of two points of view, the emissionproduced related by to physical processes the related intrinsic to binary accretion,ables, nature discussing accreting different of sources: neutron systems cataclysmic and stars, vari- the accretingnuclei. emission black The holes variety in of thespectrum, processes Galactic requiring involved the Center in combination and accreting of in systems different observational active covers techniques. galactic the whole electromagnetic [ of coalescing supermassive black holewaves binaries from and phase the transition cosmological in background the of early gravitational universe [ 10 neutron star merger has opened a new observational window in astronomy [ Gravitational waves from accreting systems 1. Introduction decades in frequency, demanding foralescences different detected observational with strategies. the groundbelong The based to compact interferometers the Advanced binary LIGO high co- tinuous and frequency emission Advanced region, Virgo from ranging pulsars from andground a the based few interferometers supernova below collapse Hz a bursts few to Hz areterferometers, some is the expected. limited future kHz, by instruments The where seismic LISA sensitivity noise, [ also of requiringdesigned space the to based con- detect in- resolved binaries,of the the merger merger of of massive stellar binary blackperform black holes, multifrequency holes with gravitational and the wave astronomy the possibility [ to final trigger stage ground based interferometers to pulsar timing techniques [ PoS(MULTIF2019)020 , 6 ]. 1 × ] 10 19 (4.1) (2.1) × 73 ], [ ]: ], [ 18 78 72 ], for about ], who sug- Rosa Poggiani 64 86 ], as discussed 64 ], [ ] and [ 3 2 77 26 Hz 2 3 f − − ], with an arm length of 2.5 the frequency of the monochro- 10 cm 24 f 1 − x F ] combine distances estimated using pc erg s 70 r 8 − 100 10 2 3 2 /
1 2 are the masses of the primary and secondary com- M M 2 the gravitational wave frequency. ] for an observation time of two years is shown in Fig. f M , 70 kHz ]. The most promising sources are the very short period 1 m f
1 M µ 30 M , 2 the time averaged X-ray flux, 2 ], [ 27 M x M − + 21 1 F 51 1 − M 10 M 10 × = 3 ], for about 500 systems. The catalogue by Ritter and Kolb [ × µ 7 = . 70 , 2 8 h M ]. The dotted curve is the sensitivity of the original LISA design, with 5 = + h 22 1 ]. The dashed curve is the confusion noise, a background of astrophysical origin M 60 = is the mode number, M m is the distance of the system and r ]. Before the advent of Gaia, the distances of cataclysmic variables have been measured with http://wwwmpa.mpa-garching.mpg.de/RKcat/ The gravitational emission from accreting neutron stars has been discussed by [ The gravitational strain estimated by [ where Cataclysmic variables are binaries composed by a white dwarf and a secondary star. The Accreting systems are binary systems, where gravitational wave emissions occurs at twice the where km, an acceleration noise extrapolated from LISA Pathfinder performances, a binary confusion 70 1 6 . The solid curve is the sky averaged design sensitivity of LISA [ 10 noise estimated by [ km arm length [ matic gravitational wave. The accreting neutron star should undergo a non axial distortion, with from unresolved binary systems [ AM CVn systems. 4. Accreting Neutron Stars 2 160 objects each, and by [ different methods. The compilation ofthe parallax, distances the used nova by expansion parallax [ and the Period-Luminosity-Colour relation by [ gested that accreting neutronbecome stars unstable. with weak When magnetic thethe growth fields gravitational time acquiring strain of is angular given instability momentum by: is can balanced by the viscous damping time, gravitational wave emission of cataclysmic variables has been estimated by [ 3. Cataclysmic Variables orbital frequency and harmonics.harmonics When is the negligible and orbital the eccentricity gravitational is wave characteristic negligible, amplitude the is contribution given by of [ Gravitational waves from accreting systems 2. Gravitational Waves from Binary Systems ponents, version 7.23, contains more than 1400cataclysmic systems. variable, The but orbital the period masses is of known the10% for of primary objects. the and majority of The missing of the masses the secondary canby mass be [ are estimated known using for the about approach by [ PoS(MULTIF2019)020 ] ]. K. 89 31 9 ]. The 10 32 × 2 Rosa Poggiani ∼ ]. The work by [ -1 10 50 ], [ . The elastic deformation ]. 26 85 . The conditions for a steady LISA noise Confusion LISA Original masses Known masses Estimated ], the dashed line is the binary − 54 1 − 60 yr -2 10
M 8 − ], who suggested that stable equilibrium ]. A rapidly rotating neutron star can po- 87 -10 23 10 (Hz) -3 − 10 3 Frequency ]; the solid curve is the instrumental sensitivity of the new 70 -4 10 ]. A detailed investigation of the evolution of the low-mass X 89 into gravitational radiation. Magnetically confined mountains on
], the dotted line of the original LISA [ 24 -5 10 -24 -20 -21 -22 -23 ]. The abundance of the spin frequencies of neutron stars around 300 Hz sug-
10 10 10 10 10 h 86 ] for accretion rates in the range 10 60 2 g cm Gravitational wave emission of cataclysmic variables with known masses (red circles) and esti- 38 ], who estimated the quadrupole moment required to balance the torque by accretion, about The knowledge of the spin and orbital periods is of great importance for the computational cost -10 80 ], producing angular momentum loss and a spin frequency decrease. An instability in rotating 37 68 The estimated strain of accretingof neutron the stars crust is due of toby the density [ order perturbations caused of by 10 electron capture reactions has been discussed Gravitational wave emission can drive an[ instability in the r-modes of young rotating neutron stars suggested that a few systemsadvanced accreting interferometers. around the The Eddington statisticsparameters rate of are can known detectable from be systems electromagnetic potentially increases measurements,the detected if since folding by data their of analysis long spin algorithms time and relyray records on orbital [ binaryies and the relationstage with of gravitational common wave envelope emission intron has accreting stars been neutron accrete stars presented at involves by a gravitational [ fractionat wave hypercritical of emission. rates, the producing Bondi-Hoyle-Lyttleton Neu- strains rate, exceeding but those they of could Sco be X-1 able [ to accrete 10 will occur when the superfluid transition temperature of hyperons is smaller than neutron stars, driven by gravitationallimit radiation on reaction the and spin affecting frequencytentially the of convert about r-modes, young 0.01 sets neutron M an stars upper [ a modulation of the X-raysome emission hundreds occurring Hz [ at the gravitational wave frequency, of the order of design LISA interferometer [ confusion noise [ gested that the angular momentum from the accretion was converted into gravitational waves [ gravitational wave emission have been discussed by [ accreting neutron stars could produce detectable gravitational waves [ Figure 2: mated masses (blue squares), adapted from [ Gravitational waves from accreting systems PoS(MULTIF2019)020 ], ], for 61 12 1 ] and − 2 ]. The 46 ] and Hidden . The S-stars Rosa Poggiani 25 10 , a supermassive − ∗ ], 0-0.187 yr ]. Searches for per- and a secondary star 28
43 ] (Swift BAT archive), 39 ]. ], [ 71 38 have been presented by [ for Cyg X-3 [ ]. This class of events can involve ∗ 1 5 − [ 1 ] (whole RXTE ASM archive). Targeted − 90 ] have frequencies in the nanoHz range and yr ] and the Advanced LIGO O1, O2 runs [ 2 3 ] and Cyg X-2 [ 33 [ − ]. 88 ∗ 4 20 ], [ ]. MWC 656 is a peculiar source, since it is the first ]. The four systems have allowed estimations of the at the center of our Galaxy [ ], 0.09-0.15 yr ], [ 45 29 29
]: Cyg X-1, Cyg X-3, MWC 656, P13 in NGC 7793. 27 42 [ ], setting upper limits of the order of 10 M 29
], [ 6 13 ] (Swift BAT and RXTE ASM archives). 67 , some orders of magnitude below the sensitivity of current 10 ], [ 69 19 for P13 [ × ], [ − ]. During the observing runs O1 and O2 of the Advanced LIGO 12 1 1 34 − -10 for Cyg X-1 [ 20 1 − − ]. Directional unmodeled searches for persistent gravitational waves from 14 ], [ 11 ]. The properties of 37 S-stars orbiting Sgr A ], up to 0.1-0.6 yr . 25 33 49 − The observations of the orbits of the S-stars provides the evidence for Sgr A No Neutron Star-Black Hole merger has been detected to date. The upper limit on the merger Sco X-1 is a potential bright source of continuous gravitational waves and has been investi- The archives of X-ray observatories allow searches for periodicities, that include orbital and ]. For reference, the best upper limits on Sco X-1 emission estimated in the searches are of the ] (RXTE ASM archive) and by [ 13 57 amplitudes in the range 10 and planned Pulsar Timing Arrays. accreting systems. Some X-ray binariesinvolving neutron have been star proposed and as black candidate holes progenitors [ of mergers merger rates: 0.028-0.4 yr detected Be/Black hole system [ 6. Galactic Center black hole with a masssistent of gravitational waves about from 4 the Galactic center have beenare performed examples with of the Extreme Mass initial Ratio [ the Inspiral inspiral (EMRI) stgae, systems with that a undergo gravitational tidaltechniques emission disruption in [ during the range that is investigated with Pulsar Timing rate estimated with Advanced LIGO is 3600 Gpc spin and orbital periods arePrecision known ephemerides for for less Low Mass than X-Ray 15%have Binaries and been are recently measured less determined using than for optical 50% spectroscopy Sco of and X-1 systems, [ respectively. [ 5. Neutron Star-Black Hole Systems These sources contain a black holewith with a a mass mass in in the the range range from from 7 5 to to 20 15 M M MWC 656 [ advanced LIGO interferometers [ gravitational waveforms of S-stars orbiting Sgr A gated by the initial andusing semicoherent advanced techniques interferometers. [ The upper limit by initial LIGO has been set order of 10 detectors upper limits have been set using model based cross-correlation searches [ Sco X-1 have been performed with the initial LIGO [ spin periods, and alsoperiodicities superorbital in periods X-ray binaries and have outburst been recurrence presented by times. [ Systematic search of Gravitational waves from accreting systems of the searches for gravitational wave emission of accreting neutron stars. In the catalogue by [ search of periodicities of X-ray[ binaries have been presented by [ Markov Models [ PoS(MULTIF2019)020 ]. 44 ] have been Rosa Poggiani 36 , main sequence
M 4 − ], with time scales rang- 60000 79 ] and OJ 287 [ in circular orbits has been dis- 16 ∗ 50000 could also be detected by LISA [ ∗ ], that include reaction effects and can 84 ]. The light curve of OJ 287 reported in Fig. 40000 83 MJD ], [ 5 82 ]). OJ 287 has been modeled as a binary black hole 30000 ], [ 37 81 Hz, the domain of pulsar timing. Upper limits on the grav- ], [ 8 ]. can be detected with one year observation. Stellar mass black − 58 inspiralling around Sgr A 41 20000
], [ -10 9 76 − theorem [
10000
19 10 11 12 13 14 15 16 17 18 V magnitude V no-hair ], who showed that compact objects with masses larger than 10 48 V band light curve of OJ 287 (data from http://altamira.asu.cas.cz/iblwg/data/oj287/ and AAVSO) Since the detected periodicities of blazars range from years to decades, the gravitational ra- Blazars are active galactic nuclei powered by accretion onto one or two supermassive black Other gravitational wave emitters could by detected with the space based interferometer LISA. Supermassive black hole binaries in active galactic nuclei can emit gravitational waves due extends for more than one century and shows two peaked outbursts with a recurrence time of set. Figure 3: diation is emitted at aboutitational 10 wave emission from supemassive black hole binaries [ holes, exhibiting variability over the whole electromagnetic spectrum [ about 12 years, associated todemonstrated the the orbital energy motion loss of via the gravitational radiation black [ holes. The timing the 2007 outburst 7. Active Galactic Nuclei system including precession [ 3 allow to test the The gravitational emission from general objects orbiting Sgr A to their orbital motion.in The the presence light of curve a of black the hole source pair (see is e.g. inferred [ looking at the periodicities Gravitational waves from accreting systems cussed by [ stars with mass lower thanholes 2.5 with M masses of about 40 M ing from minutes tomotion. decades. The presence of Blazars a pair havegravitational of wave radio black emission. holes, jets of that jets and can the show variability at an small scale apparent can superluminal produce PoS(MULTIF2019)020 ], 66 ], dynamical Rosa Poggiani 82 ]. 35 ], the impact from the accretion disk 59 ] could be the fragmentation of accretion 40 6 ]. The superluminal emission in blazars and other objects, 21 ], [ (2016) L21, (2019) 062001. (2019) 122002. (2017) 161101. (2017) 121102. (2017) 141101. (2016) 061102. (2016) 241103. (2017) 221101. 66 (2017) 47. (2017) L35. (2017) 122003. ] and could be fast enough to be detectable with ground based inter- ]. Gravitational wave bursts can occur during the initial acceleration (2011) 271102. 832 95 100 100 40 119 118 119 116 116 118 847 851 25 (2015) 062008. 107 91 PRL ApJ PRD PRL PRD PRD ApJ PRL PRL PRL ApJL PRL PRL PRD ]. Gravitational wave emission associated to the flare could occur at the same time of 17 Blazar flares can last for months, but often variability at short time scales occurs. An exam- Gravitational emission can be caused by the ejection of jet superluminal components and the Several accreting systems are candidate gravitational sources, either as binaries or because ]. [3] B. P. Abbott et al., [4] B. P. Abbott et al., [5] B. P. Abbott et al., [1] J. Aasi et al., [2] J. Abadie et al, [9] B. P. Abbott et al., [7] B. P. Abbott et al., [8] B. P. Abbott et al., [6] B. P. Abbott et al., 21 [10] B. P. Abbott et al., [11] B. P. Abbott et al., [12] B. P. Abbott et al., [13] B. P. Abbott et al., [14] B. P. Abbott et al., [ disk for a blazar hosting a single supermassive black hole [ of the jet, with a frequency spectrum in the region of the spaceple based is interferometer the LISA gamma [ variability2006 at [ the scale ofelectromagnetic minutes emission observed [ in PKS 2155-304ferometers. by HESS The in physical July mechanisms of fast flares [ precession of accretion disks [ of physical processes: cataclysmicsion variables, span X-ray the binaries, whole active gravitationaltechniques: galactic spectrum, ground nuclei. based requiring interferometry, the space Their based combination emis- interferometry, of pulsar timing. different observational References Gravitational waves from accreting systems such as microquasars, could be caused byby the a combination of central the Kerr accretion black diskBardeen-Petterson precession effect hole induced [ and the fragmentation of the tilted disk, dynamically driven by the of the secondary black holefriction in from blazars satellites infalling hosting onto pairs a of coplanar supermassive accretion black disk holes [ [ 8. 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