• Nem Talált Eredményt

MScinastronomySupervisors:Prof.LászlóÁrpádGergely,professor,UniversityofSzeged,SzegedDr.KrisztinaÉvaGabányi,researchfellow,KonkolyObservatory,BudapestSzeged2017 PhDthesisstatementsRevealingsupermassiveblackholebinariesviathesignaturesinthejetsofradio-loud

N/A
N/A
Protected

Academic year: 2022

Ossza meg "MScinastronomySupervisors:Prof.LászlóÁrpádGergely,professor,UniversityofSzeged,SzegedDr.KrisztinaÉvaGabányi,researchfellow,KonkolyObservatory,BudapestSzeged2017 PhDthesisstatementsRevealingsupermassiveblackholebinariesviathesignaturesinthejetsofradio-loud"

Copied!
8
0
0

Teljes szövegt

(1)

University of Szeged Faculty of Science and Informatics

Doctoral School of Physics

PhD thesis statements

Revealing supermassive black hole binaries via the signatures in the jets of radio-loud active galactic nuclei

Emma Kun

MSc in astronomy

Supervisors:

Prof. László Árpád Gergely, professor, University of Szeged, Szeged Dr. Krisztina Éva Gabányi, research fellow, Konkoly Observatory,

Budapest

Szeged 2017

(2)

1 Scientific background

According to the accepted galaxy evolution models, galaxies gather their masses through a sequence of accretion and merger phases. As a result, million to billion Solar mass supermassive black holes formed at the cen- tre of massive galaxies, and some of them might be members of binary systems due to the long time scale of the merger.

An accretion disk may form around the black hole due to the non- zero angular momentum of the infalling matter. As substantial amount of energy is released in the accretion disk due to its efficient mass-energy conversion, the compact centre of the galaxy becomes an active galactic nucleus (AGN).

Cosmological and galaxy evolution models render the peak of galaxy mergers to cosmological redshifts between two and three. Since at such distances it is not possible to spatially resolve sub-parsec separated binary systems, even with the astronomical techniques giving the finest angular resolutions, they can only be identified indirectly from measurements on the accretion disk and jets of either binary AGN, or active–passive pairs.

When a member of the supermassive black hole binary is radio-loud due to its relativistic jets (approximately 10 per cent of single AGN qual- ifies), a periodic jet structure might indicate, that the jet emitter black hole interacts gravitationally with another black hole. At present, radio interferometry (notably the technique of very long baseline interferomet- ry, VLBI) provides the finest angular resolution images of AGN jets. In earlier decades, periodic jet structures used to be attributed to the orbital motion of supermassive black hole binaries. However, hydrodynamical and magnetohydrodynamical simulations proved, that instabilities in the plasma could also lead to a helical structure in the jet. Therefore, periodical jet structures do not necessarily provide enough evidence for an orbiting black hole at the base of the jet. A substantial part of my PhD research targeted this ambiguity.

The periodicities in the jets I have investigated are consistent with su- permassive black hole binaries in the inspiral evolution stage. The gravi- tational lifetime of such systems is million to billion years. This begs the question of how can we identify even tighter binaries. Supermassive black hole binaries, coalescing presumably on time scale of several decades, are potential sources of the low frequency gravitational waves to be detected by the future LISA space mission. Identification of such sources is im- portant for breaking degeneracies in their parameter estimation. Particle physical processes following the final coalescence of supermassive black hole binary systems can also prove useful for this.

(3)

Identification of the origin of cosmic neutrinos detected by the antarctic IceCube Neutrino Observatory is an actively studied topic in astroparticle physics. Scientists of the Pierre Auger and IceCube Collaborations pro- posed, that the most probably sources of such neutrinos are AGN. In my thesis, I also addressed the neutrino emission following the final coales- cence of supermassive black hole binaries.

2 Research methods

In an important part of my PhD research, I have processed multi-epoch VLBI radio astronomical data of relativistic jets to analyse their kinemat- ics. The VLBI interferometric arrays provide the Fourier transform of the brightness distribution of the source, the visibility function.

In particular, I have employed the radio interferometric measurements provided by the "Monitoring Of Jets in Active galactic nuclei with VLBA Experiments" (MOJAVE) survey. This is a long-term monitoring program in operation since 1994, with the aim to observe the brightness and po- larization variability of AGN jets across the northern celestial sphere. The measurements are performed with the Very Long Baseline Array (VLBA), an interferometer array consisting of 10 radio telescopes with a diameter of 25m each. The array employs VLBI technique, reaching a resolution better than1milliarcsecs. Homogeneous data, spanning up two decades with good sampling are available in case of the brighter sources (&1Jy).

The MOJAVE group provides the calibrated visibilities of the monitored sources downloadable shortly after the observations.

I have performed the mapping and the modelfitting of the calibrated visibilities with the CalTech DIFMAP software package, which is a widely used tool to prepare radio intensity maps, and to analyse the radio inter- ferometric measurements. I have modelled the brightness distribution of the jets by two dimensional Gaussian components. The variability of the jet structure was expressed through the change in their parameters.

I have written a code in C programming language, which simulates how the flux density and the shape of the jet change in space for given input parameters, and how the ridge line evolves as projected to the plane of the sky, when the jet base is orbiting. I have derived the parameters of the supermassive black hole binary based on the position and integrated flux density variability of the jet components.

As part of my PhD research, I have investigated the origin of the cosmic high energy neutrinos detected by the Antarctic IceCube Neutrino Obser- vatory. This is located at the Amundsen–Scott South Pole Station, and uses one cubic kilometre of the Antarctic ice as detector matter. The detector

(4)

strings penetrate up to2500m deep underground, and are sensitive to the Cherenkov radiation of electrons and muons emerging from the interac- tion of electron and muon neutrinos with the ice. The IceCube Collabo- ration has detected 55 cosmic high energy neutrinos and published their parameters. I have cross-correlated the arrival direction of the track-type neutrinos with the positions of AGN given in several radio catalogues, searching for the origin of such high energy neutrinos.

3 Thesis statements

1. I have proved the connection between the low energy cut-off (LEC) seen in the radio spectrum of several extragalactic jets and the ro- tation of the central black hole. I have explained the existence of a positron population with the LEC through the decay of pions cre- ated in proton-proton collisions. I have derived the minimum pro- ton energy and velocity to form pions, then assuming the Maxwell- Boltzmann distribution of their velocities, I have determined where the temperature is high enough in an advection dominated accretion flow to create the positron population with the LEC. I have proved, that the pion formation occurs near the jet launching zone, where the velocity of 10 per cent of the protons exceeds the minimum velocity necessary to create pions. Therefore, a positron population with LEC emerges in the jet. (Kun et al., 2013)

2. I have worked out a jet kinematical model including an orbiting black hole at the jet base, which can be tested by VLBI observations of extragalactic jets. I have written a code in C programming lan- guage exploring as input parameters the jet half-opening angle, its spatial orientation, and the parameters of the binary dynamics. The output is the apparent flux density and the shape of the jet in space and as projected to the plane of the sky. Simulating the ridge line of a hypothetical jet I have found, that the integrated flux density and the core separation of the jet components depend sensitively on the jet inclination, the total mass of the black hole binary, and its mass ratio.

3. I have mapped the VLBI jet of the quasar S5 1928+738 employing the calibrated visibilities spanning almost 20 years, provided by the MOJAVE group. I have modelled the surface brightness distribution of the jet by circular Gaussian components, and derived their inte- grated flux density, core separation, and full width at half-maximum size. Based on the jet behaviour, I have confirmed the existence of a

(5)

massive black hole binary suspected at the jet base. I have proved the spin-orbit precession of the jet emitting black hole purely based on VLBI measurements, as a first in the literature. I have derived the binary parameters compatible with the VLBI measurements (orbital periodT = 4.78±0.14 yr, binary separationr = 0.0128±0.0003 pc, mass ratioν ∈[1/5÷1/3]), spin-orbit period (TSO = 4852±646 yr), and gravitational time scale of the binary coalescence (TGR = (1.44±0.19)×106yr). (Kun et al., 2014)

4. I have investigated the parsec-scale structure of the jet of the quasar PG 1302-102 based on its calibrated visibilities spanning 17 years, provided by the MOJAVE group. The quasar may harbour a su- permassive black hole binary, as inferred from its periodic optical light curve, thus I have searched the signs of this binary system at radio wavelengths. In addition to the VLBA measurements, I have processed other radio interferometric data to reveal the kiloparsec- scale morphology of the jet. I have derived the structural parame- ters of the jet. Based on these and independent estimations of the Newtonian binary parameters, I have determined a lower limit on the mass ratio (ν ≥ 0.08), and upper limits on the spin-orbit pe- riod of the binary and the gravitational time scale of its coalescence (TSO ≤1.41×104yr andTGR≤7.2×106yr, respectively). (Kun et al., 2015)

5. I have explained a high energy neutrino detection by the Antarctic IceCube Neutrino Observatory through the final coalescence of a su- permassive black hole binary. I have correlated the coordinates of flat spectrum sources in the Parkes Catalogue and the 2nd Planck Com- pact Sources Catalogue with the arrival direction of the track-type neutrinos. I have found, that the blazar PKS 0723-008 is an excellent candidate for the origin of the neutrino event ID5. I have shown, that the treble coincidence of such coordinate-matching is quite small, 10−4. I have explained the neutrino emission in the direction of PKS 0723-008, the substantially increased radio flux density of the source at2 cm wavelength and its radio flat spectrum with a scenario, in which the final coalescence of two supermassive black holes is fol- lowed by the birth of an energetic jet. (Kun et al., 2017)

(6)

4 Publications

Publications associated with the thesis:

1. Kun E., Wiita P. J., Gergely L. Á., Keresztes Z., Gopal-Krishna, Bier- mann P. L., "Constraints on supermassive black hole spins from ob- servations of active galaxy jets", 2013, Astronomische Nachrichten, 334, 1024

2. Kun E., Gabányi K. É., Karouzos M., Britzen S., Gergely L. Á., "A spinning supermassive black hole binary model consistent with VLBI observations of the S5 1928+738 jet", 2014, MNRAS, 445, 1370 3. Kun E., Frey S., Gabányi K. É., Britzen S., Cseh D., Gergely L. Á.,

"Constraining the parameters of the putative supermassive binary black hole in PG 1302–102 from its radio structure", 2015, MNRAS, 454, 1290

4. Kun E., Biermann P. L., Gergely L. Á., "A flat spectrum candidate for a track-type high energy neutrino emission event, the case of blazar PKS 0723-008", 2017, MNRAS Letters, 466, 34

Other publications, associated with the topic of the thesis:

1. Gabányi K. É, Frey S., Xiao T., Paragi Zs., An T., Kun E., Gergely L. Á., "A single radio-emitting nucleus in the dual AGN candidate NGC 5515", 2014, MNRAS, 443, 1509

2. Roland J., Britzen S.,Kun E., Henri G., Lambert S., Zensus A., "Struc- ture of the nucleus of 1928+738", 2015, A&A, 578, 86

3. De Rosa A., Bianchi S., Bogdanovi´c T., Decarli R., Herrero-Illana R., Husemann B., Komossa S., Kun E., Loiseau N., Paragi Z., Perez- Torres M., Piconcelli E., Schawinski K., Vignali C., "Multiple AGN in the crowded field of the compact group SDSS J0959+1259", 2015, MNRAS, 453, 214

4. Mohan P., An T., Frey S., Mangalam A., Gabányi K. É.,Kun E., "Parsec- scale jet properties of the quasar PG 1302-102", 2016, MNRAS, 463, 1812

5. Biermann P. L.,Caramete L. I., Fraschetti F., Gergely L. Á., Harms B. C.,Kun E., Lundquist J. P., Meli A., Nath B. B., Seo E.-S., Stanev T., Becker Tjus, J., "The Nature and Origin of Ultra-High Energy Cosmic Ray Particles", 2016, arXiv:1610.00944

(7)

Other publications by the PhD candidate:

1. Kun E., Sódor Á., Jurcsik J., Hurta Zs., Nagy I., K˝ovári Zs., Poszto- bányi K., Kovács G., Vida K., Belucz B., IBVS, 5859, 2008

2. Jurcsik J., Hurta ZS., Sódor Á., Szeidl B., Nagy I., Posztobányi K., Váradi M., Vida K., Belucz B., Dékány I., Hajdu G., K˝ovári ZS.,Kun E., MNRAS, 397, 350, 2009

3. Jurcsik J., Sódor Á., Hajdu G., Szeidl B., Dózsa Á., Posztobányi K., Smitola P., Belucz B., Fehér V., K˝ovári Zs., Kriskovics L.,Kun E., Mol- nár L., Nagy I., Vida K., Görög N., MNRAS, 423, 993, 2012

4. Sódor Á., Jurcsik J., Molnár L., Szeidl B., Hurta Zs., Bakos G. Á., Hartman J., Béky B., Noyes R.W., Sasselov D., Mazeh T., Bartus J., Belucz B., Hajdu G., K˝ovári Zs., Kun E., Nagy I., Posztobányi K., Smitola P., Vida K., ASPC, 462, 228, 2012

5. Sódor Á., Hajdu G, Jurcsik J., Szeidl B., Posztobányi K., Hurta Zs., Belucz B.,Kun E., MNRAS, 427, 1517, 2012

6. Hajdu G., Jurcsik J., Sódor Á., Szeidl B., Smitola P., Belucz B., Posz- tobányi K., Vida K.,Kun E., AN, 333, 1074, 2012

7. Jurcsik J., Smitola P., Hajdu G., Pilachowski C., Kolenberg K., Sódor Á., F ˝urész G., Moór A.,Kun E., Saha A., Prakash P., Blum P., Tóth I., 2013, ApJ, 778, 27

8. Jurcsik J., Smitola P., Hajdu G., Sódor Á., Nuspl J., Kolenberg K., F ˝urész G., Moór A.,Kun E., Pál A., Bakos J., Kelemen J., Kovács T., Kriskovics L., Sárneczky K., Szalai T., Szing A., Vida K., 2015, ApJS, 219, 25

(8)

Hivatkozások

KAPCSOLÓDÓ DOKUMENTUMOK

With the help of the heat resistance models, the surface heat transfer coefficient and the meteorolgy models, I have developed a complex energy prediction system, and

3 Not only does the non-identity of author and narrator facilitate such narrative tricks as the unreliable narrator (c.f. Booth's reference to the irony

neutrino oszcilláció felfedezése: nyugalmi tömeggel bíró részecskék Neutrino kutatásokért díjazott fizikai Nobel-díjasok.

The main results of the present paper can be summarized as follows. i) We have given a unique decomposition of the “Gauss variable” (describing the energy of a mode of a

The approaching of my dissertation was different from the above, it had different direction from that I have already explained, my investigation was focusing on the teachers of the

HTLV- I infection models have been studied by many researchers [1,4,5]and mathematical models have been developed to describe the interaction in vivo HTLV-I, the CD4 + target cells,

4  The elements were the following: I have a CV in a foreign language, I am/was a member of a talent nurturing program; I am/was a member of a college for advanced studies; I have

The authors would like to thank Professor Feng Qi and the anonymous referee for some valuable suggestions which have improved the final version of this