arXiv subjects

M. J. Valtonen

Publications and source records attributed to M. J. Valtonen.

At least 19 recordsLinked to original sources

arXiv2022

MOMO V. Effelsberg, Swift and Fermi study of the blazar and supermassive binary black hole candidate OJ 287 in a period of high activity

We report results from our ongoing project MOMO (Multiwavelength Observations and Modelling of OJ 287). In this latest publication of a sequence, we combine our Swift UVOT--XRT and Effelsberg radio data (2.6-44 GHz) between 2019 and 2022.04 with public SMA data and gamma-ray data from the Fermi satellite. The observational epoch covers OJ 287 in a high state of activity from radio to X-rays. The epoch also covers two major events predicted by the binary supermassive black hole (SMBH) model of OJ 287. Spectral and timing analyses clearly establish: a new UV-optical minimum state in 2021 December at an epoch where the secondary SMBH is predicted to cross the disk surrounding the primary SMBH; an overall low level of gamma-ray activity in comparison to pre-2017 epochs; the presence of a remarkable, long-lasting UV--optical flare event of intermediate amplitude in 2020--2021; a high level of activity in the radio band with multiple flares; and particularly a bright, ongoing radio flare peaking in 2021 November that may be associated with a gamma-ray flare, the strongest in 6 years. Several explanations for the UV--optical minimum state are explored, including the possibility that a secondary SMBH launches a temporary jet, but the observations are best explained by variability associated with the main jet.

astro-ph.HE↗

arXiv2021

Project MOMO: Multiwavelength Observations and Modelling of OJ 287

Our project MOMO (Multiwavelength observations and modelling of OJ 287) consists of dedicated, dense, long-term flux and spectroscopic monitoring and deep follow-up observations of the blazar OJ 287 at >13 frequencies from the radio to the X-ray band since late 2015. In particular, we are using Swift to obtain optical-UV-X-ray spectral energy distributions (SEDs) and the Effelsberg telescope to obtain radio measurements between 2 and 40 GHz. MOMO is the densest long-term monitoring of OJ 287 involving X-rays and broad-band SEDs. The theoretical part of the project aims at understanding jet and accretion physics of the blazar central engine in general and the supermassive binary black hole scenario in particular. Results are presented in a sequence of publications and so far included: detection and detailed analysis of the bright 2016/17 and 2020 outbursts and the long-term light curve; Swift, XMM and NuSTAR spectroscopy of the 2020 outburst around maximum; and interpretation of selected events in the context of the binary black hole scenario of OJ 287 (papers I-IV). Here, we provide a description of the project MOMO, a summary of previous results, the latest results, and we discuss future prospects.

astro-ph.HE↗

arXiv2021

X-ray spectral components of the blazar and binary black hole candidate OJ 287 (2005-2020)

We present a comprehensive analysis of all XMM-Newton spectra of OJ 287 spanning 15 years of X-ray spectroscopy of this bright blazar. We also report the latest results from our dedicated Swift UVOT and XRT monitoring of OJ 287 which started in 2015, along with all earlier public Swift data since 2005. During this time interval, OJ 287 was caught in extreme minima and outburst states. Its X-ray spectrum is highly variable and encompasses all states seen in blazars from very flat to exceptionally steep. The spectrum can be decomposed into three spectral components: Inverse Compton (IC) emission dominant at low-states, super-soft synchrotron emission which becomes increasingly dominant as OJ 287 brightens, and an intermediately-soft (Gamma_x=2.2) additional component seen at outburst. This last component extends beyond 10 keV and plausibly represents either a second synchrotron/IC component and/or a temporary disk corona of the primary supermassive black hole (SMBH). Our 2018 XMM-Newton observation, quasi-simultaneous with the Event Horizon Telescope observation of OJ 287, is well described by a two-component model with a hard IC component of Gamma_x=1.5 and a soft synchrotron component. Low-state spectra limit any long-lived accretion disk/corona contribution in X-rays to a very low value of L_x/L_Edd < 5.6 times 10^(-4) (for M_(BH, primary) = 1.8 times 10^10 M_sun). Some implications for the binary SMBH model of OJ 287 are discussed.

astro-ph.HE↗

arXiv2021

Supermassive binary black holes and the case of OJ 287

Supermassive binary black holes (SMBBHs) are laboratories par excellence for relativistic effects, including precession effects in the Kerr metric and the emission of gravitational waves. Binaries form in the course of galaxy mergers, and are a key component in our understanding of galaxy evolution. Dedicated searches for SMBBHs in all stages of their evolution are therefore ongoing and many systems have been discovered in recent years. Here we provide a review of the status of observations with a focus on the multiwavelength detection methods and the underlying physics. Finally, we highlight our ongoing, dedicated multiwavelength program MOMO (for Multiwavelength Observations and Modelling of OJ 287). OJ 287 is one of the best candidates to date for hosting a sub-parsec SMBBH. The MOMO program carries out a dense monitoring at >13 frequencies from radio to X-rays and especially with Swift since 2015. Results so far included: (1) The detection of two major UV-X-ray outbursts with Swift in 2016/17 and 2020; exhibiting softer-when-brighter behaviour. The non-thermal nature of the outbursts was clearly established and shown to be synchrotron radiation. (2) Swift multi-band dense coverage and XMM-Newton spectroscopy during EHT campaigns caught OJ 287 at an intermediate flux level with synchrotron and IC spectral components. (3) Discovery of a remarkable, giant soft X-ray excess with XMM and NuSTAR during the 2020 outburst. (4) Spectral evidence (at 2sigma) for a relativistically shifted iron absorption line in 2020. (5) The non-thermal 2020 outburst is consistent with an after-flare predicted by the SMBBH model of OJ 287.

astro-ph.HE↗

arXiv2020

The April-June 2020 super-outburst of OJ 287 and its long-term multiwavelength light curve with Swift: binary supermassive black hole and jet activity

We report detection of a very bright X-ray-UV-optical outburst of OJ 287 in April-June 2020; the second brightest since the beginning of our Swift multi-year monitoring in late 2015. It is shown that the outburst is predominantly powered by jet emission. Optical-UV-X-rays are closely correlated, and the low-energy part of the XMM-Newton spectrum displays an exceptionally soft emission component consistent with a synchrotron origin. A much harder X-ray powerlaw component (Gamma-x = 2.4, still relatively steep when compared to expectations from inverse-Compton models) is detected out to 70 keV by NuSTAR. We find evidence for reprocessing around the Fe region, consistent with an absorption line. If confirmed, it implies matter in outflow at approx 0.1c. The multi-year Swift lightcurve shows multiple episodes of flaring or dipping with a total amplitude of variability of a factor of 10 in X-rays, and 15 in the optical-UV. The 2020 outburst observations are consistent with an after-flare predicted by the binary black hole model of OJ 287, where the disk impact of the secondary black hole triggers time-delayed accretion and jet activity of the primary black hole.

astro-ph.HE↗

arXiv2018

Authenticating the Presence of a Relativistic Massive Black Hole Binary in OJ 287 Using its General Relativity Centenary Flare: Improved Orbital Parameters

Results from regular monitoring of relativistic compact binaries like PSR 1913+16 are consistent with the dominant (quadrupole) order emission of gravitational waves (GWs). We show that observations associated with the binary black hole central engine of blazar OJ 287 demand the inclusion of gravitational radiation reaction effects beyond the quadrupolar order. It turns out that even the effects of certain hereditary contributions to GW emission are required to predict impact flare timings of OJ 287. We develop an approach that incorporates this effect into the binary black hole model for OJ~287. This allows us to demonstrate an excellent agreement between the observed impact flare timings and those predicted from ten orbital cycles of the binary black hole central engine model. The deduced rate of orbital period decay is nine orders of magnitude higher than the observed rate in PSR 1913+16, demonstrating again the relativistic nature of OJ 287's central engine. Finally, we argue that precise timing of the predicted 2019 impact flare should allow a test of the celebrated black hole "no-hair theorem" at the 10% level.

astro-ph.HE↗

arXiv2016

Primary black hole spin in OJ287 as determined by the General Relativity centenary flare

OJ287 is a quasi-periodic quasar with roughly 12 year optical cycles. It displays prominent outbursts which are predictable in a binary black hole model. The model predicted a major optical outburst in December 2015. We found that the outburst did occur within the expected time range, peaking on 2015 December 5 at magnitude 12.9 in the optical R-band. Based on Swift/XRT satellite measurements and optical polarization data, we find that it included a major thermal component. Its timing provides an accurate estimate for the spin of the primary black hole, chi = 0.313 +- 0.01. The present outburst also confirms the established general relativistic properties of the system such as the loss of orbital energy to gravitational radiation at the 2 % accuracy level and it opens up the possibility of testing the black hole no-hair theorem with a 10 % accuracy during the present decade.

astro-ph.HE↗

arXiv2013

Dark energy and the structure of the Coma cluster of galaxies

{We consider the Coma cluster of galaxies as a gravitationally bound physical system embedded in the perfectly uniform static dark energy background as implied by the $Λ$CDM cosmology.} {We ask if the density of dark energy is high enough to affect the structure of a large rich cluster of galaxies?} {We use recent observational data on the cluster together with our theory of local dynamical effects of dark energy, including the zero-gravity radius $R_{\rm ZG}$ of the local force field as the key parameter.} {1) Three masses are defined which characterize the structure of a regular cluster: the matter mass $M_{\rm M}$, the dark-energy effective mass $M_{\rm DE}$ ($<0$) and the gravitating mass $M_{\rm G}$ ($= M_{\rm M} + M_{\rm DE}$). 2) A new matter density profile is suggested which reproduces well the observational data for the Coma cluster in the radius range from 1.4 Mpc to 14 Mpc and takes into account the dark energy background. 3) Using this profile, we calculate upper limits for the total size of the Coma cluster, $R \le R_{\rm ZG} \approx 20$ Mpc, and its total matter mass, $M_{\rm M} \la M_{\rm M}(R_{\rm ZG}) = 6.2 \times 10^{15} M_{\odot}$.} {The dark energy antigravity affects strongly the structure of the Coma cluster at large radii $R \ga 14$ Mpc and should be taken into account when its total mass is derived.}

astro-ph.CO↗

arXiv2012

Black hole binary OJ287 as a testing platform for general relativity

The blazar OJ287 is the most promising (and the only) case for an extragalactic binary black hole system inspiralling under the action of gravitational radiation reaction. At present, though it is not possible to directly observe the binary components, it is possible to observe the jet emanating form the primary black hole. We argue that the orbital motion of the secondary black hole is reflected in the wobble of the jet and demonstrate that the wobble is orbital position dependent. The erratic wobble of the jet, reported in Agudo et al. (2012), is analyzed by taking into account the binary nature of the system and we find that the erratic component of jet wobble is very small.

astro-ph.HE↗

arXiv2012

On the masses of OJ287 black holes

Two multifrequency campaigns were carried out on OJ287 in 2005: in April when it was in its pre-outburst state, and in November, during the main 12 yr cycle outburst. The wavelength coverage was from radio to X-rays. In the optical-to-UV range the differential spectrum between the observations has a bremsstrahlung spectral shape, consistent with gas at $3 \times 10^{5}K$ temperature. Our result supports the hydrogen column density of the OJ287 host galaxy of $\sim9.3\times 10^{20} cm^{-2}$, the average value found by Gosh & Soundararajaperumal. The $3 \times 10^{5}K$ bremsstrahlung radiation was predicted in the binary black hole model of OJ287, and it arises from a hot bubble of gas which is torn off the accretion disc by the impact of the secondary. As this radiation is not Doppler boosted, the brightness of the outburst provides an estimate for the mass of the secondary black hole, $\sim1.4\times10^{8}$ solar mass. In order to estimate the mass of the primary black hole, we ask what is the minimum mass ratio in a binary system which allows the stability of the accretion disc. By using particle simulations, we find that the ratio is $\sim1.3\times10^{2}$. This makes the minimum mass of the primary $\sim1.8\times10^{10}$ solar mass, in agreement with the mass determined from the orbit solution, $1.84 \times 10^{10}$ solar mass. With this mass value and the measured K-magnitude of the bulge of the host galaxy of OJ287, the system lies almost exactly on the previously established correlation in the black hole mass vs. K-magnitude diagramme. It supports the extension of this correlation to brighter magnitudes and to more massive black holes than has been done previously.

astro-ph.HE↗

arXiv2011

Virial estimator for dark energy

A new estimator of the local density of dark energy is suggested which comes from the virial theorem for non-relativistic gravitating systems embedded in the uniform dark energy background.

astro-ph.CO↗

arXiv2011

Testing black hole no-hair theorem with OJ287

We examine the ability to test the black hole no-hair theorem at the 10% level in this decade using the binary black hole in OJ287. In the test we constrain the value of the dimensionless parameter q that relates the scaled quadrupole moment and spin of the primary black hole: q2 = -q 2 . At the present we can say that q = 1 \pm 0.3 (one), in agreement with General Relativity and the no-hair theorems. We demonstrate that this result can be improved if more observational data is found in historical plate archives for the 1959 and 1971 outbursts. We also show that the predicted 2015 and 2019 outbursts will be crucial in improving the accuracy of the test. Space-based photometry is required in 2019 July due the proximity of OJ287 to the Sun at the time of the outburst. The best situation would be to carry out the photometry far from the Earth, from quite a different vantage point, in order to avoid the influence of the nearby Sun. We have considered in particular the STEREO space mission which would be ideal if it has a continuation in 2019 or LORRI on board the New Horizons mission to Pluto.

astro-ph.CO↗

arXiv2010

Dark energy domination in the Virgocentric flow

The standard \LambdaCDM cosmological model implies that all celestial bodies are embedded in a perfectly uniform dark energy background, represented by Einstein's cosmological constant, and experience its repulsive antigravity action. Can dark energy have strong dynamical effects on small cosmic scales as well as globally? Continuing our efforts to clarify this question, we focus now on the Virgo Cluster and the flow of expansion around it. We interpret the Hubble diagram, from a new database of velocities and distances of galaxies in the cluster and its environment, using a nonlinear analytical model which incorporates the antigravity force in terms of Newtonian mechanics. The key parameter is the zero-gravity radius, the distance at which gravity and antigravity are in balance. Our conclusions are: 1. The interplay between the gravity of the cluster and the antigravity of the dark energy background determines the kinematical structure of the system and controls its evolution. 2. The gravity dominates the quasi-stationary bound cluster, while the antigravity controls the Virgocentric flow, bringing order and regularity to the flow, which reaches linearity and the global Hubble rate at distances \ga 15 Mpc. 3. The cluster and the flow form a system similar to the Local Group and its outflow. In the velocity-distance diagram, the cluster-flow structure reproduces the group-flow structure with a scaling factor of about 10; the zero-gravity radius for the cluster system is also 10 times larger. The phase and dynamical similarity of the systems on the scales of 1-30 Mpc suggests that a two-component pattern may be universal for groups and clusters: a quasi-stationary bound central component and an expanding outflow around it, due to the nonlinear gravity-antigravity interplay with the dark energy dominating in the flow component.

astro-ph.CO↗

arXiv2009

Measuring the spin of the primary black hole in OJ287

The compact binary system in OJ287 is modelled to contain a spinning primary black hole with an accretion disk and a non-spinning secondary black hole. Using Post Newtonian (PN) accurate equations that include 2.5PN accurate non-spinning contributions, the leading order general relativistic and classical spin-orbit terms, the orbit of the binary black hole in OJ287 is calculated and as expected it depends on the spin of the primary black hole. Using the orbital solution, the specific times when the orbit of the secondary crosses the accretion disk of the primary are evaluated such that the record of observed outbursts from 1913 up to 2007 is reproduced. The timings of the outbursts are quite sensitive to the spin value. In order to reproduce all the known outbursts, including a newly discovered one in 1957, the Kerr parameter of the primary has to be $0.28 \pm 0.08$. The quadrupole-moment contributions to the equations of motion allow us to constrain the `no-hair' parameter to be $1.0\:\pm\:0.3$ where 0.3 is the one sigma error. This supports the `black hole no-hair theorem' within the achievable precision. It should be possible to test the present estimate in 2015 when the next outburst is due. The timing of the 2015 outburst is a strong function of the spin: if the spin is 0.36 of the maximal value allowed in general relativity, the outburst begins in early November 2015, while the same event starts in the end of January 2016 if the spin is 0.2

astro-ph.HE↗

arXiv2009

Black Holes in Active Galactic Nuclei

Supermassive black holes are common in centers of galaxies. Among the active galaxies, quasars are the most extreme, and their black hole masses range as high as to $6\cdot 10^{10} M_\odot$. Binary black holes are of special interest but so far OJ287 is the only confirmed case with known orbital elements. In OJ287, the binary nature is confirmed by periodic radiation pulses. The period is twelve years with two pulses per period. The last four pulses have been correctly predicted with the accuracy of few weeks, the latest in 2007 with the accuracy of one day. This accuracy is high enough that one may test the higher order terms in the Post Newtonian approximation to General Relativity. The precession rate per period is $39^\circ.1 \pm 0^\circ.1$, by far the largest rate in any known binary, and the $(1.83\pm 0.01)\cdot 10^{10} M_\odot$ primary is among the dozen biggest black holes known. We will discuss the various Post Newtonian terms and their effect on the orbit solution. The over 100 year data base of optical variations in OJ287 puts limits on these terms and thus tests the ability of Einstein's General Relativity to describe, for the first time, dynamic binary black hole spacetime in the strong field regime. The quadrupole-moment contributions to the equations of motion allows us to constrain the `no-hair' parameter to be $1.0\:\pm\:0.3$ which supports the black hole no-hair theorem within the achievable precision.

gr-qc↗

arXiv2009

Dark energy and the mass of the Local Group

Dark energy must be taken into account to estimate more reliably the amount of dark matter and how it is distributed in the local universe. For systems several Mpc across like the Local Group, we introduce three self-consistent independent mass estimators. These account for the antigravity effect of dark energy treated as Einstein's cosmological constant Lambda. The first is a modified Kahn-Woltjer model which gives a value of the Local Group mass via the particular motions of the two largest members, the Milky Way and M31. Inclusion of dark energy in this model increases the minimum mass estimate by a factor of three compared to the "classical estimate". The increase is less but still significant for different ways of using the timing argument. The second estimator is a modified virial theorem which also demonstrates how dark energy can "hide" from detection a part of the gravitating mass of the system. The third is a new zero-gravity method which gives an upper limit to the group mass which we calculate with high precision HST observations. In combination, the estimators lead to a robust and rather narrow range for a group's mass, M. For the Local Group, 3.2 < M < 3.7 x 10^{12} M_sun. Our result agrees well with the Millennium Simulation based on the LambdaCDM cosmology.

astro-ph.CO↗

arXiv2008

A massive binary black-hole system in OJ287 and a test of general relativity

Tests of Einstein's general theory of relativity have mostly been carried out in weak gravitational fields where the space-time curvature effects are first-order deviations from Newton's theory. Binary pulsars provide a means of probing the strong gravitational field around a neutron star, but strong-field effects may be best tested in systems containing black holes. Here we report such a test in a close binary system of two candidate black holes in the quasar OJ287. This quasar shows quasi-periodic optical outbursts at 12 yr intervals, with two outburst peaks per interval. The latest outburst occurred in September 2007, within a day of the time predicted by the binary black-hole model and general relativity. The observations confirm the binary nature of the system and also provide evidence for the loss of orbital energy in agreement (within 10 per cent) with the emission of gravitational waves from the system. In the absence of gravitational wave emission the outburst would have happened twenty days later.

astro-ph↗

arXiv2008

Mapping the three-body system - decay time and reversibility

In this paper we carry out a quantitative analysis of the three-body systems and map them as a function of decaying time and intial conguration, look at this problem as an example of a simple deterministic system, and ask to what extent the orbits are really predictable. We have investigated the behavior of about 200 000 general Newtonian three body systems using the simplest initial conditions. Within our resolution these cover all the possible states where the objects are initially at rest and have no angular momentum. We have determined the decay time-scales of the triple systems and show that the distribution of this parameter is fractal in appearance. Some areas that appear stable on large scales exhibit very narrow strips of instability and the overall pattern, dominated by resonances, reminds us of a traditional Maasai warrior shield. Also an attempt is made to recover the original starting conguration of the three bodies by backward integration. We find there are instances where the evolution to the future and to the past lead to different orbits, in spite of time symmetric initial conditions. This implies that even in simple deterministic systems there exists an Arrow of Time.

astro-ph↗