Continuous optical monitoring of the highly active blazar Mrk421

K. Gazeas, M. Petropoulou, A. Mastichiadis

ABSTRACT

We present the recent photometric monitoring of blazar Mrk421, obtained from the Gerostathopouleio Observatory at the University of Athens. Follow-up observations have been performed on this source after a highly energetic flare which occurred on 12 April, 2013. The flare was observed in X- rays by Nustar & Swift and in GeV-TeV gamma-rays by the Fermi satellite and MAGIC/VERITAS telescopes respectively. Continuous photometric monitoring in the optical BVRI bands during 3 months after the flaring activity reveals a quasi-periodic light variation. This is one of the few times that Mrk421 was observed for such a long period without large observational gaps in four different filters. We find a strong correlation between the different optical bands. Although we did not detect any signs of intra-day variability, the optical flux is variable in longer time scales (days/weeks) with the relative amplitude of variations being approximately the same in all four bands.

Reference: Gazeas K., Petropoulou M., Mastichiadis A., 2013, Hel.A.S. Conf. Series

Blazar Optical Sky Survey -BOSS project (2013-2017). The long-term blazar variability monitoring

K. Gazeas

ABSTRACT

Blazar Optical Sky Survey (BOSS Project) is a dedicated observational survey with the aim of monitoring known blazars in optical wavelengths. The project was initiated in March 2013 at the University of Athens Observatory (UOAO), performing ground-based optical photometric observations in parallel with orbital (SWIFT/XRT, FERMI/LAT) X-ray observatories. BOSS Project immediately met international attention, attracting the interest of several collaborators worldwide. It is currently running as an international collaboration of the National and Kapodistrian University of Athens, utilizing the robotic and remotely controlled telescope at the UOAO. Several targets of interest are monitored in the frame of BOSS Project, such as highly variable blazars and AGNs. The targets are continuously observed on a daily basis, with the aim to achieve dense temporal coverage in optical wavelengths. Furthermore, simultaneous observations in high and low energy bands are cross-correlated with BOSS database and crucial information are gathered, in order to understand the mechanisms that are taking place in these objects. In this work, some of the major achievements after the first 4 years of operation of the BOSS Project are given, while the advantage of small, robotic and remotely controlled telescopes is highlighted.

Reference: Gazeas K., 2017, Hel.A.S. Conf. Series

Long-Term Optical Monitoring of Blazars

K. Gazeas

ABSTRACT

Systematic monitoring of specific targets in the optical regime was historically applied on a very narrow sample of known variable stars. The discovery of blazars in the 20th century brought to the foreground the need for new global sky surveys, covering the entire sky and fainter sources. Full-sky surveys are conducted more easily from space observatories, while radio telescopes perform follow up observations from the ground. Blazars are detected in a wide range of energies, while they exhibit strong variability in various wavelengths from -rays and X-rays to the optical and radio domain. This results in a detailed classification, according to their emission properties in each region. The rapid variability in optical domain makes blazars interesting targets for optical sky surveys, oering a new opportunity to study their variability in the time domain. Digital sky surveys in optical and near-IR found a fertile ground with the aid of sensitive sensors. Only a few dedicated programs are focusing on blazar variability, a trend which evolved rapidly in the last decade. Modern techniques, in combination with dedicated sky survey programs lead towards a new era of long-term monitoring of blazars, aiming towards the search or variability on various time scales. In this work, an overview of blazar optical surveys and monitoring projects is given, addressing the major points of each one, and highlighting the constraints that the long-term study of blazars will bring through future international campaigns.

Reference: Gazeas K., 2019, Galaxies, 7, 58

The 2015 outburst of the OJ287 blazar

M. Valtonen, S. Zola, A. Gopakumar, K. Gazeas, W. Ogloza, M. Drozdz, M. Siwak, B. Debski, J. Dalessio, K. Sadakane, M. Kidger, K. Nilsson, A. Berdyugin, E. Lindfors, L. Takalo, K. Baliyan, M. Mugrauer, F. Alicavus, A. Erdem, J. Provencal, J. Webb, M. Zejmo, E. Sobas, H. Er, W. Keel, T. Schweyer

ABSTRACT

A model that contains a massive BH binary was proposed to explain the double peaked quasi-periodical (roughly about 12 years) outbursts of the blazar OJ287. A regular photometric monitoring of this target has been performed since the very beginning of this season with the aim of catching the next outburst, predicted by the model to occur this winter, between mid November and early January. Brightness of OJ287 was changing in the range between 14.4 and 14.8 mag in the R filter for most of this season but starting from Nov 18 we observed its gradual light increase, followed by a rapid brightness rise also announced by the ASAS project (ATEL #8372). On Dec 4, we recorded the highest brightness of about 12.9 mag (R) and OJ287 started to fade. We believe that the current outburst, consistent with the inspiralling spinning massive BH binary model for OJ287, could be the expected GR centenary flare.

Reference: Valtonen et al. 2015, ATel

Primary black hole spin in OJ 287 as determined by the general relativity centenary flare

M. Valtonen, S. Zola, S. Ciprini, A. Gopakumar, K. Matsumoto, K. Sadakane et al.

ABSTRACT

OJ287 is a quasi-periodic quasar with roughly 12 year optical cycles. It displays prominent outbursts that are predictable in a binary black hole model. The model predicted a major optical outburst in 2015 December. 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, c = 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 10% accuracy during the present decade.

Reference: Valtonen et al. 2016, ApJL, 819, L37

A Search for QPOs in the Blazar OJ287: Preliminary Results from the 2015/2016 Observing Campaign

Zola S., M. Valtonen, G. Bhatta, A. Goyal, B. Debski, A. Baran, J. Krzesinski et al.

ABSTRACT

We analyse the light curve in the R band of the blazar OJ287, gathered during the 2015/2016 observing season. We did a search for quasi-periodic oscillations (QPOs) using several methods over a wide range of timescales. No statistically significant periods were found in the high-frequency domain both in the ground-based data and in Kepler observations. In the longer-period domain, the Lomb-Scargle periodogram revealed several peaks above the 99% significance level. The longest one-about 95 days-corresponds to the innermost stable circular orbit (ISCO) period of the more massive black hole. The 43-day period could be an alias, or it can be attributed to accretion in the form of a two-armed spiral wave.

Reference: Zola et al. 2016, Galaxies, 4, 41

Polarization and Spectral Energy Distribution in OJ 287 during the 2016/17 Outbursts

M. Valtonen, Zola S., H. Jermak, S. Ciprini, R. Hudec, L. Dey, A. Gopakumar, D.L. Reichart, D.B. Caton, K. Gazeas et al.

ABSTRACT

We report optical photometric and polarimetric observations of the blazar OJ 287 gathered during 2016/17. The high level of activity, noticed after the General Relativity Centenary flare, is argued to be part of the follow-up flares that exhibited high levels of polarization and originated in the primary black hole jet. We propose that the follow-up flares were induced as a result of accretion disk perturbations, travelling from the site of impact towards the primary SMBH. The timings inferred from our observations allowed us to estimate the propagation speed of these perturbations. Additionally, we make predictions for the future brightness of OJ 287.

Reference: Valtonen et al. 2017, Galaxies, 5, 83

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

L.Dey, M. J. Valtonen, A. Gopakumar, S. Zola, R. Hudec, P. Pihajoki, S. Ciprini, K. Matsumoto, K. Sadakane et al.

ABSTRACT

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 (BBH) central engine of blazar OJ287 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 OJ287. We develop an approach that incorporates this effect into the BBH model for OJ287. This allows us to demonstrate an excellent agreement between the observed impact flare timings and those predicted from ten orbital cycles of the BBH 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 OJ287'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.

Reference: Dey et al. 2018, ApJ, 866, 11

High accuracy measurement of gravitational wave back-reaction in the OJ287 black hole binary

M.J. Valtonen, L. Dey, R. Hudec, S. Zola, A. Gopakumar, S. Mikkola, S. Ciprini, K. Matsumoto, K. Sadakane, M. Kidger, K. Gazeas, K. Nilsson, A. Berdyugin, V. Piirola, H. Jermak, K.S. Baliyan, D. E. Reichart, S. Haque and the OJ287-15/16 Collaboration

ABSTRACT

The binary black hole (BBH) central engine of OJ287 exhibits large thermal flares at least twice every 12 years. The times of these flares have been predicted successfully using the simple rule that they are generated at a constant phase angle of a quasi-Keplerian eccentric orbit. In this model a secondary black hole goes around a primary black hole, impacting the accretion disk of the latter twice per orbital period, creating the thermal flares. New measurements of the historical light curve have been combined with the observations of the 2015/2017 season. The 2015 November/December flare went into the phase of rapid flux rise on the centenary of Einstein's General Relativity, namely on November 25, and peaked on December 5. At that time OJ287 was at its brightest level in over 30 years in optical wavelengths. Using the light curve of this flare and subsequent synchrotron flares, and comparing it with the points in the historical light curve, we are able to identify the impact record since year 1886, altogether 25 impacts. Out of these, 14 are timed accurately enough to constrain the orbit of the black hole binary. The set of flare timings determines uniquely the 8 parameters of our BBH central engine model: the two masses, the primary spin, the major axis, eccentricity and the phase of the orbit, plus the two parameters of the standard accretion disk. Since the orbit solution is strongly over-determined, its parameters are known very accurately, at better than one percent level for the masses and the primary BH spin. The orbit solution shows that the period of the orbit, now 12.062 year, has decreased at the rate of 36 days per century. This corresponds to an energy loss to gravitational waves that is 6.5 +/- 4 % less than the rate predicted by the standard quadrupolar GW emission. We show that the difference is due to higher order gravitational radiation reaction contributions to BBH dynamics that includes the dominant order tail contributions. The orbital shrinkage rate agrees within error limits with the rate calculated by Damour, Gopakumar and Iyer (2004). The full list of participants in the OJ287-15/16 Collaboration is found in ApJL 819, L37, 2016.

Reference: Valtonen et al. 2018, IAU