BL Lacertae flaring activity 2019-2020 Dijana Dominis Prester, University of Rijeka, Department of Physics & G. Bonnolli, E. Lindfords, D. Morcuende, J. Strišković, S. Ventura CMC Meeting, Zagreb, 22 September 2020 CMC Meeting, Zagreb, 22.9.2020 BL Lac Flaring Activity, D. Dominis Prester 1 Outline • BL Lacertae • MAGIC paper on BL Lac flare in 2015 • BL Lac flare in May 2019 • BL Lac flares from July 2019 up to Sept 2020 • Potential alternative modeling of MAGIC BL Lac data CMC Meeting, Zagreb, 22.9.2020 BL Lac Flaring Activity, D. Dominis Prester 2 BL Lacertae • RA: 22h 02m 43.3s , dec: +42° 16ʹ 40ʺ (2000) in Constellation Lacerta (lizard) • Redshift: z=0.069 • Discovered by C. Hoffmeister (1929) and misinterpreted as variable star • Strong radio emission detection (J. Schmitt, 1968), host galaxy identified • Detected in VHE by MAGIC I mono (Albert et al, Astrophys.J.666:L17- L20,2007) CMC Meeting, Zagreb, 22.9.2020 BL Lac Flaring Activity, D. Dominis Prester 3 BL Lacertae objects • Blazars of extreme nature • Named after “The Prototype” BL Lacertae • Typically in centers of luminous elliptical galaxies • Rapid and large-amplitude flux variability • Significant optical polarization • Spectra dominated by a relatively featureless non-thermal emission continuum over the entire electromagnetic range • No strong emission lines, contrary to quasars • Core dominated radio sources • Subclasses depending on the broadband spectral shape (HBL, IBL, LBL, XBL, RBL) CMC Meeting, Zagreb, 22.9.2020 BL Lac Flaring Activity, D. Dominis Prester 4 MAGIC paper on BL Lac flare in 2015 MAGIC Collaboration et al.: BL Lac in 2015 γ γ ] VHE -ray flare. Furthermore, fast VHE -ray flares seem to be -1 rather common in BL Lac, as three have already been observed. s MJD: 57188 BL Lacertae • June 2015 flare: first single-night -2 It is rather unlikely that all three would have been produced by star-jet interaction (Aleksic´ et al., 2014a, see discussion in). detection of BL Lac in VHE (MAGIC In summary, we have tested three models to explain the fast -10 stereo) 10 variability of VHE γ-ray flux in BL Lac, but were not able to settle on preferred model. The interaction model is preferred as /dE [erg cm • Φ it matches the observed repeating multiwavelength patterns best, MAGIC ATel #7669, 18 June 2015 d 2 but in our simple blob-in-blob model it gives the worst descrip- tion of the γ-ray band data. Further observations during VHE • paper: Acciari et al (MAGIC γ-ray flares are required with strictly simultaneous optical and 10-11 Collaboration), A&A 623, A175 SED: E X-ray high cadence data. Repeating MWL patterns could play a key role in constraining the site and mechanism of fast γ-ray flares. This gives a strong motivation to have an intense long- (2019) Broad Line Region model term monitoring of BL Lac, regardless of its VHE γ-ray state. Interaction model MAGIC • 3 models proposed based on SED, Star-jet model Fermi-LAT 10-12 Acknowledgements. We would like to thank the Instituto de Astrof´ısica de none of them could be confirmed 10-1 1 10 102 103 Canarias for the excellent working conditions at the Observatorio del Roque de Energy [GeV] los Muchachos in La Palma. The financial support of the German BMBF and MPG, the Italian INFN and INAF, the Swiss National Fund SNF, the ERDF under the Spanish MINECO (FPA2015-69818-P, FPA2012-36668, FPA2015- Fig. 12. Gamma-ray SED of MJD 57188 compared to the three 68378-P, FPA2015-69210-C6-2-R, FPA2015-69210-C6-4-R, FPA2015-69210- CMC Meeting, Zagreb, 22.9.2020 BL Lac Flaring Activity, D. Dominis Prestermodels discussed in Section 4. The light blue band shows5 the C6-6-R, AYA2015-71042-P, AYA2016-76012-C3-1-P, ESP2015-71662-C2-2- systematic uncertainty of the MAGIC data. P, FPA201790566REDC), the Indian Department of Atomic Energy and the Japanese JSPS and MEXT is gratefully acknowledged. This work was also sup- ported by the Spanish Centro de Excelencia “Severo Ochoa” SEV-2016-0588 and SEV-2015-0548, and Unidad de Excelencia “Mar´ıa de Maeztu” MDM-2014- the VLBA 43 GHz core around the time of the γ-ray flare, lo- 0369, by the Croatian Science Foundation (HrZZ) Project IP-2016-06-9782 cating the active region there. The fast VHE γ-ray flare is not and the University of Rijeka Project 13.12.1.3.02, by the DFG Collaborative accompanied by a significant brightening in γ-ray, X-ray or op- Research Centers SFB823/C4 and SFB876/C3, the Polish National Research tical bands; even though we have observations from the same Centre grant UMO-2016/22/M/ST9/00382 and by the Brazilian MCTIC, CNPq day in all of these bands. We note that, the X-ray observation is and FAPERJ. The work of the author M. Vazquez Acosta is financed with grant RYC-2013-14660 of MINECO. F. D’Ammando is grateful for support from the not strictly simultaneous. National Research Council of Science and Technology, Korea (EU-16-001). We also compare the multiwavelength behaviour to the two The Fermi LAT Collaboration acknowledges generous ongoing support epochs around the fast VHE γ-ray flares observed by VERITAS. from a number of agencies and institutes that have supported both the de- We find that the lower frequency patterns seem to repeat dur- velopment and the operation of the LAT as well as scientific data analy- ing the three fast VHE γ-ray flares. As discussed in Feng et al. sis. These include the National Aeronautics and Space Administration and the Department of Energy in the United States, the Commissariat a` l’Energie (2017); Abeysekara et al. (2018), the occurence of VHE γ-ray Atomique and the Centre National de la Recherche Scientifique / Institut flares during the activity in VLBA core is in agreement with a National de Physique Nucleaire´ et de Physique des Particules in France, the model proposed by Marscher (2014). In that model the VLBA Agenzia Spaziale Italiana and the Istituto Nazionale di Fisica Nucleare in Italy, core is a conical shock. Turbulent shells of plasma pass through the Ministry of Education, Culture, Sports, Science and Technology (MEXT), High Energy Accelerator Research Organization (KEK) and Japan Aerospace that conical shock and electrons are accelerated. As the turbu- Exploration Agency (JAXA) in Japan, and the K. A. Wallenberg Foundation, the lent shells are small, they would naturally also explain the fast Swedish Research Council and the Swedish National Space Board in Sweden. VHE γ-ray flares. However, there is a significant observational Additional support for science analysis during the operations phase is grate- bias involved in two of the three VHE γ-ray observations as they fully acknowledged from the Istituto Nazionale di Astrofisica in Italy and the have been triggered by high optical and γ-ray fluxes. We there- Centre National d’Etudes´ Spatiales in France. This work performed in part un- fore considered three models to reproduce the SED in this paper. der DOE Contract DE-AC02-76SF00515. Based on observations made with the Nordic Optical Telescope, operated The models we consider (see Fig. 12), namely a fast blob by the Nordic Optical Telescope Scientific Association at the Observatorio del inside the BLR, a fast blob interacting with a larger component Roque de los Muchachos, La Palma, Spain, of the Instituto de Astrofisica de and star-jet interaction, can all reproduce the observed SED dur- Canarias. ing the 2015 June 15 flare. All of the models have some caveats. Acquisition and reduction of the MAPCAT data was supported in part by In the first model (small blob inside BLR), there is large uncer- MINECO through grants AYA2010-14844, AYA2013-40825-P, and AYA2016- 80889-P, and by the Regional Government of Andaluc´ıa through grant P09- tainty about the parameters used for the BLR, which is known FQM-4784. The MAPCAT observations were carried out at the German-Spanish to be weak in this source. In addition, there is no spatial connec- Calar Alto Observatory, which is jointly operated by the Max-Plank-Institut fur¨ tion between the two emission regions, even if in all observed Astronomie and the Instituto de Astrof´ısica de Andaluc´ıa-CSIC. cases of fast VHE γ-ray flares, we have seen activity also in The St.Petersburg University team acknowledges support from Russian the VLBA 43 GHz core. In the second model, where the emis- Science Foundation grant 17-12-01029. sion regions are co-spatial it is challenging to match the model This publication makes use of data obtained at the Metsahovi¨ Radio with the highest energy MAGIC data without overproducing the Observatory, operated by Aalto University, Finland. This study makes use of 43 GHz VLBA data from the flux in the Fermi-LAT band. The model also requires us to use a VLBA-BU Blazar Monitoring Program (VLBA-BU-BLAZAR; lower magnetic field than what VLBA observations would indi- http://www.bu.edu/blazars/VLBAproject.html), funded by NASA through cate (assuming equipartition condition). This was also found for the Fermi Guest Investigator Program. The VLBA is an instrument of the PKS 1510-089 (Aleksic´ et al., 2014b) when adopting a similar National Radio Astronomy Observatory. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated by modelling. The star-jet model has the same caveat as the small Associated Universities, Inc. The BU group acknowledges support from NASA blob inside the BLR model; there is no connection between the Fermi GI program grant 80NSSC17K0694 and US National Science Foundation generally increased flux levels in the other bands and the fast grant AST-1615796.