Multiwavelength Observations of the Blazar BL Lacertae: A New Fast TeV Gamma-Ray Flare

Abeysekara, A. U.; Benbow, W.; Bird, R.; Brantseg, Thomas; Brose, Robert; Buchovecky, M.; Buckley, J. H.; Bugaev, V.; Connolly, Michael; Cui, Wei; Daniel, M. K.; Falcone, A.; Feng, Q.; Finley, J. P.; Fortson, L.; Furniss, A.; Gillanders, G. H.; Gunawardhana, Isuru; Hütten, Moritz; Hanna, D.; Hervet, O.; Holder, J.; Hughes, G.; Humensky, T. B.; Johnson, C. A.; Kaaret, P.; Kar, P.; Kertzman, M.; Krennrich, F.; Lang, M. J.; Lin, T. T. Y.; McArthur, S.; Moriarty, P.; Mukherjee, R.; O’Brien, S.; Ong, R. A.; Otte, A. N.; Park, N.; Petrashyk, A.; Pohl, Martin; Pueschel, E.; Quinn, J.; Ragan, K.; Reynolds, P. T.; Richards, G.; Roache, E.; Rulten, C. B.; Sadeh, I.; Santander, M.; Sembroski, G. H.; Shahinyan, K.; Wakely, S. P.; Weinstein, A. J.R.; Wells, R. M.; Wilcox, P.; Williams, D. A.; Zitzer, B.; Jorstad, S. G.; Marscher, A. P.; Lister, M. L.; Kovalev, Y. Y.; Pushkarev, A. B.; Savolainen, Tuomas; Agudo, I.; Molina, S. N.; Gómez, J. L.; Larionov, V. M.; Борман, Г. А.; Mokrushina, A. A.; Tornikoski, M.; Lähteenmäki, A.; Chamani, Wara; Enestam, S.; Kiehlmann, S.; Hovatta, T.; Smith, Paul S.; Pontrelli, P.

doi:10.3847/1538-4357/aab35c

Cited by 36 publications

(31 citation statements)

References 83 publications

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“…After the passage, the two components appear to split up, resulting in an apparent inward motion of S 2. The apparent displacement of a stationary jet component matches the signature expected for a RCS zone breakout (e.g., Abeysekara et al 2018). When a moving blob with high kinetic energy starts interacting with the standing RCS localized in the region where the magnetic field becomes unstable, there could be (1) an enhancement of non-thermal emission, (2) a strong instability of the magnetic field configuration (e.g., tearing instability; Del Zanna et al 2016), and (3) a positional displacement by the underlying flow with increasing kinetic power of the jet (Hervet et al 2016).…”

Section: Positional Variations Of the Stationary Componentssupporting

confidence: 66%

Investigating the connection between γ-ray activity and the relativistic jet in 3C 273 during 2015−2019

Kim

Trippe

Kravchenko

2020

A&A

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Context. Due to its powerful radiation over the entire electromagnetic spectrum and its radio jet activity, the blazar 3C 273 offers the opportunity to study the physics of γ-ray emission from active galactic nuclei. Since a historically strong outburst in 2009, 3C 273 showed relatively weak emission in the γ-ray band over multiple years. However, recent Fermi-Large Area Telescope observations indicate elevated activity during 2015-2019. Aims. We aim at constraining the origin of the γ-ray outbursts towards 3C 273 and investigate their connection to the parsec-scale jet. Methods. We generate Fermi-LAT γ-ray light curves with multiple binning intervals and study the spectral properties of the γ-ray emission. Using a 3 mm ALMA light curve, we study the correlation between radio and γ-ray emission. Relevant activity in the parsec-scale jet of 3C 273 is investigated with 7 mm VLBA observations obtained close in time to notable γ-ray outbursts. Results. We find two prominent γ-ray outbursts in 2016 (MJD 57382) and 2017 (MJD 57883) accompanied by mm-wavelength flaring activity. The γ-ray photon index time series show a weak hump-like feature around the γ-ray outbursts. The monthly γ-ray flux-index plot indicates a transition from softer-when-brighter to harder-when-brighter at 1.03 × 10 −7 ph cm −2 s −1 . A significant correlation between the γ-ray and mm-wavelength emission is found, with the radio lagging the γ-rays by about 105-112 days. The 43 GHz jet images reveal the known stationary features (i.e., the core, S 1, and S 2) in a region upstream of the jet. We find indication for a propagating disturbance and a polarized knot between the stationary components around the times of both γ-ray outbursts. Conclusions. Our results support a parsec-scale origin for the observed γ-ray elevated activity, suggesting association with standing shocks in the jet.

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Section: Positional Variations Of the Stationary Componentssupporting

confidence: 66%

Investigating the connection between γ-ray activity and the relativistic jet in 3C 273 during 2015−2019

Kim

Trippe

Kravchenko

2020

A&A

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“…(b) Corresponding best fit to the VERITAS light curve of the 2016 BL Lacerate TeV flare (Abeysekara et al 2018). The fit has χ 2 ν = 1.95, and is consistent with the SED in panel (a).…”

Section: Fitting To the 2016 Tev Flare Of Bl Lacertaesupporting

confidence: 53%

“…The effects of changing these parameters are discussed in Section 3.2. The flaring data is taken from Abeysekara et al (2018) and is indicated by the dark blue circles. Quiescent data is show by the faint cyan circles for comparison (Abdo et al 2011). the maximum synchrotron and SSC emitted photon energies, which can be seen to vary through Fig.…”

Section: Parameter Search Resultsmentioning

confidence: 99%

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The feasibility of magnetic reconnection powered blazar flares from synchrotron self-Compton emission

Morris¹,

Potter²,

Cotter³

2019

Monthly Notices of the Royal Astronomical Society

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Order of magnitude variability has been observed in the blazar sub-class of Active Galactic Nuclei on minute timescales. These high-energy flares are often difficult to explain with shock acceleration models due to the small size of the inferred emitting region, with recent particle-in-cell (PIC) simulations showing that magnetic reconnection is a promising alternative mechanism. Here, we present a macroscopic emission model physically motivated by PIC simulations, where the energy for particle acceleration originates from the reconnecting magnetic field. We track the radial growth and relative velocity of a reconnecting plasmoid, modelling particle acceleration and radiative losses from synchrotron and synchrotron self-Compton (SSC) emission. To test the viability of magnetic reconnection as the mechanism behind rapid blazar flares we simultaneously fit our model to the observed light-curve and SED from the 2016 TeV flare of BL Lacertae. We find generally that, without considering external photons, reconnecting plasmoids are unable to produce Compton-dominant TeV flares and so cannot reproduce the observations due to overproduction of synchrotron emission. Additionally, problematically large plasmoids, comparable in size to the entire jet radius, are required to emit sufficient SSC gamma-rays to be observable. However, our plasmoid model can reproduce the rapid TeV lightcurve of the flare, demonstrating that reconnection is able to produce rapid, powerful TeV flares on observed timescales. We conclude that while reconnection can produce SSC flares on the correct timescales, the primary source of TeV emission cannot be SSC and the size of plasmoids required may be implausibly large.

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“…The particle individual Lorentz factors are often estimated to be above 10 6 for the most energetic blazars, implying long-standing and powerful particle acceleration mechanisms. While dio quasars (FSRQs) and some low-or intermediatefrequency-peaked BL Lacs (LBLs and IBLs) (Jorstad et al 2001;Marscher et al 2008;Abeysekara et al 2018). The formation of recollimation shocks (also referenced as conical standing shock or reconfinement shock) in jets is also a phenomenon naturally observed in hydrodynamic and magnetohydrodynamic jet simulations as soon as a supersonic, or super-Alfvenic, non-pressured matched flow propagates through an external medium.…”

Section: Introductionmentioning

confidence: 99%

Probing an X-Ray Flare Pattern in Mrk 421 Induced by Multiple Stationary Shocks: A Solution to the Bulk Lorentz Factor Crisis

Hervet

Williams

Falcone

et al. 2019

ApJ

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The common observations of multiple radio VLBI stationary knots in high-frequency-peaked BL Lacs (HBLs) can be interpreted as multiple recollimation shocks accelerating particles along jets. This approach can resolve the so-called "bulk Lorentz factor crisis" of sources with high Lorentz factor, deduced from maximum γ − γ opacity and fast variability, and apparently inconsistent slow/stationary radio knots. It also suggests that a unique pattern of the non-thermal emission variability should appear after each strong flare. Taking advantage of the 13 years of observation of the HBL Mrk 421 by the X-ray Telescope on the Neil Gehrels Swift Observatory (Swift-XRT), we probe for such an intrinsic variability pattern. Its significance is then statistically estimated via comparisons with numerous similar simulated lightcurves. A suggested variability pattern is identified, consistent with a main flare emission zone located in the most upstream 15.3 GHz radio knot at 0.38 mas from the core. Subsequent flux excesses in the lightcurve are consistent with a perturbation crossing all the downstream radio knots with a constant apparent speed of 45 c. The significance of the observed variability pattern not arising from stochastic processes is found above 3 standard deviations, opening a promising path for further investigations in other blazars and with other energy bands. In addition to highlight the role of stationary radio knots as high-energy particle accelerators in jets, the developed method allows estimates of the apparent speed and size of a jet perturbation without the need to directly observe any motion in jets.

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Multiwavelength Observations of the Blazar BL Lacertae: A New Fast TeV Gamma-Ray Flare

Cited by 36 publications

References 83 publications

Investigating the connection between γ-ray activity and the relativistic jet in 3C 273 during 2015−2019

Investigating the connection between γ-ray activity and the relativistic jet in 3C 273 during 2015−2019

The feasibility of magnetic reconnection powered blazar flares from synchrotron self-Compton emission

Probing an X-Ray Flare Pattern in Mrk 421 Induced by Multiple Stationary Shocks: A Solution to the Bulk Lorentz Factor Crisis

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