Multi-wavelength characterization of the blazar S5 0716+714 during an unprecedented outburst phase

Abstract

Context. The BL Lac object S5 0716+714, a highly variable blazar, underwent an impressive outburst in January 2015 (Phase A), followed by minor activity in February (Phase B). The MAGIC observations were triggered by the optical flux observed in Phase A, corresponding to the brightest ever reported state of the source in the R-band. Aims.The comprehensive dataset collected is investigated in order to shed light on the mechanism of the broadband emission. Methods. Multi-wavelength light curves have been studied together with the broadband spectral energy distributions (SEDs). The sample includes data from Effelsberg, OVRO, Metsähovi, VLBI, CARMA, IRAM, SMA, Swift-UVOT, KVA, Tuorla, Steward, RINGO3, KANATA, AZT-8+ST7, Perkins, LX-200, Swift-XRT, NuSTAR, Fermi-LAT and MAGIC. Results. The flaring state of Phase A was detected in all the energy bands, providing for the first time a multi-wavelength sample of simultaneous data from the radio band to the very-high-energy (VHE, E > 100 GeV). In the constructed SED, the Swift-XRT+NuSTAR data constrain the transition between the synchrotron and inverse Compton components very accurately, while the second peak is constrained from 0.1 GeV to 600 GeV by Fermi+MAGIC data. The broadband SED cannot be described with a one-zone synchrotron self-Compton model as it severely underestimates the optical flux in order to reproduce the X-ray to γ-ray data. Instead we use a two-zone model. The electric vector position angle (EVPA) shows an unprecedented fast rotation. An estimation of the redshift of the source by combined high-energy (HE, 0.1 GeV < E < 100 GeV) and VHE data provides a value of z = 0.31 ± 0.02stats ± 0.05sys, confirming the literature value. Conclusions. The data show the VHE emission originating in the entrance and exit of a superluminal knot in and out of a recollimation shock in the inner jet. A shock–shock interaction in the jet seems responsible for the observed flares and EVPA swing. This scenario is also consistent with the SED modeling.

Luminous and high-frequency peaked blazars: the origin of the γ-ray emission from PKS 1424+240

“…The very detection of VHE FSRQs implies that the γ-ray emission is located outside the BLR during the VHE detection, or at the most at its very edge, in order to escape the low-energy photon field and ultimately reach the observer (MAGIC Collaboration et al 2008;Aleksić et al 2011;H.E.S.S. Collaboration et al 2013;Aleksić et al 2014b;Abeysekara et al 2015;Ahnen et al 2015). For PKS 1424+240 the scenario is similar to VHE FSRQs: the detection of γ-ray photons up to 750 GeV means that the γ-ray emitting region is located outside the BLR, or that the BLR itself is extremely underluminous.…”

“…On the other hand, this absorption can be used to put constraints on the EBL itself and indeed, the VHE detection of the first blazars at redshifts z ≥ 0.15 imposed strong constraints on early EBL models (Aharonian et al 2006). Nowadays, among the VHE blazars with a spectroscopic redshift, the most distant ones are the quasars S3 0218+35 (z = 0.944, Ahnen et al 2016) and PKS 1441+25 (z = 0.939, Ahnen et al 2015;Abeysekara et al 2015). Both of these quasars have been detected at VHE only during flaring activity.…”

Gamma rays from blazars

“…The most interesting case is that of the recently detected PKS1441+25 (z = 0.940). The observed power-law spectrum [87] extends up to E max ≈ 300 GeV, which, in the rest frame of the source corresponds to E max = E max (1 + z) ≈ 580 GeV, just at the edge expected cut-off. This is clearly visible in Fig.…”

Черенковские Гамма-Телескопы: Прошлое, Настоящее, Будущее. Проект ALEGRO

“…Совре-менные методы наблюдений космических гамма-квантов позволяют охватить диапазон от 0.1 мегаэлектроноволь-та (MeV) до десятков тераэлектроновольт (TeV) [1]. Гамма-астрономия позволяет исследовать наиболее вы-сокоэнергичные явления, происходящие в Галактике и за ее пределами, связанные со взрывами звезд на позд-них стадиях эволюции (см., например, [2,3]), слияни-ем звезд, распространением ударных волн, мощными высокоскоростными истечениями, формирующимися в окрестности сверхмассивных черных дыр в ядрах актив-ных галактик (см., например, [4]). Изучение процессов, происходящих в этих физических системах, важно для создания целостной картины эволюции Вселенной и проверки адекватности теоретических моделей физи-ки элементарных частиц в диапазоне энергий выше 100 TeV, недостижимых для современных земных уско-рителей.…”