Study of the variable broadband emission of Markarian 501 during the most extreme Swift X-ray activity
Links to Fileshttps://arxiv.org/abs/2001.07729
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Type of Work33 pages
journal articles preprints
Citation of Original PublicationV. A. Acciari and S. Ansoldi and L. A. Antonelli and A. Babić and B. Banerjee and U. Barres de Almeida and J. A. Barrio and J. Becerra González and W. Bednarek and E. Bernardini and A. Berti and J. Besenrieder and W. Bhattacharyya and C. Bigongiari and O. Blanch and G. Bonnoli and G. Busetto and R. Carosi and G. Ceribella and S. Cikota and S. M. Colak and P. Colin and E. Colombo and J. L. Contreras and J. Cortina and S. Covino and V. D'Elia and P. Da Vela and F. Dazzi and A. De Angelis and B. De Lotto and M. Delfino and J. Delgado and F. Di Pierro and E. Do Souto Espi\ nera and A. Domínguez and D. Dominis Prester and M. Doro and V. Fallah Ramazani and A. Fattorini and A. Fernández-Barral and G. Ferrara and D. Fidalgo and L. Foffano and M. V. Fonseca and L. Font and C. Fruck and D. Galindo and S. Gallozzi and R. J. García López and M. Garczarczyk and S. Gasparyan and M. Gaug and P. Giammaria and N. Godinović and D. Guberman and D. Hadasch and A. Hahn and T. Hassan and J. Herrera and J. Hoang and D. Hrupec and S. Inoue and K. Ishio and Y. Iwamura and H. Kubo and J. Kushida and D. Kuveždić and A. Lamastra and D. Lelas and F. Leone and E. Lindfors and S. Lombardi and F. Longo and M. López and A. López-Oramas and B. Machado de Oliveira Fraga and C. Maggio and P. Majumdar and M. Makariev and M. Mallamaci and G. Maneva and M. Manganaro and L. Maraschi and M. Mariotti and M. Martínez and S. Masuda and D. Mazin and M. Minev and J. M. Miranda and R. Mirzoyan and E. Molina and A. Moralejo and V. Moreno and E. Moretti and P. Munar-Adrove r and V. Neustroev and A. Niedzwiecki and M. Nievas Rosillo and C. Nigro and K. Nilsson and D. Ninci and K. Nishijima and K. Noda and L. Nogués and S. Paiano and J. Palacio and D. Paneque and R. Paoletti and J. M. Paredes and G. Pedaletti and P. Peñil and M. Peresano and M. Persic and P. G. Prada Moroni and E. Prandini and I. Puljak and J. R. Garcia and M. Ribó and J. Rico and C. Righi and A. Rugliancich and L. Saha and N. Sahakyan and T. Saito and K. Satalecka and T. Schweizer and J. Sitarek and I. Šnidarić and D. Sobczynska and A. Somero and A. Stamerra and M. Strzys and T. Surić and F. Tavecchio and P. Temnikov and T. Terzić and M. Teshima and N. Torres-Albá and S. Tsujimoto and J. van Scherpenberg and G. Vanzo and M. Vazquez Acosta and I. Vovk and M. Will and D. Zarić and FACT Collaboration and : and A. Arbet-Engels and D. Baack and M. Balbo and A. Biland and M. Blank and T. Bretz and K. Bruegge and M. Bulinski and J. Buss and M. Doerr and D. Dorner and S. Einecke and D. Elsaesser and D. Hildebrand and L. Linhoff and K. Mannheim and S. Mueller and D. Neise and A. Neronov and M. Noethe and A. Paravac and W. Rhode and B. Schleicher and F. Schulz and K. Sedlaczek and A. Shukla and V. Sliusar and E. von Willert and R. Walter and C. Wendel and A. Tramacere and A. Lien and M. Perri and F. Verrecchia and M. Armas Padilla and C. Leto and A. Lähteenmäki and M. Tornikoski and J. Tammi, 2020,Study of the variable broadband emission of Markarian 501 during the most extreme Swift X-ray activity,
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Context. Markarian 501 (Mrk 501) is a very high-energy (VHE) gamma-ray blazar located at z = 0.034, which is regularly monitored by a wide range of multi-wavelength (MWL) instruments, from radio to VHE gamma rays. During a period of almost two weeks in July 2014, the highest X-ray activity of Mrk 501 was observed in∼14 years of operation of the Neil Gehrels Swift Gamma-ray Burst Observatory. Aims. We characterize the broadband variability of Mrk 501 from radio to VHE gamma rays during the most extreme X-ray activity measured in the last 14 years, and evaluate whether it can be interpreted within theoretical scenarios widely used to explain the broadband emission from blazars. Methods. The emission of Mrk 501 was measured at radio with Metsähovi, at optical–UV with KVA and Swift/UVOT, at X-ray with Swift/XRT and Swift/BAT, at gamma ray with Fermi-LAT, and at VHE gamma rays with the FACT and MAGIC telescopes. The multi-band variability and correlations were quantiﬁed, and the broadband spectral energy distributions (SEDs) were compared with predictions from theoretical models. Results. The VHE emission of Mrk 501 was found to be elevated during the X-ray outburst, with a gamma-ray ﬂux above 0.15 TeV varying from ∼0.5 to∼2 times the Crab nebula ﬂux (CU). The X-ray and VHE emission both varied on timescales of 1 day and were found to be correlated. We measured a general increase in the fractional variability with energy, with the VHE variability being twice as large as the X-ray variability. The temporal evolution of the most prominent and variable segments of the SED, characterized on a day-by-day basis from 2014 July 16 to 2014 July 31, is described with a one-zone synchrotron self-Compton model with variations in the break energy of the electron energy distribution (EED),and with some adjustments in the magnetic ﬁeld strength and spectral shape of the EED. These results suggest that the main ﬂux variations during this extreme X-ray outburst are produced by the acceleration and the cooling of the high-energy electrons. A narrow feature at∼3TeVwas observed in the VHE spectrum measured on 2014 July 19 (MJD 56857.98), which is the day with the highest X-ray ﬂux (> 0.3 keV) measured during the entire Swift mission. This feature is inconsistent with the classical analytic functions to describe the measured VHE spectra (power law,log-parabola,andlog-parabola with exponential cutoﬀ) at more than3σ.A ﬁt with a log-parabola plus a narrow component is preferred over the ﬁt with a single log-parabola at more than 4σ, and a dedicated Monte Carlo simulation estimated the signiﬁcance of this extra component to be larger than 3 σ. Under the assumption that this VHE spectral feature is real, we show that it can be reproduced with three distinct theoretical scenarios: a) a pileup in the EED due to stochastic acceleration; b) a structured jet with two-SSC emitting regions, with one region dominated by an extremely narrow EED; and c) an emission from an IC pair cascade induced by electrons accelerated in a magnetospheric vacuum gap, in addition to the SSC emission from a more conventional region along the jet of Mrk 501.