The 2009 multiwavelength campaign on Mrk 421: Variability and correlation studies

J Aleksić,K Mallot,T Terzić,S Rügamer,T Schweizer,M Villata,R Zanin,N Park,T Surić,M Capalbi,M Doert,K Meagher,S Ansoldi,M Garczarczyk,P Cassaro,F Zandanel,K Nilsson,E Bernardini,A Stamerra,R Mirzoyan,K Frantzen,J Sitarek,F Longo,M Mariotti,G Giavitto,S Lombardi,E Carmona,V Scalzotto,T C Weekes,H Prokoph,A Carramiñana,M Salvati,D Mazin,D Hildebrand,J M Miranda,S Federici,W P Chen,J Becerra González,G Hughes,A Moralejo,C Delgado Mendez,B Zitzer,J Rodriguezgarcia,M Cerruti,M Gaug,J A Barrio,M Teshima,A Wilhelm,F Dazzi,J W Moody,Y Mori,V Kadenius,A González Muñoz,D Ferenc,H Krawczynski,E Koptelova,J Cortina,J Dumm,K Satalecka,M F Aller,R Bird,R M Wagner,P Bangale,M Palatiello,S Mcarthur,O Blanch,D Nakajima,E Roache,J Grube,V M Larionov,T Sakamoto,A Sillanpää,T P Krichbaum,A Biland,D Eisenacher,J Krause,S Partini,L Font,I Nestoras,P Munar-Adrover,L Ciupik,B Mcbreen,A Treves,J Thaele,Y Khassen,U Barres De Almeida,M Pohl,P G Prada Moroni,J Rico,W Rhode,T Steinbring,D Hadasch,M Tornikoski,A C S Readhead,V Bugaev,R López-Coto,E Lorenz,X Chen,P T Reynolds,A La Barbera,J Kushida,W Benbow,M Uellenbeck,J L Contreras,A Cesarini,N Lewandowska,W Bednarek,A Overkemping,T Hovatta,M G Nikolashvili,G T Richards,E Collins-Hughes,G Gyuk,X Paredes-Fortuny,R Welsing,O M Kurtanidze,A Carosi,H A Krimm,A Falcone,A Popkow,D Garrido Terrats,L Fuhrmann,D Paneque,L Carrasco,M Makariev,S P Wakely,F Krennrich,E Colombo,P Fortin,V Stamatescu,A Pichel,I Telezhinsky,S Paiano,F Tavecchio,S Preziuso,R J García López,S R Gozzini,N Nowak,G Maier,M López,M L Knoetig,C Schultz,L Maraschi,E Angelakis,G Bonnoli,M Giroletti,A De Angelis,D Kieda,J P Finley,M Meucci,F Spanier,E Prandini,K Ragan,E Lindfors,A Orlati,T Bretz,J H Buckley,J Quinn,D Dorner,I Puljak,S Covino,A López-Oramas,S Sun,R A Ong,C Pace,C A Johnson,B Marcote,A Domínguez,T B Humensky,S Bonnefoy,B Behera,M Beilicke,D F Torres,K Mannheim,C Fruck,S Archambault,N Godinović,M Theiling,L A Antonelli,M Doro,A Varlotta,J Hose,M V Fonseca,B Jordan,M Ribó,D Tescaro,K Shahinyan,A C Rovero,A Saggion,M Perri,M Kertzman,S Kumar,D A Williams,G H Sembroski,K Berger,A Hadamek,N Mankuzhiyil,V Scapin,P Colin,P Vogler,J Storz,P Temnikov,J Holder,J L Richards,S Einecke,W Idec,P Antoranz,S Griffin,D Dominis Prester,M J Lang,R Orito,B De Lotto,R Reinthal,F Borracci,J V Tucci,A Lähteenmäki,P Moriarty,G Maneva,G Maccaferri,A C Sadun,R Mukherjee,Q Feng,R Paoletti,A N Otte,G De Caneva,W Max-Moerbeck,D Hanna,A Furniss,P Da Vela,J M Paredes,O Tibolla,D Lelas,H D Aller,L Fortson,U Menzel,J Tammi,J Tyler,H Kellermann,D Staszak,A Niedźwiecki ,Irene Albarrán Lozano ,C M Raiteri ,Francisco Prada ,M Martı́nez ,Alicia Herrero ,Philip Kaaret ,Steven N Shore ,Ana Babić ,Jean-François Rajotte ,David Fidalgo ,Iva Šnidarić ,Chien-Cheng Lin ,D Sobczyńska ,Dario Hrupec ,M Peršić ,A J.r Weinstein ,Koji Saito ,R Böck ,J Eisch ,D Elsäesser ,R.l Pearson ,Takeshi Toyama ,Yoichi Yatsu ,S Griffiths ,Wei Cui ,Emanuele Paolo Farina ,L O Takalo ,Henrike Fleischhack ,A C Zook

doi:10.1051/0004-6361/201424216

Abstract

We performed a 4.5-month multi-instrument campaign (from radio to VHE gamma rays) on Mrk421 between January 2009 and June 2009, which included VLBA, F-GAMMA, GASP-WEBT, Swift, RXTE, Fermi-LAT, MAGIC, and Whipple, among other instruments and collaborations. Mrk421 was found in its typical (non-flaring) activity state, with a VHE flux of about half that of the Crab Nebula, yet the light curves show significant variability at all wavelengths, the highest variability being in the X-rays. We determined the power spectral densities (PSD) at most wavelengths and found that all PSDs can be described by power-laws without a break, and with indices consistent with pink/red-noise behavior. We observed a harder-when-brighter behavior in the X-ray spectra and measured a positive correlation between VHE and X-ray fluxes with zero time lag. Such characteristics have been reported many times during flaring activity, but here they are reported for the first time in the non-flaring state. We also observed an overall anti-correlation between optical/UV and X-rays extending over the duration of the campaign. The harder-when-brighter behavior in the X-ray spectra and the measured positive X-ray/VHE correlation during the 2009 multi-wavelength campaign suggests that the physical processes dominating the emission during non-flaring states have similarities with those occurring during flaring activity. In particular, this observation supports leptonic scenarios as being responsible for the emission of Mrk421 during non-flaring activity. Such a temporally extended X-ray/VHE correlation is not driven by any single flaring event, and hence is difficult to explain within the standard hadronic scenarios. The highest variability is observed in the X-ray band, which, within the one-zone synchrotron self-Compton scenario, indicates that the electron energy distribution is most variable at the highest energies.

Highlights

Blazars are a class of radio-loud active galactic nuclei (AGN) where the relativistic jet is believed to be closely aligned to our line of sight
One- and multizone synchrotron selfCompton (SSC) models predict a positive correlation between X-ray and VHE flux variations (e.g., Graff et al 2008), as they are produced by the same electron population
We studied the broadband evolution of the spectral energy distributions (SED) of Mrk 421 through a 4.5 month long multi-instrument observing campaign in 2009, when the source was in its typical activity state, with a VHE flux of about half that of the Crab Nebula

Summary

Introduction

Blazars are a class of radio-loud active galactic nuclei (AGN) where the relativistic jet is believed to be closely aligned to our line of sight. They emit radiation over a broad energy range from radio to very high energy γ rays (VHE; E > 100 GeV), which is highly variable at all wavelengths. Their spectral energy distributions (SED) are dominated by the jet emission and show two bumps, one at low energies (radio, optical, X-rays) and the other at high energies (X-rays, γ rays, VHE). Most multi-wavelength programs are triggered when a source is flaring, and not when it is in low state

Results

Discussion

Conclusion