|
|
Study of the variable broadband emission of Markarian 501 during the most extreme Swift X-ray activity |
|---|---|
| Author: | Acciari, V. A.1,2; Ansoldi, S.3,4,5,6,7,8; Antonelli, L. A.9; |
| Organizations: |
1Inst Astrofis Canarias, San Cristobal la Laguna 38200, Spain. 2Univ La Laguna, Dept Astrofis, Tenerife 38206, Spain. 3Univ Udine, I-33100 Udine, Italy.
4INFN Trieste, I-33100 Udine, Italy.
5Univ Tokyo, Japanese MAG Consortium ICRR, Chiba 2778582, Japan. 6Kyoto Univ, Dept Phys, Kyoto 6068502, Japan. 7Tokai Univ, Hiratsuka, Kanagawa 2591292, Japan. 8RIKEN, Wako, Saitama 3510198, Japan. 9Natl Inst Astrophys INAF, I-00136 Rome, Italy. 10Univ Rijeka, Croatian Mag Consortium, Rijeka 51000, Croatia. 11Univ Split, FESB, Split 21000, Croatia. 12Univ Zagreb, FER, Zagreb 10000, Croatia. 13Univ Osijek, Osijek 31000, Croatia. 14Rudjer Boskovic Inst, Zagreb 10000, Croatia. 15HBNI, Saha Inst Nucl Phys, 1-AF Bidhannagar,Sect 1, Kolkata 700064, India. 16URCA, CBPF, BR-22290180 Rio De Janeiro, RJ, Brazil. 17Univ Complutense, Unidad Particulas & Cosmol UPARCOS, Madrid 28040, Spain. 18Univ Lodz, Dept Astrophys, PL-90236 Lodz, Poland. 19DESY, D-15738 Zeuthen, Germany. 20Univ Padua, I-35131 Padua, Italy. 21Ist Nazl Fis Nucl, I-35131 Padua, Italy. 22Humboldt Univ, Inst Phys, D-12489 Berlin, Germany. 23Ist Nazl Fis Nucl, I-00044 Rome, Italy. 24Univ Trieste, Dipartimento Fis, I-34127 Trieste, Italy. 25Max Planck Inst Phys & Astrophys, D-80805 Munich, Germany. 26BIST, IFAE, Barcelona 08193, Spain. 27Univ Siena, I-53100 Siena, Italy. 28INFN Pisa, I-53100 Siena, Italy. 29Univ Pisa, I-56126 Pisa, Italy. 30INFN Pisa, I-56126 Pisa, Italy. 31PIC, Barcelona 08193, Spain. 32Univ Turku, Finnish Mag Consortium Finnish Ctr Astron ESO FIN, Turku 20014, Finland. 33Univ Oulu, Astron Res Unit, Oulu 90014, Finland. 34Tech Univ Dortmund, D-44221 Dortmund, Germany. 35Univ Autonoma Barcelona, Dept Fis, Bellaterra 08193, Spain. 36Univ Autonoma Barcelona, CERES IEEC, Bellaterra 08193, Spain. 37Univ Barcelona, IEEC UB, ICCUB, Barcelona 08028, Spain. 38ICRANet Armenia NAS RA, Yerevan 0019, Armenia. 39Bulgarian Acad Sci, Inst Nucl Res & Nucl Energy, Sofia 1784, Bulgaria. 40INAF Trieste, Trieste, Italy. 41Univ Bologna, Dept Phys & Astron, Bologna, Italy. 42Swiss Fed Inst Technol, CH-8093 Zurich, Switzerland. 43Univ Geneva, Dept Astron, ISDC, CH-1290 Versoix 16, Switzerland. 44Univ Wurzburg, D-97074 Wurzburg, Germany. 45Rhein Westfal TH Aachen, Aachen, Germany. 46CRESST, Greenbelt, MD 20771 USA. 47NASA, Goddard Space Flight Ctr, Code 916, Greenbelt, MD 20771 USA. 48Univ Maryland Baltimore Cty, Dept Phys, 1000 Hilltop Circle, Baltimore, MD 21250 USA. 49Space Sci Data Ctr ASI, Snc, Via Politecn, I-00133 Rome, Italy. 50INAF Osservatorio Astron Roma, Via Frascati 33, I-00040 Monte Porzio Catone, Italy. 51Aalto Univ, Metsahovi Radio Observ, Metsahovintie 114, Kylmala 02540, Finland. 52Aalto Univ, Dept Elect & Nanoengn, POB 15500, Espoo 00076, Finland. |
| Format: | article |
| Version: | published version |
| Access: | open |
| Online Access: | PDF Full Text (PDF, 2.4 MB) |
| Persistent link: | http://urn.fi/urn:nbn:fi-fe2020070947183 |
| Language: | English |
| Published: |
EDP Sciences,
2020
|
| Publish Date: | 2020-07-09 |
| Description: |
AbstractContext: 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 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. 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 ∼3 TeV was 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, and log-parabola with exponential cutoff) at more than 3σ. 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 3σ. 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. see all
|
| Series: |
Astronomy and astrophysics |
| ISSN: | 0004-6361 |
| ISSN-E: | 1432-0746 |
| ISSN-L: | 0004-6361 |
| Volume: | 637 |
| Article number: | A86 |
| DOI: | 10.1051/0004-6361/201834603 |
| OADOI: | https://oadoi.org/10.1051/0004-6361/201834603 |
| Type of Publication: |
A1 Journal article – refereed |
| Field of Science: |
115 Astronomy and space science |
| Subjects: | |
| Funding: |
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, FPA2015-68378-P, FPA2015-69210-C6-2-R, FPA2015-69210-C6-4-R, FPA2015-69210-C6-6-R, AYA2015-71042-P, AYA2016-76012-C3-1-P,ESP2015-71662-C2-2-P, FPA2017-90566-REDC), and the Japanese JSPS and MEXT is gratefully acknowledged. This work was also supported by the Span-ish Centro de Excelencia “Severo Ochoa” SEV-2016-0588 and SEV-2015-0548,and Unidad de Excelencia “María de Maeztu” MDM-2014-0369, by the Croatian Science Foundation (HrZZ) Project IP-2016-06-9782 and the University of Rijeka Project 13.12.1.3.02, by the DFG Collaborative Research CentersSFB823/C4 and SFB876/C3, the Polish National Research Centre grant UMO-2016/22/M/ST9/00382 and by the Brazilian MCTIC, CNPq and FAPERJ. The Fermi-LAT Collaboration acknowledges generous ongoing support from a number of agencies and institutes that have supported both the development and the operation of the LAT as well as scientific data analysis. These include the National Aeronautics and Space Administration and the Department of Energy in the United States, the Commissariat à l’Energie Atomique and the Centre National de la Recherche Scientifique/Institut National de Physique Nucléaire etde Physique des Particules in France, the Agenzia Spaziale Italiana and the Istituto Nazionale di Fisica Nucleare in Italy, the Ministry of Education, Culture, Sports, Science and Technology (MEXT), High Energy Accelerator Research Organization (KEK) and Japan Aerospace Exploration Agency (JAXA) in Japan, and the K. A. Wallenberg Foundation, the Swedish Research Council and the Swedish National Space Board in Sweden. Additional support for science analysis during the operations phase is gratefully acknowledged from the Instituto Nazionale di Astrofisica in Italy and the Centre National d’Études Spatiales in France. The important contributions from ETH Zurich grants ETH-10.08-2 and ETH-27.12-1 as well as the funding by the Swiss SNF and the German BMBF (Verbundforschung Astro- und Astroteilchenphysik) and HAP (Helmoltz Alliance for Astroparticle Physics) are gratefully acknowledged. Part of this work is supported by Deutsche Forschungsgemeinschaft (DFG) within the Collaborative Research Center SFB 876, project C3. We thank the Instituto de Astrofisica de Canarias for allowing us to operate the telescope at the Observatorio del Roque de los Muchachos in La Palma, the Max-Planck-Institut fur Physik for providing us with the mount of the former HEGRA CT3 telescope, and the MAGIC Collaboration for their support. JBG acknowledges the support of the Viera y Clavijo program funded by ACIISI and ULL. C. W. is grateful for the support by the project “Promotion inklusive” of the Universität zu Köln and the German Bundesministerium für Arbeit und Soziales. This publication makes use of data obtained at Metsähovi Radio Observatory, operated by Aalto University, Finland. |
| Copyright information: |
© ESO 2020. |