Extreme HBL behavior of Markarian 501 during 2012

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Extreme HBL behavior of Markarian 501 during 2012. / MAGIC Collaboration; VERITAS Collaboration.

In: Astronomy and Astrophysics, Vol. 620, A181, 01.12.2018.

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MAGIC Collaboration ; VERITAS Collaboration. / Extreme HBL behavior of Markarian 501 during 2012. In: Astronomy and Astrophysics. 2018 ; Vol. 620.

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@article{44ab5fac8a34420eab51389a8a66716d,
title = "Extreme HBL behavior of Markarian 501 during 2012",
abstract = "Aims. We aim to characterize the multiwavelength emission from Markarian 501 (Mrk 501), quantify the energy-dependent variability, study the potential multiband correlations, and describe the temporal evolution of the broadband emission within leptonic theoretical scenarios. Methods. We organized a multiwavelength campaign to take place between March and July of 2012. Excellent temporal coverage was obtained with more than 25 instruments, including the MAGIC, FACT and VERITAS Cherenkov telescopes, the instruments on board the Swift and Fermi spacecraft, and the telescopes operated by the GASP-WEBT collaboration. Results. Mrk 501 showed a very high energy (VHE) gamma-ray flux above 0.2 TeV of ∼0.5 times the Crab Nebula flux (CU) for most of the campaign. The highest activity occurred on 2012 June 9, when the VHE flux was ∼3 CU, and the peak of the high-energy spectral component was found to be at ∼2 TeV. Both the X-ray and VHE gamma-ray spectral slopes were measured to be extremely hard, with spectral indices < 2 during most of the observing campaign, regardless of the X-ray and VHE flux. This study reports the hardest Mrk 501 VHE spectra measured to date. The fractional variability was found to increase with energy, with the highest variability occurring at VHE. Using the complete data set, we found correlation between the X-ray and VHE bands; however, if the June 9 flare is excluded, the correlation disappears (significance < 3σ) despite the existence of substantial variability in the X-ray and VHE bands throughout the campaign. Conclusions. The unprecedentedly hard X-ray and VHE spectra measured imply that their low- and high-energy components peaked above 5 keV and 0.5 TeV, respectively, during a large fraction of the observing campaign, and hence that Mrk 501 behaved like an extreme high-frequency-peaked blazar (EHBL) throughout the 2012 observing season. This suggests that being an EHBL may not be a permanent characteristic of a blazar, but rather a state which may change over time. The data set acquired shows that the broadband spectral energy distribution (SED) of Mrk 501, and its transient evolution, is very complex, requiring, within the framework of synchrotron self-Compton (SSC) models, various emission regions for a satisfactory description. Nevertheless the one-zone SSC scenario can successfully describe the segments of the SED where most energy is emitted, with a significant correlation between the electron energy density and the VHE gamma-ray activity, suggesting that most of the variability may be explained by the injection of high-energy electrons. The one-zone SSC scenario used reproduces the behavior seen between the measured X-ray and VHE gamma-ray fluxes, and predicts that the correlation becomes stronger with increasing energy of the X-rays.",
keywords = "Acceleration of particles, Astroparticle physics, BL Lacertae objects: general, BL Lacertae objects: individual: Mrk501, Radiation mechanisms: non-thermal",
author = "{MAGIC Collaboration} and {VERITAS Collaboration} and Ahnen, {M. L.} and S. Ansoldi and Antonelli, {L. A.} and C. Arcaro and A. Babić and B. Banerjee and P. Bangale and {Barresde Almeida}, U. and Barrio, {J. A.} and J. Becerragonz{\'a}lez and W. Bednarek and E. Bernardini and A. Berti and W. Bhattacharyya and O. Blanch and G. Bonnoli and R. Carosi and A. Carosi and A. Chatterjee and Colak, {S. M.} and P. Colin and E. Colombo and Contreras, {J. L.} and J. Cortina and S. Covino and P. Cumani and {Da Vela}, P. and F. Dazzi and {De Angelis}, A. and {De Lotto}, B. and M. Delfino and J. Delgado and {Di Ierro}, F. and M. Doert and A. Dom{\'i}nguez and {Dominis Prester}, D. and M. Doro and {Eisenacher Lawion}, D. and M. Engelkemeier and {Fallah Ramazani}, V. and A. Fern{\'a}ndez-Barral and D. Fidalgo and Fonseca, {M. V.} and L. Font and C. Fruck and D. Galindo and T. Hovatta and Anne L{\"a}hteenm{\"a}ki and Merja Tornikoski and Joni Tammi",
year = "2018",
month = "12",
day = "1",
doi = "10.1051/0004-6361/201833704",
language = "English",
volume = "620",
journal = "Astronomy & Astrophysics",
issn = "0004-6361",

}

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TY - JOUR

T1 - Extreme HBL behavior of Markarian 501 during 2012

AU - MAGIC Collaboration

AU - VERITAS Collaboration

AU - Ahnen, M. L.

AU - Ansoldi, S.

AU - Antonelli, L. A.

AU - Arcaro, C.

AU - Babić, A.

AU - Banerjee, B.

AU - Bangale, P.

AU - Barresde Almeida, U.

AU - Barrio, J. A.

AU - Becerragonzález, J.

AU - Bednarek, W.

AU - Bernardini, E.

AU - Berti, A.

AU - Bhattacharyya, W.

AU - Blanch, O.

AU - Bonnoli, G.

AU - Carosi, R.

AU - Carosi, A.

AU - Chatterjee, A.

AU - Colak, S. M.

AU - Colin, P.

AU - Colombo, E.

AU - Contreras, J. L.

AU - Cortina, J.

AU - Covino, S.

AU - Cumani, P.

AU - Da Vela, P.

AU - Dazzi, F.

AU - De Angelis, A.

AU - De Lotto, B.

AU - Delfino, M.

AU - Delgado, J.

AU - Di Ierro, F.

AU - Doert, M.

AU - Domínguez, A.

AU - Dominis Prester, D.

AU - Doro, M.

AU - Eisenacher Lawion, D.

AU - Engelkemeier, M.

AU - Fallah Ramazani, V.

AU - Fernández-Barral, A.

AU - Fidalgo, D.

AU - Fonseca, M. V.

AU - Font, L.

AU - Fruck, C.

AU - Galindo, D.

AU - Hovatta, T.

AU - Lähteenmäki, Anne

AU - Tornikoski, Merja

AU - Tammi, Joni

PY - 2018/12/1

Y1 - 2018/12/1

N2 - Aims. We aim to characterize the multiwavelength emission from Markarian 501 (Mrk 501), quantify the energy-dependent variability, study the potential multiband correlations, and describe the temporal evolution of the broadband emission within leptonic theoretical scenarios. Methods. We organized a multiwavelength campaign to take place between March and July of 2012. Excellent temporal coverage was obtained with more than 25 instruments, including the MAGIC, FACT and VERITAS Cherenkov telescopes, the instruments on board the Swift and Fermi spacecraft, and the telescopes operated by the GASP-WEBT collaboration. Results. Mrk 501 showed a very high energy (VHE) gamma-ray flux above 0.2 TeV of ∼0.5 times the Crab Nebula flux (CU) for most of the campaign. The highest activity occurred on 2012 June 9, when the VHE flux was ∼3 CU, and the peak of the high-energy spectral component was found to be at ∼2 TeV. Both the X-ray and VHE gamma-ray spectral slopes were measured to be extremely hard, with spectral indices < 2 during most of the observing campaign, regardless of the X-ray and VHE flux. This study reports the hardest Mrk 501 VHE spectra measured to date. The fractional variability was found to increase with energy, with the highest variability occurring at VHE. Using the complete data set, we found correlation between the X-ray and VHE bands; however, if the June 9 flare is excluded, the correlation disappears (significance < 3σ) despite the existence of substantial variability in the X-ray and VHE bands throughout the campaign. Conclusions. The unprecedentedly hard X-ray and VHE spectra measured imply that their low- and high-energy components peaked above 5 keV and 0.5 TeV, respectively, during a large fraction of the observing campaign, and hence that Mrk 501 behaved like an extreme high-frequency-peaked blazar (EHBL) throughout the 2012 observing season. This suggests that being an EHBL may not be a permanent characteristic of a blazar, but rather a state which may change over time. The data set acquired shows that the broadband spectral energy distribution (SED) of Mrk 501, and its transient evolution, is very complex, requiring, within the framework of synchrotron self-Compton (SSC) models, various emission regions for a satisfactory description. Nevertheless the one-zone SSC scenario can successfully describe the segments of the SED where most energy is emitted, with a significant correlation between the electron energy density and the VHE gamma-ray activity, suggesting that most of the variability may be explained by the injection of high-energy electrons. The one-zone SSC scenario used reproduces the behavior seen between the measured X-ray and VHE gamma-ray fluxes, and predicts that the correlation becomes stronger with increasing energy of the X-rays.

AB - Aims. We aim to characterize the multiwavelength emission from Markarian 501 (Mrk 501), quantify the energy-dependent variability, study the potential multiband correlations, and describe the temporal evolution of the broadband emission within leptonic theoretical scenarios. Methods. We organized a multiwavelength campaign to take place between March and July of 2012. Excellent temporal coverage was obtained with more than 25 instruments, including the MAGIC, FACT and VERITAS Cherenkov telescopes, the instruments on board the Swift and Fermi spacecraft, and the telescopes operated by the GASP-WEBT collaboration. Results. Mrk 501 showed a very high energy (VHE) gamma-ray flux above 0.2 TeV of ∼0.5 times the Crab Nebula flux (CU) for most of the campaign. The highest activity occurred on 2012 June 9, when the VHE flux was ∼3 CU, and the peak of the high-energy spectral component was found to be at ∼2 TeV. Both the X-ray and VHE gamma-ray spectral slopes were measured to be extremely hard, with spectral indices < 2 during most of the observing campaign, regardless of the X-ray and VHE flux. This study reports the hardest Mrk 501 VHE spectra measured to date. The fractional variability was found to increase with energy, with the highest variability occurring at VHE. Using the complete data set, we found correlation between the X-ray and VHE bands; however, if the June 9 flare is excluded, the correlation disappears (significance < 3σ) despite the existence of substantial variability in the X-ray and VHE bands throughout the campaign. Conclusions. The unprecedentedly hard X-ray and VHE spectra measured imply that their low- and high-energy components peaked above 5 keV and 0.5 TeV, respectively, during a large fraction of the observing campaign, and hence that Mrk 501 behaved like an extreme high-frequency-peaked blazar (EHBL) throughout the 2012 observing season. This suggests that being an EHBL may not be a permanent characteristic of a blazar, but rather a state which may change over time. The data set acquired shows that the broadband spectral energy distribution (SED) of Mrk 501, and its transient evolution, is very complex, requiring, within the framework of synchrotron self-Compton (SSC) models, various emission regions for a satisfactory description. Nevertheless the one-zone SSC scenario can successfully describe the segments of the SED where most energy is emitted, with a significant correlation between the electron energy density and the VHE gamma-ray activity, suggesting that most of the variability may be explained by the injection of high-energy electrons. The one-zone SSC scenario used reproduces the behavior seen between the measured X-ray and VHE gamma-ray fluxes, and predicts that the correlation becomes stronger with increasing energy of the X-rays.

KW - Acceleration of particles

KW - Astroparticle physics

KW - BL Lacertae objects: general

KW - BL Lacertae objects: individual: Mrk501

KW - Radiation mechanisms: non-thermal

UR - http://www.scopus.com/inward/record.url?scp=85058842268&partnerID=8YFLogxK

U2 - 10.1051/0004-6361/201833704

DO - 10.1051/0004-6361/201833704

M3 - Article

VL - 620

JO - Astronomy & Astrophysics

JF - Astronomy & Astrophysics

SN - 0004-6361

M1 - A181

ER -

ID: 30824891