Insights from the first flaring activity of a high synchrotron peaked blazar with X-ray polarization and VHE gamma rays
: Abe, K.; Abe, S.; Abhir, J.; Abhishek, A.; Acciari V., A.; Aguasca-Cabot, A.; Agudo, I.; Aniello, T.; Ansoldi, S.; Antonelli L., A.; Arbet Engels, A.; Arcaro, C.; Asano, K.; Babić, A.; Barres de Almeida, U.; Barrio J., A.; Barrios-Jiménez, L.; Batković, I.; Baxter, J.; Becerra González, J.; Bednarek, W.; Bernardini, E.; Bernete, J.; Berti, A.; Besenrieder, J.; Bigongiari, C.; Biland, A.; Blanch, O.; Bonnoli, G.; Bošnjak, Ž; Bronzini, E.; Burelli, I.; Campoy-Ordaz, A.; Carosi, A.; Carosi, R.; Carretero-Castrillo, M.; Castro-Tirado A., J.; Cerasole, D.; Ceribella, G.; Chai, Y.; Chilingarian, A.; Cifuentes, A.; Colombo, E.; Contreras J., L.; Cortina, J.; Covino, S.; D’Ammando, F.; D’Amico, G.; Da Vela, P.; Dazzi, F.; De Angelis, A.; De Lotto, B.; de Menezes, R.; Delfino, M.; Delgado, J.; Delgado Mendez, C.; Di Pierro, F.; Di Tria, R.; Di Venere, L.; Dinesh, A.; Dominis Prester, D.; Donini, A.; Dorner, D.; Doro, M.; Eisenberger, L.; Elsaesser, D.; Escudero, J.; Fariña, L.; Foffano, L.; Font, L.; Fröse, S.; Fukazawa, Y.; García López R., J.; Garczarczyk, M.; Gasparyan, S.; Gaug, M.; Giesbrecht Paiva J., G.; Giglietto, N.; Giordano, F.; Gliwny, P.; Godinović, N.; Gradetzke, T.; Grau, R.; Green, D.; Green J., G.; Günther, P.; Hadasch, D.; Hahn, A.; Hassan, T.; Heckmann, L.; Herrera Llorente, J.; Hrupec, D.; Imazawa, R.; Israyelyan, D.; Itokawa, T.; Jiménez Martínez, I.; Jiménez Quiles, J.; Jormanainen, J.; Kankkunen, S.; Kayanoki, T.; Kerszberg, D.; Khachatryan, M.; Kluge G., W.; Kobayashi, Y.; Konrad, J.; Kouch P., M.; Kubo, H.; Kushida, J.; Láinez, M.; Lamastra, A.; Lindfors, E.; Lombardi, S.; Longo, F.; López-Coto, R.; López-Moya, M.; López-Oramas, A.; Loporchio, S.; Lorini, A.; Lyard, E.; Majumdar, P.; Makariev, M.; Maneva, G.; Manganaro, M.; Mangano, S.; Mannheim, K.; Mariotti, M.; Martínez, M.; Maruševec, P.; Mas-Aguilar, A.; Mazin, D.; Menchiari, S.; Mender, S.; Miceli, D.; Miranda J., M.; Mirzoyan, R.; Molero González, M.; Molina, E.; Mondal H., A.; Moralejo, A.; Nakamori, T.; Nanci, C.; Neustroev, V.; Nickel, L.; Nievas Rosillo, M.; Nigro, C.; Nikolić, L.; Nilsson, K.; Nishijima, K.; Njoh Ekoume, T.; Noda, K.; Nozaki, S.; Okumura, A.; Paiano, S.; Paneque, D.; Paoletti, R.; Paredes J., M.; Peresano, M.; Persic, M.; Pihet, M.; Pirola, G.; Podobnik, F.; Prada Moroni P., G.; Prandini, E.; Principe, G.; Rhode, W.; Ribó, M.; Rico, J.; Righi, C.; Sahakyan, N.; Saito, T.; Saturni F., G.; Schmuckermaier, F.; Schubert J., L.; Sciaccaluga, A.; Silvestri, G.; Sitarek, J.; Sliusar, V.; Sobczynska, D.; Stamerra, A.; Strišković, J.; Strom, D.; Strzys, M.; Suda, Y.; Tajima, H.; Takahashi, M.; Takeishi, R.; Temnikov, P.; Terauchi, K.; Terzić, T.; Teshima, M.; Truzzi, S.; Tutone, A.; Ubach, S.; van Scherpenberg, J.; Ventura, S.; Verna, G.; Viale, I.; Vigliano, A.; Vigorito C., F.; Vitale, V.; Vovk, I.; Walter, R.; Wersig, F.; Will, M.; Yamamoto, T.; Yeung P. K., H.; Liodakis, I.; Middei, R.; Kiehlmann, S.; Gesu L., D.; Kim D., E.; Ehlert S., R.; Saade M., L.; Kaaret, P.; Maksym W., P.; Chen C., T.; De La Calle Pérez, I.; Perri, M.; Verrecchia, F.; Domann, O.; Dürr, S.; Feige, M.; Heidemann, M.; Koppitz, O.; Manhalter, G.; Reinhart, D.; Steineke, R.; Lorey, C.; McCall, C.; Jermak H., E.; Steele I., A.; Fallah Ramazani, V.; Otero-Santos, J.; Morcuende, D.; Aceituno F., J.; Casanova, V.; Sota, A.; Jorstad S., G.; Marscher A., P.; Pauley, C.; Sasada, M.; Kawabata K., S.; Uemura, M.; Mizuno, T.; Nakaoka, T.; Akitaya, H.; Myserlis, I.; Gurwell, M.; Keating G., K.; Rao, R.; Angelakis, E.; Kraus, A.
Publisher: EDP Sciences
: LES ULIS CEDEX A
: 2025
: Astronomy and Astrophysics
: Astronomy & Astrophysics
: ASTRON ASTROPHYS
: A217
: 695
: 18
: 0004-6361
: 1432-0746
DOI: https://doi.org/10.1051/0004-6361/202452785
: https://doi.org/10.1051/0004-6361/202452785
: https://research.utu.fi/converis/portal/detail/Publication/491880222
Context. Blazars exhibit strong variability across the entire electromagnetic spectrum, including periods of high-flux states commonly known as flares. The physical mechanisms in blazar jets responsible for flares remain poorly understood to date.
Aims. Our aim is to better understand the emission mechanisms during blazar flares using X-ray polarimetry and broadband observations from the archetypical TeV blazar Mrk 421, which can be studied with higher accuracy than other blazars that are dimmer and/or located farther away.
Methods. We studied a flaring activity from December 2023 that was characterized from radio to very high-energy (VHE; E>0.1 TeV) gamma rays with MAGIC, Fermi-LAT, Swift, XMM-Newton, and several optical and radio telescopes. These observations included, for the first time for a gamma-ray flare of a blazar, simultaneous X-ray polarization measurements with IXPE, in addition to optical and radio polarimetry data. We quantify the variability and correlations among the multi-band flux and polarization measurements, and describe the varying broadband emission within a theoretical scenario constrained by the polarization data.
Results. We find substantial variability in both X-rays and VHE gamma rays throughout the campaign, with the highest VHE flux above 0.2 TeV occurring during the IXPE observing window, and exceeding twice the flux of the Crab Nebula. However, the VHE and X-ray spectra are on average softer, and the correlation between these two bands is weaker than those reported in the previous flares of Mrk 421. IXPE reveals an X-ray polarization degree significantly higher than that at radio and optical frequencies, similar to previous results for Mrk 421 and other high synchrotron peaked blazars. Differently to past observations, the X-ray polarization angle varies by similar to 100 degrees on timescales of days, and the polarization degree changes by more than a factor of 4. The highest X-ray polarization degree, analyzed in 12 h time intervals, reaches 26 +/- 2%, around which an X-ray counter-clockwise hysteresis loop is measured with XMM-Newton. It suggests that the X-ray emission comes from particles close to the high-energy cutoff, hence possibly probing an extreme case of the Turbulent Extreme Multi-Zone model for which the chromatic trend in the polarization may be more pronounced than theoretically predicted. We model the broadband emission with a simplified stratified jet model throughout the flare. The polarization measurements imply an electron distribution in the X-ray emitting region with a very high minimum Lorentz factor (gamma(min)' greater than or similar to 10(4)), which is expected in electron-ion plasma, as well as a variation of the emitting region size of up to a factor of 3 during the flaring activity. We find no correlation between the fluxes and the evolution of the model parameters, which indicates a stochastic nature of the underlying physical mechanism that likely explains the lack of a tight X-ray/VHE correlation during this flaring activity. Such behavior would be expected in a highly turbulent electron-ion plasma crossing a shock front.
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Open access funding provided by Max Planck Society.
We would like to thank the Instituto de
Astrofísica de Canarias for the excellent working conditions at the Observatorio
del Roque de los Muchachos in La Palma. The financial support
of the German BMBF, MPG and HGF; the Italian INFN and INAF; the
Swiss National Fund SNF; the grants PID2019-104114RB-C31, PID2019-
104114RB-C32, PID2019-104114RB-C33, PID2019-105510GB-C31,
PID2019-107847RB-C41, PID2019-107847RB-C42, PID2019-107847RB-C44,
PID2019-107988GB-C22, PID2022-136828NB-C41, PID2022-137810NBC22,
PID2022-138172NB-C41, PID2022-138172NB-C42, PID2022-
138172NB-C43, PID2022-139117NB-C41, PID2022-139117NB-C42,
PID2022-139117NB-C43, PID2022-139117NB-C44 funded by the Spanish
MCIN/AEI/ 10.13039/501100011033 and “ERDF A way of making Europe”;
the Indian Department of Atomic Energy; the Japanese ICRR, the University
of Tokyo, JSPS, and MEXT; the Bulgarian Ministry of Education and Science,
National RI Roadmap Project DO1-400/18.12.2020 and the Academy of
Finland grant nr. 320045 is gratefully acknowledged. This work was also
been supported by Centros de Excelencia “Severo Ochoa” y Unidades “María
de Maeztu” program of the Spanish MCIN/AEI/ 10.13039/501100011033
(CEX2019-000920-S, CEX2019-000918-M, CEX2021-001131-S) and by the
CERCA institution and grants 2021SGR00426 and 2021SGR00773 of the
Generalitat de Catalunya; by the Croatian Science Foundation (HrZZ) Project
IP-2022-10-4595 and the University of Rijeka Project uniri-prirod-18-48; by
the Deutsche Forschungsgemeinschaft (SFB1491) and by the Lamarr-Institute
for Machine Learning and Artificial Intelligence; by the Polish Ministry Of
Education and Science grant No. 2021/WK/08; 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 et de 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 Istituto Nazionale di Astrofisica in Italy
and the Centre National d’Études Spatiales in France. This work performed in
part under DOE Contract DE-AC02-76SF00515. The corresponding authors
of this manuscript, namely Axel Arbet-Engels, Lea Heckmann and David
Paneque, acknowledge support from the Deutsche Forschungs gemeinschaft
(DFG, German Research Foundation) under Germany’s Excellence Strategy –
EXC-2094 – 390783311. The Imaging X-ray Polarimetry Explorer (IXPE) is a
joint US and Italian mission. The US contribution is supported by the National
Aeronautics and Space Administration (NASA) and led and managed by its
Marshall Space Flight Center (MSFC), with industry partner Ball Aerospace
(contract NNM15AA18C). The Italian contribution is supported by the Italian
Space Agency (Agenzia Spaziale Italiana, ASI) through contract ASI-OHBI-
2017-12-I.0, agreements ASI-INAF-2017-12-H0 and ASI-INFN-2017.13-H0,
and its Space Science Data Center (SSDC), and by the Istituto Nazionale di
Astrofisica (INAF) and the Istituto Nazionale di Fisica Nucleare (INFN) in
Italy. This research used data products provided by the IXPE Team (MSFC,
SSDC, INAF, and INFN) and distributed with additional software tools by the
High-Energy Astrophysics Science Archive Research Center (HEASARC), at
NASA Goddard Space Flight Center (GSFC). I. L. and S.K. were funded by the
European Union ERC-2022-STG – BOOTES – 101076343. Views and opinions
expressed are however those of the author(s) only and do not necessarily reflect
those of the European Union or the European Research Council Executive
Agency. Neither the European Union nor the granting authority can be held
responsible for them Some of the data are based on observations collected at the
Observatorio de Sierra Nevada; which is owned and operated by the Instituto de
Astrofísica de Andalucía (IAA-CSIC); and at the Centro Astronómico Hispano
en Andalucía (CAHA); which is operated jointly by Junta de Andalucía and
Consejo Superior de Investigaciones Científicas (IAA-CSIC). The research at
Boston University was supported in part by National Science Foundation grant
AST-2108622, NASA Fermi Guest Investigator grants 80NSSC21K1917 and
80NSSC22K1571, and NASA Swift Guest Investigator grant 80NSSC22K0537.
This research was conducted in part using the Mimir instrument, jointly developed
at Boston University and Lowell Observatory and supported by NASA,
NSF, and the W.M. Keck Foundation. We thank D. Clemens for guidance in the
analysis of the Mimir data. This study used observations conducted with the
1.8m Perkins Telescope (PTO) in Arizona (USA), which is owned and operated
by Boston University. This work was supported by NSF grant AST-2109127.
We acknowledge the use of public data from the Swift data archive. Based
on observations obtained with XMM-Newton, an ESA science mission with
instruments and contributions directly funded by ESA Member States and
NASA. This work has made use of data from the Joan Oró Telescope (TJO) of
the Montsec Observatory (OdM), which is owned by the Catalan Government
and operated by the Institute for Space Studies of Catalonia (IEEC). The
Submillimeter Array is a joint project between the Smithsonian Astrophysical
Observatory and the Academia Sinica Institute of Astronomy and Astrophysics
and is funded by the Smithsonian Institution and the Academia Sinica. We
recognize that Maunakea is a culturally important site for the indigenous
Hawaiian people; we are privileged to study the cosmos from its summit. The
100 m radio telescope at Eelsberg is operated by the Max-Planck-Institut für
Radioastronomie (MPIfR) on behalf of the Max-Planck-Society. Observations
with the 100 m telescope have received funding from the European Union’s
Horizon 2020 research and innovation program under grant agreement No.
101004719 (ORP). The Liverpool Telescope is operated on the island of La
Palma by Liverpool John Moores University in the Spanish Observatorio
del Roque de los Muchachos of the Instituto de Astrofisica de Canarias with
financial support from the UK Science and Technology Facilities Council.
