A1 Refereed original research article in a scientific journal
IXPE observations of the blazar Mrk 501 in 2022: a multiwavelength view; 
Authors: Lisalda, L.; Gau, E.; Krawczynski, H.; Tavecchio, F.; Liodakis, I; Gokus, A.; Rodriguez Cavero, N.; Nowak, M.; Negro, M.; Middei, R.; Perri, M.; Puccetti, S.; Jorstad, S. G.; Agudo, I; Marscher, A. P.; Agis-Gonzalez, B.; Berdyugin, A., V; Bernardos, M., I; Blinov, D.; Bonnoli, G.; Borman, G. A.; Bourbah, I. G.; Casadio, C.; Casanova, V; Castro-Tirado, A. J.; Fernandez-Garcia, E.; Garcia-Comas, M.; Grishina, T. S.; Hakala, P.; Hovatta, T.; Hu, Y. D.; Husillos, C.; Escudero, J.; Jormanainen, J.; Jose Aceituno, F.; Kagitani, M.; Kiehlmann, S.; Kontopodis, E.; Kopatskaya, E. N.; Kouch, P. M.; Kravtsov, V; Lahteenmaki, A.; Larionova, E. G.; Lindfors, E.; Mandarakas, N.; Marchini, A.; Masiero, J. R.; Mawet, D.; Max-Moerbeck, W.; Morozova, D. A.; Myserlis, I; Nilsson, K.; Panopoulou, G., V; Pearson, T. J.; Readhead, A. C. S.; Reeves, R.; Romanopoulos, S.; Sakanoi, T.; Salome, Q.; Savchenko, S. S.; Skalidis, R.; Sota, A.; Syrjarinne, I; Tinyanont, S.; Tornikoski, M.; Troitskaya, Yu, V; Troitskiy, I. S.; Vasilyev, A. A.; Vervelaki, A.; Zhovtan, A., V; Antonelli, L. A.; Bachetti, M.; Baldini, L.; Baumgartner, W. H.; Bellazzini, R.; Bianchi, S.; Bongiorno, S. D.; Bonino, R.; Brez, A.; Bucciantini, N.; Capitanio, F.; Castellano, S.; Cavazzuti, E.; Chen, C.; Ciprini, S.; Costa, E.; De Rosa, A.; Del Monte, E.; Di Gesu, L.; Di Lalla, N.; Di Marco, A.; Donnarumma, I; Doroshenko, V; Dovciak, M.; Ehlert, S. R.; Enoto, T.; Evangelista, Y.; Fabiani, S.; Ferrazzoli, R.; Garcia, J. A.; Gunji, S.; Gurwell, Mark; Hayashida, K.; Heyl, J.; Iwakiri, W.; Kaaret, P.; Karas, V; Keating, Garrett; Kislat, F.; Kitaguchi, T.; Kolodziejczak, J. J.; La Monaca, F.; Latronico, L.; Maldera, S.; Manfreda, A.; Marin, F.; Marinucci, A.; Marshall, H. L.; Massaro, F.; Matt, G.; Mitsuishi, I; Mizuno, T.; Muleri, F.; Ng, C.; O'Dell, S. L.; Omodei, N.; Oppedisano, C.; Papitto, A.; Pavlov, G. G.; Peirson, A. L.; Pesce-Rollins, M.; Petrucci, P.; Pilia, M.; Possenti, A.; Poutanen, J.; Ramsey, B. D.; Rankin, J.; Rao, R.; Ratheesh, A.; Roberts, O. J.; Romani, R. W.; Sgro, C.; Slane, P.; Soffitta, P.; Spandre, G.; Swartz, D. A.; Tamagawa, T.; Taverna, R.; Tawara, Y.; Tennant, A. F.; Thomas, N. E.; Tombesi, F.; Trois, A.; Tsygankov, S. S.; Turolla, R.; Vink, J.; Weisskopf, M. C.; Wu, K.; Xie, F.; Zane, S.
Publisher: Oxford University Press
Publication year: 2026
Journal: Monthly Notices of the Royal Astronomical Society
Article number: staf1122
Volume: 549
Issue: 1
ISSN: 0035-8711
eISSN: 1365-2966
DOI: https://doi.org/10.1093/mnras/staf1122
Publication's open availability at the time of reporting: Open Access
Publication channel's open availability : Open Access publication channel
Web address : https://doi.org/10.1093/mnras/staf1122
Self-archived copy’s web address: https://research.utu.fi/converis/portal/detail/Publication/526494956
Self-archived copy's licence: CC BY
Self-archived copy's version: Publisher`s PDF
The blazar Markarian 501 (Mrk 501) was observed on three occasions over a 4-month period between 2022 March and July with the Imaging X-ray Polarimetry Explorer (IXPE). In this paper, we report for the first time on the third IXPE observation, performed between 2022 July 9 and 12, during which IXPE detected a linear polarization degree of X = 6 ± 2 per cent at a polarization angle, measured east of north, of X = 143◦ ± 11◦ within the 2 –8 keV X-ray band. The X-ray polarization angle and degree during this observation are consistent with those obtained during the first two observations. The chromaticity of the polarization across radio, optical, and X-ray bands is likewise consistent with the result from the simultaneous campaigns during the first two observations. Furthermore, we present two types of models to explain the observed spectral energy distributions (SEDs) and energy-resolved polarization: a synchrotron self-Compton model with an anisotropic magnetic field probability distribution in the emitting volume, as well as an energy-stratified shock model. Our results support both the shock scenario as well as support that small levels of magnetic field anisotropy can explain the observed polarization.
Keywords:
BL Lacertae objects: individual: Mrk501, radiation mechanisms: non-thermal, techniques: spectroscopic
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Funding information in the publication:
The 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-2022-13-I.0, agreements ASI-INAF-2022-19-HH.0 and ASI-INFN-2017.13-H0, and its Space Science Data Center (SSDC) with agreements ASI-INAF-2022-14-HH.0 and ASI-INFN 2021-43-HH.0, 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). LL, EG, HK, and MAN acknowledge NASA support through the grants NNX16AC42G, 80NSSC20K0329, 80NSSC20K0540, NAS8-03060, 80NSSC21K1817, 80NSSC22K1291, 80NSSC22K1883, and 80NSSC23K1090. LL, EG, HK, AG, and MAN acknowledge support from the McDonnell Center for the Space Sciences at Washington University in St. Louis. IL was supported by the NASA Postdoctoral Program at the Marshall Space Flight Center, administered by Oak Ridge Associated Universities under contract with NASA. TH was supported by Academy of Finland projects 317383, 320085, 322535, and 345899. The IAA-CSIC co-authors acknowledge financial support from the Spanish ‘Ministerio de Ciencia e Innovación’ (MCIN/AEI/10.13039/501100011033) through the Center of Excellence Severo Ochoa award for the Instituto de Astrofísica de Andalucía-CSIC (CEX2021-001131-S), and through grants PID2019-107847RB-C44 and PID2022-139117NB-C44. Some of the data are based on observations collected at the Centro Astronómico Hispano en Andalucía (CAHA), operated jointly by Junta de Andalucía and Consejo Superior de Investigaciones Científicas (IAA-CSIC). Some of the data are based on observations collected at the Observatorio de Sierra Nevada, owned and operated by the Instituto de Astrofísica de Andalucía (IAA-CSIC). The POLAMI observations were carried out at the IRAM 30-m Telescope. IRAM is supported by INSU,CNRS (France), MPG (Germany), and IGN (Spain). Some of the data reported here are based on observations made with the Nordic Optical Telescope, owned in collaboration with the University of Turku and Aarhus University, and operated jointly by Aarhus University, the University of Turku, and the University of Oslo, representing Denmark, Finland, and Norway, the University of Iceland and Stockholm University at the Observatorio del Roque de los Muchachos, La Palma, Spain, of the Instituto de Astrofisica de Canarias. EL was supported by Academy of Finland projects 317636 and 320045. The data presented here were obtained [in part] with ALFOSC, which is provided by the Instituto de Astrofisica de Andalucia (IAA) under a joint agreement with the University of Copenhagen and NOT. We acknowledge funding to support our NOT observations from the Finnish Centre for Astronomy with ESO (FINCA), University of Turku, Finland (Academy of Finland, grant no. 306531). Part of the French contributions is supported by the Scientific Research National Center (CNRS) and the French spatial agency (CNES). 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. Maunakea, the location of the SMA, is a culturally important site for the indigenous Hawaiian people; we are privileged to study the cosmos from its summit. 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 has made use of data from the RoboPol program, a collaboration between Caltech, the University of Crete, IA-FORTH, IUCAA, the MPIfR, and the Nicolaus Copernicus University, which was conducted at Skinakas Observatory in Crete, Greece. DB, SK, RS, and NM, acknowledge support from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation program under grant agreement no. 771282. CC acknowledges support from the European Research Council (ERC) under the HORIZON ERC Grants 2021 program under grant agreement no. 101040021. This study used observations conducted with the 1.8-m 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 research has made use of data from the OVRO 40-m monitoring program (Richards et al. 2011), supported by private funding from the California Institute of Technology and the Max Planck Institute for Radio Astronomy, and by NASA grants NNX08AW31G, NNX11A043G, and NNX14AQ89G and NSF grants AST-0808050 and AST-1109911. SK acknowledges support from the European Research Council (ERC) under the European Unions Horizon 2020 research and innovation programme under grant agreement no. 771282. This publication makes use of data obtained at Metsähovi Radio Observatory, operated by Aalto University in Finland. AJCT, EFG, and HYD acknowledge support from Spanish MICINN project PID2020-118491GB-I00. YDH acknowledges support under the additional funding from the RYC2019-026465-I. VK acknowledges support from the Vilho, Yrjö ,and Kalle Väisälä Foundation and Suomen Kulttuurirahasto. WM gratefully acknowledges support by the ANID BASAL project FB210003 and FONDECYT 11190853.
