X-Ray Polarization of BL Lacertae in Outburst

0574030 - ASÚ 2024 RIV US eng J - Journal Article
Peirson, G. - Negro, M. - Liodakis, I. - Dovčiak, Michal - Karas, Vladimír … Total 131 authors
X-Ray Polarization of BL Lacertae in Outburst.
Astrophysical Journal Letters. Roč. 948, č. 2 (2023), č. článku L25. ISSN 2041-8205. E-ISSN 2041-8213
Institutional support: RVO:67985815
Keywords : astrophysical black holes * black hole physics * supermassive black holes
OECD category: Astronomy (including astrophysics,space science)
Impact factor: 7.9, year: 2022
Method of publishing: Open access

We report the first >99% confidence detection of X-ray polarization in BL Lacertae. During a recent X-ray/γ-ray outburst, a 287 ks observation (2022 November 27-30) was taken using the Imaging X-ray Polarimetry Explorer (IXPE), together with contemporaneous multiwavelength observations from the Neil Gehrels Swift observatory and XMM-Newton in soft X-rays (0.3-10 keV), NuSTAR in hard X-rays (3-70 keV), and optical polarization from the Calar Alto and Perkins Telescope observatories. Our contemporaneous X-ray data suggest that the IXPE energy band is at the crossover between the low- and high-frequency blazar emission humps. The source displays significant variability during the observation, and we measure polarization in three separate time bins. Contemporaneous X-ray spectra allow us to determine the relative contribution from each emission hump. We find >99% confidence X-ray polarization Π2--4keV=21.7+5.6−7.9% and electric vector polarization angle ψ 2-4keV = -28.°7 ± 8.°7 in the time bin with highest estimated synchrotron flux contribution. We discuss possible implications of our observations, including previous IXPE BL Lacertae pointings, tentatively concluding that synchrotron self-Compton emission dominates over hadronic emission processes during the observed epochs.
Permanent Link: https://hdl.handle.net/11104/0344391