K. Nilsson
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View article: Detection of Compton Scattering in the Jet of 3C 84
Detection of Compton Scattering in the Jet of 3C 84 Open
3C 84 is the brightest cluster galaxy in the Perseus Cluster. It is among the closest radio-loud active galaxies and among the very few that can be detected from low-frequency radio up to TeV γ -rays. Here we report on the first X-ray pola…
View article: CAZ catalog and optical light curves of 7918 blazar-selected AGN
CAZ catalog and optical light curves of 7918 blazar-selected AGN Open
Active Galactic Nuclei (AGN) are some of the brightest and most variable objects in the universe. Those with relativistic jets observed at small viewing angles are blazars. Due to Doppler-boosting, blazars exhibit extreme stochastic variab…
View article: Identifying the Secondary Jet in the RadioAstron Image of OJ 287
Identifying the Secondary Jet in the RadioAstron Image of OJ 287 Open
The 136 yr long optical light curve of OJ 287 is explained by a binary black hole model where the secondary is in a 12 yr orbit around the primary. Impacts of the secondary on the accretion disk of the primary generate a series of optical …
View article: Identifying the secondary jet in the RadioAstron image of OJ~287
Identifying the secondary jet in the RadioAstron image of OJ~287 Open
The 136 year long optical light curve of OJ~287 is explained by a binary black hole model where the secondary is in a 12 year orbit around the primary. Impacts of the secondary on the accretion disk of the primary generate a series of opti…
View article: Optical polarization properties of the closest tidal disruption event AT 2023clx indicate origin from tidal stream shocks
Optical polarization properties of the closest tidal disruption event AT 2023clx indicate origin from tidal stream shocks Open
Polarization observations of tidal disruption events offer unique insights into the accretion processes around supermassive black holes. Here, we present optical polarization observations of the nearby event AT 2023clx, obtained using the …
View article: Determining the origin of the X-ray emission in blazars through multiwavelength polarization
Determining the origin of the X-ray emission in blazars through multiwavelength polarization Open
The origin of the high-energy emission in astrophysical jets from black holes is a highly debated issue. This is particularly true for jets from supermassive black holes, which are among the most powerful particle accelerators in the Unive…
View article: High Optical-to-X-Ray Polarization Ratio Reveals Compton Scattering in BL Lacertae’s Jet
High Optical-to-X-Ray Polarization Ratio Reveals Compton Scattering in BL Lacertae’s Jet Open
Blazars, supermassive black hole systems with highly relativistic jets aligned with the line of sight, are the most powerful long-lived emitters of electromagnetic emission in the Universe. We report here on a radio-to-gamma-ray multiwavel…
View article: Optimizing the hunt for extraterrestrial high-energy neutrino counterparts
Optimizing the hunt for extraterrestrial high-energy neutrino counterparts Open
It has been a decade since the IceCube collaboration began detecting high-energy (HE) neutrinos originating from cosmic sources. Despite a few well-known individual associations and numerous phenomenological, observational, and statistical…
View article: The polarisation behaviour of OJ 287 viewed through radio, millimetre, and optical observations between 2015 and 2017
The polarisation behaviour of OJ 287 viewed through radio, millimetre, and optical observations between 2015 and 2017 Open
OJ 287 is a bright blazar with century-long observations, and one of the strongest candidates to host a supermassive black hole binary. Its polarisation behaviour between 2015 and 2017 (MJD 57300–58000) contains several interesting events …
View article: The polarisation behaviour of OJ 287 viewed through radio, millimetre and optical observations between 2015 and 2017
The polarisation behaviour of OJ 287 viewed through radio, millimetre and optical observations between 2015 and 2017 Open
OJ 287 is a bright blazar with century-long observations, and one of the strongest candidates to host a supermassive black hole binary. Its polarisation behaviour between 2015 and 2017 (MJD 57300-58000) contains several interesting events …
View article: Association of the IceCube neutrinos with blazars in the CGRaBS sample
Association of the IceCube neutrinos with blazars in the CGRaBS sample Open
The origin of high-energy (HE) astrophysical neutrinos has remained an elusive hot topic in the field of HE astrophysics for the past decade. Apart from a handful of individual associations, the vast majority of HE neutrinos arise from unk…
View article: IXPE observation of PKS 2155–304 reveals the most highly polarized blazar
IXPE observation of PKS 2155–304 reveals the most highly polarized blazar Open
We report the X-ray polarization properties of the high-synchrotron-peaked (HSP) blazar PKS 2155−304 based on observations with the Imaging X-ray Polarimetry Explorer (IXPE). We observed the source between Oct 27 and Nov 7, 2023. We also c…
View article: Galaxy-group-associated distances to Very High Energy gamma-ray emitting BL Lacs KUV 00311-1938 and S2 0109+22
Galaxy-group-associated distances to Very High Energy gamma-ray emitting BL Lacs KUV 00311-1938 and S2 0109+22 Open
Blazars constitute the most numerous source class in the known extragalactic population of very high energy (VHE) gamma-ray sources. However, determining their redshifts is often challenging due to weak or non-existent emission lines in th…
View article: Galaxy group-associated distances to very high energy gamma-ray emitting BL Lacs KUV 00311−1938 and S2 0109+22
Galaxy group-associated distances to very high energy gamma-ray emitting BL Lacs KUV 00311−1938 and S2 0109+22 Open
Blazars constitute the most numerous source class in the known extragalactic population of very high energy (VHE) gamma-ray sources. However, determining their redshifts is often challenging due to weak or non-existent emission lines in th…
View article: The extreme coronal line emitter AT 2022fpx: varying optical polarization properties and late-time X-ray flare
The extreme coronal line emitter AT 2022fpx: varying optical polarization properties and late-time X-ray flare Open
Supermassive black holes disrupt passing stars, producing outbursts called tidal disruption events (TDEs). TDEs have recently gained attention due to their unique dynamics and emission processes, which are still not fully understood. Espec…
View article: IXPE observation of PKS 2155-304 reveals the most highly polarized blazar
IXPE observation of PKS 2155-304 reveals the most highly polarized blazar Open
We report the X-ray polarization properties of the high-synchrotron-peaked (HSP) blazar PKS 2155$-$304 based on observations with the Imaging X-ray Polarimetry Explorer (IXPE). We observed the source between Oct 27 and Nov 7, 2023. We also…
View article: Evidence of Jet Activity from the Secondary Black Hole in the OJ 287 Binary System
Evidence of Jet Activity from the Secondary Black Hole in the OJ 287 Binary System Open
We report the study of a huge optical intraday flare on 2021 November 12 at 2 a.m. UT in the blazar OJ 287. In the binary black hole model, it is associated with an impact of the secondary black hole on the accretion disk of the primary. O…
View article: Evidence of jet activity from the secondary black hole in the OJ287 binary system
Evidence of jet activity from the secondary black hole in the OJ287 binary system Open
We report the study of a huge optical intraday flare on November 12, 2021, at 2 am UT, in the blazar OJ287. In the binary black hole model it is associated with an impact of the secondary black hole on the accretion disk of the primary. Ou…
View article: The extreme coronal line emitter AT 2022fpx: Varying optical polarization properties and late-time X-ray flare
The extreme coronal line emitter AT 2022fpx: Varying optical polarization properties and late-time X-ray flare Open
Supermassive black holes disrupt passing stars, producing outbursts called tidal disruption events (TDEs). TDEs have recently gained attention due to their unique dynamics and emission processes, which are still not fully understood. Espec…
View article: X-Ray Polarization of the BL Lacertae Type Blazar 1ES 0229+200
X-Ray Polarization of the BL Lacertae Type Blazar 1ES 0229+200 Open
We present polarization measurements in the 2–8 keV band from blazar 1ES 0229+200, the first extreme high synchrotron peaked source to be observed by the Imaging X-ray Polarimetry Explorer (IXPE). Combining two exposures separated by about…
View article: X-ray Polarization of the BL Lac Type Blazar 1ES 0229+200
X-ray Polarization of the BL Lac Type Blazar 1ES 0229+200 Open
We present polarization measurements in the $2-8 \thinspace \mathrm{keV}$ band from blazar 1ES 0229+200, the first extreme high synchrotron peaked source to be observed by the Imaging X-ray Polarimetry Explorer (IXPE). Combining two exposu…
View article: Variability studies of active galactic nuclei from the long-term monitoring program with the Cherenkov Telescope Array
Variability studies of active galactic nuclei from the long-term monitoring program with the Cherenkov Telescope Array Open
Blazars are active galactic nuclei (AGN) with a relativistic jet oriented toward the observer. This jet is composed of accelerated particles which can display emission over the entire electromagnetic spectrum. Spectral variability has been…
View article: On the need of an ultramassive black hole in OJ 287
On the need of an ultramassive black hole in OJ 287 Open
The highly variable blazar OJ~287 is commonly discussed as an example of a binary black hole system. The 130 year long optical light curve is well explained by a model where the central body is a massive black hole of 18.35$\times$10$^9$ s…
View article: Observational Implications of OJ 287’s Predicted 2022 Disk Impact in the Black Hole Binary Model
Observational Implications of OJ 287’s Predicted 2022 Disk Impact in the Black Hole Binary Model Open
We present a summary of the results of the OJ 287 observational campaign, which was carried out during the 2021/2022 observational season. This season is special in the binary model because the major axis of the precessing binary happens t…
View article: Variability studies of active galactic nuclei from the long-term monitoring program with the Cherenkov Telescope Array
Variability studies of active galactic nuclei from the long-term monitoring program with the Cherenkov Telescope Array Open
Blazars are active galactic nuclei (AGN) with a relativistic jet oriented\ntoward the observer. This jet is composed of accelerated particles which can\ndisplay emission over the entire electromagnetic spectrum. Spectral variability\nhas b…
View article: On the need of an ultramassive black hole in OJ 287
On the need of an ultramassive black hole in OJ 287 Open
The highly variable blazar OJ 287 is commonly discussed as an example of a binary black hole system. The 130 yr long optical light curve is well explained by a model where the central body is a massive black hole of 18.35 $\times$ 109 sola…
View article: Observational Implications of OJ 287’s Predicted 2022 Disk Impact in the Black Hole Binary Model
Observational Implications of OJ 287’s Predicted 2022 Disk Impact in the Black Hole Binary Model Open
We present a summary of the results of the OJ 287 observational campaign, which was carried out during the 2021/2022 observational season. This season is special in the binary model because the major axis of the precessing binary happens t…
View article: Refining the 2022 OJ 287 impact flare arrival epoch
Refining the 2022 OJ 287 impact flare arrival epoch Open
The bright blazar OJ~287 routinely parades high brightness bremsstrahlung flares, which are explained as being a result of a secondary supermassive black hole (SMBH) impacting the accretion disc of a more massive primary SMBH in a binary s…
View article: Refining the OJ 287 2022 impact flare arrival epoch
Refining the OJ 287 2022 impact flare arrival epoch Open
The bright blazar OJ 287 routinely parades high brightness bremsstrahlung flares, which are explained as being a result of a secondary supermassive black hole (SMBH) impacting the accretion disc of a more massive primary SMBH in a binary s…
View article: Optical polarimetric, photometric and spectroscopic observations of the TDE AT 2020mot with Nordic Optical Telescope
Optical polarimetric, photometric and spectroscopic observations of the TDE AT 2020mot with Nordic Optical Telescope Open
The dataset contains: 1. Polarization data from November 10th, 2020: raw FITS images of the tidal disruption event AT 2020mot (polAT2020mot.zip), master bias, master flat-fields (calibs.zip) and raw FITS images of a polarization standard s…