arXiv subjects

H. Jermak

Publications and source records attributed to H. Jermak.

14 recordsLinked to original sources

arXiv2026

The 4 meter New Robotic Telescope project: an updated report

The New Robotic Telescope (NRT) is an international collaboration to build and operate a 4 m diameter fully robotic telescope. The telescope will take advantage of the superb atmospheric conditions at the Observatory of the Roque de los Muchachos (ORM). In conjunction with a large aperture, entirely robotic operation, quick response, and a set of versatile instrumentation in the optical and near-infrared this guarantees a high scientific impact focused mainly in the area of time domain astronomy. This paper presents the scientific motivation and the status of the project, discussing possible technical solutions under evaluation for the optics, mechanics and control system.

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arXiv2026

POLAMI Multi-Wavelength Polarization Study of AGN Jets: A Millimeter-Optical Comparison

Millimeter-band polarimetry offers a powerful probe of AGN jets, accessing regions less affected by opacity and Faraday rotation than at longer radio wavelengths. As part of the POLAMI program, we have conducted 14 years of 1 mm and 3 mm polarization monitoring of a sample of gamma-ray-bright blazars with the IRAM 30-m telescope, complemented here with long-term optical polarimetric observations from multiple facilities. We aim to test whether current models of parsec-scale jet physics are consistent with observed multi-band polarization behavior. Using a Bayesian framework, we derive intrinsic mean flux densities and modulation indices for total flux and fractional polarization, and characterize EVPA variability using circular statistics. We then examine how these quantities reflecting variability properties across millimeter and optical bands relate to synchrotron peak frequency, jet orientation, and radio/gamma-ray luminosities. BL Lac objects exhibit, on average, higher fractional polarization and lower EVPA variability than FSRQs at all wavelengths. Fractional polarization increases with frequency, consistent with increasingly ordered magnetic fields at shorter wavelengths. BL Lacs also show more frequent alignment of EVPAs between optical and millimeter bands, whereas FSRQs display weaker coherence. EVPA variability correlates positively with radio and gamma-ray luminosities and negatively with synchrotron peak frequency, most strongly in the optical. We further find a positive correlation between EVPA spread and fractional polarization variability, suggesting a direct link between magnetic-field structure and polarization dynamics.

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arXiv2025

The polarisation behaviour of OJ 287 viewed through radio, millimetre and optical observations between 2015 and 2017

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 that we re-contextualise in this study. We collected optical photometric and polarimetric data from several telescopes and obtained high-cadence light curves from this period. In the radio band, we collected mm-wavelength polarisation data from the AMAPOLA program. We combined these with existing multifrequency polarimetric radio results and the results of very-long-baseline-interferometry imaging with the Global mm-VLBI Array at 86 GHz. In December 2015, an optical flare was seen according to the general relativistic binary black hole model. We suggest that the overall activity near the accretion disk and the jet base during this time may be connected to the onset of a new moving component K seen in the jet in March 2017. With the additional optical data, we find a fast polarisation angle rotation of 210 degrees coinciding with the December 2015 flare, hinting at a possible link between these events. Based on the 86-GHz images, we calculated a new speed of 0.12 mas/yr for K, which places it inside the core at the time of the 2015 flare. This speed also supports the scenario where the passage of K through the quasi-stationary feature S1 could have been the trigger for the very-high-energy gamma-ray flare of OJ 287 seen in February 2017. With the mm-polarisation data, we established that these bands follow the cm-band data but show a difference during the time of K passing through S1. This indicates that the mm-bands trace the substructures of the jet still unresolved in the cm-bands.

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arXiv2023

GRB 210619B: first gamma-ray burst detection by the novel polarimeter MOPTOP

GRB~210619B was a bright long gamma-ray burst (GRB) which was optically followed up by the novel polarimeter MOPTOP on the Liverpool Telescope (LT). This was the first GRB detection by the instrument since it began science observations. MOPTOP started observing the GRB 1388 seconds after the Swift Burst Alert Telescope (BAT) trigger. The $R$ band light-curve decays following a broken power law with a break time of 2948 s after the trigger. The decay index values are $α_1 = 0.84 \pm 0.03$ (pre-break) and $α_2 = 0.54 \pm 0.02$ (post-break), indicating that the observation was most probably during the forward shock-dominated phase. We find a polarization upper limit of $\sim7$\%. In the forward shock we expect the polarization to mostly come from dust in the local ambient medium which only produces low degrees of polarization. Hence our non-detection of polarization is as expected for this particular burst.

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arXiv2022

RINGO3 polarimetry of very young ZTF supernovae

The early phases of the observed evolution of the supernovae (SNe) are expected to be dominated by the shock breakout and ``flash" ionization of the surrounding circumstellar medium. This material arises from the last stages of the evolution of the progenitor, such that photometry and spectroscopy of SNe at early times can place vital constraints on the latest and fastest evolutionary phases leading up to stellar death. These signatures are erased by the expansion of the ejecta within ~5 days after explosion. Here we present the earliest constraints, to date, on the polarization of ten transients discovered by the Zwicky Transient Facility (ZTF), between June 2018 and August 2019. Rapid polarimetric followup was conducted using the Liverpool Telescope RINGO3 instrument, including 3 SNe observed within <1 day of detection by the ZTF. The limits on the polarization within the first 5 days of explosion, for all SN types, is generally <2%, implying early asymmetries are limited to axial ratios >0.65 (assuming an oblate spheroidal configuration). We also present polarimetric observations of the Type I Superluminous SN 2018bsz and Type II SN 2018hna, observed around and after maximum light.

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arXiv2022

Polarimetry and Photometry of Gamma-Ray Bursts Afterglows with RINGO3

We present photometric and polarimetric measurements of gamma-ray burst (GRB) optical afterglows observed by the RINGO3 imaging polarimeter over its $\sim$7 year lifetime mounted on the Liverpool Telescope. During this time, RINGO3 responded to 67 GRB alerts. Of these, 28 had optical afterglows and a further ten were sufficiently bright for photometric and polarimetric analysis ($R\lessapprox{17}$). We present high quality multicolour light curves of ten sources: GRB 130606A, GRB 130610A, GRB 130612A, GRB 140430A, GRB 141220A, GRB 151215A, GRB 180325A, GRB 180618A, GRB 190114C, and GRB 191016A and polarimetry for seven of these (excluding GRB 130606A, GRB 130610A, and GRB 130612A, which were observed before the polarimetry mode was fully commissioned). Eight of these ten GRBs are classical long GRBs, one sits at the short-long duration interface with a $T_{90}$ $\sim$ 4 seconds and one is a classical short, hard burst with extended emission. We detect polarization for GRB 190114C and GRB 191016A. While detailed analyses of several of these GRBs have been published previously, here we present a uniform re-reduction and analysis of the whole sample and investigation of the population in a broad context relative to the current literature. We use survival analysis to fully include the polarization upper limits in the comparison with other GRB properties, such as temporal decay rate, isotropic energy and redshift. We find no clear correlation between polarization properties and wider sample properties and conclude that larger samples of early time polarimetry of GRB afterglows are required to fully understand GRB magnetic fields.

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arXiv2022

Multiwavelength astrophysics of the blazar OJ 287 and the project MOMO

We are carrying out the densest and longest multiyear, multiwavelength monitoring project of OJ 287 ever done. The project MOMO (Multiwavelength Observations and Modelling of OJ 287) covers wavelengths from the radio to the high-energy regime. A few selected observations are simultaneous with those of the Event Horizon Telescope (EHT). MOMO aims at understanding disk-jet physics and at testing predictions of the binary black hole scenario of OJ 287. Here, we present a discussion of extreme outburst and minima states in context, and then focus on the recent flux and spectral evolution between 2021 and May 2022, including an ongoing bright radio flare. Further, we show that there is no evidence for precursor flare activity in our optical-UV-X-ray light curves that would be associated with any secondary supermassive black hole (SMBH) disk impact and that was predicted to start as thermal flare on 2021 December 23.

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arXiv2021

GRB 191016A: A highly collimated gamma-ray burst jet with magnetised energy injection

Long gamma-ray burst GRB 191016A was a bright and slow rising burst that was detected by the \textit{Swift} satellite and followed up by ground based Liverpool Telescope (LT). LT follow-up started $2411$-s after the \textit{Swift} Burst Alert Telescope (BAT) trigger using imager IO:O around the time of the late optical peak. From $3987-7687$-s, we used the LT polarimeter RINGO3 to make polarimetric and photometric observations of the GRB simultaneously in the $V,R$ and $I$ bands. The combined optical light curve shows an initial late peak followed by a decline until 6147-s, 6087-s, and 5247-s for $I,R$ and $V$ filters respectively followed by a flattening phase. There is evidence of polarization at all phases including polarization ($P = 14.6 \pm 7.2 \%$) which is coincident with the start of the flattening phase. The combination of the light curve morphology and polarization measurement favours an energy injection scenario where slower magnetised ejecta from the central engine catches up with the decelerating blast wave. We calculate the minimum energy injection to be $ΔE / E>0.36$. At a later time combining the optical light curve from BOOTES (reported via GCN) and IO:O we see evidence of a jet break with jet opening angle 2 \degree.

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arXiv2019

Investigating the multiwavelength behaviour of the flat spectrum radio quasar CTA 102 during 2013-2017

We present a multiwavelength study of the flat-spectrum radio quasar CTA 102 during 2013-2017. We use radio-to-optical data obtained by the Whole Earth Blazar Telescope, 15 GHz data from the Owens Valley Radio Observatory, 91 and 103 GHz data from the Atacama Large Millimeter Array, near-infrared data from the Rapid Eye Monitor telescope, as well as data from the Swift (optical-UV and X-rays) and Fermi ($γ$ rays) satellites to study flux and spectral variability and the correlation between flux changes at different wavelengths. Unprecedented $γ$-ray flaring activity was observed during 2016 November-2017 February, with four major outbursts. A peak flux of (2158 $\pm$ 63)$\times$10$^{-8}$ ph cm$^{-2}$ s$^{-1}$, corresponding to a luminosity of (2.2 $\pm$ 0.1)$\times$10$^{50}$ erg s$^{-1}$, was reached on 2016 December 28. These four $γ$-ray outbursts have corresponding events in the near-infrared, optical, and UV bands, with the peaks observed at the same time. A general agreement between X-ray and $γ$-ray activity is found. The $γ$-ray flux variations show a general, strong correlation with the optical ones with no time lag between the two bands and a comparable variability amplitude. This $γ$-ray/optical relationship is in agreement with the geometrical model that has successfully explained the low-energy flux and spectral behaviour, suggesting that the long-term flux variations are mainly due to changes in the Doppler factor produced by variations of the viewing angle of the emitting regions. The difference in behaviour between radio and higher energy emission would be ascribed to different viewing angles of the jet regions producing their emission.

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arXiv2018

RINGO3 polarimetry of the Type I superluminous SN 2017egm

The origin of the luminosity of superluminous supernovae (SLSNe) is an unresolved mystery, and a number of very different physical scenarios (including energy injection from magnetars, collision with a dense circumstellar medium and pair instability-induced explosions) have been invoked. The application of polarimetry to normal SNe has been shown to probe the three-dimensional structure of exploding stars, providing clues to the nature of the explosion mechanism. We report imaging linear polarimetry observations of the Type I SLSN 2017egm, in the galaxy NGC 3191, conducted with the Liverpool Telescope and the RINGO3 instrument. Observations were acquired at four epochs, spanning 4 - 19 days after light-curve maximum, however, polarization was not detected at a level of $>3σ$. At +7 and +15 days, and in the average over all epochs, we find a possible polarization signal, detected at a significance of $\approx 2σ$ in the "blue" channel. This signal is seen, primarily, in the Stokes $q$ parameter, with a corresponding polarization angle consistent with the orientation of the spiral arm in proximity to the position of SN 2017egm. We interpret this as indicating that any polarization, if present, originates from dust in the host galaxy rather than being intrinsic to the SN itself. Despite its apparent peculiarities, compared to other Type I SLSNe, the polarization characteristics of SN 2017egm are consistent with the previously reported low polarization of other SLSNe of this variety.

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arXiv2018

High accuracy measurement of gravitational wave back-reaction in the OJ287 black hole binary

Blazar OJ287 exhibits large thermal flares at least twice every 12 years. The times of these flares have been predicted successfully using the model of a quasi-Keplerian eccentric black hole binary where the secondary impacts the accretion disk of the primary, creating the thermal flares. New measurements of the historical light curve have been combined with the observations of the 2015 November/December flare to identify the impact record since year 1886, and to constrain the orbit of the binary. The orbit solution shows that the binary period, now 12.062 year, is decreasing at the rate of 36 days per century. This corresponds to an energy loss to gravitational waves that is 6.5 +- 4 % less than the rate predicted by the standard quadrupolar gravitational wave (GW) emission. We show that the difference is due to higher order gravitational radiation reaction terms that include the dominant order tail contributions.

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arXiv2018

Stochastic modeling of multiwavelength variability of the classical BL Lac object OJ 287 on timescales ranging from decades to hours

We present the results of our power spectral density analysis for the BL Lac object OJ\,287, utilizing the {\it Fermi}-LAT survey at high-energy $γ$-rays, {\it Swift}-XRT in X-rays, several ground-based telescopes and the {\it Kepler} satellite in the optical, and radio telescopes at GHz frequencies. The light curves are modeled in terms of continuous-time auto-regressive moving average (CARMA) processes. Owing to the inclusion of the {\it Kepler} data, we were able to construct \emph{for the first time} the optical variability power spectrum of a blazar without any gaps across $\sim6$ dex in temporal frequencies. Our analysis reveals that the radio power spectra are of a colored-noise type on timescales ranging from tens of years down to months, with no evidence for breaks or other spectral features. The overall optical power spectrum is also consistent with a colored noise on the variability timescales ranging from 117 years down to hours, with no hints of any quasi-periodic oscillations. The X-ray power spectrum resembles the radio and optical power spectra on the analogous timescales ranging from tens of years down to months. Finally, the $γ$-ray power spectrum is noticeably different from the radio, optical, and X-ray power spectra of the source: we have detected a characteristic relaxation timescale in the {\it Fermi}-LAT data, corresponding to $\sim 150$\,days, such that on timescales longer than this, the power spectrum is consistent with uncorrelated (white) noise, while on shorter variability timescales there is correlated (colored) noise.

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arXiv2016

The RINGO2 and DIPOL Optical Polarisation Catalogue of Blazars

We present ~2000 polarimetric and ~3000 photometric observations of 15 gamma-ray bright blazars over a period of 936 days (11/10/2008 - 26/10/2012) using data from the Tuorla blazar monitoring program (KVA DIPOL) and Liverpool Telescope (LT) RINGO2 polarimeters (supplemented with data from SkyCamZ (LT) and Fermi-LAT gamma-ray data). In 11 out of 15 sources we identify a total of 19 electric vector position angle (EVPA) rotations and 95 flaring episodes. We group the sources into subclasses based on their broadband spectral characteristics and compare their observed optical and gamma-ray properties. We find that (1) the optical magnitude and gamma-ray flux are positively correlated, (2) EVPA rotations can occur in any blazar subclass, 4 sources show rotations that go in one direction and immediately rotate back, (3) we see no difference in the gamma-ray flaring rates in the sample; flares can occur during and outside of rotations with no preference for this behaviour, (4) the average degree of polarisation (DoP), optical magnitude and gamma-ray flux are lower during an EVPA rotation compared with during non-rotation and the distribution of the DoP during EVPA rotations is not drawn from the same parent sample as the distribution outside rotations, (5) the number of observed flaring events and optical polarisation rotations are correlated, however we find no strong evidence for a temporal association between individual flares and rotations and (6) the maximum observed DoP increases from ~10% to ~30% to ~40% for subclasses with synchrotron peaks at high, intermediate and low frequencies respectively.

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arXiv2016

Primary black hole spin in OJ287 as determined by the General Relativity centenary flare

OJ287 is a quasi-periodic quasar with roughly 12 year optical cycles. It displays prominent outbursts which are predictable in a binary black hole model. The model predicted a major optical outburst in December 2015. We found that the outburst did occur within the expected time range, peaking on 2015 December 5 at magnitude 12.9 in the optical R-band. Based on Swift/XRT satellite measurements and optical polarization data, we find that it included a major thermal component. Its timing provides an accurate estimate for the spin of the primary black hole, chi = 0.313 +- 0.01. The present outburst also confirms the established general relativistic properties of the system such as the loss of orbital energy to gravitational radiation at the 2 % accuracy level and it opens up the possibility of testing the black hole no-hair theorem with a 10 % accuracy during the present decade.

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