Long-term multi-band photometric monitoring of Mrk 501

Arbet-Engels, Axel; Baack, Dominik; Balbo, Matteo; Biland, A.; Bretz, T.; Buß, Jens; Dorner, D.; Eisenberger, Laura; Elsäesser, D.; Hildebrand, D.; Iotov, Roman; Kalenski, Adelina; Mannheim, K.; Mitchell, Alison; Neise, Dominik; Noethe, Maximilian; Paravac, Aleksander; Rhode, W.; Schleicher, Bernd; Sliusar, Vitalii; Walter, R.

doi:10.1051/0004-6361/202141886

“…For Mrk 501, the data from Swift-UVOT in the UVW2 band were taken from Arbet-Engels et al (2021), covering a noncontinuous period between 2015 June and 2018 April. From optical to radio, the data are taken from Abdo et al (2011b).…”

Section: Uv Optical and Radio Datamentioning

confidence: 99%

“…A few years later, in 2009, the Fermi collaboration organized a multiwavelength campaign to study the Mrk 501 SED, which was built with data from radio to gamma-rays; the MAGIC telescope participated with 16.2 hr of observation and the VERITAS array telescopes with 9.7 hr, of which 2.4 hr were during a high-activity state of the source; an SSC model was fit to the data, showing that relativistic proton shock waves are related to the bulk of the energy dissipation within the source emission zone (Abdo et al 2011b). Also, between 2012 December and 2018 April, FACT monitored Mrk 501 at TeV energies for a total of 1344 hr, distributed over 633 nights (Arbet-Engels et al 2021).…”

Section: Introductionmentioning

confidence: 98%

Long-term Spectra of the Blazars Mrk 421 and Mrk 501 at TeV Energies Seen by HAWC

Albert¹,

Alfaro²,

Álvarez³

et al. 2022

ApJ

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The High Altitude Water Cherenkov (HAWC) Gamma-Ray Observatory surveys the very high-energy sky in the 300 GeV to >100 TeV energy range. HAWC has detected two blazars above 11σ, Markarian 421 (Mrk 421) and Markarian 501 (Mrk 501). The observations are comprised of data taken in the period between 2015 June and 2018 July, resulting in ∼1038 days of exposure. In this work, we report the time-averaged spectral analyses for both sources, above 0.5 TeV. Taking into account the flux attenuation due to the extragalactic background light, the intrinsic spectrum of Mrk 421 is described by a power law with an exponential energy cutoff with index α = 2.26 ± 0.12 stat − 0.2 + 0.17 sys and energy cutoff E c = 5.1 ± 1.6 stat − 2.5 + 1.4 sys TeV, while the intrinsic spectrum of Mrk 501 is better described by a simple power law with index α = 2.61 ± 0.11 stat − 0.07 + 0.01 sys . The maximum energies at which the Mrk 421 and Mrk 501 signals are detected are 9 and 12 TeV, respectively. This makes these some of the highest energy detections to date for spectra averaged over years-long timescales. Since the observation of gamma radiation from blazars provides information about the physical processes that take place in their relativistic jets, it is important to study the broadband spectral energy distributions (SEDs) of these objects. For this purpose, contemporaneous data in the gamma-ray band to the X-ray range, and literature data in the radio to UV range, were used to build time-averaged SEDs that were modeled within a synchrotron-self Compton leptonic scenario.

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“…The correlation between the GeV and radio light curves is also strong in Mrk 501 with radio variations lagging behind the GeV ones by 170−250 days (Arbet-Engels et al 2021b). To further probe the connection between these bands, we searched for the delayed response profile, which, when convolved with the GeV light curve, can mimic the radio variations.…”

Section: Mrk 501mentioning

confidence: 94%

Radio-γ-ray response in blazars as a signature of adiabatic blob expansion

Tramacere

¹

,

Sliusar

²

,

Walter

³

et al. 2022

A&A

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Context. Multi-wavelength light curves in long-term campaigns show that, for several blazars, the radio emission occurs with a significant delay with respect to the γ-ray band, with timescales ranging from weeks to years. Such observational evidence has long been a matter of debate, and is usually interpreted as a signature of the γ-ray emission originating upstream in the jet, with the emitting region becoming radio transparent at larger scales. Aims. In this paper, we show, by means of self-consistent numerical modelling, that the adiabatic expansion of a relativistic blob can explain these delays, reproducing lags compatible with the observed timescales. Methods. We use the JetSeT framework to reproduce the numerical modelling of the radiative and accelerative processes, reproducing the temporal evolution of a single blob, from the initial flaring activity and the subsequent expansion. We follow the spectral evolution and the corresponding light curves, investigating the relations among the observed parameters, rise time, delay, and decay time, and we identify the link with physical parameters. Results. We find that, when adiabatic expansion is active, lags due to the shift of the synchrotron frequency occur. The corresponding time lags have an offset equal to the distance in time between the flaring onset and the beginning of the expansion, whilst the rising and decaying timescales depend on the velocity of the expansion and on the time required for the source to exhibit a synchrotron self-absorption frequency below the relevant radio spectral window. We derive an inter-band response function, embedding the aforementioned parameters, and we investigate the effects of the competitions between radiative and adiabatic cooling timescales on the response. We apply the response function to long-term radio and γ-ray light curves of Mrk 421, Mrk 501, and 3C 273, finding satisfactory agreement on the log-term behaviour, and we use a Monte Carlo Markov chain approach to estimate some relevant physical parameters. We discuss applications of the presented analysis to polarization measurements and to jet collimation profile kinematics. The collimation profiles observed in radio images are in agreement with the prediction from our model.

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“…Using a 5.5 year data set from Mrk 501, from 2012 to 2018, the FACT collaboration (Arbet-Engels et al 2021) has recently shown a positive correlation between the Fermi-LAT fluxes and those from OVRO, with a relatively flat behaviour and with time lags extending from -300 days to +300 days; the significance of such correlated behaviour was not computed (see Fig. 9 of Arbet-Engels et al 2021). In our study, that employs a 12-year data set, we show that the correlation is statistically significant (> 3σ) only for time lags larger than -100 days, implying the radio emission is connected to the γ-rays with a delay larger than 3 months.…”

Section: Multi-band Variability and Correlationsmentioning

confidence: 99%

“…As summarized in , Mrk 501 was regularly observed by the first generation of VHE instruments (HEGRA, Whipple, CAT) from 1996 to 2000 as shown by the light curve (LC) in Fig. A.1. Subsequently, the new generation of imaging atmospheric Cherenkov telescopes (IACTs), MAGIC, H.E.S.S., VERITAS and FACT, have been observing the source since 2005 together with regular observations in other wavebands Anderhub et al 2009;Aleksić et al 2015a;Acciari et al 2011;Aliu, E. et al 2016;Abdo et al 2011a;Ahnen et al 2017aAhnen et al , 2018Furniss et al 2015;Acciari et al 2020a;Cologna et al 2017;Arbet-Engels et al 2021). A coarse overview of the broadband emission of Mrk 501 from the year 2005 to the year 2020 is shown in Fig.…”

Section: Introductionmentioning

confidence: 99%

Multi-messenger characterization of Mrk 501 during historically low X-ray and $γ$-ray activity

Abe,

Acciari

et al. 2022

Preprint

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Aims. This work aims to characterize the broadband emission of the nearby TeV blazar Mrk 501 during long periods of very low activity, and interpret such emission within widely used theoretical scenarios. Methods. We employ 4 years of multi-wavelength (MWL) observations of Mrk 501 performed from 2017 to 2020 with a multitude of instruments, involving, among others, MAGIC, Fermi-LAT, NuSTAR, Swift, GASP-WEBT, and OVRO. During this period, Mrk 501 showed an extremely low broadband activity, which may help to unravel its baseline emission. We characterize the dynamics of the emission through its multi-band fractional variability and correlations, and investigate the underlying high-energy particle population and emission mechanisms within a range of theoretical scenarios considering both leptonic and hadronic origins. Results. Despite the low broadband activity, significant flux variations are detected at all wavebands, with a trend of increasing variability with energy, and the highest flux variations occurring at X-rays and VHE γ-rays. A correlation between the X-rays and VHE γ-rays is measured with a statistical significance above 3σ, hence supporting leptonic scenarios to explain the most variable parts of the spectral energy distribution (SED), also during low activity states. Extending our data set to 12-years (from 2008 to 2020), we find significant correlations (> 3σ) between the X-ray and HE γ-ray emission on timescales that range from weeks to years, indicating, for the first time, a common physical origin driving the flux variability between these two bands. We additionally find a positive correlation between the HE γ-ray and radio fluxes, with the radio emission lagging the HE γ-ray emission by more than 100 days. This is consistent with the HE γ-ray emission zone being located upstream of the radiobright regions of the jet of Mrk 501. Furthermore, inside our 4-year data set, Mrk 501 showed a historically low activity in both X-rays and VHE γ-rays from mid-2017 to mid-2019 with a stable VHE flux (> 0.2 TeV) of ∼5% the emission of the Crab Nebula. The broadband SED of this 2-year long low-state period, the potential baseline emission of Mrk 501, can be adequately characterized with a one-zone leptonic model, a one-zone lepto-hadronic and a purely hadronic model that fulfill the neutrino flux constraints from IceCube. Furthermore, we explore the time evolution of the SED towards the historically low-state, revealing that the stable baseline emission may be ascribed to a standing shock, while the variable emission may be attributed to an additional expanding or traveling shock.

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Long-term multi-band photometric monitoring of Mrk 501

Cited by 9 publications

References 89 publications

Long-term Spectra of the Blazars Mrk 421 and Mrk 501 at TeV Energies Seen by HAWC

Long-term Spectra of the Blazars Mrk 421 and Mrk 501 at TeV Energies Seen by HAWC

Radio-γ-ray response in blazars as a signature of adiabatic blob expansion

Multi-messenger characterization of Mrk 501 during historically low X-ray and $γ$-ray activity

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