Context.
The origin of the
γ
-ray emission of the blazar
Mrk 421
is still a matter of debate.
Aims.
We used 5.5 years of unbiased observing campaign data, obtained using the FACT telescope and the
...Fermi
-LAT detector at TeV and GeV energies, the longest and densest so far, together with contemporaneous multi-wavelength observations, to characterise the variability of
Mrk 421
and to constrain the underlying physical mechanisms.
Methods.
We studied and correlated light curves obtained by ten different instruments and found two significant results.
Results.
The TeV and X-ray light curves are very well correlated with a lag of < 0.6 days. The GeV and radio (15 Ghz band) light curves are widely and strongly correlated. Variations of the GeV light curve lead those in the radio.
Conclusions.
Lepto-hadronic and purely hadronic models in the frame of shock acceleration predict proton acceleration or cooling timescales that are ruled out by the short variability timescales and delays observed in Mrk 421. Instead the observations match the predictions of leptonic models.
Aims. The nearby TeV blazar 1ES 1959+650 (z = 0.047) was reported to be in flaring state during June–July 2016 by Fermi-LAT, FACT, MAGIC and VERITAS collaborations. We studied the spectral energy ...distributions (SEDs) in different states of the flare during MJD 57530–57589 using simultaneous multiwaveband data with the aim of understanding the possible broadband emission scenario during the flare. Methods. The UV-optical and X-ray data from UVOT and XRT respectively on board Swift and high energy γ-ray data from Fermi-LAT were used to generate multiwaveband lightcurves as well as to obtain high flux states and quiescent state SEDs. The correlation and lag between different energy bands was quantified using discrete correlation function. The synchrotron self-Compton (SSC) model was used to reproduce the observed SEDs during flaring and quiescent states of the source. Results. A good correlation is seen between X-ray and high energy γ-ray fluxes. The spectral hardening with increase in the flux is seen in X-ray band. The power law index vs. flux plot in γ-ray band indicates the different emission regions for 0.1–3 GeV and 3–300 GeV energy photons. Two zone SSC model satisfactorily fits the observed broadband SEDs. The inner zone is mainly responsible for producing synchrotron peak and high energy γ-ray part of the SED in all states. The second zone is mainly required to produce less variable optical-UV and low energy γ-ray emission. Conclusions. Conventional single zone SSC model does not satisfactorily explain broadband emission during observation period considered. There is an indication of two emission zones in the jet which are responsible for producing broadband emission from optical to high energy γ-rays.
Recent advancements in large language models (LMM; e.g., ChatGPT (OpenAI, San Francisco, California, USA)) have seen widespread use in various fields, including healthcare. This case study reports on ...the first use of LMM in a pretreatment discussion and in obtaining informed consent for a radiation oncology treatment. Further, the reproducibility of the replies by ChatGPT 3.5 was analyzed. A breast cancer patient, following legal consultation, engaged in a conversation with ChatGPT 3.5 regarding her radiotherapy treatment. The patient posed questions about side effects, prevention, activities, medications, and late effects. While some answers contained inaccuracies, responses closely resembled doctors’ replies. In a final evaluation discussion, the patient, however, stated that she preferred the presence of a physician and expressed concerns about the source of the provided information. The reproducibility was tested in ten iterations. Future guidelines for using such models in radiation oncology should be driven by medical professionals. While artificial intelligence (AI) supports essential tasks, human interaction remains crucial.
We present the results from the timing and spectral study of Mrk 421 based mainly on the Swift data in the X-ray energy range obtained during the time interval 2015 December-2018 April. The most ...extreme X-ray flaring activity on long-term, daily, and intraday timescales was observed during the 2 month period that started in 2017 December, when the 0.3-10 keV flux exceeded a level of 5 × 10−9 erg cm−2 s−1, recorded only twice previously. While the TeV-band and X-ray variabilities were mostly correlated, the source often varied in a complex manner in the MeV-GeV and radio-UV energy ranges, indicating that the multifrequency emission of Mrk 421 could not always be generated in a single zone. The longer-term flares at X-rays and γ-rays showed a lognormal character, possibly indicating a variability imprint of the accretion disk onto the jet. A vast majority of the 0.3-10 keV spectra were consistent with the log-parabolic model, showing relatively low spectral curvature and correlations between the different spectral parameters, predicted in the case of the first- and second-order Fermi processes. The position of the synchrotron spectral energy distribution peak showed an extreme variability on diverse timescales between the energies Ep < 0.1 and >15 keV, with 15% of the spectra peaking at the hard X-ray, and was related to the peak height as with ∼ 0.6, which is expected for the transition from Kraichnan-type turbulence into the "hard sphere" one. The 0.3-300 GeV spectra showed features of the hadronic contribution, jet-star interaction, and upscatter in the Klein-Nishina regime in different time intervals.
We present the results of the Swift observations of the nearby BL Lac object Mrk 421 during 2013 November-2015 June. The source exhibited a strong long-term variability in the 0.3-10 keV band, with a ...maximum-to-minimum flux ratio of 13, and underwent X-ray flares by a factor of 1.8-5.2 on timescales of a few weeks or shorter. The source showed 48 instances of intraday flux variability in this period, which sometimes was observed within the 1 ks observational run. It was characterized by fractional amplitudes of 1.5(0.3)%-38.6(0.4)% and flux doubling/halving times of 2.6-20.1 hr. The X-ray flux showed a lack of correlation with the TeV flux on some occasions (strong TeV flares were not accompanied by comparable X-ray activity and vice versa), indicating that the high-energy emission in Mrk 421 was generated from an emission region more complex than a single zone. The best fits of the 0.3-10 keV spectra were mainly obtained using the log-parabola model, showing a strong spectral variability that generally followed a "harder-when-brighter" trend. The position of the synchrotron spectral energy distribution peak showed an extreme range from a few eV to ∼10 keV that happens rarely in blazars.
Abstract
The X-ray variability of the BL Lacertae source Mrk 501 was studied during 11.5 yr of monitoring with Swift. Here, we report the results of this study pertaining to the epoch of 2014 ...March–October, when our target showed the most powerful and long-lasting X-ray flaring activity. This epoch was characterized by X-ray flares varying in amplitude by factors of 2–5 on time-scales of a few weeks or shorter. We detected 35 instances of the intraday variability, sometimes occurring within the 1 ks observational runs. The X-ray flux was generally correlated with the TeV flux, while the 0.3–300 GeV and optical-UV fluxes did not show a significant correlation. Some notable incidences of more complicated variability patterns could also be recognized, indicating that the high-energy emission in Mrk 501 arose from an emission region more complex than a single zone. The best fits of the 0.3–10 keV spectra were mainly obtained using the logparabola model. Strong spectral variability was detected, affecting the slope but not the curvature of the spectrum. In strong flares, the spectral index became harder than 1.70. The spectral evolution was characterized by a harder-when-brighter behaviour, shifting the peak of the spectral energy distribution by about 20 keV that happens rarely in blazars.
The flat-spectrum radio quasar CTA 102 experienced a prolonged state of enhanced activity across the entire observed electromagnetic spectrum during 2016-2017, most pronounced during a major outburst ...between 2016 December and 2017 May. Fermi-LAT observed a flux of (2.2 0.2) × 10−5 photons cm−2 s−1 at energies above 100 MeV on 2017 April 19 during a single orbit. We report here the detection of significant (4.7 ) flux variations down to timescales of ∼5 minutes during this orbit. The measured variability timescale is much shorter than the light-travel time across the central black hole (∼70 minutes) indicating a very compact emission region within the jet, similar to that seen in IC 310, Mrk 501, or PKS 1222+21 from MAGIC observations. This short-timescale variability is unexpected since the γ-ray spectrum shows no sign of attenuation due to pair creation in interactions with photons from the broad emission line region, and therefore must be assumed to originate far from the black hole. The observed fast variability could either indicate the dissipation of magnetic islands or protons in a collimated beam from the base of the jet encountering the turbulent plasma at the end of the magnetic nozzle.
Aims. We aim to characterize the multiwavelength emission from Markarian 501 (Mrk 501), quantify the energy-dependent variability, study the potential multiband correlations, and describe the ...temporal evolution of the broadband emission within leptonic theoretical scenarios. Methods. We organized a multiwavelength campaign to take place between March and July of 2012. Excellent temporal coverage was obtained with more than 25 instruments, including the MAGIC, FACT and VERITAS Cherenkov telescopes, the instruments on board the Swift and Fermi spacecraft, and the telescopes operated by the GASP-WEBT collaboration. Results. Mrk 501 showed a very high energy (VHE) gamma-ray flux above 0.2 TeV of ∼0.5 times the Crab Nebula flux (CU) for most of the campaign. The highest activity occurred on 2012 June 9, when the VHE flux was ∼3 CU, and the peak of the high-energy spectral component was found to be at ∼2 TeV. Both the X-ray and VHE gamma-ray spectral slopes were measured to be extremely hard, with spectral indices < 2 during most of the observing campaign, regardless of the X-ray and VHE flux. This study reports the hardest Mrk 501 VHE spectra measured to date. The fractional variability was found to increase with energy, with the highest variability occurring at VHE. Using the complete data set, we found correlation between the X-ray and VHE bands; however, if the June 9 flare is excluded, the correlation disappears (significance < 3σ) despite the existence of substantial variability in the X-ray and VHE bands throughout the campaign. Conclusions. The unprecedentedly hard X-ray and VHE spectra measured imply that their low- and high-energy components peaked above 5 keV and 0.5 TeV, respectively, during a large fraction of the observing campaign, and hence that Mrk 501 behaved like an extreme high-frequency-peaked blazar (EHBL) throughout the 2012 observing season. This suggests that being an EHBL may not be a permanent characteristic of a blazar, but rather a state which may change over time. The data set acquired shows that the broadband spectral energy distribution (SED) of Mrk 501, and its transient evolution, is very complex, requiring, within the framework of synchrotron self-Compton (SSC) models, various emission regions for a satisfactory description. Nevertheless the one-zone SSC scenario can successfully describe the segments of the SED where most energy is emitted, with a significant correlation between the electron energy density and the VHE gamma-ray activity, suggesting that most of the variability may be explained by the injection of high-energy electrons. The one-zone SSC scenario used reproduces the behavior seen between the measured X-ray and VHE gamma-ray fluxes, and predicts that the correlation becomes stronger with increasing energy of the X-rays.
Context
. We are operating an elastic light detecting and ranging system (LIDAR) for the monitoring of atmospheric conditions during regular observations of the MAGIC telescopes.
Aims
. We present ...and evaluate methods for converting aerosol extinction profiles, obtained with the LIDAR, into corrections of the reconstructed gamma-ray event energy and instrument response functions of Imaging Atmospheric Cherenkov Telescopes.
Methods
. We assess the performance of these correction schemes with almost seven years of Crab Nebula data obtained with the MAGIC telescopes under various zenith angles and different aerosol extinction scenarios of Cherenkov light.
Results
. The methods enable the reconstruction of data taken under nonoptimal atmospheric conditions with aerosol transmissions down to ~0.65 with systematic uncertainties comparable to those for data taken under optimal conditions. For the first time, the correction of data affected by clouds has been included in the assessment. The data can also be corrected when the transmission is lower than 0.65, but the results are less accurate and suffer from larger systematics.
Supermassive black holes with masses of millions to billions of solar masses are commonly found in the centers of galaxies. Astronomers seek to image jet formation using radio interferometry but ...still suffer from insufficient angular resolution. An alternative method to resolve small structures is to measure the time variability of their emission. Here we report on gamma-ray observations of the radio galaxy IC 310 obtained with the MAGIC (Major Atmospheric Gamma-ray Imaging Cherenkov) telescopes, revealing variability with doubling time scales faster than 4.8 min. Causality constrains the size of the emission region to be smaller than 20% of the gravitational radius of its central black hole. We suggest that the emission is associated with pulsar-like particle acceleration by the electric field across a magnetospheric gap at the base of the radio jet.
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