ABSTRACT
1ES 1959+650, a high-energy peaked BL Lac object (HBL) with redshift z = 0.047, is known to exhibit flux and spectral variability in different energy bands. In this work, we primarily ...considered the simultaneous Fermi-LAT and Swift-XRT data of 1ES 1959+650 to study the flux and spectral variability in the energy ranges (0.1–300 GeV) and (0.6–10 keV), respectively. Using the Fermi-LAT light curve, a stretch of quiescent state and three high flux states of the source were identified. The flux and the spectral variability were studied using flare profiles and flux-index loops. In the γ-ray energies, 1ES 1959+650 clearly showed the evolution ‘softer-when-brighter’ whereas in the X-rays it showed the trend ‘harder-when-brighter’. 1ES 1959+650 also showed quick changes in spectral shape in the γ-ray band when the γ-ray flux was changing during the flares. The spectral energy distributions (SEDs) of the source were constructed using simultaneous data from Fermi-LAT, Swift-XRT, Swift-UVOT during its evolution. The TeV data from TACTIC imaging telescope were also used to construct the SED in the quiescent state. The spectral modelling of the SEDs revealed that due to the spectral variability of 1ES 1959+650, the standard leptonic one zone model cannot be used to explain the emission from this source. Instead a two zone leptonic model is needed to explain the observed SEDs from this blazar.
Polarimetric tomography of blazar jets Barres de Almeida, Ulisses; Tavecchio, Fabrizio; Mankuzhiyil, Nijil
Monthly notices of the Royal Astronomical Society,
07/2014, Letnik:
441, Številka:
4
Journal Article
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In this paper, we propose a way of using optical polarization observations to provide independent constraints and to guide the modelling of the spectral energy distribution (SED) of blazars. This is ...particularly useful when two-zone models are required to fit the observed SED. As an example, we apply the method to the 2008 multiwavelength campaign of PKS 2155–304, for which the required polarization information was already available. We find that this approach is able to simultaneously describe the SED and the variability of the source, which is otherwise difficult to interpret. More generally, by using polarization data to disentangle different active regions within the source, the method reveals otherwise unseen correlations in the multiwavelength behaviour, which are important for SED modelling.
MAGIC is a system of two Imaging Atmospheric Cherenkov Telescopes located in the Canary island of La Palma. Since autumn 2009 both telescopes have been working together in stereoscopic mode, ...providing a significant improvement with respect to the previous single-telescope observations. We use observations of the Crab Nebula taken at low zenith angles to assess the performance of the MAGIC stereo system. The trigger threshold of the MAGIC telescopes is 50−60GeV. Advanced stereo analysis techniques allow MAGIC to achieve a sensitivity as good as (0.76±0.03)% of the Crab Nebula flux in 50h of observations above 290GeV. The angular resolution at those energies is better than ∼0.07°. We also perform a detailed study of possible systematic effects which may influence the analysis of the data taken with the MAGIC telescopes.
We present a long-term multi-wavelength study of the flat spectrum radio quasar 3C 279 using near simultaneous observations available from July 01, 2012 and June 31, 2018 (MJD 56109-58301). The data ...set includes measurements from the TACTIC, Fermi-LAT, Swift-XRT, Swift-UVOT, SMARTS, Steward-SPOL, and OVRO. The TACTIC telescope has monitored the source 3C 279 for ∼ 70 h between 2013 and 2018 in the energy range of > 0.85 TeV and yields null result. We have analysed the Fermi-LAT data to obtain the 5-day binned light curve in the energy range 0.1–300 GeV. One low and six high emission states are identified in the Fermi-LAT light curve. The high emission states are modelled with an exponential rise and decay time profile using 1-day averaged flux points and have been characterized as the asymmetric flares. The spectral analysis of near simultaneous X-ray and γ-ray data from the Swift-XRT and Fermi-LAT respectively indicates harder when brighter trend during the high activity states. The time averaged broadband spectral energy distributions corresponding to the seven states are successfully reproduced under the framework of a simple one zone leptonic emission model with IR photons originating from the dusty torus as the dominant target for the inverse Compton scattering by the relativistic electrons. Results obtained from the broadband modelling suggest that the non-thermal emission region in the jet is above the broadline region. This is also supported by the average value of seed factor estimated using the derived model parameters. A positive correlation between the bulk Lorentz factor of the emission zone and average γ-ray flux measurements for each state indicates that an increase in the bulk Lorentz factor can be the dominant cause for the observed flares from 3C 279. We also discuss the implications of the obtained model parameters in detail to understand the long-term behaviour of the source.
Very high energy (VHE) Delta *g-ray emission from the flat spectrum radio quasar (FSRQ) PKS 1222+21 (4C 21.35, z = 0.432) was detected with the MAGIC Cherenkov telescopes during a short observation ...(~0.5 hr) performed on 2010 June 17. The MAGIC detection coincides with high-energy MeV/GeV Delta *g-ray activity measured by the Large Area Telescope (LAT) on board the Fermi satellite. The VHE spectrum measured by MAGIC extends from about 70 GeV up to at least 400 GeV and can be well described by a power-law dN/dE E -- Delta *G with a photon index Delta *G = 3.75 ? 0.27stat ? 0.2syst. The averaged integral flux above 100 GeV is (4.6 ? 0.5) X 10--10 cm--2 s--1 (~1 Crab Nebula flux). The VHE flux measured by MAGIC varies significantly within the 30 minute exposure implying a flux doubling time of about 10 minutes. The VHE and MeV/GeV spectra, corrected for the absorption by the extragalactic background light (EBL), can be described by a single power law with photon index 2.72 ? 0.34 between 3 GeV and 400 GeV, and is consistent with emission belonging to a single component in the jet. The absence of a spectral cutoff constrains the Delta *g-ray emission region to lie outside the broad-line region, which would otherwise absorb the VHE Delta *g-rays. Together with the detected fast variability, this challenges present emission models from jets in FSRQs. Moreover, the combined Fermi/LAT and MAGIC spectral data yield constraints on the density of the EBL in the UV-optical to near-infrared range that are compatible with recent models.
One fundamental question about pulsars concerns the mechanism of their pulsed electromagnetic emission. Measuring the high-end region of a pulsar's spectrum would shed light on this question. By ...developing a new electronic trigger, we lowered the threshold of the Major Atmospheric γ-ray Imaging Cherenkov (MAGIC) telescope to 25 giga--electron volts. In this configuration, we detected pulsed γ-rays from the Crab pulsar that were greater than 25 giga--electron volts, revealing a relatively high cutoff energy in the phase-averaged spectrum. This indicates that the emission occurs far out in the magnetosphere, hence excluding the polar-cap scenario as a possible explanation of our measurement. The high cutoff energy also challenges the slot-gap scenario.
The Perseus galaxy cluster was observed by the MAGIC Cherenkov telescope for a total effective time of 24.4 hr during 2008 November and December. The resulting upper limits on the gamma-ray emission ...above 100 GeV are in the range of 4.6-7.5 x 10{sup -12} cm{sup -2} s{sup -1} for spectral indices from -1.5 to -2.5, thereby constraining the emission produced by cosmic rays, dark matter annihilations, and the central radio galaxy NGC 1275. Results are compatible with cosmological cluster simulations for the cosmic-ray-induced gamma-ray emission, constraining the average cosmic ray-to-thermal pressure to <4% for the cluster core region (<8% for the entire cluster). Using simplified assumptions adopted in earlier work (a power-law spectrum with an index of -2.1, constant cosmic ray-to-thermal pressure for the peripheral cluster regions while accounting for the adiabatic contraction during the cooling flow formation), we would limit the ratio of cosmic ray-to-thermal energy to E{sub CR}/E{sub th} < 3%. Improving the sensitivity of this observation by a factor of about 7 will enable us to scrutinize the hadronic model for the Perseus radio mini-halo: a non-detection of gamma-ray emission at this level implies cosmic ray fluxes that are too small to produce enough electrons through hadronic interactions with the ambient gas protons to explain the observed synchrotron emission. The upper limit also translates into a level of gamma-ray emission from possible annihilations of the cluster dark matter (the dominant mass component) that is consistent with boost factors of {approx}10{sup 4} for the typically expected dark matter annihilation-induced emission. Finally, the upper limits obtained for the gamma-ray emission of the central radio galaxy NGC 1275 are consistent with the recent detection by the Fermi-LAT satellite. Due to the extremely large Doppler factors required for the jet, a one-zone synchrotron self-Compton model is implausible in this case. We reproduce the observed spectral energy density by using the structured jet (spine-layer) model which has previously been adopted to explain the high-energy emission of radio galaxies.
•Observation with TACTIC telescope in search for TeV gamma-rays above 0.85 TeV energy from NGC 1275.•Nearly simultaneous observation with Fermi-LAT, Swift-XRT, Swift-UVOT and OVRO to understand the ...broad-band emission.•Variability study in different energy band.•Comparing the broad-band spectral energy distributions in different emission states.
Located in the Perseus galaxy cluster, NGC 1275 (z=0.0179), is the brightest radio galaxy detected in both high energy (HE ; E > 100 MeV) and very high energy (VHE ; E > 100 GeV) regimes. Here we present the results from the observations of NGC 1275 with TACTIC for 37.1 h between December, 2016 and February, 2017. In the absence of a statistically significant VHE γ-ray detection from the TACTIC observations, we estimate the 3σ upper limit on the integral flux above 0.85 TeV to be ∼2.85×10−11ergcm−2s−1. We also report the results of near simultaneous multiwavelength observations of the source from the Fermi-LAT, Swift-XRT/UVOT and OVRO. We find the source to be in flaring state on the night of 31 December, 2016 – 1 January, 2017 when the HE γ-ray flux above 0.1 GeV went up to ∼2.0×10−6phcm−2s−1 which is approximately 4 times the flux level during its low state. We present the broad-band spectral energy distributions (SED) of the source during its flaring and low states. It is evident from the SED that the VHE upper limit obtained from the TACTIC observations is consistent with the low emission state of the source.
Here, the Major Atmospheric Gamma-ray Imaging Cherenkov (MAGIC) telescopes observed S2 0109+22 in 2015 July during its flaring activity in high-energy gamma-rays observed by Fermi-Large Area ...Telescope. We analyse the MAGIC data to characterize the very high energy (VHE) gamma-ray emission of S2 0109+22, which belongs to the subclass of intermediate synchrotron peak (ISP) BL Lacertae (BL Lac) objects. We study the multifrequency emission in order to investigate the source classification. Finally, we compare the source long-term behaviour to other VHE gamma-ray emitting (TeV) blazars. We performed a temporal and spectral analysis of the data centred around the MAGIC interval of observation (MJD 57225–57231). Long-term radio and optical data have also been investigated using the discrete correlation function. The redshift of the source is estimated through optical host-galaxy imaging and also using the amount of VHE gamma-ray absorption. The quasi-simultaneous multifrequency spectral energy distribution (SED) is modelled with the conventional one-zone synchrotron self-Compton (SSC) model. MAGIC observations resulted in the detection of the source at a significance level of 5.3σ. The VHE gamma-ray emission of S2 0109+22 is variable on a daily time scale. VHE gamma-ray luminosity of the source is lower than the average of TeV BL Lacs. The optical polarization and long-term optical/radio behaviour of the source are different from the general population of TeV blazars. All these findings agree with the classification of the source as an ISP BL Lac object. As a result, we estimate the source redshift as z = 0.36 ± 0.07. The SSC parameters describing the SED are rather typical for blazars.
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