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Register a new userMrk 421 and 501 above 60 GeV: the Influence of CELESTEs Energy Scale on the Study of Flares and Spectra
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Authors
E. Brion
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The CELESTE atmospheric Cherenkov detector ran until June 2004. It has detected several gamma-ray flares of Mrk 421 since 1999. The new data analysis provides better background rejection. We compare our light curves with X-ray data. We significantly improved our understanding of the atmosphere, and of the optical throughput of the detector. This will allow a spectral measurement for Mrk 421 with smaller uncertainties and a more sensitive search for a signal from Mrk 501.
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The CELESTE atmospheric Cherenkov detector ran until June 2004. It has observed the blazars Mrk 421, 1ES 1426+428 and Mrk 501. We significantly improved our understanding of the atmosphere using a LIDAR, and of the optical throughput of the detector using stellar photometry. The new data analysis provides better background rejection. We present our light curve for Mrk 421 for the 2002-2004 season and a comparison with X-ray data and the 2004 observation of 1ES 1426+428. The new analysis will allow a more sensitive search for a signal from Mrk 501.
The CELESTE atmospheric Cherenkov detector, running until June 2004 at the Themis solar facility, has taken data on compact sources such as pulsars and blazars. We will take stock of the experiment, in particular regarding the latest improvements of the detector simulation and data analysis. These changes provide us with a new analysis of old data with smaller uncertainties. We present here the evidence for a weak signal from Mrk 501 in 2000-2001.
Energy spectra of gamma-ray blazars may contain an imprint from the cosmic infrared background radiation due to gamma-ray absorption (pair-production) by soft photons constituting the extragalactic background light (EBL). The signature of this imprint depends on the spectral shape of the EBL. In this work we correct the observed spectra of Mrk 421 and Mrk 501 for absorption using different possible realizations of the EBL, consistent with the most recent detections and limits. We present the intrinsic gamma-ray spectrum of these sources for the different EBL scenarios. These spectra reveal their true peak energy and luminosities, which provide important information on the nature and physical characteristics of the particle acceleration mechanism operating in these sources.
Mrk 421 and Mrk 501 are two close, bright and well-studied high-synchrotron-peaked blazars, which feature bright and persistent GeV and TeV emission. We use the longest and densest dataset of unbiased observations of these two sources, obtained at TeV and GeV energies during five years with FACT and Fermi-LAT. To characterize the variability and derive constraints on the emission mechanism, we augment the dataset with contemporaneous multi-wavelength observations from radio to X-rays. We correlate the light curves, identify individual flares in TeV energies and X-rays, and look for inter-band connections, which are expected from the shock propagations within the jet. For Mrk 421, we find that the X-rays and TeV energies are well correlated with close to zero lag, supporting the SSC emission scenario. The timing between the TeV, X-ray flares in Mrk 421 is consistent with periods expected in the case of Lense-Thirring precession of the accretion disc. The variability of Mrk 501 on long-term periods is also consistent with SSC, with a sub-day lag between X-rays and TeV energies. Fractional variability for both blazars shows a two bump structure with the highest variability in the X-ray and TeV bands.
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 $11sigma$, Markarian 421 (Mrk 421) and Markarian 501 (Mrk 501). The observations are comprised of data taken in the period between June 2015 and July 2018, resulting in a $sim 1038$ days of exposure. In this work we report the time-averaged spectral analysis for both sources above 0.5 TeV. Taking into account the flux attenuation due to the extragalactic background light (EBL), the intrinsic spectrum of Mrk 421 is described by a power law with an exponential energy cut-off with index $alpha=2.26pm(0.12)_{stat}(_{-0.2}^{+0.17})_{sys}$ and energy cut-off $E_c=5.1pm(1.6)_{stat}(_{-2.5}^{+1.4})_{sys}$ TeV, while the intrinsic spectrum of Mrk 501 is better described by a simple power law with index $alpha=2.61pm(0.11)_{stat}(_{-0.07}^{+0.01})_{sys}$. 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 broad-band spectral energy distribution (SED) of these objects. To this purpose, contemporaneous data from the Large Area Telescope on board the {em Fermi} satellite and literature data, in the radio to X-ray range, were used to build time-averaged SEDs that were modeled within a synchrotron self-Compton leptonic scenario to derive the physical parameters that describe the nature of the respective jets.
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