Topic
HEGRA
About: HEGRA is a research topic. Over the lifetime, 333 publications have been published within this topic receiving 11299 citations. The topic is also known as: HEGRA.
Papers published on a yearly basis
Papers
TL;DR: In this article, a power law-type energy spectrum of the combined data set can be approximated by a power-law type energy spectrum: d?/dE =?0?,?0 = 10-11?photons?cm-2 s-1 TeV-1, and? = -2.62? 0.02stat? 0.05sys.
Abstract: The Crab supernova remnant has been observed regularly with the stereoscopic system of five imaging air Cerenkov telescopes that was part of the High Energy Gamma Ray Astronomy (HEGRA) experiment. In total, close to 400 hr of useful data have been collected from 1997 to 2002. The differential energy spectrum of the combined data set can be approximated by a power law-type energy spectrum: d?/dE = ?0 ?, ?0 = 10-11?photons?cm-2 s-1 TeV-1, and ? = -2.62 ? 0.02stat ? 0.05sys. The spectrum extends up to energies of 80?TeV and is well matched by model calculations in the framework of inverse Compton scattering of various seed photons in the nebula, including for the first time a recently detected compact emission region at millimeter wavelengths. The observed indications for a gradual steepening of the energy spectrum in data is expected in the inverse Compton emission model. The average magnetic field in the emitting volume is determined to be 161.6 ? 0.8stat ? 18sys ?G. The presence of protons in the nebula is not required to explain the observed flux, and upper limits on the injected power of protons are calculated to be as low as 20% of the total spin-down luminosity for bulk Lorentz factors of the wind in the range of 104-106. The position and size of the emission region have been studied over a wide range of energies. The position is shifted by 13'' to the west of the pulsar, with a systematic uncertainty of 25''. No significant shift in the position with energy is observed. The size of the emission region is constrained to be less than 2' at energies between 1 and 10?TeV. Above 30?TeV the size is constrained to be less than 3'. No indication of pulsed emission has been found, and upper limits in differential bins of energy have been calculated reaching typically 1%-3% of the unpulsed component.
354 citations
TL;DR: In this article, the Synchrotron Self-Compton (SSC) model was used to model the Spectral Energy Distributions (SED) of a TeV blazar.
Abstract: Following the detection of strong TeV gamma-ray flares from the BL Lac object 1ES 1959+650 with the Whipple 10 m Cherenkov telescope on May 16 and 17, 2002, we performed intensive Target of Opportunity (ToO) radio, optical, X-ray and TeV gamma-ray observations from May 18, 2002 to August 14, 2002. Observations with the X-ray telescope RXTE and the Whipple and HEGRA gamma-ray telescopes revealed several strong flares, enabling us to sensitively test the X-ray/gamma-ray flux correlation properties. Although the X-ray and gamma-ray fluxes seemed to be correlated in general, we found an ``orphan'' gamma-ray flare that was not accompanied by an X-ray flare. After describing in detail the radio (UMRAO, VLA), optical (Boltwood, Abastumani), X-ray (RXTE) and gamma-ray (Whipple, HEGRA) light curves and Spectral Energy Distributions (SEDs) we present initial modeling of the SED with a simple Synchrotron Self-Compton (SSC) model. With the addition of another TeV blazar with good broadband data, we consider the set of all TeV blazars to begin to look for a connection of the jet properties to the properties of the central accreting black hole thought to drive the jet. Remarkably, the temporal and spectral X-ray and gamma-ray emission characteristics of TeV blazars are very similar, even though the masses estimates of their central black holes differ by up to one order of magnitude.
320 citations
TL;DR: In this paper, the authors observed that the synchrotron power is observed to peak at hard X-ray energies, a behavior never seen before in this or any other blazar.
Abstract: The BL Lac object Mkn 501, one of the only three extragalactic sources (with Mkn 421 and 1ES 2344+514) so far detected at TeV energies, was observed with the BeppoSAX satellite on 7, 11, and 16 April 1997 during a phase of high activity at TeV energies, as monitored with the Whipple, HEGRA and CAT Cherenkov telescopes. Over the whole 0.1-200 keV range the spectrum was exceptionally hard (alpha =< 1, with F_nu ~ nu^{-alpha}) indicating that the X-ray power output peaked at (or above) ~100 keV. This represents a shift of at least two orders of magnitude with respect to previous observations of Mkn 501, a behavior never seen before in this or any other blazar. The overall X-ray spectrum hardens with increasing intensity and, at each epoch, it is softer at larger energies. The correlated variability from soft X-rays to the TeV band points to models in which the same population of relativistic electrons produces the X-ray continuum via synchrotron radiation and the TeV emission by inverse Compton scattering of the synchrotron photons or other seed photons. For the first time in any blazar the synchrotron power is observed to peak at hard X-ray energies. The large shift of the synchrotron peak frequency with respect to previous observations of Mkn 501 implies that intrinsic changes in the relativistic electron spectrum caused the increase in emitted power. Due to the very high electron energies, the inverse Compton process is limited by the Klein-Nishina regime. This implies a quasi-linear (as opposed to quadratic) relation of the variability amplitude in the TeV and hard X-ray ranges (for the SSC model) and an increase of the inverse Compton peak frequency smaller than that of the synchrotron peak frequency.
298 citations
TL;DR: In this article, the authors consider the implications of the recent determination of the universal infrared background for the propagation of photons up to 20 TeV from the active galaxy Markarian 501 as observed by HEGRA.
277 citations
TL;DR: In this article, the average magnetic field in the emitting volume is determined to be $(161.6\pm0.8mathrm{stat}\pm18_\mathrm {sys}) \mu$G. The presence of protons in the nebula is not required to explain the observed flux and upper limits on the injected power of proton are calculated being as low as 20 % of the total spin down luminosity for bulk Lorentz factors of the wind in the range of $10^4-10^6$.
Abstract: The Crab supernova remnant has been observed regularly with the stereoscopic system of 5 imaging air Cherenkov telescopes that was part of the High Energy Gamma Ray Astronomy (HEGRA) experiment. In total, close to 400 hours of useful data have been collected from 1997 until 2002. The spectrum extends up to energies of 80 TeV and is well matched by model calculations in the framework of inverse Compton scattering of various seed photons in the nebula including for the first time a recently detected compact emission region at mm-wavelengths. The observed indications for a gradual steepening of the energy spectrum in data is expected in the inverse Compton emission model.The average magnetic field in the emitting volume is determined to be $(161.6\pm0.8mathrm{stat}\pm18_\mathrm{sys}) \mu$G. The presence of protons in the nebula is not required to explain the observed flux and upper limits on the injected power of protons are calculated being as low as 20 % of the total spin down luminosity for bulk Lorentz factors of the wind in the range of $10^4-10^6$.The position and size of the emission region have been studied over a wide range of energies. The position is shifted by 13\arcsec to the west of the pulsar with a systematic uncertainty of 25\arcsec. No significant shift in the position with energy is observed. The size of the emission region is constrained to be less than 2\arcmin at energies between 1 and 10 TeV. Above 30 TeV the size is constrained to be less than 3\this http URL indications for pulsed emission has been found and upper limits in differential bins of energy have been calculated reaching typically 1-3 % of the unpulsed component.
227 citations
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Performance Metrics
| Year | Papers |
|---|---|
| 2021 | 1 |
| 2020 | 2 |
| 2018 | 2 |
| 2017 | 4 |
| 2015 | 6 |
| 2014 | 1 |