VHE Gamma-Ray Observation of the Crab Nebula and its Pulsar with the MAGIC telescope (original) (raw)
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VHE γ-Ray Observation of the Crab Nebula and its Pulsar with the MAGIC Telescope
The Astrophysical …, 2008
We report about very high energy (VHE) -ray observations of the Crab Nebula with the MAGIC telescope. The -ray flux from the nebula was measured between 60 GeVand 9 TeV. The energy spectrum can be described by a curved power law dF /dE ¼ f 0 (E/300 GeV) ½ aþb log 10 ( E = 300 GeV ) with a flux normalization f 0 of (6:0 AE 0:2 stat ) ; 10 À10 cm À2 s À1 TeV À1 , a ¼ À2:31 AE 0:06 stat , and b ¼ À0:26 AE 0:07 stat . The peak in the spectral energy distribution is estimated at 77 AE 35 GeV. Within the observation time and the experimental resolution of the telescope, the -ray emission is steady and pointlike. The emission's center of gravity coincides with the position of the pulsar. Pulsed -ray emission from the pulsar could not be detected. We constrain the cutoff energy of the pulsed spectrum to be less than 27 GeV, assuming that the differential energy spectrum has an exponential cutoff. For a superexponential shape, the cutoff energy can be as high as 60 GeV.
The Crab Pulsar and Nebula as Seen in Gamma-Rays
Universe
Slightly more than 30 years ago, Whipple detection of the Crab Nebula was the start of Very High Energy gamma-ray astronomy. Since then, gamma-ray observations of this source have continued to provide new surprises and challenges to theories, with the detection of fast variability, pulsed emission up to unexpectedly high energy, and the very recent detection of photons with energy exceeding 1 PeV. In this article, we review the impact of gamma-ray observations on our understanding of this extraordinary accelerator.
MAGIC studies of the Crab Pulsar and Nebula spectra for energies above 20 GeV
Proceedings of 36th International Cosmic Ray Conference — PoS(ICRC2019), 2019
The Crab Nebula is the most studied object in the gamma-ray sky. Yet there are many important unanswered questions on the interrelation between the gamma-ray emission from the Pulsar and the Nebula. We present the results of 112 hours of observations conducted with the MAGIC Telescopes by using the stereoscopic Sum-Trigger-II, a novel trigger system essentially halving the lower energy threshold of the telescopes. In order to process the data, a dedicated analysis aiming for the lowest energies is applied. From these observations, we detect pulsed gamma-ray emission down to 27 GeV, which allows us to perform a detailed spectral study. Due to the sound statistical basis, we perform short-time variability studies of the Pulsar and test possible correlations with the nebular flares detected by Fermi-LAT.
2011
We use 73 h of stereoscopic data taken with the MAGIC telescopes to investigate the very high-energy (VHE) gamma-ray emission of the Crab pulsar. Our data show a highly significant pulsed signal in the energy range from 50 to 400 GeV in both the main pulse (P1) and the interpulse (P2) phase regions. We provide the widest spectra to date of the VHE components of both peaks, and these spectra extend to the energy range of satellite-borne observatories. The good resolution and background rejection of the stereoscopic MAGIC system allows us to cross-check the correctness of each spectral point of the pulsar by comparison with the corresponding (strong and well-known) Crab nebula flux. The spectra of both P1 and P2 are compatible with power laws with photon indices of 4.0 \pm 0.8 (P1) and 3.42 \pm 0.26 (P2), respectively, and the ratio P1/P2 between the photon counts of the two pulses is 0.54 \pm 0.12. The VHE emission can be understood as an additional component produced by the inverse Compton scattering of secondary and tertiary e\pm pairs on IR-UV photons.
Detection of Gamma Rays of up to 50 T[CLC]e[/CLC]V from the Crab Nebula
The Astrophysical Journal, 1998
Gamma rays with energies greater than 7 TeV from the Crab pulsar/nebula have been observed at large zenith angles, using the Imaging Atmospheric Technique from Woomera, South Australia. CANGAROO data taken in 1992CANGAROO data taken in , 1993 and 1995 indicate that the energy spectrum extends up to at least 50 TeV, without a change of the index of the power law spectrum.
Very high-energy observations of the Crab nebula with the GRAAL experiment
2001
The ``Gamma Ray Astronomy at ALmeria'' (GRAAL) experiment uses 63 heliostat-mirrors with a total mirror area of ~ 2500 m2 from the CESA-1 field to collect Cherenkov light from airshowers. The detector is located in a central solar tower and detects photon-induced showers with an energy threshold of 250 +- 110 GeV and an asymptotic effective detection area of about 15000 m2. Data sets taken in the period September 1999 - September 2000 in the direction of the Crab pulsar were analysed for high energy gamma-ray emission. Evidence for gamma-ray flux from the Crab pulsar with an integral flux of 2.2 +- 0.4 (stat) +1.9−1.5^{+1.9}_{-1.5}+1.9−1.5 (syst) x 10$^{-9}$ cm$^{-2}$ s$^{-1}$ above threshold and a significance of 4.5 sigma in a total (usable) observing time of 7 hours and 10 minutes on source was found. No evidence for emission from the other sources was seen. The effect of field-of-view restricted to the central part of a detected airshower on the lateral distribution and timing prope...
The spectrum of TeV gamma rays from the Crab nebula
The Astrophysical …, 1998
The spectrum of gamma rays from the Crab Nebula has been measured in the energy range 500 GeVÈ8 TeV at the Whipple Observatory by the atmospheric Cerenkov technique. Two methods of analysis that were used to derive spectra, in order to reduce the chance of calibration errors, gave good agreement, as did analysis of observations made with changed equipment several years apart. It is concluded that stable and reliable energy spectra can now be made in the TeV range. The spectrum can be represented in this energy range by the power-law Ðt, J \ (3.20^0.17^0.6) ] 10~7 ] (E/1 TeV)~2.49B0.06B0.04 m~2 s~1 TeV~1, or by the following form, which extends much better to the GeV domain : m~2 s~1 TeV~1 (E in TeV). J \ (3.25^0.14^0.6) ] 10~7E~2.44B0.06B0.04~0.151 log10 E The integral Ñux above 1 TeV is (2.1^0.2^0.3) ] 10~7 m~2 s~1. Using the complete spectrum of the Crab Nebula, the spectrum of relativistic electrons is deduced, and the spectrum of the inverse Compton emission that they would generate is in good agreement with the observed gamma-ray Ñux from 1 GeV to many TeV, if the magnetic Ðeld in the region where these scattered photons originate (essentially the X-rayÈemitting region, around 0.4 pc from the pulsar) is D16 nT (160 kG), in reasonable agreement with the Ðeld deduced by Aharonian & Atoyan. If the same Ðeld strength were present throughout the nebula, there would be no clear need for an additional radiation source in the GeV domain such as has recently been suggested ; the results give an indication that the magnetic Ðeld is well below the often-assumed equipartition strength (35È60 nT). Further accurate gamma-ray spectral measurements over the range from 1 GeV to tens of TeV have the potential to probe the growth in the magnetic Ðeld in the inner region of the nebula.
On the origin of variable gamma-ray emission from the Crab nebula
Monthly Notices of the Royal Astronomical Society, 2011
The oblique geometry of the pulsar wind termination shock ensures that the Doppler beaming has a strong impact on the shock emission. We illustrate this using the recent relativistic magnetohydrodynamic (MHD) simulations of the Crab nebula and the analysis of oblique shocks. We also show that the observed size, shape and distance from the Crab pulsar of the Crab nebula inner knot are consistent with its interpretation as a Doppler-boosted emission from the termination shock. If the electrons responsible for the synchrotron gamma-rays are accelerated only at the termination shock, then their short lifetime ensures that these gammarays originate close to the shock and are also strongly affected by the Doppler beaming. As a result, the bulk of the observed synchrotron gamma-rays of the Crab nebula around 100 MeV may come from its inner knot. This hypothesis is consistent with the observed optical flux of the inner knot, provided its optical-gamma spectral index is the same as the injection spectral index found in the Kennel & Coroniti model of the nebula spectrum. The observed variability of synchrotron gamma-ray emission on the time-scale of the wisp production can be caused by the instability of the termination shock discovered in recent numerical simulations. Given the small size of the knot, it is also possible that the 2010 September gamma-ray flare of the Crab nebula also came from the knot, though the actual mechanism remains unclear. The model predicts correlation of the temporal variability of the synchrotron gamma-ray flux in the Fermi and Astro-revilatore Gamma a Immagini LEggero (AGILE) windows with the variability of the un-pulsed optical flux from within 1 arcsec of the Crab pulsar.
Fermi Large Area Telescope Observations of the Crab Pulsar And Nebula
Astrophysical Journal, 2010
We report on γ-ray observations of the Crab Pulsar and Nebula using 8 months of survey data with the Fermi Large Area Telescope (LAT). The high quality light curve obtained using the ephemeris provided by the Nançay and Jodrell Bank radio telescopes shows two main peaks stable in phase with energy. The first γ-ray peak leads the radio main pulse by (281 ± 12 ± 21) µs, giving new constraints on the production site of non-thermal emission in pulsar magnetospheres. The first uncertainty is due to γ-ray statistics, and the second arises from the rotation parameters. The improved sensitivity and the unprecedented statistics afforded by the LAT enable precise measurement of the Crab Pulsar spectral parameters: cut-off energy at E c = (5.8 ± 0.5 ± 1.2) GeV, spectral index of Γ = (1.97 ± 0.02 ± 0.06) and integral photon flux above 100 MeV of (2.09 ± 0.03 ± 0.18) × 10 −6 cm −2 s −1 . The first errors represent the statistical error on the fit parameters, while the second ones are the systematic uncertainties. Pulsed γ-ray photons are observed up to ∼ 20 GeV which precludes emission near the stellar surface, below altitudes of around 4 to 5 stellar radii in phase intervals encompassing the two main peaks. A detailed phase-resolved spectral analysis is also performed: the hardest emission from the Crab Pulsar comes from the bridge region between the two γ-ray peaks while the softest comes from the falling edge of the second peak. The spectrum of the nebula in the energy range 100 MeV -300 GeV is well described by the sum of two power-laws of indices Γ sync = (3.99 ± 0.12 ± 0.08) and Γ IC = (1.64 ± 0.05 ± 0.07), corresponding to the falling edge of the synchrotron and the rising edge of the inverse Compton components, respectively. This latter, which links up naturally with the spectral data points of Cherenkov experiments, is well reproduced via inverse Compton scattering from standard Magnetohydrodynamics (MHD) nebula models, and does not require any additional radiation mechanism.
The Astrophysical Journal, 2000
The Crab Nebula has been observed by the HEGRA (High-Energy Gamma-Ray Astronomy) stereoscopic system of imaging airČerenkov telescopes (IACTs) for a total of about 200 hrs during two observational campaigns: from Septem-. The recent detailed studies of system performance give an energy threshold and an energy resolution for γ-rays of 500 GeV and ∼ 18%, respectively. The Crab energy spectrum was measured with the HEGRA IACT system in a very broad energy range up to 20 TeV, using observations at zenith angles up to 65 degrees. The Crab data can be fitted in the energy range from 1 to 20 TeV by a simple power-law, which yields dJ γ /dE = (2.79 ± 0.02 ± 0.5) · 10 −7 ( E 1 TeV ) −2.59±0.03±0.05 ph m −2 s −1 TeV −1 . The Crab Nebula energy spectrum, as measured with the HEGRA IACT system, agrees within 15% in the absolute scale and within 0.1 units in the power law index with the latest measurements by the Whipple, CANGAROO and CAT groups, consistent within the statistical and systematic errors quoted by the experiments. The pure power-law spectrum of TeV γ-rays from the Crab Nebula constrains the physics parameters of the nebula environment as well as the models of photon emission.