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Register a new userInvestigating the energy distribution of the high-energy particles in the Crab nebula
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The Crab nebula is a prominent pulsar wind nebula (PWN) detected in multiband observations ranging from radio to very high-energy (VHE) $gamma$-rays. Recently, $gamma$-rays with energies above $1 mathrm{PeV}$ had been detected by the Large High Altitude Air Shower Observatory (LHAASO), and the energy of the most energetic particles in the nebula can be constrained. In this paper, we investigate the broadest spectral energy distribution of the Crab nebula and the energy distribution of the electrons emitting the multiwavelength nonthermal emission based on a one-zone time-dependent model. The nebula is powered by the pulsar, and high-energy electrons/positrons with a broken power-law spectrum are continually injected in the nebula as the pulsar spins down. Multiwavelength nonthermal emission is generated by the leptons through synchrotron radiation and inverse Compton scattering. Using appropriate parameters, the detected fluxes for the nebula can be well reproduced, especially for the $gamma$-rays from $10^2,mathrm{MeV}$ to $1,mathrm{PeV}$. The results show that the detected $gamma$-rays can be produced by the leptons via the inverse Compton scattering, and the lower limit of the Lorentz factor of the most energetic leptons is $sim 8.5times10^{9}$. It can be concluded that there are electrons/positrons with energies higher than $4.3$,PeV in the Crab nebula.
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The SPI spectrometer aboard the INTEGRAL mission observes regularly the Crab Nebula since 2003. We report on observations distributed over 5.5 years and investigate the variability of the intensity and spectral shape of this remarkable source in the hard X-rays domain up to a few MeV. While single power law models give a good description in the X-ray domain (mean photon index ~ 2.05) and MeV domain (photon index ~ 2.23), crucial information are contained in the evolution of the slope with energy between these two values. This study has been carried out trough individual observations and long duration (~ 400 ks) averaged spectra. The stability of the emission is remarkable and excludes a single power law model. The slopes measured below and above 100 keV agree perfectly with the last values reported in the X-ray and MeV regions respectively, but without indication of a localized break point. This suggests a gradual softening in the emission around 100 keV and thus a continuous evolution rather than an actual change in the mechanism parameters. In the MeV region, no significant deviation from the proposed power law model is visible up to 5-6 MeV. Finally, we take advantage of the spectroscopic capability of the instrument to seek for previously reported spectral features in the covered energy range with negative results for any significant cyclotron or annihilation emission on 400 ks timescales. Beyond the scientific results, the performance and reliability of the SPI instrument is explicitly demonstrated, with some details about the most appropriate analysis method.
HAWC has developed new energy algorithms using an artificial neural network for event-by-event reconstruction of Very High Energy (VHE) primary gamma ray energies. Unlike previous estimation methods for HAWC photons, these estimate photon energies with good energy precision and accuracy in a range from 1 TeV to greater than 100 TeV. Photon emission at the highest energies is of interest in understanding acceleration mechanisms of astrophysical sources and where the acceleration might cut off. We apply the new HAWC reconstruction to present the preliminary measurement of the highest energies at which photons are emitted by the Crab Nebula and by six additional sources in the galactic plane which emit above 50 TeV. We have observed photons above 200 TeV at 95% confidence. We also compare fits to the HAWC Crab spectrum with other measurements and theoretical models of the Crab spectrum.
The MAGIC stereoscopic system collected 69 hours of Crab Nebula data between October 2009 and April 2011. Analysis of this data sample using the latest improvements in the MAGIC stereoscopic software provided an unprecedented precision of spectral and night-by-night light curve determination at gamma rays. We derived a differential spectrum with a single instrument from 50 GeV up to almost 30 TeV with 5 bins per energy decade. At low energies, MAGIC results, combined with Fermi-LAT data, show a flat and broad Inverse Compton peak. The overall fit to the data between 1 GeV and 30 TeV is not well described by a log-parabola function. We find that a modified log-parabola function with an exponent of 2.5 instead of 2 provides a good description of the data ($chi^2=35/26$). Using systematic uncertainties of red the MAGIC and Fermi-LAT measurements we determine the position of the Inverse Compton peak to be at (53 $pm$ 3stat + 31syst -13syst) GeV, which is the most precise estimation up to date and is dominated by the systematic effects. There is no hint of the integral flux variability on daily scales at energies above 300 GeV when systematic uncertainties are included in the flux measurement. We consider three state- of-the-art theoretical models to describe the overall spectral energy distribution of the Crab Nebula. The constant B-field model cannot satisfactorily reproduce the VHE spectral measurements presented in this work, having particular difficulty reproducing the broadness of the observed IC peak. Most probably this implies that the assumption of the homogeneity of the magnetic field inside the nebula is incorrect. On the other hand, the time-dependent 1D spectral model provides a good fit of the new VHE results when considering a 80 {mu}G magnetic field. However, it fails to match the data when including the morphology of the nebula at lower wavelengths.
The Crab nebula is a supernova remnant exhibiting a highly polarized synchrotron radiation at radio and millimeter wavelengths. It is the brightest source in the microwave sky with an extension of 7 by 5 arcminutes and commonly used as a standard candle for any experiment which aims at measuring the polarization of the sky. Though its spectral energy distribution has been well characterized in total intensity, polarization data are still lacking at millimetre wavelengths. We report in this paper high resolution (18 arcsec FWHM) observations of the Crab nebula in total intensity and linear polarization at 150 GHz with the NIKA camera. NIKA, operated at the IRAM 30 m telescope from 2012 to 2015, is a camera made of Lumped Element Kinetic Inductance Detectors (LEKIDs) observing the sky at 150 and 260 GHz. From these observations we are able to reconstruct the spatial distribution of the polarization degree and angle of the Crab nebula, which is found to be compatible with previous observations at lower and higher frequencies. Averaging across the source and using other existing data sets we find that the Crab nebula polarization angle is consistent with being constant over a wide range of frequencies with a value of -87.7$^circ$ +- 0.3 in Galactic coordinates. We also present the first estimation of the Crab nebula spectral energy distribution polarized flux in a wide frequency range: 30-353 GHz. Assuming a single power law emission model we find that the polarization spectral index $beta_{pol}$ = - 0.347 +- 0.026 is compatible with the intensity spectral index $beta$ = - 0.323 +- 0.001.
We investigate the supernova remnant (SNR) 3C 397 and its neighboring pulsar PSR J1906+0722 in high energy gamma rays by using nearly six years of archival data of {it Large Area Telescope} on board {it Fermi Gamma Ray Space Telescope} (Fermi-LAT). The off-pulse analysis of gamma-ray flux from the location of PSR J1906+0722 reveals an excess emission which is found to be very close to the radio location of 3C 397. Here, we present the preliminary results of this gamma-ray analysis of 3C 397 and PSR J1906+0722.
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