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Post Info TOPIC: The Crab Nebula
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RE: The Crab Nebula
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The Crab Nebula
Exposure: 2 minutes
Date: 20th October, 2012



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Blobrana


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Title: Aqueye optical observations of the Crab Nebula pulsar
Authors: C. Germanà, L. Zampieri, C. Barbieri, G. Naletto, A. Cadez, M. Calvani, M. Barbieri, I. Capraro, A. Di Paola, C. Facchinetti, T. Occhipinti, A. Possenti, D. Ponikvar, E. Verroi, P. Zoccarato

We observed the Crab pulsar in October 2008 at the Copernico Telescope in Asiago - Cima Ekar with the optical photon counter Aqueye (the Asiago Quantum Eye) which has the best temporal resolution and accuracy ever achieved in the optical domain (hundreds of picoseconds). Our goal was to perform a detailed analysis of the optical period and phase drift of the main peak of the Crab pulsar and compare it with the Jodrell Bank ephemerides. We determined the position of the main peak using the steepest zero of the cross-correlation function between the pulsar signal and an accurate optical template. The pulsar rotational period and period derivative have been measured with great accuracy using observations covering only a 2 day time interval. The error on the period is 1.7 ps, limited only by the statistical uncertainty. Both the rotational frequency and its first derivative are in agreement with those from the Jodrell Bank radio ephemerides archive. We also found evidence of the optical peak leading the radio one by ~230 microseconds. The distribution of phase-residuals of the whole dataset is slightly wider than that of a synthetic signal generated as a sequence of pulses distributed in time with the probability proportional to the pulse shape, such as the average count rate and background level are those of the Crab pulsar observed with Aqueye. The counting statistics and quality of the data allowed us to determine the pulsar period and period derivative with great accuracy in 2 days only. The time of arrival of the optical peak of the Crab pulsar leads the radio one in agreement with what recently reported in the literature. The distribution of the phase residuals can be approximated with a Gaussian and is consistent with being completely caused by photon noise (for the best data sets).

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Blobrana


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Title: A Cool Dust Factory in the Crab Nebula: A Herschel Study of the Filaments
Authors: H. L. Gomez, O. Krause, M. J. Barlow, B. M. Swinyard, P. J. Owen, C. J. R. Clark, M. Matsuura, E. L. Gomez, J. Rho, M.-A. Besel, J. Bouwman, W. K. Gear, Th. Henning, R. J. Ivison, E. T. Polehampton, B. Sibthorpe

Whether supernovae are major sources of dust in galaxies is a long-standing debate. We present infrared and submillimetre photometry and spectroscopy from the Herschel Space Observatory of the Crab Nebula between 51 and 670 micron as part of the Mass Loss from Evolved StarS program (MESS). We compare the emission detected with Herschel with multiwavelength data including millimetre, radio, mid-infrared and archive optical images. We carefully remove the synchrotron component using the Herschel and Planck fluxes measured in the same epoch. The contribution from line emission is removed using Herschel spectroscopy combined with Infrared Space Observatory archive data. Several forbidden lines of carbon, oxygen and nitrogen are detected where multiple velocity components are resolved, deduced to be from the nitrogen-depleted, carbon-rich ejecta. No spectral lines are detected in the SPIRE wavebands; in the PACS bands, the line contribution is 5 and 10% at 70 and 100 micron and negligible at 160 micron. After subtracting the synchrotron and line emission, the remaining far-infrared continuum can be fit with two dust components. Assuming standard interstellar silicates, the mass of the cooler component is 0.24(+0.32)(-0.08) solar masses for T = 28.1(+5.5)(-3.2)K. Amorphous carbon grains require 0.11 ± 0.01 solar masses of dust with T = 33.8(+2.3)(-1.8) K. A single temperature modified-blackbody with 0.14Msolar and 0.08Msolar for silicate and carbon dust respectively, provides an adequate fit to the far- infrared region of the SED but is a poor fit at 24-500 micron. The Crab Nebula has condensed most of the relevant refractory elements into dust, suggesting the formation of dust in core-collapse supernova ejecta is efficient.

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Blobrana


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Title: Highly magnetised region in pulsar wind nebulae and origin of the Crab gamma-ray flares
Authors: Y. E. Lyubarsky

The recently discovered gamma-ray flares from the Crab nebula are generally attributed to the magnetic energy release in a highly magnetised region within the nebula. I argue that such a region naturally arises in the polar region of the inner nebula. In pulsar winds, efficient dissipation of the Poynting flux into the plasma energy occur only in the equatorial belt where the energy is predominantly transferred by alternating fields. At high latitudes, the pulsar wind remains highly magnetised therefore the termination shock in the polar region is weak and the postshock flow remains relativistic. I study the structure of this flow and show that the flow at first expands and decelerates and then it converges and accelerates. In the converging part of the flow, the kink instability triggers the magnetic dissipation. The energy release zone occurs at the base of the observed jet. A specific turbulence of relativistically shrinking magnetic loops efficiently accelerates particles so that the synchrotron emission in the hundreds MeV band, both persistent and flaring, comes from this site.

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Title: First Detection of the Crab Pulsar above 100 GeV
Authors: A. Nepomuk Otte, for the VERITAS Collaboration

We present the detection of pulsed gamma-ray emission from the Crab pulsar above 100 GeV with the VERITAS array of atmospheric Cherenkov telescopes. Gamma-ray emission at theses energies was not expected in pulsar models. The detection of pulsed emission above 100 GeV and the absence of an exponential cutoff makes it unlikely that curvature radiation is the primary production mechanism of gamma rays at these energies.

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Supernova 1054
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Title: The Supernova of 1054AD, the Armenian chronicle of Hetum, and Cronaca Rampona
Authors: V. G. Gurzadyan

The rareness of nearby supernovae ensures particular value to the historic records for determination of their light curves. We provide the translation of 13th century Armenian chronicle of Hetum, which by its unexpected association to Cronaca Rampona and other chronicles can influence the debates whether there are reliable European records of the supernova of 1054 AD, as well as the analysis of the records vs the conjunction with the Moon and their role in assigning of the Type I or II to that supernova.

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Blobrana


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SN 1054
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SN 1054 is a supernova that was first observed as a new "star" in the sky on 4 July 1054 AD, hence its name, and that lasted for a period of around two years. 
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Crab pulsar
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Title: Recent glitches detected in the Crab pulsar
Authors: Jingbo Wang, Na Wang, Hao Tong, Jianping Yuan

From 2000 to 2010, monitoring of radio emission from the Crab pulsar at Xinjiang Observatory detected a total of nine glitches. The occurrence of glitches appears to be a random process as described by previous researches. A persistent change in pulse frequency and pulse frequency derivative after each glitch was found. There is no obvious correlation between glitch sizes and the time since last glitch. For these glitches \Delta\nu_{p} and \Delta\dot{\nu}_{p} span two orders of magnitude. The pulsar suffered the largest frequency jump ever seen on MJD 53067.1. The size of the glitch is ~6.8 x 10^{-6} Hz, ~ 3.5 times that of the glitch occured in 1989 glitch, with a very large permanent changes in frequency and pulse frequency derivative and followed by a decay with time constant ~ 21 days. The braking index presents significant changes. We attribute this variation to a varying particle wind strength which may be caused by glitch activities. We discuss the properties of detected glitches in Crab pulsar and compare them with glitches in the Vela pulsar.

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Blobrana


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Posts: 131433
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RE: The Crab Nebula
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Title: First Detection of a Pulsar above 100 GeV
Authors: A. Nepomuk Otte, for the VERITAS Collaboration

We present the detection of pulsed gamma-ray emission from the Crab Pulsar above 100 GeV with the VERITAS array of atmospheric Cherenkov telescopes. Gamma-ray emission at theses energies is not expected in present pulsar models. We find that the photon spectrum of pulsed emission between 100 MeV and 400 GeV can be described by a broken power law, and that it is statistically preferred over a power law with an exponential cut-off. In the VERITAS energy range the spectrum can be described with a simple power law with a spectral index of -3.8 and a flux normalization at 150 GeV that is equivalent to 1 % of the Crab Nebula gamma-ray flux. The detection of pulsed emission above 100 GeV and the absence of an exponential cutoff rules out curvature radiation as the primary gamma-ray-producing mechanism. The pulse profile exhibits the characteristic two pulses of the Crab Pulsar at phases 0.0 and 0.4, albeit 2-3 times narrower than below 10 GeV. The narrowing can be interpreted as a tapered particle acceleration region in the magnetosphere. Our findings require that the emission region of the observed gamma rays be beyond 10 stellar radii from the neutron star.

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Title: A new interpretation of Giant radio pulses from the Crab pulsar
Authors: N. Lewandowska, C. Wendel, V. Kondratiev, D. Elsässer, K. Mannheim

The Crab pulsar experienced a major flare in 2010 as observed by Fermi LAT. Observations by the Hubble Space Telescope indicate that the flare was accompanied by a structural change in the anvil region of the Crab Nebula. In the framework of a photometric analysis we reconstruct the energetics of this event. Reconnection zones near the light cylinder are expected to release energy by accelerating beams of electrons, leading to flares of varying amplitude. In this case the major flare would have reduced the magnetic energy stored in the reconnection zones, and would thus have had an impact on the properties of the giant radio flares presumably originating from these regions. We test this scenario by observing giant radio pulses with the Westerbork Synthesis Radio Telescope.

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