The Spectrum of Teravolt Gamma Rays from the Crab Nebula

Journal Article · Sat Aug 01 04:00:00 EDT 1998 · Astrophysical Journal

DOI:https://doi.org/10.1086/306005· OSTI ID:300132

Hillas, A M ^[1]; Akerlof, C W ^[2]; Biller, S D ^[1]; Buckley, J H ^[3]; Carter-Lewis, D A; Catanese, M ^[4]; Cawley, M F ^[5]; Fegan, D J ^[6]; Finley, J P; Gaidos, J A ^[7]; Krennrich, F ^[4]; Lamb, R C ^[8]; Lang, M J ^[9]; Mohanty, G ^[4]; Punch, M ^[6]; Reynolds, P T ^[3]; Rodgers, A J; Rose, H J ^[1]; Rovero, A C ^[10]; Schubnell, M S ^[2] ; Sembroski, G H ^[7]; Vacanti, G; others, and

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1. Department of Physics and Astronomy, University of Leeds, Leeds LS2 9JT (United Kingdom)
2. Randall Laboratory of Physics, University of Michigan, Ann Arbor, MI 48109-1120 (United States)
3. Whipple Observatory, Harvard-Smithsonian Center for Astrophysics, PO Box 97, Amado, AZ 85645-0097 (United States)
4. Department of Physics and Astronomy, Iowa State University, Ames, IA 50011-3160 (United States)
5. Physics Department, St.Patrick`s College, Maynooth (Ireland)
6. Department of Experimental Physics, University College, Belfield, Dublin 4 (Ireland)
7. Department of Physics, Purdue University, West Lafayette, IN 47907 (United States)
8. Space Sciences Laboratory, California Institute of Technology, Pasadena, CA 91125 (United States)
9. Physics Department, University College, Galway (Ireland)
10. Instituto de Astronomia y Fisica del Espacio (CONICET) C.C. 67, Suc. 28, 1428 Buenos Aires (Argentina)

The spectrum of gamma rays from the Crab Nebula has been measured in the energy range 500 GeV{endash}8 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 fit, {ital J} = (3.20 {plus_minus} 0.17 {plus_minus} 0.6) {times} 10{sup {minus}7} {times} ({ital E}/1 TeV){sup {minus}2.49{plus_minus}0.06{plus_minus}0.04} m{sup {minus}2} s{sup {minus}1} TeV{sup {minus}1}, or by the following form, which extends much better to the GeV domain: J=(3.25{plus_minus}0.14{plus_minus}0.6){times}10{sup {minus}7} E{sup {minus}2.44{plus_minus}0.06{plus_minus}0.04{minus}0.151log{sub 10} E} m{sup {minus}2} s{sup {minus}1} TeV{sup {minus}1} ({ital E} in TeV). The integral flux above 1 TeV is (2.1 {plus_minus} 0.2 {plus_minus} 0.3) {times} 10{sup {minus}7} m{sup {minus}2} s{sup {minus}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 flux from 1 GeV to many TeV, if the magnetic field in the region where these scattered photons originate (essentially the X-ray{endash}emitting region, around 0.4 pc from the pulsar) is {approximately}16 nT (160 {mu}G), in reasonable agreement with the field deduced by Aharonian & Atoyan. If the same field 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 field is well below the often-assumed equipartition strength (35{endash}60 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 field in the inner region of the nebula. {copyright} {ital {copyright} 1998.} {ital The American Astronomical Society}

• OSTI ID: 300132
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 2 Vol. 503; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

66 PHYSICS
COMPTON EFFECT
CRAB NEBULA
GAMMA ASTRONOMY
GAMMA RAYS:OBSERVATIONS
GAMMA SPECTRA
INTERSTELLAR MAGNETIC FIELDS
ISM:INDIVIDUAL:(CRAB NEBULA)
NEBULAE
RADIATION MECHANISMS:NONTHERMAL
SUPERNOVA REMNANTS
TEV RANGE