AGILE OBSERVATIONS OF THE 'SOFT' GAMMA-RAY PULSAR PSR B1509 - 58

Journal Article · Mon Nov 01 00:00:00 EDT 2010 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/723/1/707· OSTI ID:21467171

Pilia, M ^[1]; Pellizzoni, A; Esposito, P; Burgay, M; Possenti, A; D'Amico, N ^[2]; Trois, A; Monte, E Del; Tavani, M; Argan, A; Costa, E ^[3]; Verrecchia, F; Santolamazza, P ^[4]; Weltevrede, P; Johnston, S ^[5]; Fuschino, F ^[6]; Chen, A; Giuliani, A; Caraveo, P; Mereghetti, S ^[7]

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1. Dipartimento di Fisica, Universita dell'Insubria, Via Valleggio 11, I-22100 Como (Italy)
2. INAF-Osservatorio Astronomico di Cagliari, localita Poggio dei Pini, strada 54, I-09012 Capoterra (Italy)
3. INAF/IASF-Roma, Via del Fosso del Cavaliere 100, I-00133 Roma (Italy)
4. ASI-ASDC, Via G. Galilei, I-00044 Frascati, Roma (Italy)
5. Australia Telescope National Facility, CSIRO, P.O. Box 76, Epping NSW 1710 (Australia)
6. INAF/IASF-Bologna, Via Gobetti 101, I-40129 Bologna (Italy)
7. INAF/IASF Milano, Via E. Bassini 15, I-20133 Milano (Italy)

We present the results of new AGILE observations of PSR B1509 - 58 performed over a period of {approx}2.5 years following the detection obtained with a subset of the present data. The modulation significance of the light curve above 30 MeV is at a 5{sigma} confidence level and the light curve is similar to those found earlier by COMPTEL up to 30 MeV: a broad asymmetric first peak reaching its maximum 0.39 {+-} 0.02 cycles after the radio peak plus a second peak at 0.94 {+-} 0.03. The gamma-ray spectral energy distribution of the pulsed flux detected by COMPTEL and AGILE is well described by a power law (photon index {alpha} = 1.87 {+-} 0.09) with a remarkable cutoff at E{sub c} = 81 {+-} 20 MeV, representing the softest spectrum observed among gamma-ray pulsars so far. The pulsar luminosity at E > 1 MeV is L{sub {gamma}} = 4.2{sup +0.5}{sub -0.2} x 10{sup 35} erg s{sup -1}, assuming a distance of 5.2 kpc, which implies a spin-down conversion efficiency to gamma rays of {approx}0.03. The unusual soft break in the spectrum of PSR B1509 - 58 has been interpreted in the framework of polar cap models as a signature of the exotic photon-splitting process in the strong magnetic field of this pulsar. In this interpretation, our spectrum constrains the magnetic altitude of the emission point(s) at 3 km above the neutron star surface, implying that the attenuation may not be as strong as formerly suggested because pair production can substitute photon splitting into regions of the magnetosphere where the magnetic field becomes too low to sustain photon splitting. In the case of an outer-gap scenario or the two-pole caustic model, better constraints on the geometry of the emission would be needed from the radio band in order to establish whether the conditions required by the models to reproduce AGILE light curves and spectra match the polarization measurements.

• OSTI ID: 21467171
• Journal Information: Astrophysical Journal, Vol. 723, Issue 1; Other Information: DOI: 10.1088/0004-637X/723/1/707; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTROPHYSICS
COSMOLOGY AND ASTRONOMY
ENERGY SPECTRA
GAMMA RADIATION
LUMINOSITY
MAGNETIC FIELDS
NEUTRON STARS
NEUTRONS
PAIR PRODUCTION
PHOTONS
PULSARS
BARYONS
BOSONS
COSMIC RADIO SOURCES
ELECTROMAGNETIC RADIATION
ELEMENTARY PARTICLES
FERMIONS
HADRONS
INTERACTIONS
IONIZING RADIATIONS
MASSLESS PARTICLES
NUCLEONS
OPTICAL PROPERTIES
PARTICLE PRODUCTION
PHYSICAL PROPERTIES
RADIATIONS
SPECTRA
STARS