BeppoSAX observation of PSR B1937+21

¹ IASF–CNR, via U. La Malfa 153, 90146 Palermo, Italy
² Max–Planck–Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
³ University of Manchester, Jodrell Bank, Macclesfield SK11 9DL, UK
⁴ SRON National Institute for Space Research, Sorbonnelaan 2, 3584 CA Utrecht, The Netherlands
⁵ Max–Planck–Institut für extraterrestrische Physik, Giessenbachstraße, 85740 Garching, Germany

Corresponding author: L. Nicastro, nicastro@pa.iasf.cnr.it

Received: 30 June 2003
Accepted: 10 October 2003

Abstract

We present the results of a BeppoSAX observation of the fastest rotating pulsar known: PSR B1937+21. The ~200 ks observation (78.5 ks MECS/34 ks LECS on-source time) allowed us to investigate with high statistical significance both the spectral properties and the pulse profile shape. The pulse profile is clearly double peaked at energies ≳4 keV. Peak widths are compatible with the instrumental time resolution and the second pulse lags the main pulse 0.52 in phase, like is the case in the radio. In the 1.3–4 keV band we detect a ~45% DC component; conversely the 4–10 keV pulsed fraction is consistent with 100%. The on-pulse spectrum is fitted with an absorbed power-law of spectral index ~1.2, harder than that of the total flux which is ~1.9. The total unabsorbed (2–10 keV) flux is erg cm^-2 s^-1, implying a luminosity of ( kpc)² erg s^-1 and a X-ray efficiency of , where Θ is the solid angle spanned by the emission beam. These results are in agreement with those obtained by ASCA and a more recent Rossi-XTE observation. The hydrogen column density cm^-2 is ~10 times higher than expected from the radio dispersion measure and average Galactic density of e^-. Though it is compatible (within ) with the Galactic (H i derived) value of cm^-2, inspection of dust extinction maps reveal that the pulsar falls in a highly absorbed region. In addition, 1.4 GHz radio map shows that the nearby (likely unrelated) H ii source 4C21.53W is part of a circular emission region ~4' across.