Astronomy and Astrophysics – Astronomy
Scientific paper
Mar 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995a%26a...295..413s&link_type=abstract
Astronomy and Astrophysics (ISSN 0004-6361), vol. 295, no. 2, p. 413-419
Astronomy and Astrophysics
Astronomy
7
Energy Spectra, Power Spectra, Pulsars, Stellar Mass Accretion, X Ray Astronomy, X Ray Binaries, X Ray Spectra, Periodic Variations, Pulse Rate, Pulsed Radiation, Rosat Mission
Scientific paper
An outburst of Cep X-4 (GS 2138+56) was witnessed by ROSAT in one of two pointed observations. We locate Cep X-4 at a position of alpha(2000) = 21 hr 39 min 31.8 sec +/- 1.6 sec and delta(2000) = 56 deg 59 min 00.8 sec +/- 7.6 sec. The pulsar appeared in two extreme intensity states, in an outburst and a quiescent state in which the source flux was reduced by a factor of approximately 1000. X-ray pulsations were observed during the outburst with a period of 66.2552 +/- 0.0007 s. Compared to the latest observed pulse period with GINGA this leads to a spin down between the two observed outbursts of p-dot/p = +1.8 x 10-5/yr. The pulse profile between 0.1 and 2.5 keV varies with energy indicating a transition from a single peak main pulse above 1 keV to a double peaked shape below 1 keV. The energy spectrum could be fitted very well with a power law of photon index 1.0, which is typical for accretion powered pulsars. The analysis of pulse phase resolved energy spectra indicates a significant softening of the spectra between the main and the interpulse. We set a lower limit of 1 kpc to the distance.
Kahabka Peter
Schulz Norbert S.
Zinnecker Hans
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