arXiv subjects

T. Oosterbroek

Publications and source records attributed to T. Oosterbroek.

77 records · Page 5Linked to original sources

arXiv1997

A BeppoSAX observation of the X-ray pulsar 1E 2259+586 and the supernova remnant G109.1-1.0 (CTB 109)

The 7 s X-ray pulsar 1E2259+586 and the supernova remnant (SNR) G109.1-1.0 (CTB 109) were observed by BeppoSAX in 1996 November. The pulse period of 6.978914 +/- 0.000006 s implies that the source continues its near constant spin-down trend. The 0.5-10 keV pulse shape is characterized by a double peaked profile, with the amplitude of the second peak ~50% of that of the main peak. The pulse profile does not exhibit any strong energy dependence. We confirm the ASCA discovery of an additional low-energy spectral component from 1E2259+586. This can best be modeled as a 0.44 keV blackbody, but we cannot exclude that some, or all, of this emission arises from the part of the SNR that lies within the pulsar's extraction region. The spectrum of G109.1-1.0 is well fit with a non-equilibrium ionization plasma model with a best-fit temperature of 0.95 keV. The derived mass for the X-ray emitting plasma (~15-20 solar masses) and its near cosmic abundances imply that the X-ray emission comes mainly from mildly enriched, swept-up circumstellar material. The spectrum is strongly out of equilibrium with an ionization age of only 3000 yr. This age is in good agreement with that derived from hydrodynamic simulations of the SNR using the above X-ray temperature.

astro-ph↗

arXiv1997

The BeppoSAX LECS X-ray spectrum of Hercules X-1

We present 0.1-10 keV observations of Her X-1 obtained with the Low-Energy Spectrometer Concentrator instrument onboard the BeppoSAX satellite during the main on-state of the 35 day cycle. We confirm the existence of an intense 0.093 keV blackbody component and a broad emission feature at 0.94 keV. The pulse phase dependence of these components is similar, suggesting a common origin. This is most likely fluorescent excitation of moderately ionized ($ξ\sim$10--100) material located at the inner edge of the accretion disk.

astro-ph↗

arXiv1997

The complex X-ray spectrum of the low-mass X-ray binary 4U 1626-67

We report on observations of the X-ray pulsar 4U 1626-67 by the LECS instrument on-board Bepposax. We confirm the recent ASCA discovery of excess emission near 1 keV (Angelini et al. 1995). The pulse period of 7.66794 +/- 0.00004 s indicates that the source continues to spin-down. The phase averaged spectrum is well fit by an absorbed power-law of photon index 0.61 +/- 0.02 and a blackbody of temperature 0.33 +/- 0.02 keV, together with an emission feature at 1.05 +/- 0.02 keV. This spectral shape is similar to that observed by ASCA during the spin-down phase, but significantly different from measurements during spin-up. This suggests that the change in spectrum observed by ASCA may be a stable feature during spin-down intervals. The source intensity is a factor ~2 lower than observed by ASCA three years earlier, confirming that 4U 1626-67 continues to become fainter with time.

astro-ph↗

arXiv1997

Low-energy line emission from Cygnus X-2 observed with the BeppoSAX LECS

We present a 0.2-10 keV spectrum of the low-mass X-ray binary Cygnus X-2 obtained using the Low Energy Concentrator Spectrometer on-board Bepposax. The spectrum can be described by a cut-off power-law model with absorption of (2.28 +/- 0.07) 10^{21} atoms/cm^2, a power-law index of 0.78 +/- 0.02 and a cut-off energy of 4.30 +/- 0.08 keV (68% confidence errors), except at energies near ~1 keV where excess emission is present. This can be modeled by a broad Gaussian line feature with an energy of 1.02 +/- 0.04 keV, a full width half-maximum of 0.47 +/- 0.07 keV and an equivalent width of 74 +/-^{25}_{11} eV. This result confirms earlier reports of line emission near 1 keV and shows the intensity and structure of the feature to be variable.

astro-ph↗

arXiv1997

GX 17+2: X-ray spectral and timing behaviour of a bursting Z source

We investigated the properties of the Z pattern of the low-mass X-ray binary GX 17+2 in the X-ray colour-colour diagrams (CDs) and hardness-intensity diagrams (HIDs), and of the power spectra as a function of position in the Z, using all EXOSAT ME data. The Z pattern in the CD does not move to within 2 per cent between observations separated by 1 day to 1.5 years. The power spectra and the characteristics of the Z pattern both support the division of the Z sources into two sub-groups, GX 17+2 being in the group together with Sco X-1 and GX 349+2. It has been noted previously that the maximum frequency of the horizontal branch quasi-periodic oscillations in GX 17+2 is lower than for Cyg X-2, GX 5-1 and GX 340+0. We suggest that an asymmetry in the magnetic field giving rise to polar caps with different emission characteristics may be the origin of this. This may also explain the occurrence of bursts in GX 17+2. We also report the detection of two new bursts in the EXOSAT data of GX 17+2, which we interpret as type I bursts. No regular pulsations are observed during these two bursts nor during the bursts previously detected in GX 17+2 with EXOSAT, with upper limits to the pulsed amplitude of 1.5 per cent for pulsations with a frequency below 512 Hz. Three of the four bursts occurred in the normal branch, while one occurred in the lower part of the flaring branch.

astro-ph↗