Timing studies on RXTE observations of SAX J2103.5+4545

Abstract

SAX J2103.5+4545 has been continuously monitored for ∼900 d by the Rossi X‐ray Timing Explorer (RXTE) since its outburst in 2002 July. Using these observations and previous archival RXTE observations of SAX J2103.5+4545, we refined the binary orbital parameters and find the new orbital period as P= (12.665 36 ± 0.000 88) d and the eccentricity as 0.4055 ± 0.0032. With these new orbital parameters, we constructed the pulse frequency and pulse frequency derivative histories of the pulsar and confirmed the correlation between X‐ray flux and pulse frequency derivative presented by Baykal, Stark & Swank. We constructed the power spectra for the fluctuations of pulse frequency derivatives and found that the power‐law index of the noise spectra is 2.13 ± 0.6. The power‐law index is consistent with random walk in pulse frequency derivative and is the steepest among the HMXRBs. X‐ray spectra analysis confirmed the inverse correlation trend between power‐law index and X‐ray flux found by Baykal et al.

Recent activity of the Be/X-ray binary system SAX J2103.5+4545

“…We would like to point out that the poor quality of this spectrum is probably not only related to the very low flux level of the source (∼0.074 mCrab), but also to the fact that this short ∼3 ks observation was taken in WT mode, which is more suitable for timing analysis and for source fluxes between 1-600 mCrab. The photon indexes (Γ < 1) are consistent with the values previously reported for SAX J2103.5+4545 when it was at high luminosities (İnam et al 2004;Baykal et al 2002Baykal et al , 2007Filippova et al 2004;Camero Arranz et al 2007;Reig et al 2010). At low states, our value of the photon index during quiescence is slightly higher than previous measurements, although still compatible taking into account the uncertainties.…”

“…Top: long-term spin frequency history of SAX J2103.5+4545 since its discovery in 1997. To visualize this plot more clearly we do not display the results from Baykal et al (2002Baykal et al ( , 2007, our first XRT frequency determination from Table 3, and some values from Sidoli et al (2005). Middle: long-term optical light curve of this source.…”

“…Two years after its discovery, SAX J2103.5+4545 was found to be active again in 1999 October by the All-Sky Monitor on board RXTE (Baykal et al 2000). A large flare followed by the main outburst was observed by RXTE in 2001 March (Baykal et al 2002) and in 2002 June (Baykal et al 2007;Camero Arranz et al 2007). …”

High-mass X-ray binaries in the Milky Way

“…The source was discovered as a X-ray pulsar with the period P spin = 358.6 s based on the data of the BeppoSAX observatory (Hulleman et al, 1998). A subsequent monitoring of the pulse period revealed its strong evolution and periods of a drastic acceleration of the neutron star rotation (Sidoli et al, 2005a;Baykal et al, 2007). The accurate X-ray coordinates of the source, obtained with the XMM-Newton observatory allowed to determine unambiguously its optical counterpart, which turned out an O-B star with strong emission lines (Filippova et al, 2004).…”

“…The spectral class of the optical star was determined as B0Ve (Reig, 2011). A distance to the source is estimated as ≃ 4.5 − 6.9 kpc (Baykal et al, 2007). The broadband spectrum of SAX J2103.5+4545, obtained with data of RXTE and INTEGRAL observatories is typical for X-ray pulsars and can be described by a powerlaw with high energy cutoff (see, e.g., Baykal et al, 2002;Lutovinov et al, 2003c;Filippova et al, 2004;Ducci et al, 2008).…”