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Register a new userDiscovery of Soft Spectral Component and Transient 22.7s Quasi Periodic Oscillations of SAX J2103.5+4545
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S. C. Inam
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XMM-Newton observed SAX J2103.5+4545 on January 6, 2003, while RXTE was monitoring the source. Using RXTE-PCA dataset between December 3, 2002 and January 29, 2003, the spin period and average spin-up rate during the XMM-Newton observations were found to be $354.7940pm0.0008$ s and $(7.4pm0.9)times10^{-13}$Hz s$^{-1}$ respectively. In the power spectrum of the 0.9-11 keV EPIC-PN lightcurve, we found quasi periodic oscillations around 0.044 Hz (22.7 s) with an rms fractional amplitude $sim $6.6 %. We interpreted this QPO feature as the Keplerian motion of inhomogenuities through the inner disk. In the X-ray spectrum, in addition to the power law component with high energy cutoff and $sim6.4$ keV fluorescent iron emission line (Baykal et al., 2002), we discovered a soft component consistent with a blackbody emission with ${rm{kT}}sim1.9$keV. The pulse phase spectroscopy of the source revealed that the blackbody flux peaked at the peak of the pulse with an emission radius $sim 0.3$ km, suggesting the polar cap on the neutron star surface as the source of blackbody emission. The flux of the iron emission line at $sim 6.42$ keV was shown to peak at the off-pulse phase, supporting the idea that this feature arises from fluorescent emission of the circumstellar material around the neutron star rather than the hot region in the vicinity of the neutron star polar cap.
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We investigated the optical, X-ray, and gamma-ray variability of the pulsar SAX J2103.5+4545. Our timing and spectral analyses of the X-ray and gamma-ray emissions from the source using RXTE and INTEGRAL data show that the shape of its spectrum in the energy range 3 -- 100 keV is virtually independent of its intensity and the orbital phase. Based on XMM-Newton data, we accurately (5 arcsec) localized the object and determined the optical counterpart in the binary. We placed upper limits on the variability of the latter in the R band and the H-alpha line on time scales of the orbital and pulse periods, respectively.
We performed a detailed study of the 2007 outburst of the 352s pulsar SAXJ2103.5+4545, a Be/X-ray transient observed by INTEGRAL, to study its spectral and temporal properties during the evolution of the outburst. SAXJ2103.5+4545 was observed with IBIS/ISGRI from 25 to 27 April 2007 and from 6 to 8 May 2007. The 20-100keV spectrum is well described by a bremsstrahlung model with a temperature kT = 24keV. The pulse profiles are variable with time and energy. A pulse period derivative of pdot = -3.4E-7 s/s has been observed during the outburst. Instead, a spin-down of pdot = 5.5E-9 s/s is observed between the 2007 outburst reported here and the previous one occurred in December 2004. This is the largest spin-down measured for SAXJ2103.5+4545 since its discovery. We estimate a neutron star magnetic field in the range (1.6-3)E13 G using the Ghosh & Lamb torque model.
We present an INTEGRAL data analysis of the X-ray transient object{SAX J2103.5+4545} during two outbursts detected in December 2002. The INTEGRAL coordinates and error circle agree with the position of the recently proposed optical counterpart. A power-law plus cut-off model provided a good fit to the 4-150 keV spectrum yielding a photon index of 1.0+-0.1, a cut-off energy E_cut=7.6+-2.0 keV and a folding energy E_fold=30.9+-2.5 keV. The X-ray luminosity in the 4-150 keV energy range was found to be 6.0x10^36 erg/s, assuming a distance of 6.5 kpc. This luminosity, together with the derived photon index, indicate that the source is in a bright state. A 354.9$+-0.5 second pulse period is measured. This value is significantly smaller than previous measurements, indicating a long-term spin-up episode.
We present an X-ray spectral and timing analysis of two $NuSTAR$ observations of the transient Be X-ray binary SAX J2103.5+4545 during its April 2016 outburst, which was characterized by the highest flux since $NuSTAR$s launch. These observations provide detailed hard X-ray spectra of this source during its bright precursor flare and subsequent fainter regular outburst for the first time. In this work, we model the phase-averaged spectra for these observations with a negative and positive power law with an exponential cut-off (NPEX) model and compare the pulse profiles at different flux states. We found that the broad-band pulse profile changes from a three peaked pulse in the first observation to a two peaked pulse in the second observation, and that each of the pulse peaks has some energy dependence. We also perform pulse-phase spectroscopy and fit phase-resolved spectra with NPEX to evaluate how spectral parameters change with pulse phase. We find that while the continuum parameters are mostly constant with pulse phase, a weak absorption feature at ~12 keV that might, with further study, be classified as a cyclotron line, does show strong pulse phase dependence.
We present an X-ray timing and spectral analysis of the Be/X-ray binary SAX J2103.5+4545 at a time when the Be stars circumstellar disk had disappeared and thus the main reservoir of material available for accretion had extinguished. In this very low optical state, pulsed X-ray emission was detected at a level of L_X~10^{33} erg/s. This is the lowest luminosity at which pulsations have ever been detected in an accreting pulsar. The derived spin period is 351.13 s, consistent with previous observations. The source continues its overall long-term spin-up, which reduced the spin period by 7.5 s since its discovery in 1997. The X-ray emission is consistent with a purely thermal spectrum, represented by a blackbody with kT=1 keV. We discuss possible scenarios to explain the observed quiescent luminosity and conclude that the most likely mechanism is direct emission resulting from the cooling of the polar caps, heated either during the most recent outburst or via intermittent accretion in quiescence.
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