ترغب بنشر مسار تعليمي؟ اضغط هنا

Timing and spectral study of XB 1254-690 using new RXTE PCA data

224   0   0.0 ( 0 )
 نشر من قبل Arunava Mukherjee
 تاريخ النشر 2011
  مجال البحث فيزياء
والبحث باللغة English




اسأل ChatGPT حول البحث

We have analyzed the new Rossi X-ray Timing Explorer Proportional Counter Array data of the atoll neutron star (NS) low-mass X-ray binary (LMXB) system XB 1254-690. The colour-colour diagram shows that the source was in the high-intensity banana state. We have found two low-frequency candidate peaks with single trial significances of ~ 2.65 X 10^{-8} and ~ 7.39 X 10^{-8} in the power spectra. After taking into account the number of trials, the joint probability of appearance of these two peaks in the data set only by chance is ~ 4.5 X 10^{-4}, and hence a low-frequency QPO can be considered to be detected with a significance of ~ 4.5 X 10^{-4}, or, ~ 3.5sigma for the first time from this source. We have also done the first systematic X-ray spectral study of XB 1254-690, and found that, while one-component models are inadequate, three-component models are not required by the data. We have concluded that a combined broken-powerlaw and Comptonization model best describes the source continuum spectrum among 19 two-component models. The plasma temperature (~ 3 keV) and the optical depth (~ 7) of the Comptonization component are consistent with the previously reported values for other sources. However, the use of a broken-powerlaw component to describe NS LMXB spectra has recently been started, and we have used this component for XB 1254-690 for the first time. We have attempted to determine the relative energy budgets of the accretion disc and the boundary layer using the best-fit spectral model, and concluded that a reliable estimation of these budgets requires correlations among time variations of spectral properties in different wavelengths.



قيم البحث

اقرأ أيضاً

We present photometric and spectroscopic observations of the low mass X-ray binary GR Mus (XB 1254-690), and find strong evidence for the presence of a negative superhump with a period that is 2.4+/-0.3% shorter than the orbital. This provides furthe r support that GR Mus indeed harbours a precessing accretion disk (with a period of 6.74+/-0.07 day) that has retrograde precession and is completely tilted out of the orbital plane along its line of nodes. This tilt causes a large fraction of the gas in the accretion stream to either over- or underflow the accretion disk instead of hitting the disk rim, and could be a feature of all low mass X-ray binaries with characteristics similar to GR Mus (i.e. the so-called atoll sources). Furthermore, we also find marginal evidence for the presence of a positive superhump, suggesting that the accretion disk in GR Mus is eccentric due to tidal resonances. If true, than the relationship between the positive superhump period excess and the mass ratio (q) provides a constraint of q=M_donor/M_NS=0.33-0.36. Together with the radial velocity semi-amplitude measurements of the compact object, and previous modeling of the inclination we obtain a mass for the neutron star of 1.2<M_NS/M_sun<1.8 (95% confidence).
Rossi X-ray Timing Explorer (RXTE)/Proportional Counter Array (PCA) observations of IGR J19294+1816 covering two outburst episodes are reported. The first outburst happened during MJD 54921-54925 (2009 C.E.) and the second one happened during MJD 554 99-55507 (2010 C.E.). In both the cases the PCA observations were made during the decay phase of the outburst, with the source exhibiting temporal and spectral evolution with the change in flux. At the bright flux level an absorption feature at 35.5 keV is detected in the spectra which may be attributed to Cyclotron Resonance Scattering Feature corresponding to a magnetic field of B = 4.13*10^12 Gauss. This is also detected at a lower significance in two other observations. In addition an Fe line emission at 6.4 keV is prominently detected during the highest flux. X-ray pulsations are detected in 9 out of 10 observations; no pulsations were found in the observation with the lowest flux level. During this observation with the lowest flux the pulsation phenomenon becomes detectable only at the soft X-ray bands.
We present the results from an X-ray variability study of IRAS 13224-3809. This is probably the best source for X-ray reverberation studies since it is X-ray bright, extremely variable, and it has been extensively observed with XMM-Newton. We used al l the archival XMM-Newton data from the three EPIC cameras (to increase the signal-to-noise) and, given the many observations of the source, we were able to compute the time-lags spectra in three different flux levels/periods. We fitted the time-lags and energy spectra, simultaneously, using a new X-ray reverberation code which computes the time dependent reflection spectra of the disc as a response to an X-ray flash from a point source located on the axis of the black-hole (BH) accretion disc (lamp-post geometry). To the best of our knowledge, this is the first time for an AGN that both time-lags and energy spectra are fitted by a model simultaneously in different flux periods. The model fits in the case when the BH is rapidly rotating are significantly better than the model fits in the case of a Schwarzschild BH. This result strongly favours the hypothesis of a rotating central BH in this source. We also detect significant variations in the height of the X-ray corona. The X-ray height appears to increase from 3-5 gravitational radii when the X-ray luminosity is of the order of 1.5-3 percent of the Eddington limit, up to 10 gravitational radii, when the luminosity doubles.
We provide new observations of the LMC X-1 O star and its extended nebula structure using spectroscopic data from VLT/UVES as well as H$alpha$ imaging from the Wide Field Imager on the Max Planck Gesellschaft / European Southern Observatory 2.2m tele scope and ATCA imaging of the 2.1 GHz radio continuum. This nebula is one of the few known to be energized by an X-ray binary. We use a new spectrum extraction technique that is superior to other methods to obtain both radial velocities and fluxes. This provides an updated spatial velocity of $simeq 21.0~pm~4.8$ km s$^{-1}$ for the O star. The slit encompasses both the photo-ionized and shock-ionized regions of the nebula. The imaging shows a clear arc-like structure reminiscent of a wind bow shock in between the ionization cone and shock-ionized nebula. The observed structure can be fit well by the parabolic shape of a wind bow shock. If an interpretation of a wind bow shock system is valid, we investigate the N159-O1 star cluster as a potential parent of the system, suggesting a progenitor mass of $sim 60$ M$_{odot}$ for the black hole. We further note that the radio emission could be non-thermal emission from the wind bow shock, or synchrotron emission associated with the jet inflated nebula. For both wind and jet-powered origins, this would represent one of the first radio detections of such a structure.
114 - S.C.Inam , E. Beklen (2 2009
We present timing and spectral analysis of RXTE-PCA observations of SMC X-1 between January 1996 and December 2003. From observations around 30 August 1996 with a time span of $sim 6$ days, we obtain a precise timing solution for the source and resol ve the eccentricity as 0.00089(6). We find an orbital decay rate of $dot P_{orb}/P_{orb} =-3.402(7) times 10^{-6}$ yr$^{-1}$ which is close to the previous results. Using our timing analysis and the previous studies, we construct a $sim 30$ year long pulse period history of the source. We show that frequency derivative shows long (i.e. more than a few years) and short (i.e. order of days) term fluctuations. From the spectral analysis, we found that all spectral parameters except Hydrogen column density showed no significant variation with time and X-ray flux. Hydrogen column density is found to be higher as X-ray flux gets lower. This may be due to the increase in soft absorption when the pulsar is partially obscured as in Her X-1 or may just be an artifact of the tail of a soft excess in energy spectrum.
التعليقات
جاري جلب التعليقات جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
mircosoft-partner

هل ترغب بارسال اشعارات عن اخر التحديثات في شمرا-اكاديميا