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Register a new userEpisodic Torque-Luminosity Correlations and Anticorrelations of GX 1+4
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M.M. Serim
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We analyse archival CGRO-BATSE X-ray flux and spin frequency measurements of GX 1+4 over a time span of 3000 days. We systematically search for time dependent variations of torque luminosity correlation. Our preliminary results indicate that the correlation shifts from being positive to negative on time scales of few 100 days.
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We present analysis of RXTE--PCA observations of GX 1+4 between March 3, 2001 and January 31, 2003 together with the CGRO--BATSE X-ray flux and frequency derivative time series between 1991 and 1999. From the timing analysis of RXTE-PCA observations, we are able to phase connect pulse arrival times of the source within two different time intervals and obtain corresponding timing solutions. Using these pulse arrival times, we contribute to long term pulse frequency history of the source. We look for episodic correlations and anti-correlations between torque and X-ray luminosity using CGRO--BATSE X-ray flux and frequency derivative time series and find that correlation state of GX 1+4 seems to change on $sim$ 100-200 days long intervals. We estimate torque noise of the source and observe flickering noise ($f^{-1}$). We achieve to measure the longest observed timescale for a noise process among accretion powered X-ray pulsars by extending the noise estimate for a time scale ranging from 31 days to 44 years. Spectral analysis of individual RXTE-PCA observations indicates a significant correlation between iron line flux and unabsorbed X-ray flux. Pulse phase resolved spectra of the source indicate a broadening of iron line complex at the bin corresponding to the pulse minimum.
Context. GX 1+4 belongs to a rare class of X-ray binaries with red giant donors, symbiotic X-ray binaries. The system has a history of complicated variability on multiple timescales in the optical light and X-rays. The nature of this variability remains poorly understood. Aims. We study variability of GX 1+4 on long time-scale in X-ray and optical bands. Methods. The presented X-ray observations are from INTEGRAL Soft Gamma-Ray Imager and RXTE All Sky Monitor. The optical observations are from INTEGRAL Optical Monitoring Camera. Results. The variability of GX 1+4 both in optical light and hard X-ray emission (>17 keV) is dominated by ~50-70d quasi-periodic changes. The amplitude of this variability is highest during the periastron passage, while during the potential neutron star eclipse the system is always at minimum, which confirms the 1161d orbital period that has had been proposed for the system based on radial velocity curve. Neither the quasi-periodic variability or the orbital period are detected in soft X-ray emission (1.3-12.2 keV), where the binary shows no apparent periodicity.
Compact radio jets are ubiquitous in stellar-mass black-hole binaries in their hard spectral state. Empirical relations between the radio and narrow-band X-ray fluxes have been used to understand the connection between their accretion discs and jets. However, a narrow-band (e.g., 1--10 or 3--9 keV) X-ray flux can be a poor proxy for either the bolometric luminosity or the mass accretion rate. Here, we study correlations between the radio and unabsorbed broad-band X-ray fluxes, the latter providing good estimates of the bolometric flux. We consider GX 339--4, the benchmark object for the main branch of the correlation, and H1743--322, the first source found to be an outlier of the correlation. The obtained power-law dependencies of the radio flux on the bolometric flux have significantly different indices from those found for the narrow X-ray bands. Also, the radio/bolometric flux correlations for the rise of the outbursts are found to be significantly different from those for the outburst decline. This points to a possible existence of a jet hysteresis in the radio/X-ray source evolution, in addition to that seen in the hardness/flux diagram of low-mass X-ray binaries. The correlation during the rise of the outbursts is similar for both GX 339--4 and H1743--322. The correlation for the decline of the outbursts for H1743--322 lies below that of GX 339--4 at intermediate X-ray fluxes, whereas it approaches the standard correlation at lower X-ray luminosities. We also compare these correlations to those for the high-mass X-ray binaries Cyg X-1 and Cyg X-3.
We present results obtained from a Suzaku observation of the accretion powered X-ray pulsar GX 1+4. Broad-band continuum spectrum of the pulsar was found to be better described by a simple model consisting of a blackbody component and an exponential cutoff power-law than the previously used compTT continuum model. Though the pulse profile had a sharp dip in soft X-rays ($<$10 keV), phase-resolved spectroscopy confirmed that the dimming was not due to increase in photoelectric absorption. Phase-sliced spectral analysis showed the presence of a significant spectral modulation beyond 10 keV except for the dip phase. A search for the presence of cyclotron resonance scattering feature in the Suzaku spectra yielded a negative result. Iron K-shell (K$_alpha$ and K$_beta$) emission lines from nearly neutral iron ions ($<$Fe III) were clearly detected in the source spectrum. A significant K$_alpha$ emission line from almost neutral Ni atoms was detected for the first time in this source. We estimated the iron abundance of $sim$80 % of the solar value and Ni/Fe abundance ratio of about two times of the solar value. We searched for a iron Ly$_alpha$ emission line and found a significant improvement in the spectral fitting by inclusion of this line.
We report the discovery of radio emission from the accreting X-ray pulsar and symbiotic X-ray binary GX 1+4 with the Karl G. Jansky Very Large Array. This is the first radio detection of such a system, wherein a strongly magnetized neutron star accretes from the stellar wind of an M-type giant companion. We measure a $9$ GHz radio flux density of $105.3 pm 7.3$ $mu$Jy, but cannot place meaningful constraints on the spectral index due to a limited frequency range. We consider several emission mechanisms that could be responsible for the observed radio source. We conclude that the observed properties are consistent with shocks in the interaction of the accretion flow with the magnetosphere, a synchrotron-emitting jet, or a propeller-driven outflow. The stellar wind from the companion is unlikely to be the origin of the radio emission. If the detected radio emission originates from a jet, it would show that that strong magnetic fields ($geq 10^{12}$ G) do not necessarily suppress jet formation.
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