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Register a new userINTEGRAL observation of hard X-ray variability of the TeV binary LS5039 / RX J1826.2-1450
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LS 5039/RX J1826.2-1450 is one of the few High Mass X-ray binary systems from which radio and high energy TeV emission has been observed. Moreover, variability of the TeV emission with orbital period was detected. We investigate the hard X-ray (25 - 200keV) spectral and timing properties of the source with the monitoring IBIS/ISGRI instrument on-board the INTEGRAL satellite. We present the analysis of INTEGRAL observations for a total of about 3 Msec exposure time, including both public data and data from the Key Programme. We search for flux and spectral variability related to the orbital phase. The source is observed to emit from 25 up to 200 keV and the emission is concentrated around inferior conjunction. Orbital variability in the hard X-ray band is detected and established to be in phase with the orbitally modulated TeV emission observed with H.E.S.S. For this energy range we determine an average flux for the inferior conjunction phase interval of $(3.54 pm 2.30) times 10^{-11}$ erg cm$^{-2}$ s$^{-1}$, and a flux upper limit for the superior conjunction phase interval of $1.45 times 10^{-11}$ erg cm$^{-2}$ s$^{-1}$ (90% conf. level respectively). The spectrum for the inferior conjunction phase interval follows a power law with an index $Gamma = 2.0^{+0.2}_{-0.2} $ (90% conf. level).
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Recent XMM-Newton and Chandra observations of the high mass X-ray binary LS 5039 / RX J1826.2-1450 caught the source in a faint X-ray state. In contrast with previous RXTE observations, we fail to detect any evidence of iron line emission. We also fail to detect X-ray pulsations. The X-ray spectrum can be well fitted by a simple powerlaw, slightly harder than in previous observations, and does not require the presence of any additional disk or blackbody component. XMM-Newton data imply an X-ray photoelectric absorption ($N_{rm H} sim 7 times 10^{21}$ cm$^{-2}$) consistent with optical reddening, indicating that no strong local absorption occurs at the time of these observations. We discuss possible source emission mechanisms and hypotheses on the nature of the compact object, giving particular emphasis to the young pulsar scenario.
Magnetars persistent emission above 10 keV was recently discovered thanks to the imaging capabilities of the IBIS coded mask telescope on board the INTEGRAL satellite. The only two sources that show some degree of long term variability are SGR 1806-20 and 1RXS J170849.0-400910. We find some indications that variability of these hard tails could be the driver of the spectral variability measured in these sources below 10 keV. In addition we report for the first time the detection at 2.8 sigma level of pulsations in the hard X-ray tail of SGR 1806-20.
Aims: Active Galactic Nuclei are known to be variable throughout the electromagnetic spectrum. An energy domain poorly studied in this respect is the hard X-ray range above 20 keV. Methods: The first 9 months of the Swift/BAT all-sky survey are used to study the 14 - 195 keV variability of the 44 brightest AGN. The sources have been selected due to their detection significance of >10 sigma. We tested the variability using a maximum likelihood estimator and by analysing the structure function. Results: Probing different time scales, it appears that the absorbed AGN are more variable than the unabsorbed ones. The same applies for the comparison of Seyfert 2 and Seyfert 1 objects. As expected the blazars show stronger variability. 15% of the non-blazar AGN show variability of >20% compared to the average flux on time scales of 20 days, and 30% show at least 10% flux variation. All the non-blazar AGN which show strong variability are low-luminosity objects with L(14-195 keV) < 1E44 erg/sec. Conclusions: Concerning the variability pattern, there is a tendency of unabsorbed or type 1 galaxies being less variable than the absorbed or type 2 objects at hardest X-rays. A more solid anti-correlation is found between variability and luminosity, which has been previously observed in soft X-rays, in the UV, and in the optical domain.
We present the first results of the observations of the X-ray pulsars LMC X-4, 4U0352+309 and EXO1722-363 performed with the INTEGRAL observatory. The LMC X-4 was investigated during the whole superorbital cycle ($sim$30 days) and it was found that its period was not stable at this time scale. We detected a variable X-ray flux (18-60 keV) from the pulsar EXO1722-363, which could be connected with the orbital motion in the binary system. A more accurate position and the estimate of the orbital period for this source are reported. We also investigated a hard X-ray spectrum of 4U0352+309 (X Persei) measured with INTEGRAL and report the detection of the cyclotron absorption line at about 29 keV.
Many X-ray accreting pulsars have a soft excess below 10 keV. This feature has been detected also in faint sources and at low luminosity levels, suggesting that it is an ubiquitous phenomenon. In the case of the high luminosity pulsars (Lx > 10^36 erg/s), the fit of this component with thermal emission models usually provides low temperatures (kT < 0.5 keV) and large emission regions (R > a few hundred km); for this reason, it is referred to as a `soft excess. On the other hand, we recently found that in persistent, low-luminosity (Lx ~ 10^34 erg/s) and long-period (P > 100 s) Be accreting pulsars the observed excess can be modeled with a rather hot (kT > 1 keV) blackbody component of small area (R < 0.5 km), which can be interpreted as emission from the NS polar caps. In this paper we present the results of a recent XMM-Newton observation of the Galactic Be pulsar RX J0440.9+4431, which is a poorly studied member of this class of sources. We have found a best-fit period P = 204.96(+/-0.02) s, which implies an average pulsar spin-down during the last 13 years, with dP/dt ~ 6x10^(-9) s/s. The estimated source luminosity is Lx ~ 8x10^(34) erg/s: this value is higher by a factor < 10 compared to those obtained in the first source observations, but almost two orders of magnitude lower than those measured during a few outbursts detected in the latest years. The source spectrum can be described with a power law plus blackbody model, with kTbb = 1.34(+/-0.04) keV and Rbb = 273(+/-16) m, suggesting a polar-cap origin of this component. Our results support the classification of RX J0440.9+4431 as a persistent Be/NS pulsar, and confirm that the hot blackbody spectral component is a common property of this class of sources.
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