New measurement of orbital and spin period evolution of the accretion disc corona source 4U 1822−37

Abstract

4U 1822−37 is a low mass X‐ray binary (LMXB) system with an accretion disc corona. It is one of the very few LMXBs that shows narrow X‐ray eclipses and small amplitude pulsations of the neutron star. The X‐ray eclipse is an excellent reference for measurement of orbital evolution of the binary, and we have obtained 16 new mid‐eclipse time measurements of this source during the last 13 years using X‐ray observations made with the RXTE‐PCA, RXTE‐ASM, Swift‐XRT, XMM–Newton and Chandra observatories. These, along with the earlier known mid‐eclipse times have been used to accurately determine the time‐scale for a change in the orbital period of 4U 1822−37. We have derived an orbital period Porb= 0.23210887(15) d, which is changing at the rate of d d−1 (at T0= MJD 45614). The time‐scale for a change in the orbital period is of 4.9(1.1) × 106 yr. We also report the detection of 0.59290132(11) s (at T0= MJD 51975) X‐ray pulsations from the source with a long‐term average of −2.481(4) × 10−12 s s−1, i.e. a spin‐up time‐scale () of 7578(13) yr. In view of these results, we have discussed various mechanisms that could be responsible for the orbital evolution in this system. Assuming the extreme case of conservative mass transfer, we have found that the measured requires a large mass transfer rate of (4.2–5.2) × 10−8 M⊙ yr−1 which together with the spin‐up rate implies a magnetic field strength in the range of (1–3) × 108 G. Using the long‐term RXTE‐ASM light curve, we have found that the X‐ray intensity of the source has decreased over the last 13 yr by ∼40 per cent and there are long‐term fluctuations at time‐scales of about a year. In addition to the long‐term intensity variation, we have also observed significant variation in the intensity during the eclipse. Variation was also seen in the pulse profile, which could be due to changes in the accretion geometry. We briefly discuss the implications of these results on our understanding of the properties of the neutron star and the accretion geometry in this source.

X-ray spectroscopy of the ADC source X1822-371 withChandraandXMM-Newton

“…Iaria et al (2011) obtaineḋ P orb = 1.59(9) × 10 −10 s/s from the combined X-ray/optical/UV data set, consistent with the previous measurements. A similar value of the orbital period derivative (Ṗ orb = 1.3(3) × 10 −10 s/s) was independently obtained by Jain et al (2010) by analysing data in the X-ray band.…”

Search for pulsations in the LMXB EXO 0748–676

“…This is a well established technique and has been successfully used to determine the spin period and orbital parameters in various sources (Jain, Dutta & Paul, 2007;Jain, Paul & Dutta, 2010). The burst oscillations from EXO 0748-676 have been reported to be centered at 44.7±0.06 Hz (Villarreal & Strohmayer 2004).…”

The puzzling orbital period evolution of the LMXB AX J1745.6−2901

“…see discussion in Knigge et al 2011). Indeed, despite the large allowed range of model parameters (possibly translating into more than one order of magnitude on efficiency of angular momentum removal), magnetic breaking often fails to reproduce measured values of the orbital period derivative, at least in the case of conservative mass transfer (Di Salvo et al 2008;Hartman et al 2008;Hu et al 2008;Burderi et al 2010;Jain et al 2010;Gonzalez-Hernandez et al 2012;2014). Additional mechanisms, typically involving outflows, are generally necessary to explain these discrepancies (Di Salvo et al 2008;Hartman et al 2008;Burderi et al 2010).…”