The disc–jet coupling in the neutron star X-ray binary Aquila X-1

Abstract

We study the accretion/ejection processes (i.e. disc/jet coupling) in the neutron star X-ray binary Aquila X-1 via a multiwavelength approach. We use in the radio band the publicly available Very Large Array archive containing observations of the object between 1986 and 2005, in the X-ray band the archival Rossi X-ray Timing Explorer data (Proportional Counter Array and High Energy X-ray Timing Experiment) between 1997 and 2008, and in optical (R band) observations with the Small and Moderate Aperture Research Telescope System recorded between 1998 and 2007. In the combined data set, we find three outbursts for which quasi-simultaneous radio, optical (R band) and X-ray data exist and focus on them to some extent. We provide evidence that the disc/jet coupling in Aquila X-1 is similar to what has been observed in black hole X-ray binaries, at least from the point of view of the behaviour in the hardness-intensity diagrams (the hysteresis effect included), when the phenomenology of the jet is taken into account. Although based on a very small number of observations, a radio/Xray correlation seems to exist for this system, with a slope of α = 0.40 ± 0.07 (F radio ∝ F α X ), which is different than the slope of α = 1.40 ± 0.25 found for another atoll source, 4U 1728−34, but interestingly enough is relatively close to the values obtained for several black hole X-ray binaries. No significant correlation is found between the radio and optical (R-band) emissions. We also report a significant drop in the radio flux from Aquila X-1 above an X-ray flux of ∼5 × 10 −9 erg cm −2 s −1 . This behaviour, also reported in the neutron star X-ray binary 4U 1728−34, may be analogous to the suppression of radio emission in black hole X-ray binaries in bright, soft X-ray states. It suggests that from this point of view neutron star X-ray binaries can mimic the behaviour of black hole X-ray binaries in suppressing the jet in soft/disc-dominated X-ray states.

Investigating accretion disk – radio jet coupling across the stellar mass scale

“…While full details of the observations and analysis may be found in Miller-Jones et al (2010), we summarize the most salient points here. While hysteresis in the HID of Aql X-1 is well known (Maitra & Bailyn 2004), there have been few previously-reported radio detections (Tudose et al 2009). Our monitoring campaign provided the most complete radio coverage to date of an entire outburst of Aql X-1, finding the radio emission to be consistent with being activated by transitions from a hard spectral state to a soft state, and also by the reverse transition, just as seen in BH systems.…”

Relevance of jet emitting disc physics to microquasars: application to Cygnus X-1

“…Kording et al 2006;Kording et al 2008;Tudose et al 2009), argues for an ejection process that is also independent of the central object. This seems to be confirmed by the lack of correlation between jet power or jet velocities and measured values of black hole spins (Fender et al 2010).…”

Accretion-outflow connection in the outliers of the “universal” radio/X-ray correlation

“…To locate H 1743−322 with regards to the universal radio/X-ray correlation of black holes and neutron stars X-ray binaries, we also plot on Fig. 1 the data from the black holes GX 339-4 (Corbel et al, in prep), V404 Cyg (Gallo et al 2003;Corbel et al 2008), Swift J1753.5-0127 (Soleri et al 2010) and GRO J1655-40 and from the neutron stars Aql X-1 (Tudose et al 2009;Miller-Jones et al 2010) and 4U 1728-34 (Migliari & Fender 2006). Fig.…”