Abstract for Proposal 088486

Using the newly discovered X-ra- IR Type-I bursts to probe jet-disk interaction

During AO 18 our team discovered the presence of two IR bursts lagging thermonuclear Type-I X-ray bursts: this allowed us to put the first constraints on the orbital period of the source 4U 1728-34. Moreover, the profiles of the newly discovered IR bursts showed intriguing 'dips' just after the onset of the X-ray bursts. The aim of this proposal is to use the novel method of X-ray-IR burst lag to measure the orbital period of 4U 1728-34 and two other sources, and to quantify the presence of 'dips' in their IR reverberation, signatures that would indicate burst-induced changes in the geometry of the accretion flow. We therefore ask to perform 4 (total 56ks) XMM pointings to be matched by 4 (total 14h) HAWK-I@VLT observations of 4U 1728-34, 4U 1705-44 and 4U 1636-53.



Details on Observing Strategy and Trigger Criteria
Reaction time needed >= 7 days (as required for joint XMM/VLT proposal) Triggers: 4U 1728-34: 1 Trigger when the source is the soft state (Swift BAT <0.01 count per second) 1 Trigger when the source is the hard state (Swift BAT >=0.01 count per second) 4U 1705-44: 1 Trigger when the source is the hard state(i.e. MAXI count rate < 0.5 count per sec) 4U 1636-53 1 Trigger when the source is the hard state(i.e. MAXI count rate < 0.4 count per sec)