Proposal Details - 0920024
Hard X-ray study of the ultra-compact X-ray binary 4U 0614+091 (Chenevez)

Proposal Abstract

A dedicated INTEGRAL monitoring program of 4U 0614+091 is proposed, to study its emission properties in hard X-rays. This source is situated in a region of the sky well outside the Galactic bulge and is thus one of the low-mass X-ray binaries being least observed by INTEGRAL. However, 4U 0614+091 is an interesting target for several reasons: not only it does harbour the closest active neutron star X-ray binary, it is also an ultra-compact system and a micro-quasar, thus exhibiting variations at very different time scales and over the whole electro-magnetic spectrum, such as synchrotron jet emission, X-ray flaring states, and thermonuclear X-ray bursts. Moreover, the high-energy persistent emission from the source is characterised by a particularly hard (non thermal) X-ray tail. Therefore, the INTEGRAL instrumentation is exploited, to survey the dynamical behaviour of the source, and better describe its spectrum in hard X-rays. The monitoring observations (for a total of 500 ks exposure) will make it possible to follow the evolution of the long-term persistent-emission variability, as well as to investigate the activity of shorter time scale processes. In fact, 4U 0614+091 is also known for having exhibited usual short X-ray bursts, an hours-long superburst, and intermediately-long bursts with super expansion of the neutron star's photosphere. The proposed observing strategy will for instance allow to relate the bursting behaviour of the source to its broadband emission, and especially to its flaring activity on time scales of days to weeks.

Observation Strategy (Recommended by TAC)

Total of 500 ks using the standard HEX pattern, centered on RA, Dec = 94.280, 9.137 (l, b = 200.877, -3.364), to be split into ten 50.4 ks observations (4 HEX each with exposure time of 1800 s per pointing) approximately regularly distributed along the visibility periods in 2012 (February - April and August - October). Two of these observations will be accompanied by contemporaneous 10 ks XMM-Newton observations (i.e., a total of 20 ks of XMM-Newton observing time).

Proposal grade: C

Data Rights (Recommended by TAC)

The TAC granted data rights for 4U 0614+091

Exposure Map

The exposure maps are in galactic coordinates using the Aitoff projection and units of seconds, and the colour scale is indicated at the bottom. The green lines provide the 100, 300 and 500 ksec contour.