Title: Simultaneous Broad Band, from Radio to Gamma-ray, Observations of Z sources: Are their Hard Tails

Title: Simultaneous Broad Band, from Radio to Gamma-ray, Observations of Z sources: Are their Hard Tails a Signature of Jets?

Proposal ID: 0120226
Subject category: Compact Object
Principal investigator: Di Salvo
Institute: University of Amsterdam

Abstract

We propose INTEGRAL observations of three selected Z sources with an exposure time of 300 ks for each source. These observations will be part of a campaign of coordinated multiwavelength observations in the radio, optical/IR, X-ray, and gamma-ray bands. This project is specifically aimed at studying the recently discovered hard power-law tails in luminous Z sources. A detailed study in the gamma band with good sensitivity instruments such as IBIS and SPI will address the question of the origin (thermal or non thermal) of these hard components. Moreover, these high-energy tails seem to be present (or more prominent) at low inferred accretion rate, i.e. at periods of maximum radio emission from these sources. This correlation between radio emission (probably due to Jets) and hard tails indicates Jets as the origin of hard components in luminous Z sources. Besides the already known correlation between inferred mass accretion rate (as defined by the position in the X-ray color-color diagram) and fast time variability, the simultaneous variation of the radio emission could reveal a new key parameter able to explain the observational properties of this kind of sources, affecting their emission from radio to gamma wavelengths.