Proposal number: 2036 PI last name: Jorstad Title: Mechanisms of X-Ray production in LSP and ISP blazars Abstract: The investigators propose to observe an X-ray flaring blazar of the low-synchrotron-peak (LSP) or intermediate-synchrotron-peak (ISP) type with the Imaging X-ray Polarimetry Explorer (IXPE) using a 900 ks exposure to measure linear polarization parameters. We propose also 20 ks and 14 ks observations with the NuSTAR and Swift telescopes simultaneously with the IXPE long-look. We will organize polarization observations at lower frequencies. The polarization measured by IXPE, combined with the simultaneous 0.3-70 keV continuum spectrum along with mm-wave and optical polarization, will provide a definitive test of the synchrotron self-Compton and external Compton models for X-ray emission from an LSP blazar or for the hard X-ray emission from an ISP blazar.
Proposal number: 2037 PI last name: Tagliacozzo Title: Constraining the coronal geometry in the Seyfert galaxy NGC 5506 with X-Ray polarimetry Abstract: We propose to observe the Seyfert NGC 5506 (one of the brightest sources not yet observed by IXPE) for 1 Ms (MDP = 2%-3%). The well known shape of the high energy spectrum and the physical properties of the corona appear to be rather extreme (Ec > 350 keV, kT ~ 400 keV). However, spectroscopy alone was not enough to distinguish between coronal models. X-ray polarimetry can remove the degeneracies, since polarization properties depend on the degree of symmetry of the system. IXPE observed three RQ AGN so far, but only one provided a > 3sigma detection. These observations indicate a hint of alignment between the primary continuum PA and the radio jet, favouring radially extended coronae. The observation of NGC 5506 could provide a further step in the understanding of AGN coronal properties.
Proposal number:: 2121 PI last name: Di Marco Title: Polarimetric study of the ultra-compact H-deficient system 4U 0614+091 Abstract: UCXBs are LMXBs with a short orbital period and H-deficient companions. X-ray polarimetric results for the UCXB 4U 1820-303 showed a peculiar behavior that, if confirmed to be common to other UCXBs, can be used as a signature for their identification. We propose to observe the brightest UCXB with a CO/ONeMg WD companion: 4U 0614+091. The reflection in this system is different compared to other LMXBs as a result of a different surrounding material. This new observation, combined with the spectral modeling of reflection, will give fundamental information to improve our understanding of accretion flow in H-deficient systems. Simultaneous observations at other wavelengths will allow for a comparison of the polarization in different bands, corresponding to different emission regions.
Proposal number: 2142 PI last name: Soffitta Title: Probing the accretion ejection-geometry of the hyper-Eddington black-hole binary SS 433 with X-Ray spectro-polarimetry Abstract: SS 433 is the only micro-quasar with hadronic persistent jets and, at variance with other binary systems, is characterized by a non-transient supercritical accretion of gas. SS433 is X-ray faint due to heavy absorption. Recent observations of highly obscured sources have shown reflection-dominated X-ray spectra thought to be the walls of wind outflow originating from the accretion disk to form a reflection cone. IXPE observation of SS 433 (500 ks) would for the first time unambiguously constrain its reflector geometry and nature (wind or thick disk). This would be the first X-ray polarization observation of the central engine of this exotic X-ray binary and it will help to probe the rare high Eddington accretion regime in galactic accreting sources and show its X-ray Ultra Luminous nature.
Proposal number: 2151 PI last name: Steiner Title: A test of disk-jet misalignment and black hole spin measurement for the X-Ray binary H1743-322 Abstract: The BH microquasar H1743-322 is uniquely poised to deliver key insights into questions on putative misalignment between the binary orbital and BH spin axes. H1743 is a propitious source with recurrent transient activity, a high expected PD (owing both to its high inclination and its predicted low spin), and is one of the strongest and most prolific sources of QPOs. The leading model of QPO production requires significant misalignment, but this prediction hasn't been readily testable. An IXPE campaign of 320ks divided between two observations of H1743, one in a hard state and the other in a soft/thermal state, will enable a direct constraint on potential misalignment, testing the QPO mechanism. Moreover, this campaign will also produce an orthogonal constraint on H1743's spin.
Proposal number: 2154 PI last name: Anitra Title: Exploring X-Ray polarization of the high-inclined low-mass X-Ray pulsar 4U 1822-37 Abstract: Recent advancements in polarimetric capabilities with IXPE have opened new opportunities to understand the geometry of X-ray pulsars (XRPs) in low-mass X-ray binaries (LMXBs). Among XRPs, 4U 1822 37 stands out for its peculiar geometrical configuration and remains one of the most puzzling sources despite numerous studies. The detected cyclotron resonance line, the high inclination angle, and the theorized presence of an extended optically thin corona make this source an ideal target for IXPE observation. We request the first IXPE observation of 4U 1822 37 with a total exposure of 500 ks to ensure a minimum detectable polarization of 2%. To achieve comprehensive spectral and temporal analysis, we also request joint NuSTAR (80 ks) and NICER (50 ks) observations.
Proposal number: 2156 PI last name: Bhargava Title: Identifying the geometry of weakly magnetized low mass x-ray binary Aql X-1 using joint IXPE, NICER and NuSTAR Abstract: Aquila X-1 is one of the most recurrent transient sources in the X-ray sky. It shows clear hysteresis during its spectral evolution. To investigate the longstanding question of the geometry of spectral components, we propose joint observations of the source during its next outburst using IXPE, NICER, and NuSTAR for a total exposure of 400 ks, 10 ks, and 40 ks respectively. The proposed observations will provide first-ever estimates of X-ray polarization in this source during the soft and hard states. The spectro-polarimetric study will provide crucial insights into the geometry of the corona and its orientation relative to the thermal component. Comparing the X-ray polarization estimates with radio polarization will yield strong constraints on the origin of non-thermal emission in Aql X-1.
Proposal number: 2184 PI last name: Ratheesh Title: Solving the mystery behind the X-Ray dimming of GRS 1915+105 using X-Ray polarimetry Abstract: GRS 1915+105 is currently in a noval obscured state, adding to the exotic variability it has exhibited in the past. The X-ray spectrum is heavily absorbed locally and dominated by reflection features. The primary source of this obscuration is believed to be a Compton-thick accretion disk wind. There is an ongoing debate about whether the source is undergoing super-Eddington accretion or if the accretion rate has decreased and the source transited into low hard state. X-ray Polarimetry, as an excellent tool for estimating the geometry of reflecting matter, could help resolve this by determining the opening angle of the wind and derive the intrinsic luminosity. Further, IXPE observations would also help to understand the nature of aperiodic X-ray flares in the source.
Proposal number: 2191 PI last name: Parra Title: A novel view of disk winds in outbursting black hole low-mass X-Ray binaries with X-Ray spectro-polarimetry Abstract: The first IXPE observations of wind emitting BHLMXBs showed that the wind is likely to play a pivotal role in the significant polarization of these sources. While the scattering of the incident flux in the outflowing material leads to a polarization signal, different launching mechanisms are expected to leave different imprints on the polarization measurements, and the results are also extremely dependent on the wind structure. New IXPE data of more high-inclined sources will be tremendously helpful to understand and disentangle the dependence of the wind and inclination angle on the polarization properties. We request an IXPE ToO observation of a high-inclined BHLMXB with wind detections, in the soft state, plus 15ks of NICER exposure, and 20ks of NuSTAR exposure, for spectral coverage.
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