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Cycle 2 Accepted IXPE GO Program Abstracts

Proposal Number: 2003
Proposal Type: REGULAR
PI Name: FREDERIC MARIN
Title: SEMPER PUGNANTI: TOWARDS A CORONA POLARIZATION MEASUREMENT IN MCG-05-23-16
Abstract: MCG-05-23-16 is a nearby Seyfert-1.9 galaxy with bright, stable X-ray emission, making it ideal for detailed X-ray polarimetric studies. Previous IXPE observations revealed only an upper limit on polarization, highlighting a critical tension between optical/infrared and X-ray data regarding the AGN s inclination and corona geometry. This proposal seeks an additional 510 ks of IXPE observation, a relatively small and cost-effective request compared to other Seyfert observations. Adding this new data to the previous observations will achieve an unprecedented Minimum Detectable Polarization of 1.68%. This study aims to finally determine the geometry of the X-ray corona and provide an independent measurement to the AGN orientation.

Proposal Number: 2006
Proposal Type: REGULAR
PI Name: LAURA DI GESU
Title: ACCELERATING PARTICLES TO THE EXTREME: IXPE OBSERVATIONS OF FLARES OF TEV BLAZARS
Abstract: The origin of major flaring activity in high-energy peaked BL Lac objects (HBL) is still an open question. The X-ray polarization offers a unique view of the particle acceleration process in astrophysical jets, yet, thus far, it has been exploited only for the case of HBL in the average state. We propose IXPE observations of HBLs during TeV flares. We will discriminate among particle acceleration processes during the flare, constrain the energy/particle distribution, and probe the connection between flaring activity and X-ray polarization angle rotation. These observations will provide us with unprecedented insight into the inner physics of jets in an extreme regime that is still completely unexplored by IXPE.

Proposal Number: 2013
Proposal Type: REGULAR
PI Name: ROGER ROMANI
Title: A POLARIZATION PROBE OF THE CRAB PULSAR'S GEOMETRY
Abstract: Pulsars' high energy emission has long defied localization; polarization's sensitivity to the projected magnetic field is a key tool in this quest. While the Crab pulsar optical polarization has been well measured for decades, models have limited success in matching the sweeps. X-rays emit closer to the acceleration site with less de-polarization; initial IXPE Crab observations found several high polarization phase bins, differing substantially from the optical. Existing phase-resolved measurements are count-limited; deeper exposure is needed to really map the sweeps. We propose additional exposure to quadruple the Crab's IXPE S/N. Careful analysis of these data will reveal details of the polarization that could unlock the mysteries of the high energy emission zone.

Proposal Number: 2014
Proposal Type: REGULAR
PI Name: ROGER ROMANI
Title: A POLARIZED BEAM FROM THE LIGHTHOUSE
Abstract: IXPE finds high polarization in the X-ray synchrotron nebula of energetic pulsars. These pulsar wind nebulae are either embedded in a parent supernova remnant or bounded by a bow shock as the pulsar moves super-sonically through the ISM, leaving a synchrotron trail. A handful of bow shock pulsars show additional linear X-ray nebulae at large angle to the pulsar proper motion, known as pulsar filaments or misaligned outflows. We propose an observation of the brightest pulsar filament, the PSR J1101 6101 Lighthouse nebula. A sensitive observation opens a new IXPE source class, measuring the filament polarization to reveal the magnetic field orientation and uniformity. It can also measure the bow shock PWN's polarization and may detected polarization from the pulsar itself.

Proposal Number: 2017
Proposal Type: REGULAR
PI Name: KARRI KOLJONEN
Title: IS MICROQUASAR GRS 1915+105 CURRENTLY IN A SUPER-EDDINGTON ACCRETION STATE?
Abstract: We propose an IXPE observation of GRS 1915+105 during its unusual obscured accretion state. Currently, GRS 1915+105 exhibits strong radio flaring and shares X-ray spectral properties similar to other X-ray binaries experiencing super-Eddington accretion rates (such as V404 Cyg, Cyg X-3, V4641 Sgr). These similarities strongly suggest super-Eddington accretion in GRS 1915+105, offering a rare opportunity to study this high accretion rate phase in detail. The potential detection of a high polarization degree would signify that the received emission is seen as scattered, in accordance with super-Eddington accretion. This discovery could hold profound implications for our understanding of black hole accretion processes and their impact on the surrounding environment.

Proposal Number: 2022
Proposal Type: REGULAR
PI Name: PHILIP KAARET
Title: X-RAY POLARIZATION OF THE WESTERN LOBE OF SS 433
Abstract: How astrophysical systems translate the kinetic energy of bulk motion into the acceleration of particles to very high energies is a pressing question. SS 433 is a microquasar that emits bipolar jets. The X-ray synchrotron emission from the acceleration region in the eastern lobe is highly polarized indicating that the magnetic field is parallel to the jet and mostly uniform. Recent observations have revealed an acceleration region in the western lobe. The western lobe is much more compact, suggesting differences in jet collimation. We propose an IXPE observation to determine the direction and uniformity of the magnetic field. Comparison of the two lobes will help advance our understanding the magnetic field geometry in particle acceleration regions in astrophysical jets.

Proposal Number: 2030
Proposal Type: REGULAR
PI Name: ALEXANDER SALGANIK
Title: THE FIRST POLARIMETRIC STUDY OF THE SYMBIOTIC X-RAY BINARY: GX 1+4
Abstract: We propose the first polarimetric study of the symbiotic X-ray binary GX 1+4 using IXPE. GX 1+4 is a unique symbiotic system with a neutron star (NS) accreting from the dense wind of an M6III red giant companion. The long 1160-day orbital period, symbiotic nature, and distinct accretion characteristics of the NS make it an ideal candidate for investigating the geometry of the accretion-powered pulsar. Through a 400 ks IXPE observation we aim to measure the polarization degree and angle with high precision, perform phase-resolved spectro-polarimetric analysis, and derive the geometric configuration of the pulsar. These observations will contribute significantly to our understanding of the physics of X-ray pulsars and the broader population of magnetized NSs.

Proposal Number: 2034
Proposal Type: THEORY
PI Name: HAOCHENG ZHANG
Title: BRIDGE THE GAP: A UNIFIED MODEL OF RADIO TO X-RAY POLARIZATION WITH LARGE-SCALE JET DYNAMICS AND LOCAL BLAZAR FLARING RE
Abstract: Together with radio polarimetry, IXPE provides the unique opportunity to study the HSP blazar magnetic field evolution in both the large-scale jet dynamics and flaring regions. We propose to simulate the multi-wavelength flux and polarization variations under a unified physical paradigm using combined MHD and polarized radiation transfer simulations. We will address three questions: Q1. What is the ratio between average radio, optical, and X-ray polarization degree? Q2. Is there a preferred orientation for HSP X-ray polarization angle? Q3. Is there any physical correlation between radio, optical, and X-ray flux and polarization? The proposed studies will great enhance the scientific return of IXPE and motivate multi-wavelength polarization studies of blazars using IXPE for years to come.

Proposal Number: 2036
Proposal Type: REGULAR
PI Name: SVETLANA 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
Proposal Type: REGULAR
PI Name: DANIELE 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: 2041
Proposal Type: REGULAR
PI Name: SERGEY TSYGANKOV
Title: EVOLVING ACCRETION GEOMETRY IN TRANSIENT X-RAY PULSARS
Abstract: Launch of IXPE opened a new era in studies of magnetized NSs and allowed to determine basic geometry parameters for several XRPs and magnetars. The activity of transient X-ray sky did not allow, however, to observe up to now any truly extreme XRP, i.e. one accreting at super-critical luminosities exceeding ~5x10^37 erg/s when the geometry of emission region is expected to change dramatically with the onset of an accretion column. Observing such a source would allow to test the theory behind the formation of the accretion columns, and thus refine models describing interaction of matter with extreme magnetic and radiation fields. The proposed program aims to address this shortcoming and will contribute to the understanding of XRPs in general and the legacy of the IXPE mission.

Proposal Number: 2067
Proposal Type: REGULAR
PI Name: RICCARDO MIDDEI
Title: THE GOLDEN YEAR TO OBSERVE PG 1553+113 WITH IXPE, X-RAY POLARIMETRY IN THE EPOCH OF THE GAMMA-RAY FLARE
Abstract: The gamma-ray high-energy BL Lac object PG 1553+113 is a particularly special target for IXPE, especially during the next IXPE observing year. This source is, in fact, known to for a long-term quasi-periodic oscillation (QPO) activity in the gamma-rays with an approximate period of 2.2 years. The forthcoming gamma-ray flare is expected to happen around July 2025 the 20th, for the first time during the IXPE visibility window. Thus, we propose 3*120 ks long IXPE observations (total 360 ks) of PG 1553+113. In particular, we aim at tracking the X-ray polarization properties of the source during and after the gamma-ray flare, this providing unique pieces of information on how particles are arranged (co-spaciality/segregation) and accelerated in the jet of PG 1553+113.

Proposal Number: 2081
Proposal Type: REGULAR
PI Name: ANTONELLA TARANA
Title: WEAKLY MAGNETIZED NEUTRON-STAR X-RAY BINARIES IN THE HARD STATE: THE CHALLENGING CASE OF 4U 1812-12
Abstract: The Imaging X-ray Polarimetry Explorer (IXPE) is providing first X-ray polarimetric information on weakly magnetized neutron stars, trying to asses nature and geometry of the X-ray corona and its relation to the accretion flow near neutron stars. Up to now, no hard spectral state has been observed. We propose to observe the burster 4U 1812-12 for a total of 650 ks, with the goal of obtaining results from both its steady persistent hard spectral emission and its burst emission.

Proposal Number: 2090
Proposal Type: THEORY
PI Name: HAOCHENG ZHANG
Title: SHOCK OR RECONNECTION: WHAT DRIVES HSP BLAZAR FLARES?
Abstract: We propose to use a new numerical approach that combines to magnetohydrodynamics and stochastic diffusion equation simulations to consistently model fluid dynamics and particle acceleration and transport consistently on realistic blazar parameters and scales. We will address three main questions for shock and reconnection: Q1. What are the X-ray polarization angle swing amplitude and rotation rate? Q2. What are the characteristic X-ray polarization degree distribution and polarized flux variation amplitude and duration? Q3. Are the optical and X-ray flux and/or polarization variations correlated, in particular, are there delayed and/or orphan optical/X-ray polarization angle swings? Our proposal will settle the debate on particle acceleration mechanism by comparing with IXPE observations.

Proposal Number: 2093
Proposal Type: REGULAR
PI Name: THOMAS MACCARONE
Title: TESTING DISK WIND FORMATION MODELS WITH UW CRB'S POLARIZATION
Abstract: Despite its short orbital period, the accretion disk corona source UW CrB shows clear evidence for disk winds. The standard thermal launching model predicts that winds should be weak or absent in such short period systems. Recent analysis shows that this wind is likely to be strongly asymmetric, generated only from the outer part of the eccentric, precessing accretion disk. If this is the case, then the X-ray polarization of UW CrB should be significantly stronger than that in other accretion disk corona sources, because the direction of scattering will be closer to constant. We propose testing this with IXPE observations. If the polarization is, indeed, higher than typical for ADC sources, it will indicate that thermal disk launching is possible even in short period systems.

Proposal Number: 2094
Proposal Type: THEORY
PI Name: MATTHEW BARING
Title: X-RAY POLARIZATION SIGNALS FROM EXTENDED MAGNETAR SURFACES
Abstract: Magnetars, the most magnetic neutron stars, provide a cosmic testbed for the QED physics of vacuum birefringence. IXPE has delivered important X-ray polarization results for surface emission below 5 keV from 4 magnetars. This project will hone an existing radiative transfer code for neutron star atmospheres to deliver state-of-the art models of X-ray anisotropy and polarization from extended magnetar surface regions. It will precisely treat the vacuum resonance resulting from the competition between plasma and vacuum birefringence, and include vacuum birefringent propagation of light through the magnetosphere. Energy-dependent IXPE pulse profiles of intensity and polarization will help constrain the locale of surface hotspots and the level of toroidal twist of the global magnetic field.

Proposal Number: 2095
Proposal Type: REGULAR
PI Name: DHEERAJ PASHAM
Title: IXPE OBSERVATIONS OF THE NEWLY FORMED X-RAY CORONA IN THE CHANGING LOOK AGN 1ES1927+654/ASASSN-18EL
Abstract: The geometry of X-ray coronae of Active Galactic Nuclei (AGN) has been a long-standing puzzle in high-energy astrophysics. Recent IXPE observations of three radio-quiet AGN have demonstrated the power of X-ray polarization to differentiate between various geometries. Here, we propose a 800 ks exposure of an extraordinary AGN 1ES1927+654/ASASSN-18el that has formed an X-ray corona very recently, in the past few years. Our aim is to measure/constrain the X-ray polarization, compare the results with simulations to differentiate between various models and understand the structure of the newly formed coronae. 1ES1927+654/ASASSN-18el is the only system with a newly formed X-ray corona that is also bright enough to be observable with IXPE.

Proposal Number: 2098
Proposal Type: REGULAR
PI Name: JAMES STEINER
Title: FIRST POLARIMETRIC LOOK INTO THE HEARTBEAT STATE OF ACCRETING BLACK HOLES WITH 4U 1630-47
Abstract: The high sensitivity of polarimetry to disk structure and corona geometry makes it the key to a more complete understanding of the disk-corona changes in different spectral and timing states. The "heartbeat" state, in which the data shows highly structured variability, is a window to look into the disk-corona geometry and changes. We aim to conduct a first polarimetric observation of the heartbeat state to gain new insights into the driving factors behind this phenomenon, via a 300ks IXPE observation of the source 4U 1630-47, supplemented by daily NICER monitoring.

Proposal Number: 2102
Proposal Type: REGULAR
PI Name: HONGHUI LIU
Title: EXPLORING THE SUPER-EDDINGTON REGIME OF SWIFT J0243.6+6124 WITH IXPE
Abstract: We propose to observe Swift J0243.6+6124 in its super-Eddington/ULX state with IXPE. We request three observations, each with a net exposure of 100 ks, to be taken simultaneously with our already accepted NuSTAR, Insight-HXMT, and NICER observations. These observations will be crucial for understanding the accretion geometry of X-ray pulsars.

Proposal Number: 2103
Proposal Type: REGULAR
PI Name: JOSEPHINE WONG
Title: PROBING X-RAY POLARIZATION OF KES 75 (G29.7-0.3)'S WIND NEBULA POWERED BY MAGNETAR-LIKE PSR J1846-0258
Abstract: SNR Kes 75 hosts a dynamic wind nebula powered by a young PSR J1846-0258 that evolves energetically like a rotation-powered pulsar but occasionally undergoes magnetar-like bursts. Only a radio PWN PD = 10% measurement exists. With a 1Ms observation, we have MDP99 = 4.85% in the quiescent state and can expect a detection of the integrated PWN. Using a more sensitive technique to separate the pulsar and the nebula components, we can detect polarization in both with careful binning. Augmented with a 2021 eVLA observation, a 1Ms IXPE observation of Kes 75's PWN complex can have great scientific return, helping us to investigate the connection between magnetars and rotation-powered pulsars and build our growing database of PWN X-ray polarization measurements to constrain emission models.

Proposal Number: 2107
Proposal Type: THEORY
PI Name: HUI LI
Title: PROBING THE MAGNETIC FLUX AND PARTICLE ACCELERATION IN THE EASTERN LOBE OF SS 433
Abstract: The IXPE observation of SS433 opens a new window to study the evolution of jet s magnetic fields and the associated particle acceleration. We proposed to carry out high-resolution global 3D MHD jet simulations to study the kink instability along with the particle acceleration in kink-produced magnetic turbulence. Specifically, we will address: Q1. What physical processes led to large-scale coherent B fields parallel to jet? Q2. What are the particle acceleration processes operating in this region? Q3. What are the key model features for future SS433 IXPE observations and other galactic jet sources? The proposed studies will significantly enhance the scientific return of IXPE and motivate future studies of galactic jets using IXPE.

Proposal Number: 2111
Proposal Type: REGULAR
PI Name: FABIO LA MONACA
Title: PROBING THE ORBITAL POLARIMETRIC VARIABILITY OF THE YOUNG AND POTENTIALLY TILTED NEUTRON STAR CIR X-1
Abstract: Cir X-1 is a weakly magnetized NS-XRB system characterized by an eccentric 16.5 d orbit, during which its flux and spectrum change significantly, very different from any other known XRBs. Those X-ray flux variations are due to orbital variations in the mass accretion rate. Previous IXPE measurements observed a rotation of the PA in different phases along the orbit. As Cir X-1 is among the few NS-XRBs that show both radio and X-ray jets, it is possible to compare the PA with their directions. The measured PA is not consistent with the radio jet position, and neither can the variations be explained by a precession model. Thus, we want to monitor these PA variations along the orbit to relate them to the accreting mass changes aiming to resolve the puzzle of the observed PA rotation.

Proposal Number: 2114
Proposal Type: REGULAR
PI Name: RICCARDO FERRAZZOLI
Title: ONE OF A KIND: X-RAY POLARIMETRY OF RX J1713.7-3946 SOUTHWESTERN RIM
Abstract: We propose an IXPE observation of the southwestern rim of the supernova remnant (SNR) RX J1713.7-3946 to test models suggesting that magnetic field direction and polarization degree (PD) are influenced by shock velocity and ambient density. This target is ideal due to its interaction with a dense molecular cloud and varying shock velocities. We anticipate observing a tangential magnetic field, similar to the previously observed northwest, but a lower PD. This study will enhance our understanding of magnetic turbulence in young SNRs and provide insights into cosmic ray acceleration processes. We request 1 Ms of IXPE observation time to achieve these objectives, ensuring spatial resolution and sensitivity to detect and analyze polarization variations across the SW rim.

Proposal Number: 2121
Proposal Type: REGULAR
PI Name: ALESSANDRO 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: 2138
Proposal Type: REGULAR
PI Name: ALESSANDRO PAPITTO
Title: POLARIZED X-RAYS FROM ACCRETING MILLISECOND PULSARS: A PATHWAY TO THE EQUATION OF STATE OF NEUTRON STARS
Abstract: Modelling the waveform of the X-ray pulse of accreting ms pulsars (AMSP) to constrain the equation of state of neutron stars requires an extremely high number of counts to break the degeneracy between the many parameters that shape it. IXPE observations of an AMSP recently discovered polarized X-ray emission at a degree of ~2% but could not detect spin phase-resolved variability. Here, we propose a longer 900 ks-long ToO observation of the next outburst of an AMSP to constrain the binary inclination and the spot latitude to within a few degrees. This information will serve as a key prior to fit the waveform observed by instruments with a larger effective area (e.g. NICER, XMM-Newton) and constrain the mass and the radius of these neutron stars with an accuracy of a few per cent.

Proposal Number: 2142
Proposal Type: REGULAR
PI Name: PAOLO 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: 2147
Proposal Type: REGULAR
PI Name: ALESSANDRO DI MARCO
Title: STUDYING THE ACCRETION DISK CORONA GEOMETRY IN THE DIPPING SOURCE GX 13+1
Abstract: Accreting weakly magnetized NSs in LMXBs exhibit remarkable physical phenomenology with X-ray emission originating near the NS from the accretion inflow in the inner disk region, where boundary/spreading layers (BL/SL) are expected. An optically thin accretion disk corona (ADC) extending above the disk can also be present, but its nature and geometry are not yet fully understood. Observations report hints for it in some highly inclined dipping sources. We propose to observe GX 13+1 during its 24.5 d periodic dip, when the central region is obscured. This observation allows us to study the accretion geometry at different stages of the dip (ingress, dip, egress) and correlate the observation of different emission regions (BL/SL vs ADC) with the rotation of the polarization angle.

Proposal Number: 2151
Proposal Type: REGULAR
PI Name: JAMES 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: 2152
Proposal Type: REGULAR
PI Name: SUDIP CHAKRABORTY
Title: DECIPHERING THE COMPTONIZATION PROPERTIES OF LOW-LUMINOSITY AGN THROUGH X-RAY POLARIMETRY
Abstract: Through their place in the universality of Comptonization processes in tau-kTe space, Low-Luminosity Active Galactic Nuclei (LLAGN) are key to the puzzle of non-thermal emission from accreting black holes. However, to decipher the exact nature of the Comptonizing 'corona', its geometry and emission mechanism have to be understood beyond the limits of spectro-timing techniques. To break the degeneracies related to coronae, we propose upto 1.4 Ms IXPE polarimetry observations in the relatively pristine 2-8 keV band for upto 2 carefully selected Compton-thin LLAGN (NGC 2110 600ks, NGC 3227 800ks) using IXPE. The detected polarization degree and angle will help answer our two central questions: the exact geometry of the corona, and the contrast in coronal properties between brighter and LLAGN.

Proposal Number: 2153
Proposal Type: REGULAR
PI Name: MANEL ERRANDO
Title: IXPE OBSERVATIONS OF THE NEXT OUTBURST OF THE NAKED-EYE RECURRENT NOVA T CORONA BOREALIS
Abstract: T Corona Borealis, a recurrent nova, is set to experience a thermonuclear ignition event before 2026. During its last nova event in 1946, it reached a visible magnitude of 3.0, becoming visible to the naked eye. The X-ray flux is expected to peak above 1E-9 erg cm-2 s-1 in the IXPE band. We propose an observation campaign of T CrB with IXPE to cover the initial and late stages of the nova event evolution. This strategy aims to provide X-ray polarization measurements with MDP_99 of ~3%. It will enable us to capture the initial shock interactions of the nova ejecta with the red giant donor, along with the transition to the characteristic thermal emission of the late super-soft state.

Proposal Number: 2154
Proposal Type: REGULAR
PI Name: ALESSIO 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
Proposal Type: REGULAR
PI Name: YASH 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: 2157
Proposal Type: REGULAR
PI Name: KAITO NINOYU
Title: ACHIEVING NEW POLARIZATION PROPERTIES OF HMXBS WITH STRONG STELLAR WIND ON 4U 1700-377
Abstract: We propose 150 ks observations of 4U 1700-377 to study the physics of stellar wind and mass accretion in high mass X-ray Binary (HMXB) probed by polarized light. 4U 1700-377 is one of the most famous HMXBs and has not been observed with IXPE before. This object is unique in that it has an eclipse period and is relatively bright, allowing us to observe polarized X-rays scattered by the stellar wind. We plan to systematically investigate the physical structure of the stellar wind and the polarization properties of HMXB by observing one cycle of the orbital phase of 4U 1700-377 with IXPE.

Proposal Number: 2158
Proposal Type: LARGE
PI Name: STEVEN EHLERT
Title: IN SEARCH OF UNIQUE POLARIZATION SIGNALS IN THE PERSEUS CLUSTER
Abstract: We propose a deep (2.5 Ms) observation of the Perseus Cluster to test the X-ray polarization predictions at three sites. A ~ 5% polarization signal is predicted at distances of 100 kpc away from the central galaxy NGC 1275 at the 6.7 keV Fe XXV K-alpha emission line due to resonant scattering. Axion-like particles, a theorized but yet-undetected extension of the Standard Model, are predicted to induce large, energy dependent X-ray polarization signals throughout the ICM. Finally, the central galaxy NGC 1275 has been recently observed to a have high sub-mm polarization of 17%. We will be able to detect X-ray polarization of NGC 1275 down to below 3%, allowing a unique opportunity to investigate the seed photons that are Compton scattered into the observed X-ray emission.

Proposal Number: 2162
Proposal Type: REGULAR
PI Name: SAYANTAN BHATTACHARYA
Title: JOINT OBSERVATION OF EXO 0748 676 WITH IXPE, NUSTAR, AND NICER AFTER ITS RE-EMERGENCE FROM 16 YEARS OF QUIESCENCE
Abstract: We propose the first-ever X-ray polarization measurements for EXO 0748 676 using 260 ks of IXPE observation. This NS-LMXB, recently back from quiescence after 16 years, will be one of the few high inclination (75-82 deg) sources ever observed for polarization. It provides an edge-on view through the material surrounding the accretion disk, allowing us to study polarization across various features of its light curve pre-burst, post-burst, dip, and non-dip. Simultaneous NICER (10 ks) and NuSTAR (20 ks) observations will constrain the spectral shape (0.2 79 keV) and support precise timing analysis. This study aligns with IXPE's science goals and will enhance our understanding of polarization mechanisms in NS-LMXBs.

Proposal Number: 2176
Proposal Type: REGULAR
PI Name: QI FENG
Title: SEARCHING FOR NEUTRINO-EMITTING BLAZARS WITH X-RAY POLARIZATION MEASUREMENTS
Abstract: We propose 200 ks of high-risk high-reward IXPE ToO observations of a blazar in spatial coincidence with an IceCube neutrino event. The trigger criteria (a 2-10 keV flux >10^-11 erg s^-1 cm^-2 and a power-law index <=2) ensure an MDP99 of ~15%. These observations will strongly constrain the nature of the blazar emission and potentially disentangle the degeneracy between leptonic and hadronic models. If a high polarization degree (~20%) and a hard X-ray spectrum were detected, it would be a smoking gun for the hadronic origin of the X-ray emission and a neutrino-emitting blazar. If a lower value or an upper limit of the PD was measured, it would still constrain the relative contributions between leptonic and lepto-hadronic components and the detailed emission mechanisms in the blazar.

Proposal Number: 2184
Proposal Type: REGULAR
PI Name: AJAY 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: 2186
Proposal Type: REGULAR
PI Name: ROMANA MIKUSINCOVA
Title: THE FIRST X-RAY POLARIZATION MEASUREMENT OF THE POLAR-SCATTERED SEYFERT 1 GALAXY FAIRALL 51
Abstract: We propose a 1 Ms observation of the polar-scattered Seyfert 1 (S1) galaxy Fairall 51 accompanied by a NICER campaign consisting of 30 2-ks snapshots. The source has one of the highest optical polarizations among S1 galaxies ever observed. We aim to conduct the first ever measurement of its X-ray polarization and to study its connection to the optical/UV wavebands. Through this relation, we can draw estimates on the geometry of the torus and absorbers in the vicinity of the source. A simultaneous NICER observation will be beneficial to conduct a spectro-polarimetric analysis with the presence of complex absorption and scattering component. This will help us better understand the geometry and processes in polar-scattered S1 objects, which is crucial in enhancing our understanding of AGN.

Proposal Number: 2189
Proposal Type: REGULAR
PI Name: DHEERAJ PASHAM
Title: IXPE TOO OBSERVATIONS OF A NEWLY LAUNCHED HIGHLY RELATIVISTIC JET BY A COSMOLOGICAL BLACK HOLE AFTER IT DISRUPTS A STAR
Abstract: Relativistic jets launched by a subset of stellar Tidal Disruption Events (TDEs) offer a rare opportunity to probe the fundamental physics driving these powerful jets as they emerge. A key unresolved question in the study of relativistic TDEs is the origin of their X-ray emission. Two mechanisms have been proposed: synchrotron radiation and synchrotron self-Compton scattering. While multi-wavelength photometry helps model jet properties, it cannot distinguish between these two processes. X-ray polarization, however, provides a clear pathway to resolve this ambiguity. We propose a 150 ks IXPE ToO observation of a future relativistic TDE which will provide crucial insights into the mechanisms of X-ray production in jetted TDEs, advancing our understanding of these extraordinary cosmic events

Proposal Number: 2190
Proposal Type: REGULAR
PI Name: OLIVIER HERVET
Title: EVOLUTION OF X-RAY POLARIZATION AFTER STRONG FLARES: TESTING THE SCENARIO OF SUCCESSIVE RECOLLIMATION SHOCKS IN MRK 421
Abstract: We aim to probe the X-ray polarization of Mrk 421 for 15 days after a strong outburst. Based on a previous X-ray study of Mrk 421, we expect to see secondary flares attesting to the propagation of a perturbation through stationary recollimation shocks. From IXPE polarization evolution after a strong flare, helped with simultaneous low-frequency polarization data and multiwavelength (MWL) facilities such as Swift, Fermi-LAT, and VERITAS, we will deeply test this scenario. Any secondary flare observed, even if not directly linked to the recollimation shock scenario, will benefit from this simultaneous MWL coverage and provide unprecedented material to characterize blazars' variability. We expect a trigger rate of ~1/year.

Proposal Number: 2191
Proposal Type: REGULAR
PI Name: MAXIME 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.

Proposal Number: 2195
Proposal Type: THEORY
PI Name: NICOLA OMODEI
Title: ADVANCING IXPEOBSSIM: ENHANCING SIMULATION & ANALYSIS FOR IXPE
Abstract: ixpeobssim is an open-source framework tailored for the Imaging X-ray Polarimetry Explorer (IXPE), enabling realistic simulations and comprehensive data analysis. Released in September 2022, it has been widely adopted by the IXPE community, with thousands of installations and usage in numerous publications. The package has been crucial for IXPE sensitivity studies and in supporting the General Observer program. This proposal seeks to advance ixpeobssim by enhancing simulation accuracy and analysis quality. Our objectives include maintaining user support, leveraging the HEASARC calibration database to improve the current PSF model, and implementing libraries to evaluate and correct polarization leakage, particularly relevant for extended sources.

Proposal Number: 2211
Proposal Type: REGULAR
PI Name: SUDIP CHAKRABORTY
Title: FACE-OFF WITH A FACE-ON SYSTEM: POLARIMETRIC DIAGNOSTIC OF THE PERSISTING LOW-INCLINATION LMXB AT2019WEY
Abstract: AT 2019wey is low mass black hole binary in outburst since 2019. The peculiar property of the source is that it has been consistently in the hard state with occasional transition to intermediate and high soft states. IXPE has proven its capabilities in deciphering the Coronal geometry of black hole binaries and AGNs. However, the parameter space of low viewing angle of the Corona was never explored before. The persistent nature of this source gives us an opportunity to observe this source in the IXPE GO2 to fill this gap and broaden our understanding of the comptonizing Corona.

Proposal Number: 2215
Proposal Type: THEORY
PI Name: RAZIEH EMAMI
Title: POLARIMETRIC SIGNATURES OF CHANGING LOOK AGN
Abstract: We investigate the primary role of changes in the accretion rate, as a key driver in the recently discovered set of changing look AGN systems where the driving mechanism responsible for their rapid flux variabilities remains inclusive. We employ cutting-edge, first-principle developments in 2-temperature, radiation-inclusive General Relativistic Magnetohydrodynamics (GRMHD) simulations of H-AMR model, where electron and ion temperatures are decoupled. We will make mock polarized images and compute the polarization degree and polarization angle for a handful of different GRMHD simulations with different BH mass and spin, spanning a wide range of accretion rates in each. We present this novel tool to community to make a comprehensive first principle comparison with the ongoing IXPE results.

Proposal Number: 2219
Proposal Type: REGULAR
PI Name: GEORGE YOUNES
Title: POLARIZATION PROPERTIES OF THE PERSISTENT X-RAY EMISSION FROM THE RADIO-LOUD MAGNETAR 1E 1547.0-5408
Abstract: Due to their immense surface magnetic-field strength, magnetars soft X-ray emission should exhibit high polarization signatures, with strong phase- and energy-dependent variations. This was recently confirmed with IXPE observations of several magnetars, establishing their detailed spectro-polarimetric properties and constraining several key physical elements that are unattainable otherwise. Here, we propose a 1 Ms observation of the radio-loud magnetar 1E 1547.0-5048 to establish its surface composition, gaseous atmosphere or condensed matter, constrain its geometry, search for signatures of high-B QED effects, and compare to the rest of the IXPE-observed sample.

Proposal Number: 2224
Proposal Type: THEORY
PI Name: YAJIE YUAN
Title: X-RAY POLARIZATION OF KINK-UNSTABLE JETS FROM FIRST-PRINCIPLES SIMULATIONS
Abstract: The mechanism behind nonthermal particle acceleration in blazar jets remains a mystery. Recent IXPE observations of blazars have provided unprecedented X-ray polarization data, offering new insights into the physical conditions within the emitting regions of these jets. This opens a critical opportunity to differentiate between competing theoretical models of particle acceleration. We propose to improve the theoretical modeling by focusing on one realistic particle acceleration process---the kink instability in the jet. Starting from first-principles plasma kinetic simulations, we will make predictions of the nonthermal particle distribution and radiation signatures to compare with IXPE and multiwavelength observations.

Proposal Number: 2226
Proposal Type: REGULAR
PI Name: SEAN GUNDERSON
Title: X-RAY POLARIMETRY OF ACCRETING WHITE DWARFS: A CASE STUDY OF EX HYDRAE
Abstract: We propose to observe the nearby intermediate polar EX Hya for 500 ks. As an intermediate polar, EX Hya generates X-rays through accretion onto the white dwarf s magnetic poles from a truncated accretion disk. The accretion columns form standing shocks above the surface, the height of which is critical to the observed flux. Photometric spectra can be used to estimate the shock height, but these results are unconstrained due to degeneracies in the spectra. The degeneracies can be broken if we know how much of the flux is source versus reflected light from scattering off the white dwarf surface, which polarization can tell us. EX Hya is an ideal candidate for an observation with IXPE as our viewing angle of the reflection is nearly 90 degrees, maximizing the polarization fraction.

Proposal Number: 2239
Proposal Type: REGULAR
PI Name: MASON NG
Title: X-RAY POLARIMETRIC OBSERVATIONS OF TYPE I X-RAY BURSTS FROM THE CLOCKED BURSTER
Abstract: Type I X-ray bursts represent some of the most extreme accretion phenomena, yet IXPE has not published analysis of type I X-ray bursts from any neutron star low-mass X-ray binary system so far. This presents a gap in our understanding of accretion phenomena in a strong gravity environment, such as that around a neutron star, which IXPE is poised to address. In this observing proposal, we propose triggering Target of Opportunity (ToO) observations of the known neutron star low-mass X-ray binary GS 1826-238, the Clocked Burster, which displays type I X-ray bursts at high recurrence rates during the spectrally hard state.