An X-ray view on compact objects in polarized light

INAF-IAPS - Unit Activities

Assessments for next-generation polarimetric missions

The INAF team has extensive expertise on the measurement of X-ray polarization from astronomical sources, which allowed us to evaluate the observability of the simulated effects and then direct our efforts along the most promising avenues. The resulting scientific requirements were also a driver for next-generation polarimetric missions in which our team has a leading role.

Contribution to the interpretation of the IXPE data and contribution in refinement of requirements for future missions and target selection

Our project was timely since it extended over the entire phase-1 of IXPE operations and covered the developing phase of the polarimetric missions currently in the study phase. Therefore its results were instrumental in the interpretation of IXPE data and helped in refining the design and the target selection of future missions.

Observation simulations tools as support to theoretical modeling

The INAF-IAPS unit was responsible for the development of the observation-simulation tools and for the support of theoretical modeling with instrumental feedback. The IAPS group has decades-long experience in devising, building X-ray polarimeters and analyzing calibration data for proposed, operational and planned missions.

Staff Members

Name & Surname	Role	Effort (PM)
Dr. Sergio Fabiani	First researcher - PI	6.5
Dr. Fabio Muleri	First researcher	4.5
Dr. Paolo Soffitta	Research director	3.0
Dr. Lorenzo Marra	Research fellow	12.0

Publications

• Gnarini A.,... Fabiani S. et al., First spectropolarimetric observation of the neutron star low-mass X-ray binary GX 3+1, A&A, 692, 123 (2024)
• Ursini F., ... Fabiani S. et al., X-ray spectropolarimetry of the bright atoll Serpens X-1, A&A, 690, 200 (2024)
• Mastroserio G.,... Fabiani S. et al., X-ray and optical polarization aligned with the radio jet ejecta in GX 339-4, ApJL, 978, 19 (2025)
• Tarana A.,... Fabiani S.,... Soffitta P. et al., X-ray spectro-polarimetry analysis of the weakly magnetized neutron star X-ray binary GX 9+1, A&A, 698, 245 (2025)
• Rigoselli M.,... Marra L., Muleri F. et al., IXPE detection of highly polarized X-rays from the magnetar 1E 1841−045, ApJL, 985, 34 (2025)
• Ewing M.,... Marra L., et al., The very high X-ray polarisation of accreting black hole IGR J17091-3624 in the hard state, MNRAS, 541, 1774 (2025)
• Marra L. et al., Polarization properties of thermal accretion disk emission. I. Direct radiation, A&A, 705, 8 (2026)
• Marra L.,... Fabiani S.,... Muleri F.,... Soffitta P. et al., Exploring MAXI J1744-294: IXPE insights into a Newly Discovered X-ray Transient ApJ (submitted)
• Podgorny J.,... Marra L., et al., X-ray polarization of reflected thermal emission A&A (submitted)
• Mandel S.,... Marra L., et al., A multiwavelength study of the Galactic center black hole candidate MAXI J1744-294 ApJ (submitted)
• Mikusincova R., Marra L.,... Fabiani S.,... Muleri F.,... Soffitta P. et al., The First X-Ray Polarimetry of an Eclipsing Low-Mass X-Ray Binary: Serendipitous IXPE Observation of AX J1745.6--2901 ApJ (submitted)

Space Mission DDTs Requested

Proposer	Notes
Lorenzo Marra	An IXPE DDT observation of the recently discovered X-ray transient MAXI J1744–294 was performed in April 2025 for a total exposure time of 150 ks. In addition, simultaneous observations with NuSTAR, Swift, NICER, and MeerKAT were requested to ensure comprehensive multi-wavelength coverage of this intriguing source.
Lorenzo Marra	Requested a Swift/XRT DDT observation of the HMXRB source SS 433 in 2025, to be performed simultaneously with the IXPE observation of the source (PI: Paolo Soffitta) carried out in November. This request was approved for a total exposure time of 10 ks, divided into 5 poitings. A further request for a 40 ks XRISM observation to be performed simultaneously with the same IXPE observation was rejected.
Lorenzo Marra	Approved IXPE DDT to observe the black hole LMXRB 4U 1957+11 with IXPE for a total exposure of 700 ks, performed in November 2025. The goal of this observation is to confirm or reject the hint of a polarization angle rotation observed during the first IXPE observation of the source conducted in 2023.
Lorenzo Marra	Requested a IXPE DDT observation of the black hole GS 1354-64 for a total exposure of 150 ks, performed in February 2026. The request was approved with the goal of following the source during different spectral states in this new outburst.

Conferences and Presentations

Event	Date	Presenter	Contribution
Vasto Accretion Meeting 2025, Vasto (I)	23-27 June 2025	Lorenzo Marra	Contributed talk
11th Microquasar workshop, Cefalù (I)	15-19 September 2025	Lorenzo Marra	Contributed talk
ASI annual workshop on the missions in Operative Phase, Roma (I)	28-29 October 2025	Lorenzo Marra	Contributed talk
11th FERO meeting, Prague (CZ)	25-27 November 2025	Lorenzo Marra	Invited talk