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XRISM spectroscopy of a crowded Galactic center region -- I. Disentangling the sources in the field of view

Maxime Parra, Kai Matsunaga, Shifra Mandel, Kaya Mori, Hideki Uchiyama, Masayoshi Nobukawa, Tahir Yaqoob, Takayuki Hayashi, Misaki Mizumoto, Shinya Yamada, Megumi Shidatsu, Paul A. Draghis, Efrain Gatuzz, John A. Tomsick, Charles J. Hailey, Chichuan Jin, Benjamin Levin, Gabriele Ponti, Mark Reynolds

Abstract

The Galactic center is a complex and crowded region hosting the supermassive black hole Sgr A*, numerous accreting compact objects, and diffuse X-ray emission. This paper presents the first in a series of studies analyzing the XRISM observation of the X-ray transient MAXI J1744-294/Swift J174540.2-290037, located $\sim18''$ from Sgr A*. The observation, conducted in March 2025, along with XMM-Newton and NuSTAR coverage, aimed to investigate the Fe emission features of MAXI J1744-294 during its outburst. However, the region surrounding the source is heavily contaminated by X-ray emission from various diffuse and point sources, including strong line contributions from the supernova remnant Sgr A East and the Galactic center X-ray emission (GCXE). Additionally, the nearby neutron star low-mass X-ray binary (NS-LMXB) AX J1745.6-2901 was also in outburst during the XRISM observation, further complicating the spectral analysis. This study focuses on disentangling the contributions of these overlapping sources by robustly modeling the background contamination and spatial-spectral mixing. We describe the methodologies, region selection, and data reduction techniques applied to the different instruments. Two complementary approaches -- empirical and physical modeling -- are employed to characterize diffuse emission and point-source contributions. The results provide a foundation for the detailed spectral analysis of MAXI J1744-294, AX J1745.6-2901, and the surrounding interstellar medium (ISM), which will be presented in subsequent papers. This study highlights the challenges and robust solutions for analyzing XRISM/Resolve data from crowded regions in conjunction with other X-ray telescope data.

XRISM spectroscopy of a crowded Galactic center region -- I. Disentangling the sources in the field of view

Abstract

The Galactic center is a complex and crowded region hosting the supermassive black hole Sgr A*, numerous accreting compact objects, and diffuse X-ray emission. This paper presents the first in a series of studies analyzing the XRISM observation of the X-ray transient MAXI J1744-294/Swift J174540.2-290037, located from Sgr A*. The observation, conducted in March 2025, along with XMM-Newton and NuSTAR coverage, aimed to investigate the Fe emission features of MAXI J1744-294 during its outburst. However, the region surrounding the source is heavily contaminated by X-ray emission from various diffuse and point sources, including strong line contributions from the supernova remnant Sgr A East and the Galactic center X-ray emission (GCXE). Additionally, the nearby neutron star low-mass X-ray binary (NS-LMXB) AX J1745.6-2901 was also in outburst during the XRISM observation, further complicating the spectral analysis. This study focuses on disentangling the contributions of these overlapping sources by robustly modeling the background contamination and spatial-spectral mixing. We describe the methodologies, region selection, and data reduction techniques applied to the different instruments. Two complementary approaches -- empirical and physical modeling -- are employed to characterize diffuse emission and point-source contributions. The results provide a foundation for the detailed spectral analysis of MAXI J1744-294, AX J1745.6-2901, and the surrounding interstellar medium (ISM), which will be presented in subsequent papers. This study highlights the challenges and robust solutions for analyzing XRISM/Resolve data from crowded regions in conjunction with other X-ray telescope data.

Paper Structure

This paper contains 29 sections, 17 figures, 4 tables.

Table of Contents

  1. Introduction
  2. Observations and Region Selection
  3. XRISM
  4. Resolve
  5. Xtend
  6. XMM-Newton
  7. Data reduction
  8. XRISM
  9. Resolve
  10. Xtend
  11. Diffuse emission modeling in the PV Phase
  12. Resolve
  13. Big M1744 region - empirical modeling
  14. Small M1744 region - physical modeling
  15. Xtend
  16. ...and 14 more sections

Figures (17)

  • Figure 1: (Left) Comparison between a stacked [0.7-7] keV Chandra image of the galactic center and the XRISM Resolve 6x6 pixel field of view for the 2025 Director's Discretionary Time observation of MAXI J1744-294. We highlight the position of Sgr A*, MAXI J1744-294 and AX J1745.6-2901. (Right) Zoom of the central region of the Chandra image, highlighting the position of known X-ray transients in green, MAXI J1744-294 in cyan, and Sgr A* in black.
  • Figure 2: XRISM Sky images from the 2025 DDT Observation, in the [2-10] keV band (top left, Resolve), [0.3-10] keV band (bottom left, Xtend), and [7-10] keV band (right, Resolve and Xtend) computed from the reprocessed event files, after proximity and rise-time event screening, along with Flickering Pixel removal (see Section \ref{['subsubsec:xtend']}) and with all Resolve event grades. The circles show the projected positions of MAXI J1744-294 and AX J1745.6-2901.
  • Figure 3: (Left) Distribution of PSF fractions in each pixel from the DDT observation, for MAXI J1744-294 (green, upper quadrants), AX J1745.6-2901 (red, bottom quadrants), the GCXE (blue, left quadrants), and Sgr A East (magenta, right quadrants). (Right) distribution of PSF fractions in each pixel from the PV observation, for AX J1745.6-2901 (red, bottom thirds), the GCXE (blue, left thirds), and Sgr A East (magenta, right thirds). The MAXI J1744-294 PSF fraction is not represented in the right panel as the source was not yet active in the PV observation. In both panels, the colormaps of each source are normalized with respect to their respective cumulated PSF fraction across the Resolve FoV.
  • Figure 4: [2-10] keV band Resolve Sky images, computed similarly to Fig. \ref{['fig:XRISM_FoV_2025']} for the 2025 DDT observation (Left), and the 2024 PV phase observation used to estimate the diffuse emission (Right). We highlight the two regions used for MAXI J1744-294 in cyan (big region) and green (small region), and the region used for AX J1745.6-2901 in red. Pixel numbers are overlaid for reference.
  • Figure 5: [2-10] keV band Xtend Sky images computed similarly to Fig. \ref{['fig:XRISM_FoV_2025']} for the 2025 DDT (left) and the 2024 PV Phase (right) observations, highlighting the regions used to model MAXI J1744-294.
  • ...and 12 more figures