4U1538-522
Directions of the stellar spins and orbital motion of binary systems are essential for understanding their evolution and supernovae. However, unlike easily measurable rotational and binary periods, their orientation (or alignment) is difficult to determine. We discovered that the orbital and rotational directions are co-aligned at the neutron star in the high-mass X-ray binary 4U 1538-522, through the phase delay of the 6.4 keV Fe emission line in the Suzaku, NuSTAR, and NICER observations. Using Resolve, we can further determine the rotational direction of the optical primary star QV Nor of this system. Expanding this methodology opens a new field for studying X-ray binaries, analogous in X-ray astronomy to the Rossiter effect in exoplanets. \end{small}
obsid = 202088010 / Unique Observation/Sequence Number
object = 4U1538-522 / Object name
pi_name = ENOTO TERUAKI / Proposal Principal Investigator Name
ra = 235.600603102383 / Right Ascension (Pointing Position) (deg)
dec = -52.3869742526321 / Declination (Pointing Position) (deg)
roll_angle = 120.968378015524 / Roll Angle (deg)
start_time = 2026-03-23T00:42:04 / Start Time of the Observation
stop_time = 2026-03-26T11:01:04 / Stop Time of the Observation
exposure = 186785.32766 / Effective Total Observation Exposure (s)
public_date= 2027-04-03 / Public Date