DETERMINING THE MAGNETIC FIELD STRENGTH OF THE LOW MASS X-RAY BINARY PULSAR GX 1+4: A UNIQUE MAGNETAR BINARY?
One of the big questions in neutron stars is how the strong magnetic field is formed and evolved. We propose a 40 ks observation of a low-mass X-ray binary pulsar GX 1+4, which has long been suspected to have a very high magnetic field strength, perhaps ~ 1e14 G. Thanks to the excellent energy resolution of the Resolve, the proposed observation enables us for the first time to resolve the profile of the Fe K alpha lines and to measure the magnetic field strength above 1e13 G, which is impossible to probe using the cyclotron resonance scattering feature (CRSF). From this observation we can determine whether or not the source is the first magnetar binary ever detected. Moreover, Resolve may provide a unique opportunity to search for the proton CRSF.
TELESCOP= 'XRISM ' / Mission name INSTRUME= 'XTEND ' / Instrument name OBS_ID = '201018010' / Observation identification string OBJECT = 'GX1+4 ' / Object name OBSERVER= 'TOSHIHIRO TAKAGI' / PI name OBS_MODE= 'POINTING' / POINTING or SLEW or ALL RA_OBJ = 263.009 / [deg] Object Right ascension DEC_OBJ = -24.7456 / [deg] Object Declination RA_PNT = 263.005599813049 / Pointing RA DEC_PNT = -24.747120558746 / Pointing DEC RA_NOM = 263.007525585089 / [deg] Nominal aspect point R.A. DEC_NOM = -24.7452375802524 / [deg] Nominal aspect point Dec. PA_NOM = 93.0802889869987 / [deg] Nominal aspect point roll. TELAPSE = 110604.963135988 / Elapsed time DATE-OBS= '2025-03-25T06:15:22.036864' / Start date DATE-END= '2025-03-26T12:58:47' / Stop date ONTIME = 39743.55319 / On-source time EXPOSURE= 39743.55319 / Exposure time PROCVER = '03.00.013.010' / Processing script version MKFFF = 'ISAS/JAXA' / Origin of First FITS file ORIGIN = 'GSFC/NASA' / Origin of Processed FITS file SOFTVER = 'Hea_21Aug2024_V6.34_XRISM_21Aug2024_V001' / Version of HEADAS used CALDBVER= 'gen20241115_xtd20241115_rsl20241115' / Version of CALDB used DATE = '2025-04-11T06:15:51' / Date and time this file was created or updated SIB2_VER= 'V03.01 ' / SIB2 version JAXA