4U 1907+09

• persistent High Mass X-ray Binary
• discovered by the Uhuru survey in 1971 ()
• famous source with a long spin-down, torque reversal to spin-up in 2003, and a another torque reversal back to spin-down in 2007.
• investigated a lot with INTEGRAL and RXTE, a little with Suzaku (). XMM data exist but are not published.
• CRSF at 18 and 38keV found in BeppoSAX, fundamental line confirmed with Suzaku, but for 1. harmonic S/N too low.
• Coordinates : RA 19h 09' 37.9" , DEC +09° 49' 49"
• Magnetic field strength: ~2.1x10¹² G ()

Orbit

Orbital period^* : 8.3753(1) days
Eccentricity^* : 0.28(4)
Orbital epoch^* : 50134.76(6) MJD
Longitude of periastron^* : 330(7)°
Projected semimajor axis length^* : 83(2) lt-s

^* From ()

Companion

Typ^* : O8–O9 Ia supergiant (T_eff = 30500 K, R = 26 R_sun, L = 5x10⁵ L_sun, D > 5 kpc)
Mass loss rate (stellar wind)^* : 7x10^-6 M_sun yr^-1

^* From ()

Accretion

• wind driven accretion (close orbit, high mass loss of the companion)
• wind & stream accretion (suggested by ()), explaining the double peaked lightcurve (see plot below):

Plot left shows the double peaked light curve folded onto the orbital period and a zero phase at periastron based on data from the RXTE All-Sky Monitor.

Plot right shows the binary geometry including the mid-line of the stream (dashed line) and neutron star (filled circle) on its orbit (dotted line) around the companion star (open circle) at four orbital phases: 0.15 (top-left), 0.35 (top-right), 0.6 (bottom-left) and 0.95 (bottom-right)

Pulsation

Pulse profile :

• Pulse period = ~441 s with long periods of constant P_dot interrupted by sudden torque reversals.

Plot () shows the pulse period history.
Section E & D: P_dot = +0.230 s yr^-1 dropping to P_dot = +0.115 s yr^-1 in the end
Section C: P_dot = -0.158 s yr^-1 (after torque reversal)
Section A: P_dot = 0.226 s yr^-1

References