View source for GX 1+4

[[Category:Accreting X-ray Pulsars]]

Also known as: V* V2116 Oph [http://simbad.u-strasbg.fr/simbad/sim-id?Ident=GX+1%2B4&NbIdent=1&Radius=2&Radius.unit=arcmin&submit=submit+id Simbad] <ref name="Lewin71" />

'''Monitoring data''':
[http://www.batse.msfc.nasa.gov/batse/pulsar/data/sources/gx1p4.html CGRO/BATSE] 
[http://xte.mit.edu/asmlc/srcs/gx1+4.html RXTE/ASM]
[http://swift.gsfc.nasa.gov/docs/swift/results/transients/GX1p4/ Swift/BAT]
[http://maxi.riken.jp/top/index.php?cid=1&jname=J1732-247 MAXI]
[http://gammaray.nsstc.nasa.gov/gbm/science/pulsars/lightcurves/gx1p4.html Fermi/GBM pulsed flux]

= Coordinates = 

{| class="wikitable"
| RA 
| 17h 32m 02.16s 
| Dec 
| -24° 44' 44.2" 
|- 
| RA 
|     263.009000 
| Dec 
|     -24.745611 
|- 
| l  
|         1.9370 
| b   
|       +04.7949 
|}
= Binary system =

Distance estimated between 3 and 15 kpc by <ref name="ChakrabartyRoche97" />. 
<ref name="Hinkle06" />  determine a distance of 4.3 kpc.

== Orbit ==

{| class="wikitable"
! Parameter               
! Value        
! Unit               
! Reference                                                                                                                                                              
|- 
| P<sub>orb</sub>         
| 1160.8±12.4  
| days               
| <ref name="Hinkle06" />  
|- 
| T<sub>periastron</sub>  
| 2451943±53   
| JD                 
| <ref name="Hinkle06" />  
|- 
| a sin i                 
| 232.2±6.0    
| 10<sup>6</sup> km  
| <ref name="Hinkle06" />  
|- 
| a sin i                 
| 776±20       
| lt-sec             
| derived from above                                                                                                                                                     
|- 
| e                       
| 0.101±0.022  
|                    
| <ref name="Hinkle06" />  
|- 
| ω<sub>periastron</sub>  
| 168±17       
|                    
| <ref name="Hinkle06" />  
|- 
| Mass function           
| 0.371±0.026  
| M<sub>sol</sub>    
| <ref name="Hinkle06" />  
|}

'''Note''': In the past an orbital period of ~304 d has been assumed for this
source, based on variations in the pulse period of the neutron star
(see, e.g., <ref name="Pereira99" />).
== Optical Companion ==
 
'''Names''': V2116Oph, 2MASS J17320215-2444442<br /> 
Cool, low- to intermediate-mass, first-ascent giant or asymptotic giant branch (AGB) star (<ref name="Hinkle06" />).

{| class="wikitable"
!Parameter 
!Value 
!Unit 
!Reference 
|- 
|Mass 
| <1.22 
| M<sub>sol</sub> 
| <ref name="Hinkle06" /> 
|- 
|K 
| ~8 
| mag 
| <ref name="Hinkle06" /> 
|}

= Available data =
* '''ASCA''': 41ksec GIS exposure (Sep 1994)
* '''RXTE''': many monitorings 1996-1997 and 2001-2002, mostly individual obs <3ksec, 1996 up to 50ksec
* '''Chandra''': ACIS-s observations 20ksec and 57ksec (Apr and Aug 2002)
* '''XMM Newton''': slew data only (detected as XMMSL1 J173202.0-244446 with 14cts/sec)
* '''BeppoSAX''': ~210ksec awarded in AO1 and AO4
* '''INTEGRAL''': frequent monitoring as part of Galactic Centre observations
* '''Swift''': 55ksec XRT exposure (Feb 2006)
* '''Suzaku''': 100ksec observation Okt 2010?

= Description =

GX 1+4 is the prototype of the small but growing subclass of accreting X-ray pulsars called Symbiotic X-ray Binaries (SyXB), by analogy with symbiotic stars, in which a white dwarf accretes from the wind of a M-type giant companion.

[[File:gx1_4_pspinevolution.png|200px|]]

The system was discovered in 1970 by a balloon X-ray observation at energies above 15 keV showing pulsations with a period of about two minutes (<ref name="Lewin71" />). In the following years it was one of the brightest X-ray sources in the Galactic centre region during the 1970's, spinning up strongly.

Following an extended low state in the early 1980’s it has been generally spinning down strongly, increasing its pulse period by ~50% over the last 30 years (<ref name="GonzalezGalan12" />).<br /> 

Currently, there is no well established value of the magnetic field of GX 1+4. Assuming standard accretion disk theory (e.g., <ref name="GhoshLamb79a" />, <ref name="GhoshLamb79b" />), the magnetic field has been estimated to be B ∼10<sup>13</sup> − 10<sup>14</sup> G by different authors
(e.g., <ref name="Dotani89" />, <ref name="Mony91" />, <ref name="CuiSmith04" />), 
which would be among the largest measured for any accreting X-ray pulsar. 
On the other hand, <ref name="Rea05" /> and <ref name="Ferrigno07" /> find weak evidence for
possible CRSFs in in the X-ray spectra which would point to a value of B ∼10<sup>12</sup> G for the magnetic field, i.e., 1-2 orders of magnitude lower.

== Flux ==

GX 1+4 is a persistent source, but with strong, irregular flux variations on various timescales
([http://swift.gsfc.nasa.gov/docs/swift/results/transients/GX1p4/ Swift/BAT lightcurve]).

== Spectrum ==

The observed spectrum of GX 1+4 can be described by a typical accreting X-ray pulsar spectrum, i.e., 
a cut-off power law or a comptonization model, always showing also strong intrinsic absorption and an iron line. But it is one of the hardest spectra found among all X-ray binary pulsars.
Using the correlation between magnetic field strength and spectral hardness observed in
various sources (e.g., <ref name="Coburn02" />) this would indicate a magnetic field 
in excess of 10<sup>13</sup> G.

== Pulse Profile ==

At first approximation the pulse profiles for GX 1+4 display a single broad peak at all energies
(see, e.g., <ref name="Naik05" />). The detailed shape is variable and frequently displays substructure 
indicative of a superposition of two peaks (see, e.g., <ref name="Ferrigno07" />).

'''References'''