View source for SAX J2103.5+4545

[[Category:Accreting X-ray Pulsars]]

Also known as: GSC 03588-00834 [http://simbad.u-strasbg.fr/simbad/sim-id?Ident=SAX+J2103.5%2B4545&NbIdent=1&Radius=2&Radius.unit=arcmin&submit=submit+id Simbad], XTE J2103+457

'''Monitoring data''':
[http://xte.mit.edu/asmlc/srcs/saxj2103.5+4545.html RXTE/ASM]
[http://swift.gsfc.nasa.gov/docs/swift/results/transients/weak/SAXJ2103.5p4545/ Swift/BAT]
[http://maxi.riken.jp/top/index.php?cid=1&jname=J2103+457 MAXI]

= Coordinates = 
RA 21h 03m 35.71s, Dec +45° 45' 05.5"<br />
RA 315.05992 	 , Dec +45.75153 <br />
l  87.1303       , b -0.6848

= Binary system =

Distance: 5 kpc (<ref name="Baykal00" />), 6.5 kpc (<ref name="Reig04" />)

== Orbit ==

{| class="wikitable"
! Parameter               
! Value      
! Unit    
! Reference            
|- 
| P<sub>orb</sub>         
| 12.68(25)  
| days    
| <ref name="Baykal00" /> 
|- 
| T<sub>periastron</sub>  
| 51519.3(2) 
| MJD     
| <ref name="Baykal00" /> 
|- 
| a sin i                 
| 72(6)      
| lt-sec  
| <ref name="Baykal00" /> 
|- 
| e                       
| 0.4(2)     
|         
| <ref name="Baykal00" /> 
|- 
| omega                   
| 240(30)    
| degrees 
| <ref name="Baykal00" /> 
|}
== Optical Companion ==
 
'''Name''': not reported in <ref name="Reig04" /> <br />
B0Ve star with double-peaked H<sub>alpha</sub> emission line

{| class="wikitable"
!Parameter 
!Value 
!Unit 
!Reference 
|- 
| B   
| 15.3  
| mag 
| <ref name="Reig04" /> 
|- 
| V   
| 14.2  
| mag 
| <ref name="Reig04" /> 
|- 
| R   
| 13.7  
| mag 
| <ref name="Reig04" /> 
|}
''Note:'' <ref name="Hulleman98" /> suggested the B star HD 200709 as possible counterpart. The distance to this star is, however, around 0.7 kpc and therefore ruled out due to the findings of <ref name="Baykal00" /> and <ref name="Reig04" />.

= Description =

In February 1997, BeppoSAX discovered the transient source SAX J2103.5+4545, which was in an unusual long outburst until September of the same year (<ref name="Hulleman98" />). The pulse period was found to be around 358.61(3) s and the spectrum could be described well by an absorbed powerlaw (<ref name="Hulleman98" />). Six years later, <ref name="Reig03" /> found a possible optical counterpart using the 1.3-m telescope at the Skinakas Observatory. The spectrum showed a prominent, double-peaked H<sub>alpha</sub> emission line.

== Spectrum ==

The spectrum of SAX J2103.5+4545 can be described well by an absorbed cutoff powerlaw with an additional black body and a source intrinsic iron line (<ref name="Blay04" />, <ref name="Inam04" />). Depending on the used detectors, the spectral parameters were found as follows:
{| class="wikitable"
! Parameter          
! Value<sup>1</sup> 
! Value<sup>2</sup> 
! Unit 
|- 
| N<sub>H</sub>      
| 0.66(2)           
|                   
| cm<sup>-2</sup> 
|- 
| Gamma              
| 0.77(5)           
| 1.0(1)            
|                 
|- 
| E<sub>cut</sub>    
| 7.89 (fix)        
| 7.6(20)           
| keV             
|- 
| E<sub>fold</sub>   
| 27.1 (fix)        
| 30.9(25)          
| keV             
|- 
| kT<sub>bbody</sub> 
| 1.88(2)           
|                   
| keV             
|}
sup>1</sup> <ref name="Inam04" />, XMM- and RXTE observations <br />
<sup>2</sup> <ref name="Blay04" />, INTEGRAL observations

No cyclotron absorption feature was found in the spectrum yet. This might be due to the fact, that the magnetic field of the source is in the order of 12(3)x10<sup>12</sup> G (<ref name="Baykal02" />), which would imply the fundamental cyclotron line to be around 140 keV.

== Pulse Period & Profiles ==

Since its discovery in 1999 the pulse period of SAX J2103.5+4545 changed from 358.61(3) s to 354.7940(8) s at the end of 2002, indicating a long-term spin-up trend (<ref name="Hulleman98" />, <ref name="Baykal02" />, respectively). This same trend was confirmed by [(biblio:Blay04)], who analyzed an INTEGRAL obvseration of the 2002 outburst. The spin-up rate during the 2002 outburst could be measured to be around 7.4(9)x10<sup>-13</sup>Hz s<sup>-1</sup> (<ref name="Baykal02" />).

The pulse profile of the source shows a strong energy dependance. At energies below 20 keV, the profile is dominated by a single, broad peak with a leading shoulder (<ref name="Inam04" />). For higher energies a secondary peak arises, which becomes more prominent with increasing energy. This behaviour can be explained by a polar cap diffusion model (<ref name="Falanga05" />). Note, that this energy dependance is in contrast to other transient Be-binaries, like [[GRO J1008-57]] or [[XTE J1946+274]].

'''References'''