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Park High Energy Phenomena in the Galactic Center

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					    High Energy Phenomena in the Galactic Center,
            Paris, France, June 15, 2005



A Candidate Neutron Star & Its
  Association with Sgr A East
            Sangwook Park
   Department of Astronomy & Astrophysics
      The Pennsylvania State University

                                       Collaborators:
                                       Michael Muno (UCLA)
                                       Frederick Baganoff (MIT)
                                       Yoshitomo Maeda (ISAS)
                                       Mark Morris (UCLA)
                                       George Chartas (Penn State)
                                       Divas Sanwal (Penn State)
                                       David Burrows (Penn State)
                                       Gordon Garmire (Penn State)
    Introduction

• Sgr A East:                     • ACIS-I: Sgr A*
  -Nonthermal radio shell         • 1999-9 ~ 2002-6:
  -X-ray detected by                       7 GTO & 5 GO obs
        ROSAT, ASCA, Beppo-SAX             => ~590 ks
  -Chandra: Maeda et al. (2002) •      Spatially-resolved spectroscopy
   MM SNR, kT=2 keV, CIE                with high photon statistics
   E ~ 2 x 1049 ergs, M ~ 2 Msun         - to test “Chandra vs XMM”
   Fe-rich center: He-like Fe line       - to test SN type
   Abund ratios => Type II SN      •   Core-collapse SN: potential NS
  -XMM: Sakano et al. (2004)            => CXOGC J174545.5-285829
   SNR, central He- & H-like Fe            (Muno et al. 2003)
     => kT=1 keV & 4 keV, CIE      •   Is CXOGC J174545.5-285829
    Abund pattern =>Type Ia or II?     a NS associated with SNR Sgr A
    “Neutral” Fe (6.4 keV)             East?
3-Color & Fe EW images
              Park et al. 2005, ApJ, in press

                              He-like Fe XXV (E ~ 6.6 keV)
                                                Ar Hea (3.1 keV)




                                                 Ca Hea (3.9 keV)




  Red: 1.5-4.5 keV
  Green: 4.5-6.0 keV
  Blue: 6.0-8.0 keV
Sgr A East: Spectra & Fe Mass


 Fe ejecta mass:                         1.5-8 keV
  EM => nFe ~ 0.12 f-0.5 cm-3
                          Plume
  MFe < 0.15 - 0.27 Msun
 kT=1.3 keV
 Fe=1 solar
 Type Ia: MFe ~ 0.5 – 0.8 Msun (Nomoto et al. 1997a)
 Type II: MFe ~ 0.15 Msun for Mstar = 13 – 15 Msun
          MFe ~ 0.05 – 0.08 Msun for Mstar = 18 – 70 Msun
          (Nomoto et al. 1997b)
 => Sgr A East is likely from a core-collapse SN.
                            Center

   kT=1.1 keV + 5.3 keV
   Fe=5.8 solar
Neutron Star Candidate: “the Cannonball”

                N
                    The cannonball
High velocity NS?
           E                                            =1.6
 - Tail: ~0.1 pc physical size
                                                        Lx=3x1033 ergs s-1
 - ~2’ from “center”: v ~ (455-912)/sina km s      -1

   for SNR age ~ 5000 – 10000 yr                 No varibility detected
 - Mach number ~ 2.2: v ~ 880 km s-1
   for ISM kT ~ 1 keV
 - Pressure balance: PPWN (Edot/4cR2) = Ptherm (2nekT) = Pram (v2)
         S              N
                      where  = 2.36-0.021 Edot-0.5 (Gotthelf 2003),
                     v ~ 550 km s-1
=>Three velocities from independent estimates are consistent.
=>Also consistent with typical Galactic high-velocity pulsars
  (e.g. Cordes & Chernoff 1998).
Summary
• CXOGC J174545.5-285829 (the Cannonball): A High-V NS?
   - Cometary morphology
   - X-ray spectrum: Hard, nonthermal continuum,  = 1.6
   - X-ray luminosity Lx = 3 x 1033 ergs s-1
   - No variability
• Associated with Sgr A East?
  - Proximity to Sgr A East: estimated velocities are reasonable
  - Positional coincidence at the “tip” of Sgr A East Plume
  - Cometary tail extending toward Sgr A East
  - Sgr A East is likely a core-collapse SNR: MFe < 0.27 Msun
However, no evidence for a “pulsar”:
  - XMM/PN places an upper limit of ~40% on the pulsed fraction
    at P > 147 ms.
  => High time-resolution, high-sensitivity X-ray/radio
     observations are necessary.

				
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