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SgrA* X-ray Flares with XMM-Newton

SgrA* X-ray Flares with XMM-Newton. P. Goldoni, A. Goldwurm, P. Ferrando, F. Daigne, A. Decourchelle,E. Brion, G. Belanger Service d’Astrophysque / CEA – Saclay, France R.S. Warwick Physics Dept., Leicester University, UK P. Predehl, D. Porquet, B. Aschenbach MPE – Garching, Germany.

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SgrA* X-ray Flares with XMM-Newton

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  1. SgrA* X-ray Flares with XMM-Newton P. Goldoni, A. Goldwurm, P. Ferrando, F. Daigne, A. Decourchelle,E. Brion, G. Belanger Service d’Astrophysque / CEA – Saclay, France R.S. Warwick Physics Dept., Leicester University, UK P. Predehl, D. Porquet, B. Aschenbach MPE – Garching, Germany

  2. SgrA* • Compact radio source at the dynamical center of our Galaxy • Very high column density along the line-of-sight NH ~ 1-2 x 1023 cm-2=> Only detectable in radio, IR, X-rays, an gamma-rays • Motions of stars: => M = 3.5 ± 1.5 x 106 solar mass (Schödel et al. 2002)=> Supermassive Black Hole • Radio: very well known, bright, weakly variable source, 106 day period

  3. X-ray observations of SgrA* • Only observable above 2 keV • Old generation of X-ray satellites (e.g, ASCA, BeppoSAX): spatial confusion with other objects • Chandra • L (2-10 keV) ~ 2.2 x 1033 erg/s(Baganoff et al. 2003) => 10-11 x Eddington Luminosity (~4.5 x 1044 erg/s) • , photon index ~ 2.5 roughly compatible with ADAF model

  4. Flare detected with Chandra in Sep 2000 • Chandradetected a 10 ks flare in October 2000 (Baganoff et al.2001b) • Sgr A* peakLX(2-10 keV)  1035 erg s–1 ~50 times stronger than in quiescence • Hard spectrum:  1.3 • Fast variations, ~600 sec, small emission region ~ 20 Rs for 3 million solar masses BH, argument against ADAF model • Liu & Melia (2001) viscosity decrease in hot circularized accretion flow • Markoff et al. 2001 Sudden shock acceleration

  5. XMM-Newton GTO observations-I • PI Anne Decourchelle Joint Saclay/Leicester/MPE program • Main scientific goal GC region diffuse emission • Total observing time on Sgr A*: 75 ksec • XMM observations in september 2000 => solar flare • Spring 2001 => solar flare • September 2001 initial phases of a Sgr A* flare (Goldwurm et al. 2002 ApJ)

  6. The XMM-Newton Observation of the GN • Performed on 4th September 2001 • Exposure ~ 26 ks • EPIC in Full Frame Imaging mode : MOS 1, MOS 2, PN, Medium Filter • RGS in spectral+Q mode, OM blocked • MOS 1+2 central CCD: ~ 4.5 cts/s • Some proton flares observed XMM-Newton EPIC MOS 1 + 2 EPIC MOS 1+2 Central CCD 2-10 keV Count Rate (20s bin) Complex region, diffuse emission + point sources : excess around Sgr A*

  7. R= 10"

  8. Search for Variability of Sgr A* • Confused region for the XMM PSF (15" HPD) • Optimized selections to search for Sgr A* contribution • Region within 10" from Sgr A* (60 % flux) in the 2-10 keV band • Use of Chandra results to model the contribution of other sources (Baganoff et al. 01) • Search for a variable central source MOS 1+2 0.5 - 7 keV R= 10" MOS Image (pixels = 1.1"  1.1") with point sources detected by Chandra

  9. 900 s 7  excess Light Curves from data within 10" from Sgr A* within 10’’ from Sgr A* MOS 1 + 2 region at 1’ from Sgr A* PN Comparison of Count Rate (2-10 keV, 180 s bin) from within 10’’ from Sgr A*andCR from a different region (same CCD) Count Rate from within 10’’ from Sgr A* for both MOS andPN (300 s less of data) : zoom around the end of the observation

  10. Sgr A* position Images before and during the flare MOS 1+2 2-10 keV MOS 1+2 2-10 keV 5' 1000 s before flare 1000 s during flare The flare is clearly located at the center of the image compatible with a point source close to Sgr A*

  11. 1.5"Offset from Sgr A* Flaring source location • PSF fitting of central source on the last 1000 s image • Central source located at (J2000) R.A. = 17h 45m 39.99s Dec. = –29° 00' 26.7" (+/- 0.4" stat. err.) • 1.5" from Sgr A* radio position (1.4" in Dec.), compatible with residual systematic errors for XMM • Search & location of other point sources in the total MOS 1+2 0.5-4 keV image (all CCDs) • 6 point sources identified with stars • Average and rms offset RA =–0.03" Dec = 0.20" rmsRA =0.29" rmsDec = 1.5“ • Consistent with syst. uncertainties => The flaring source is identified with Sgr A* MOS 1+2 2-10 keV 1000 s during flare

  12. Spectra from data within 10" from Sgr A* before the flare Spectral fit of MOS and PN data with model used for Chandra data of quiescent state • Best fit (2= 1.35, =121) Thermal Component (diffuse) NH = 11.1 ± 0.6 1022 cm-2 kT = 1.3 ± 0.08 keV P–L (point sources + background)  = 2.1 ± 0.3 P-L for Sgr A* (fixed to Chandra fit)  = 2.7 MOS 1 + 2 PN • Quiescent spectrum compatible with Chandra measures • Well fitted by Thermal spectrum (Raymond & Smith 77) with kT ~ 1.3 keV + Power law for point sources and background • Sgr A* component (12 % of total emission) not required but consistent

  13. Spectral Hardening during the Flare MOS 1 + 2 MOS during flare H/R = F(4-10 keV) / F(2.5-4 keV) Hardness Ratio MOS before flare Time (s) Spectral fit of MOS + PN data during flare (last 900 s for MOS, last 600 s for PN) with model used for the quiescent state • Thermal and point sources components fixed, Sgr A* Power-Law free • Best fit (2= 0.9, =27) for Sgr A* Power-Law (NH = 9.8 1022 cm-2fixed to Chandra value)  = 0.9 ± 0.5

  14. Spectra Parameters during the Flare Spectral fit using the data before flare as background component • Power-Law model (= 0.98, =20) NH = 9.8 1022 cm-2 (fixed)  = 0.7 ± 0.6 • Similar result if dust scattering is included • Luminosity 2–10 keV (8 kpc) : 3.8 ± 0.7 1034 erg s-1 MOS 1+2 PN • XMM 2001 flare strongly resembles the early phase of the Chandra 2000 flare • Increase of factor 3 in 900 s, implies Sgr A* flux increase of factor 30 • Spectrum compatible with hard slope • No indication of lag between soft and hard

  15. XMM Flare Chandra Flare XMM Flare Correlation with Radio data • 106 day radio cycle from VLA data (Zhao et al. 99) • XMM 2001 flare at time phase preceding the main radio peak (d64) • Chandra flare : 6 days after (d70) • Recent radio data show increase in the cycle period (Yuan & Zhao 02) • Flare close to local max in 2001 Radio LC

  16. New Chandra 2002 observations • 500 ksec observations with multiwavelength coverage (Keck, VLA,…) • Results not yet published, ~0.6 +/-0.3 flares/day, mostly weaker (factor ~10) • No obvious correlation with other wavelengths

  17. XMM-Newton GTO Observations II • 50 ksec pointing on Sgr A* to be performed • ~30 ksec in February 2002, observation not completed • Remaining time in October 2002 • Brightest flare from Sgr A* !! (Porquet et al. 2003 A&A)

  18. October 2002: X-ray flare from Sgr A* (XMM-Newton) • flare duration ~ 2.7 ks, i.e less than one hour • Shorter variation ~200 sec, ~7 Rs • flux amplication ~ 160(peak of the flare/ quiescent) (~ x 3.5 October 2000, Chandra) • symmetrical light curve shape • Similar light curve shape in the"soft" (2-5 keV) and in the "hard" (5-10 keV) energy bands: • no significant spectral evolution between the rise and decay phase

  19. XMM/EPIC spectrum photon spectral index : G= 2.5± 0.3XMM, 10/2002 Very softcompared to the previous ones: G ~1.3Chandra, 10/2000 G ~1.0XMM, 09/2001

  20. Comparisons with flare models • The characteristics of this brightest flare in October 2002 (XMM) challenge theoretical Sgr A* flare modelling: • Circularized flow(Liu & Melia 2002): when the viscosity increases SSC of mm to sub-mm photons is the dominant process:soft spectrum predicted. • A similar increase in the mm and sub-mm, not IR is expected: but not yet reported • Jet model (Markoff et al. 2001)when the jet power or accretion rate increase:soft spectrum predicted • Simultaneous flaring at all frequencies are expected: but not yet reported • Star-disk interaction (Nayakshin et al. 2003): for kT=1 and 70 keVa soft spectrum (G~ 2.3) is predictedbut very fine-tuned. X-rays have become fundamental to solve Sgr A* puzzle

  21. INTEGRAL/ISGRI Observations of SgrA* • Spring 2003, 1Msec exposure: Detection of a source at a position compatible with SgrA* in the 20-40 and 40-100 keV band, implied luminosity ~1035 erg s-1

  22. INTEGRAL/ISGRI Observations of SgrA*: variability SgrA* 20-40 keV light Curve: Hints of Variability on a 40 min. timescale But angular resolution 12’ and position error ~0.8’

  23. Present state of Observations • Rapid / high-amplitude X-ray flaring of Sgr A* is not a rare event • From XMM and Chandra results : ~0.6+/-0.3 flares/day • Hard and soft spectra are observed, non definitive hints on accretion regime and emission mechanisms • Possible hard X-ray source/flaring but source confusion is still a problem • Constraints on models, e.g. in case of change in mass accretion and SSC is the main X-ray radiative mechanism the increase in radio should be comparable (Liu & Melia 02) , in all models correlated variability is predicted • Fast IR variability has very recently been observed (Genzel et al. 2003) • No radio variability of such amplitude has been ever observed Long XMM/INTEGRAL observations with ground based Radio, submm, IR coverage are needed

  24. XMM-Newton AO-3 • Proposal (Goldwurm et al.) to observe SgrA* for 500 ksec (large program), accepted, 4 orbits granted. Goals • 1) detect the largest possible number of flares with max. sensitivity • 2) Correlate with Simultaneous hard X-rays (INTEGRAL), radio (VLA) and IR(ESO)

  25. Perspectives • Detection of several flares with different spectra • Modelization of X-ray sources in IBIS/ISGRI error box => hard X-ray spectrum of SgrA* • Monitoring of radio,submm and IR flux/variability • Strongest possible constraints on SgrA* emission mechanisms and accretion regime

  26. XMM-Newton October 2002 SgrA* Flare Movie (MPE)

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