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The Impact of Chandra on M31 and M33 X-ray Studies Ben Williams (UW) X-rays from Nearby Galaxies September 5, 2007 Collaborators Michael Garcia (CfA) Jose Galache (CfA) Albert Kong (MIT) Sachi Naik (ISAS) Robin Barnard (Open) Jeff McClintock (CfA) Joseph Gelfand (CfA) Lorant Sjouwerman (NRAO) Frank Primini (CfA) Julian Osborne (Leicester) Ulrich Kolb (Open) Stephen Murray (CfA) Rosanne Di Stefano (CfA) Paul Callanan (Cork) Paul Plucinsky (CfA) Terry Gaetz (CfA) Manami Sasaki (CfA) Knox Long (STScI) Tsevi Mazeh (TAU) Avi Shporer (TAU) Wolfgang Pietsch (MPI) Frank Haberl (MPI) Parviz Ghavamian (JHU) Jack Hughes (Rutgers) Frank Winkler (Midd) William Blair (JHU) Richard Edgar (CfA) Robert Kirshner (CfA) Miguel de Avillez (Vienna) Dieter Breitschwerdt (Vienna) Ralph Tϋllmann (CfA) Randall Smith (JHU) Thomas Pannuti (Morehead) David Helfand (Columbia) Luciana Bianchi (JHU) Jonathan Grindlay (CfA) Kip Kuntz (JHU) David Thilker (JHU) Motivation: Why M31 and M33 • Interpretation of distant galaxies, where less detail is available. • Most nearby examples of early and late type spiral galaxies. • Probe endpoint of stellar evolution, which drives galaxy evolution. • Additional samples for any class of X-ray sources, ULX, more galactic nuclei. • Disks not edge on. • Sources at a common distance. Outline I. Nuclei Chandra’s abilities to resolve the crowded nucleus. II. SNRs Resolved Multiwavelength Studies (X-ray, optical, radio). III. Transients Well-sampled long-term light curves and counterpart candidates. IV. Conclusions Nuclei • M31 and M33 offer 2 of the closest spiral galaxy nuclei other than the Milky Way • Chandra can potentially resolve the weak nuclear emission. • The best places to study under-luminous nuclei. Nuclei Bondi radius resolved by Chandra (Garcia et al. 2005). X-ray Optical (X-ray contours) Chandra-HRC image of M31 nucleus and optical overlaid with X-ray contours Correcting for small extraction radius and absorption (assuming Γ=1.7, NH=7X1020 cm-2), gives 9X1035 erg/s (0.3-7 keV). Nuclei Variability on timescales of < Months. Lightcurve Nucleus Nuclei • Like Milky Way, low luminosity for mass and gas density • Accretion rate is similar to star formation in nuclear cluster Lx/LBondi (max luminosity from observed gas density in a classical accretion disk) vs. Lx/LBondi RBondi (radius of accretion influence) for several SMBHs. M31 MWG RBondi (arcsec) •For M31, LBondi = 5X1041 erg/s, assuming ne = 0.1 cm-3 (Dosaj et al. 2002) (~1 M๏ /yr) •Observed accretion (2x10-6 M๏/yr) ~mass and age of nuclear cluster (10-6-10-5 M๏/yr [Chang et al. 2007]) Nuclei M33 has a ULX within 0.6′′ of the nucleus (Dubus & Rutledge 2002). Not associated with the nucleus (Gebhardt et al. 2001; Long et al. 2002) M33 Nucleus in U-band (Dubus et al. 1999) Optical Nucleus dominated by star cluster (Long et al. 2002) (LX (0.3-8 keV) = 1.5 x 1039 erg/s) BH mass <1500 M๏ Close-up of M33 Nucleus in Chandra-HRC image. Yellow circle is 0.6′′ positional error with respect to the nucleus. Nuclei The ULX is variable and dwarfs any contribution from the nucleus to the X-ray emission by a factor of at least 14 (Dubus et al. 2004). Lightcurve Radial Profile Spectral variability, UV spectrum (40 Myr old starburst, Long et al. 2002) and lack of optical counterpart all consistent with a black hole binary, perhaps an HMXB like LMC X-3 (La Parola et al. 2003; Foschini et al. 2004). Nuclei The Chandra ACIS Survey of M33 (ChASeM33) data may be able to separate the extended nuclear emission from the ULX. Model PSF ACIS Image Pileup makes central ~2.5” difficult to interpret! Nuclei Only diffuse emission is seen outside of 2.5”. Perhaps more detailed analysis and simulations will show more. Nuclei • M31 is only resolved with Chandra, and shows faint emission from the nucleus, of similar type to Milky Way. • M33 nucleus is yet to be detected behind the ULX, even with Chandra resolution. Supernova Remnants (SNRs) • Key for learning current SN rate, SN feedback effects, and shock physics. • Chandra resolves X-ray counterparts to known SNRs and discovers new SNRs from their resolved X-ray appearance. • Resolved SNR studies constrain ages and shock properties. http://chandra.harvard.edu/photo/2005/casa Chandra Discovers and Resolves M31 SNRs 1 2 • Two resolved discoveries • Intermediate age • Low density ISM kT=0.17, t~17 kyr, n=0.2 kT=0.3, t~9 kyr, n=0.3 Williams et al. 2004 Chandra Discovers and Resolves M31 SNRs 1 2 X-ray contours Radio image Kong et al. 2003 Radio discoveries confirmed by resolved Chandra imaging Williams et al. 2004 SNR r3-63: The Brightest X-ray SNR • X-ray bright • Old • Low density ISM Williams et al. 2005 Kong et al. 2002b; Williams et al. 2005a Radius = 21 pc LX(0.3-7)~1037 erg/s kT ~ 0.16 keV 0.1<n0<0.3 cm-3 Age ~ 20 kyr (Kong et al. 2002b; Williams et al. 2005a) X-ray SNRs: M33 ChASeM33: X-ray remnants appear to trace the southern spiral structure (Plucinsky et al. 2007). Ha Green circles mark SNRs. Great correspondence: Younger SNRs? High ISM density? IR 3.6 μm 9.3′ X 15.6′ (Also see work by Ghavamian et al. and Pietsch et al) SNRs The brightest one (SNR21; Gordon et al. 1998) has a wellsampled X-ray spectrum and an interesting morphology (Gaetz et al. 2007). Narrow-band optical image of the H II region NGC592. The strong [S II] emission of the SNR makes it appear green in this image. Red=Ha, Green=[S II], Blue=[O III] SNR21 Smoothed Chandra Deconvolved Chandra Narrow-band optical (continuum subtracted) Narrow-band optical To H II Region Core High-mass progenitor? Relatively Young Hot High ISM density LX(0.25-4.5) = 1037 erg/s Vshock ~ 600 km/s Radius = 10 pc kT ~ 0.46 keV n ~ 2 cm-3 Age ~ 7 kyr Log[E0(ergs)] ~ 51.25 Gaetz et al. 2007 M33 SNRs: More to come • Strong emission lines suggest it is O-rich (J. Hughes et al., in prep) • We are detecting the ejecta directly! • Very young; a gem for studying heavy element creation and distribution. ACIS-I Spectrum Initial spectral fitting suggests high O/Fe, Ne/Fe, and Mg/Fe ratios, comparable to the known O-rich SMC SNR 1E 0102-7219 SNRs M31 and M33 both have SNRs well-resolved by Chandra. M31 ISM appears to be of generally low density. Many optical SNRs in M33 are strong X-ray emitters. (Young? More dense ISM?) X-ray Transients (XRTs) • Chandra’s resolution and pointing capabilities (rotating solar panels) both key for this research. • Large fraction of Galactic LMXBs that exhibit bright (>1037 erg/s) transient outbursts have been shown to contain black holes (McClintock & Remillard 2004). • There are only ~20 such objects in the Galaxy, and each is vital for studies of accretion physics in the strong gravity regime. Finding more is worthwhile. (In addition to our work, lots of great work by, e.g. Trudolyubov et al.; Pietsch et al.) M31 Transient Population 8 Years of Chandra Observations (1999-2007) ACIS-I More than 50 transients! HRC The Transient Population: Movie ACIS-I central 5’ X 5’ 4-12 ks images >2e36 erg/s Red = 0.3-1 keV Green = 1-2 keV Blue = 2-7 keV The Transient Population: Movie ACIS-I central 5’ X 5’ 4-12 ks images >2e36 erg/s Red = 0.3-1 keV Green = 1-2 keV Blue = 2-7 keV Luminosity The Transient Population: Lightcurves Stars: HRC Full Squares: ACIS-I Open Squares: ACIS-S Circles: XMM Time Williams et al. 2006b Williams et al. 2005 Similar Global Properties to Galactic transients Distribution of Decay Times Distribution of Peak Luminosities Williams et al. 2006b log (d) = 1.5 +/- 0.5 (Galactic is 1.2 +/- 0.4; Chen et al. 1997) Most sources 1037<LX<1038 (Galactic sample has mean of LX=0.2 LEdd; Chen et al. 1997) Cumulative number with lower duty cycle Similar Global Properties to Galactic transients • The best light curves allow duty cycle constraints. • About half are constrained to <0.1, and nearly all are <0.2. • Constrains NS/BH ratio! Fundamental stellar evolution/IMH parameter. Williams et al. 2006b Duty Cycle About 1/100 sources > 2*1036 erg/s is transient. If transients are black holes, and others are neutron stars, then NS/BH1*(dc/0.01). Optical Luminosity and Orbital Period Optical Luminosity •Orbital Period of Galactic LMXBs is correlated with Optical and X-ray luminosity (van Paradijs & McClintock 1994). Blue points show more recent transients during outburst. • Possible Explanation: larger disks, which may be associated with longer period binaries, glow brighter in optical. LX * Orbital Period2/3 The first XRT follow-up with ACS was 16’ off-axis Linear decay indicates large disk Flux X-rays on X-rays off Time • If this is the counterpart, Lx=1.4E38 erg/s , MV ~ -0.3, P ~ 1 day. Williams et al. 2005b Optical on Optical off Flux A more typical follow-up was only 4’ off-axis Optical on Optical off X-rays on X-rays off Time • • • • 0.2” error circle Counterpart faded, but is blended with another star If star to NE in blend is the counterpart, MV ~ -1.2, Lx ~ 6E37 erg/s, P~8 days If counterpart is a third unresolved source, MV > -1.2 and P < 8 days (Williams et al. 2005c) The Search continues… • Thirteen transients followed up so far, with luminosities ranging from 1036 – 1038 erg/s (Williams et al.; Galache et al.) • Follow-up optical continues, but more difficult with WFPC2.. • Periods still range from 1-23 days, with most being <5 days, similar to the distribution of Galactic XRTs. • Period distribution is a fundamental constraint for models of binary formation and evolution. X-ray Transients in M33 • Smaller galaxy, no large bulge, therefore no old and dense population of stars. • Transients may not be dominated by LMXBs. • ChASeM33 scheduling not optimal for transient search. • Most of the galaxy has been observed more than once. Relative Flux Seven Good Candidates Found Time Active and Quiescent X-ray Images Different Exposure Times! Low-count spectra are of a wide variety Hard Soft Softer The hardest spectra have photon indices of <1, possible HMXBs. Different from M31, where all of the spectra have been soft (Γ>1.5). The soft spectra have photon indices of ~1.5-2.0, possible LMXBs or AGNs. Softer spectrum is blackbody with 0.04<kT<0.5 keV, possible BHB. Low-count spectra are of a wide variety Flux Black: XMM-PN 02-Aug-2000 Resid Red: XMM-PN 04-Aug-2000 0.35 keV Softest! 1.0 Green: Chandra ACIS-S 30-Aug2000 Supersoft source with kT = 50 eV (agrees with Grimm et al. 2007) (See work on periodicities in SSSs in M31 by Trudolyubov et al. 2007, King et al. 2002 Optical counterparts XRT-1 XRT-3 XRT-4 Soft Transient – Red variable Star Hard Transients (HMXBs) – Blue Variable Stars Infrared counterparts from Spitzer XRT-7 XRT-2,4,5 Stern et al. 2005 One transient has the IR colors of an AGN; the rest are consistent with stars. Transients in M33 7 (6 new) transient candidates found in M33 3 could be LMXBs in different states 2 are likely HMXBs 1 is a supersoft source 1 is likely an AGN These transients appear to be generally fainter and more spectrally diverse than those we often see in M31. Still more ChASeM33 data to be analyzed. Conclusions: Comparing Galaxies Property M31 Milky Way M33 Type Metal-rich, luminous early spiral Moderately metalrich intermediate spiral Metal-poor low luminosity, late spiral Nucleus Very faint, massive black hole Very faint, lowermass black hole Dominated by ULX, little or no massive black hole. Transients (LMXBs) Soft spectra, short Soft spectra, short Small sample, faint, periods, 30 day periods, 30 day and diverse decay times. decay times. classification. SNRs Low ISM density X-ray bright are intermediate age Distance uncertainties; extinction; difficult comparison Good correspondence between X-ray and optical; Young? XLF Relatively steep, dominated by old population (Kong et Both HMXB and LMXB populations Dominated by young population HMXBs al, Voss & Gilfanov, Trudolyubov et al., etc.). (e.g. Grimm et al. 2002) (Grimm et al. 2005)