tidal disruptions of stars by supermassive black holes

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Tidal Disruptions of Stars by Supermassive Black Holes. Suvi Gezari (Caltech) Chris Martin & GALEX Team Bruno Milliard (GALEX) Stephane Basa (SNLS). Outline. Probing the mass of dormant black holes in galaxies Tidal disruption theory Candidates discovered by ROSAT - PowerPoint PPT Presentation

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  • Tidal Disruptions of Stars by Supermassive Black HolesSuvi Gezari (Caltech)

    Chris Martin & GALEX Team

    Bruno Milliard (GALEX)Stephane Basa (SNLS)

  • OutlineProbing the mass of dormant black holes in galaxies

    Tidal disruption theory

    Candidates discovered by ROSAT

    Search for flares with GALEX

    GALEX tidal disruption flare detections

    Future detections

  • Probing the Mass of DormantSupermassive Black HolesDirect dynamical measurement of MBH is possible when Rinf GMBH/2 is resolved.

    Kormendy & Bender (1999)Ghez+ (2005)Milky WayM31

  • Probing the Mass of DormantSupermassive Black HolesA dormant black hole will be revealed when a star approaches closer than RTRstar(MBH/Mstar)1/3, and is tidally disrupted.

    This is a rare event in a galaxy, occurring only once every 103-105 yr depending on MBH and the nuclear density profile of the galaxy.

    Rees (1988)

  • Probing the Mass of DormantSupermassive Black HolesL LEdd = 1.3x1044 (MBH/106 Msun) ergs s-1

    Blackbody spectrum: Teff=(LEdd/4RT2)1/4.

    Start of flare: (t0-tD) k-3/2MBH1/2

    Power-law decay: dM/dt (t-tD)-5/3.

    The temperature, luminosity, and decay of the flare can be used as a direct probe of MBH.

    Evans & Kochanek (1989)t-5/3

  • Previous Tidal Disruption Event CandidatesThe ROSAT All-sky survey in 1990-1991 sampled hundreds of thousands of galaxies in the soft X-ray band (0.1-2.4 keV).

    Detected a large amplitude soft X-ray flare from 3 galaxies which were classified as non-active from ground based spectra.

    Follow-up narrow-slit HST/STIS spectroscopy confirmed the ground-based classifications of 2 of the galaxies (Gezari+ 2003).

    Halpern, Gezari, & Komossa (2004)Lflare/L10yr = 240Lflare/L10yr = 1000Lflare/L10yr = 6000HST Chandra

  • Searching for Flares with GALEX50 cm telescope with a 1.2 deg2 field of view.Simultaneous FUV/NUV imaging and grism spectraData is time-tagged photon data (t=5ms) accumulated in 1.5 ks eclipses.Some deep fields are revisited over a baseline of 2-4 years to complete deep observations.Take advantage of the UV sensitivity, temporal sampling, and large survey volume of GALEX to search for flares.

    1350 1750 2800 | | |

  • Searching for Flares with GALEXAssume L=LEdd, and Teff=2.5x105 (MBH/106 Msun)1/12 K.The large K correction makes flares detectable out to high z.Estimated attenuation by HI absorption for z>0.6 from Madau (1995)Contrast with host early type spirals and elliptical galaxies not a problem for detection in the UV.

    1350 1750 2800 | | |Gezari+ (in prep)5x107 Msun1x106 Msun

  • Searching for Flares with GALEXEstimate black hole mass function from Ferguson & Sandage (1991) luminosity function of E+S0 galaxies.Multiply by a factor of 2 for bulges in early-type spirals.Use MBH dependent event rate from Wang & Merritt (2004).Assume fraction of flares that radiate at LEdd from Ulmer (1999).Multiply by volume to which an LEdd flare can be detected in the FUV by a GALEX DIS exposure.

    1350 1750 2800 | | |Gezari+ (in prep)

  • Searching for Flares with GALEXMatch UV sources that vary between yearly epochs at the 5 level with the CFHT Legacy Survey optical catalog.Rule out sources with optical hosts with the colors and morphology of a star or quasar.Follow up galaxy hosts that do not have an hard X-ray detection with optical spectroscopy to look for signs of an AGN.Trigger Chandra TOO X-ray observations of our best candidates.

    1350 1750 2800 | | |Gezari+ (in prep)starsQSOsgalaxiesx : X-ray source

  • Tidal Disruption Flare DetectionsAEGIS DEEP2 spectrum and ACS image of an early-type galaxy at z=0.3698.No evidence of Seyfert-like emission lines.No detection of hard X-rays.Archival Chandra observations during the flare detected a variable extremely soft X-ray source coincident with the galaxy.

    1350 1750 2800 | | |Gezari+ (2006)

  • Tidal Disruption Flare DetectionsTOO VLT spectrum and CFHTLS image of an early-type galaxy at z=0.326.No evidence of Seyfert-like emission lines.No detection of hard X-rays.First optical detection of a tidal disruption flare.Triggered a Chandra TOO observation which detected an extremely soft X-ray source coincident with the galaxy.

    1350 1750 2800 | | |Gezari+ (in prep)

  • Tidal Disruption Flare DetectionsWell described by a t-5/3 power-law decay.MBH=k3[(t0-tD)/0.11]2 *106 Msun1350 1750 2800 | | |Gezari+ (2006)Gezari+ (in prep)(t0-tD)/(1+z)=0.1-0.7 yr k3 (1-4)x107 Msun(t0-tD)/(1+z)=0.450.4 yr k3 (1.70.3)x107 Msun

  • Tidal Disruption Flare DetectionsTBB few x 105 K RBB 1 x 1013 cm RT= 1.5 x 1013 (MBH/107 Msun)1/3 cmRSch= 3 x 1012 (MBH/107 Msun) cmGezari+ (2006)Gezari+ (in prep)Lbol = 6.5x1044 ergs s-1Lbol > 1x1044 ergs s-1

  • Future DetectionsGALEX has proven to be successful in detecting tidal disruption flares.

    Goal is to measure the detailed properties and rate of the events to probe accretion physics, the mass of the black hole, and evolution of the tidal disruption rate.

    The next generation of optical synoptic surveys such as Pan-STARRs and LSST have the potential to detect hundreds of events.

    With a large sample we can probe the evolution of the black hole mass function, independent of studies of active galaxies.

  • Stay Tuned for More Flares!

    The spectrum of a tidal disruption flare is characterized by blackbody radiation from a thick disk with Rbb=RT, radiatig at Ledd.

    The decay of the flare is determined by the rate of return of mass to pericenter, which declines over time as a t-5/3 power-law.