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Death Throes of an Unlucky Star

Death Throes of an Unlucky Star. (aka Swift J164449.3+573451) Prof. David Burrows, Penn State. We now know that most galaxies have a supermassive black hole (SMBH) at their center Most of these black holes are inactive (very weak emission)

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Death Throes of an Unlucky Star

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  1. Death Throes of an Unlucky Star (aka Swift J164449.3+573451) Prof. David Burrows, Penn State

  2. We now know that most galaxies have a supermassive black hole (SMBH) at their center • Most of these black holes are inactive (very weak emission) • Why? Need to have material falling onto BH to make an AGN • Can a dormant SMBH become active? Liverpool GRBs

  3. Tidal Disruption of Stars Artist’s conception of a star being ripped apart by a black hole. NASA Liverpool GRBs

  4. Tidal disruption models • Tidal disruption of star results in • ~ ½ of star generating accretion disk around BH • ~ ½ of star being ejected • Captured gas falls back onto black hole with accretion rate proportional to t-5/3 Liverpool GRBs

  5. Tidal disruption models • Expect optical, UV, X-ray flares from: • Compression of star during close pass • Emission from accretion disk • Outflowing wind • Characteristic luminosities of ~ 1042 – 1044 erg/s (at low end of known AGN luminosity distribution) • Estimated rate is once every 104 – 106 years (per galaxy) Liverpool GRBs

  6. X-ray flares NGC 5905 / IC 3599: bright X-ray flares in galaxies that show no signs of AGN behavior. Dotted line shows expected t-5/3 decay ROSAT: Komossa and Bade, 1999 Liverpool GRBs

  7. GALEX candidate TDEs GALEX: Gezari+ 2009 GALEX: Gezari+ 2008 Liverpool GRBs

  8. March 28, 2011 NASA’s Swift satellite detects a bright flash of X-rays from the constellation Draco. Liverpool GRBs

  9. Automated notifications TITLE:           GCN/SWIFT NOTICE NOTICE_DATE:     Mon 28 Mar 11 13:18:15 UT NOTICE_TYPE:     Swift-BAT GRB Position TRIGGER_NUM:     450158,   Seg_Num: 0 GRB_RA:          251.233d {+16h 44m 56s} (J2000),                 251.284d {+16h 45m 08s} (current),                 251.009d {+16h 44m 02s} (1950) GRB_DEC:         +57.590d {+57d 35' 25"} (J2000),                 +57.570d {+57d 34' 12"} (current),                 +57.680d {+57d 40' 49"} (1950) GRB_ERROR:       3.00 [arcmin radius, statisticalonly] GRB_INTEN:       0 [cnts]    Image_Peak=7382 [image_cnts] TRIGGER_DUR:     1208.000 [sec]   (=20.1 [min]) TRIGGER_INDEX:   20000     E_range: 15-50 keV BKG_INTEN:       0 [cnts] BKG_TIME:        0.00 SOD {00:00:00.00} UT BKG_DUR:         0 [sec] GRB_DATE:        15648 TJD;    87 DOY;   11/03/28 GRB_TIME:        46665.20 SOD {12:57:45.20} UT GRB_PHI:         -23.31 [deg] GRB_THETA:        39.76 [deg] SOLN_STATUS:     0x13 RATE_SIGNIF:     0.00 [sigma] IMAGE_SIGNIF:    7.60 [sigma] MERIT_PARAMS:     +1  +0  +0  +7  +1  -2  +0  +0 +18  +0 SUN_POSTN:         6.90d {+00h 27m 36s}   +2.98d {+02d 58' 54"} SUN_DIST:        100.82 [deg]   Sun_angle= 7.7 [hr] (West of Sun) MOON_POSTN:      302.67d {+20h 10m 41s}  -17.21d {-17d 12' 50"} MOON_DIST:        85.99 [deg] MOON_ILLUM:      30 [%] GAL_COORDS:       86.72, 39.43 [deg] galacticlon,lat of the burst (or transient) ECL_COORDS:      216.97, 77.54 [deg] eclipticlon,lat of the burst (or transient) COMMENTS:        SWIFT-BAT GRB Coordinates.   COMMENTS:        This is an image trigger.  (The RATE_SIGNIF & BKG_{INTEN, TIME, DUR} areundefined.)   COMMENTS:        A point_sourcewasfound.   COMMENTS:        This does not match any source in the on-boardcatalog.   COMMENTS:        This does not match any source in the groundcatalog.   COMMENTS:        This is a GRB.   COMMENTS:        This triggeroccurred at longitude,latitude = 182.91,10.69 [deg].   Alert arrived at 9:21 AM EDT, during our daily planning telecon.

  10. GCN Circular TITLE:           GCN/SWIFT NOTICE NOTICE_DATE:     Mon 28 Mar 11 13:18:15 UT NOTICE_TYPE:     Swift-BAT GRB Position TRIGGER_NUM:     450158,   Seg_Num: 0 GRB_RA:          251.233d {+16h 44m 56s} (J2000),                 251.284d {+16h 45m 08s} (current),                 251.009d {+16h 44m 02s} (1950) GRB_DEC:         +57.590d {+57d 35' 25"} (J2000),                 +57.570d {+57d 34' 12"} (current),                 +57.680d {+57d 40' 49"} (1950) GRB_ERROR:       3.00 [arcmin radius, statisticalonly] GRB_INTEN:       0 [cnts]    Image_Peak=7382 [image_cnts] TRIGGER_DUR:     1208.000 [sec]   (=20.1 [min]) TRIGGER_INDEX:   20000     E_range: 15-50 keV BKG_INTEN:       0 [cnts] BKG_TIME:        0.00 SOD {00:00:00.00} UT BKG_DUR:         0 [sec] GRB_DATE:        15648 TJD;    87 DOY;   11/03/28 GRB_TIME:        46665.20 SOD {12:57:45.20} UT GRB_PHI:         -23.31 [deg] GRB_THETA:        39.76 [deg] SOLN_STATUS:     0x13 RATE_SIGNIF:     0.00 [sigma] IMAGE_SIGNIF:    7.60 [sigma] MERIT_PARAMS:     +1  +0  +0  +7  +1  -2  +0  +0 +18  +0 SUN_POSTN:         6.90d {+00h 27m 36s}   +2.98d {+02d 58' 54"} SUN_DIST:        100.82 [deg]   Sun_angle= 7.7 [hr] (West of Sun) MOON_POSTN:      302.67d {+20h 10m 41s}  -17.21d {-17d 12' 50"} MOON_DIST:        85.99 [deg] MOON_ILLUM:      30 [%] GAL_COORDS:       86.72, 39.43 [deg] galacticlon,lat of the burst (or transient) ECL_COORDS:      216.97, 77.54 [deg] eclipticlon,lat of the burst (or transient) COMMENTS:        SWIFT-BAT GRB Coordinates.   COMMENTS:        This is an image trigger.  (The RATE_SIGNIF & BKG_{INTEN, TIME, DUR} areundefined.)   COMMENTS:        A point_sourcewasfound.   COMMENTS:        This does not match any source in the on-boardcatalog.   COMMENTS:        This does not match any source in the groundcatalog.   COMMENTS:        This is a GRB.   COMMENTS:        This triggeroccurred at longitude,latitude = 182.91,10.69 [deg].   Alert arrived at 9:21 AM EDT, during our daily planning telecon. TITLE:   GCN CIRCULAR NUMBER:  11823 SUBJECT: GRB 110328A: Swift detection of a burst DATE:    11/03/28 13:32:29 GMT J. R. Cummings (NASA/UMBC), S. D. Barthelmy (GSFC), ... report on behalf of the Swift Team: At 12:57:45 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 110328A (trigger=450158).  Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 251.233, +57.590 which is   RA(J2000)  =  16h 44m 56s Dec(J2000) = +57d 35' 25" with an uncertainty of 3 arcmin (radius, 90% containment, including systematicuncertainty).  As istypical for 20-min long image triggers, the BAT lightcurvedoes not show anythingsignificant. The XRT beganobserving the fieldat 13:22:19.8 UT, 1474.6 seconds after the BAT trigger. XRT found a bright, uncatalogued X-ray source locatedat RA, Dec 251.2054, +57.5808 whichisequivalent to:   RA(J2000)  = 16h 44m 49.29s Dec(J2000) = +57d 34' 50.8" with an uncertainty of 6.3 arcseconds (radius, 90% containment). This location is 62 arcseconds from the BAT onboard position, within the BAT errorcircle. No event data are yetavailable to determine the column densityusing X-ray spectroscopy. UVOT took a findingchartexposure of 150 seconds with the White filter starting 1482 seconds after the BAT trigger. No credibleafterglow candidate has been found in the initial data products. The 2.7'x2.7' sub-image covers 100% of the XRT errorcircle. The typical 3-sigma upperlimit has been about 19.6 mag. The 8'x8' region for the list of sources generated on-boardcovers 100% of the XRT errorcircle. The list of sources istypicallycomplete to about 18 mag. No correction has been made for the expected extinction corresponding to E(B-V) of 0.02. BurstAdvocate for thisburstis J. R. Cummings (jayc AT milkyway.gsfc.nasa.gov). Please contact the BA by email if yourequireadditional information regarding Swift followup of thisburst. In extremely urgent cases, after trying the BurstAdvocate, youcan contact the Swift PI by phone (see Swift TOO web site for information: http://www.swift.psu.edu/too.html.)

  11. GCN Circular TITLE:           GCN/SWIFT NOTICE NOTICE_DATE:     Mon 28 Mar 11 13:18:15 UT NOTICE_TYPE:     Swift-BAT GRB Position TRIGGER_NUM:     450158,   Seg_Num: 0 GRB_RA:          251.233d {+16h 44m 56s} (J2000),                 251.284d {+16h 45m 08s} (current),                 251.009d {+16h 44m 02s} (1950) GRB_DEC:         +57.590d {+57d 35' 25"} (J2000),                 +57.570d {+57d 34' 12"} (current),                 +57.680d {+57d 40' 49"} (1950) GRB_ERROR:       3.00 [arcmin radius, statisticalonly] GRB_INTEN:       0 [cnts]    Image_Peak=7382 [image_cnts] TRIGGER_DUR:     1208.000 [sec]   (=20.1 [min]) TRIGGER_INDEX:   20000     E_range: 15-50 keV BKG_INTEN:       0 [cnts] BKG_TIME:        0.00 SOD {00:00:00.00} UT BKG_DUR:         0 [sec] GRB_DATE:        15648 TJD;    87 DOY;   11/03/28 GRB_TIME:        46665.20 SOD {12:57:45.20} UT GRB_PHI:         -23.31 [deg] GRB_THETA:        39.76 [deg] SOLN_STATUS:     0x13 RATE_SIGNIF:     0.00 [sigma] IMAGE_SIGNIF:    7.60 [sigma] MERIT_PARAMS:     +1  +0  +0  +7  +1  -2  +0  +0 +18  +0 SUN_POSTN:         6.90d {+00h 27m 36s}   +2.98d {+02d 58' 54"} SUN_DIST:        100.82 [deg]   Sun_angle= 7.7 [hr] (West of Sun) MOON_POSTN:      302.67d {+20h 10m 41s}  -17.21d {-17d 12' 50"} MOON_DIST:        85.99 [deg] MOON_ILLUM:      30 [%] GAL_COORDS:       86.72, 39.43 [deg] galacticlon,lat of the burst (or transient) ECL_COORDS:      216.97, 77.54 [deg] eclipticlon,lat of the burst (or transient) COMMENTS:        SWIFT-BAT GRB Coordinates.   COMMENTS:        This is an image trigger.  (The RATE_SIGNIF & BKG_{INTEN, TIME, DUR} areundefined.)   COMMENTS:        A point_sourcewasfound.   COMMENTS:        This does not match any source in the on-boardcatalog.   COMMENTS:        This does not match any source in the groundcatalog.   COMMENTS:        This is a GRB.   COMMENTS:        This triggeroccurred at longitude,latitude = 182.91,10.69 [deg].   2nd alert arrived at 9:57 AM EDT, 36 minutes after the first one. TITLE:   GCN CIRCULAR NUMBER:  11824 SUBJECT: GRB 110328A: a second trigger, probably a hard X-ray transient (Swift J164449.3+573451) DATE:    11/03/28 14:33:10 GMT FROM:    Scott Barthelmy at NASA/GSFC S. D. Barthelmy (GSFC), W. H. Baumgartner (GSFC/UMBC), and cast of thousands report on behalf of the Swift Team: At 13:40:41 UT, the Swift Burst Alert Telescope (BAT) re-triggered on what we are tentatively calling GRB 110328A (trigger=450161).   The BAT on-board calculated location is consistent with the coordinates reported for GRB 110328A (GCN Circ 11823; Cummings et al). Both this trigger and the earlier trigger (450158) were image triggers, so the light curves do not show any significant features. The current trigger was on the rise to the SAA.  The source is brightening. It is quite rare for BAT to trigger a second time on a GRB, so this is either an unusually long GRB, GRB 110328A, or a new galactic transient, Swift J164449.3+573451.  The galactic coordinates are longitude=86.71, latitude=+39.44. We note that the XRT was in Windowed Timing mode during the entire previous observing window, indicating that the X-ray counterpart was quite bright (> 10 cps).  This also suggests either a very long-lived GRB or a galactic transient. We encourage observations at other wavelengths to help determine the nature of this object. /too.html.)

  12. First 3 days Unlike a GRB, this object triggered Swift 4 times over 2 consecutive days. The light curve was unlike anything we had ever seen with Swift in the previous 6 years. Possible Galactic transient? Liverpool GRBs

  13. First 3 days Unlike a GRB, this object triggered Swift 4 times over 2 consecutive days. The light curve was unlike anything we had ever seen with Swift in the previous 6 years. Possible Galactic transient? No: the object is 4.5 billion light years from Earth! z = 0.354 (Levan+ 2011) Liverpool GRBs

  14. At z=0.354, the peak isotropic luminosity is > 1048 erg/s. This direction was observed serendipitously by ROSAT, XMM, Swift/BAT, and MAXI. The source brightened by at least 100x over the past several years, and by about 104 since 1991. Total energy emitted in X-rays: ~8 x 1053 ergs Liverpool GRBs

  15. Clearly not a GRB! Liverpool GRBs

  16. Extreme properties • Extremely high luminosity => powered by gravity • EddingtonLuminosity: L ~ 1.3 x 1044 (M/106 M ) erg/s • Relation between BH Mass and galactic bulge luminosity gives • Mass estimate: M < 20 x 106 M • Rapid time variability => emission comes from a very small region of space • Mass estimate: M > 106 M (Campana 2011, GCN Circ. 11843) • High luminosity (1045– 1048erg/s) implies a jet (beaming factor ~1000) (Campana 2011, GCN Circ. 11843) Liverpool GRBs

  17. Gas accretes in disk, radiation emerges along axis from powerful relativistic jet. Liverpool GRBs

  18. NIR/optical observations show high extinction: the source is only seen in H, K bands. We derive Av ~ 4.5, roughly consistent with NH ≈ 1.5 x 1022 cm-2 derived from the X-ray spectrum.Host galaxy shows no evidence of nuclear activity. Liverpool GRBs

  19. SED at peak flux is explained by single synchrotron component, with IC suppressed by γ-γ pair production to explain LAT and VERITAS upper limits. This implies a bulk Lorentz factor Γ < 20 * Data: Green: bright early flares Cyan: very low state (4.5 days) Black: plateau (8 days) Models: Red: magnetically-dominated synchrotron model for the bright flares (green data points). Low energy electrons suppressed to fit NIR-to-X-ray slope. Blue: corresponding model for the low state (cyan data points). *Γ= (1 – v2/c2)-1/2 (Γ=20 for v=99.9% c) Liverpool GRBs

  20. Long-term behavior: more than a year after the initial BAT trigger, this source continues to be highly variable, with dramatic dips in the X-ray count rate at increasing intervals. The source is still quite bright, with isotropic luminosities of ~ 1045 ergs/s. Overall decay rate is about t-4/3. Liverpool GRBs

  21. Fits to averaged data (averaging in log L and log t) confirm that the late-time decay rate is close to t-4/3 (courtesy John Cannizzo). Liverpool GRBs

  22. Tidal disruption events are expected to have a characteristic fall-back decay that goes like t-5/3. The bolometric light curve should follow this trend, though the light curve in any band may differ substantially from it (Lodato & Rossi 2011). t-5/3 t-5/12 Tidal disruption of solar-type star by 106 MBH. Lodato & Rossi 2011 Liverpool GRBs

  23. Tidal disruption events are expected to have a characteristic fall-back decay that goes like t-5/3. The bolometric light curve should follow this trend, though the light curve in any band may differ substantially from it (Lodato & Rossi 2011). t-5/3 t-4/3 t-5/12 Tidal disruption of solar-type star by 106 MBH. Lodato & Rossi 2011 Liverpool GRBs

  24. Variability • Extremely variable compared to GRBs • Periodicity: no coherent periodicity found (hints of periodic dips at 2.5-3σ; Burrows+11, Saxton+12) • Dips are dominated by changes in flux normalization • Dips: long term p-p variability by 10x • jet precession? Possibly warped disk around rapidly spinning BH (Lei+12; Bardeen-Petterson effect due to stellar orbit not being in BH equatorial plane, leads to jet precession) Liverpool GRBs

  25. Variability • Extremely variable compared to GRBs • Periodicity: no coherent periodicity found (hints of periodic dips at 2.5-3σ; Burrows+11, Saxton+12) • Dips are dominated by changes in flux normalization • Dips: long term p-p variability by 10x • jet precession? Possibly warped disk around rapidly spinning BH (Lei+12; Bardeen-Petterson effect due to stellar orbit not being in BH equatorial plane, leads to jet precession)Aperiodic • disk instabilities? • ? Liverpool GRBs

  26. Alternative scenarios • Synchrotron vs Inverse Compton X-ray data can be interpreted as synchrotron radiation (Burrows+2011) or as Inverse Compton radiation (Bloom+2011), depending on the interpretation of the NIR data. We obtain AV ~ 4.5, while Bloom et al. obtain AV ~ 1.5. Burrows+2011 Bloom+2011 Liverpool GRBs

  27. Alternative scenarios • Nature of system • Star may be on deeply plunging orbit, resulting in capture rather than shredding (tidal obliteration, with stellar fallback taking place in first few days, followed by accretion disk decay; Cannizzo+2011) • System may be WD captured by intermediate mass black hole (time-scale arguments, Krolik & Piran2011) Liverpool GRBs

  28. What about Sgr A*? • What would happen if a star was captured by the MW central BH? • MBH ~ 4 M6 • Lx ~ 4 x 1032 erg/s ~ 0.1 L • Jet like Swift J1644: 200 erg/cm2/s @ Earth • Class Y200 solar flare, 40x brighter than strongest • Integrated flux: ~ 104 J/m2 • 10% of the fluence thought necessary to produce mass extinctions from a 10s GRB (Thomas+2005) Liverpool GRBs

  29. What about Sgr A*? • Gas cloud heading for Sgr A* (Gillessen+2012) • Closest approach: July 2013 @ 36 light hours • M ~ 3ME • Swift campaign • Chandra campaign? • Stay tuned Credit: ESO/MPE/Marc Schartmann Liverpool GRBs

  30. Summary • SED: 20% -50% of bolometric energy in the X-ray band. Total isotropic X-ray energy in first year is ~ 9 x 1053 ergs. • X-ray variability and NIR host luminosity => 1 < M6 < 20 • Ledd ~ M6  1044 erg s-1 => strong relativistic jet pointed towards us • Steep βox ~ 1/3 requires depletion of low energy electrons => strong B • LAT / Veritas upper limits require γ-γabsorption => Γ < 20 • This event is unlike anything else seen by Swift => rate ~ 1/yr in 4π • (Except possibly Swift J2058.4+0516, 18-20 May 2011) • Above imply accretion onto a massive black hole ( ~ 106.5 M) • If TDE: event rate => Γ~ 10-20 or θ ~ 5° • If restarted AGN: event rate => Γ~ 3 or θ ~ 13° • Strong relativistic jet results in unique properties of this event Liverpool GRBs

  31. The End The End Liverpool GRBs Credit: AuroreSimmonet, Sonoma State University

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