Death Throes of

an Unlucky Star

(aka Swift J164449.3+573451)

Prof. David Burrows,Penn State

Liverpool GRBs 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?

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Tidal Disruption of Stars

Artist’s conception of a star being ripped apart by a black hole.

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NASA

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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

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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)

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X-ray flares

ROSAT: Komossa and Bade, 1999

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

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GALEX candidate TDEs

GALEX: Gezari+ 2008GALEX: Gezari+ 2009

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March 28, 2011

NASA’s Swift satellite detects a bright flash of X-rays from the constellation Draco.

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Automated notificationsTITLE: GCN/SWIFT NOTICENOTICE_DATE: Mon 28 Mar 11 13:18:15 UTNOTICE_TYPE: Swift-BAT GRB PositionTRIGGER_NUM: 450158, Seg_Num: 0GRB_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, statistical only]GRB_INTEN: 0 [cnts] Image_Peak=7382 [image_cnts]TRIGGER_DUR: 1208.000 [sec] (=20.1 [min])TRIGGER_INDEX: 20000 E_range: 15-50 keVBKG_INTEN: 0 [cnts]BKG_TIME: 0.00 SOD {00:00:00.00} UTBKG_DUR: 0 [sec]GRB_DATE: 15648 TJD; 87 DOY; 11/03/28GRB_TIME: 46665.20 SOD {12:57:45.20} UTGRB_PHI: -23.31 [deg]GRB_THETA: 39.76 [deg]SOLN_STATUS: 0x13RATE_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] galactic lon,lat of the burst (or transient)ECL_COORDS: 216.97, 77.54 [deg] ecliptic lon,lat of the burst (or transient)COMMENTS: SWIFT-BAT GRB Coordinates. COMMENTS: This is an image trigger. (The RATE_SIGNIF & BKG_{INTEN, TIME, DUR} are undefined.) COMMENTS: A point_source was found. COMMENTS: This does not match any source in the on-board catalog. COMMENTS: This does not match any source in the ground catalog. COMMENTS: This is a GRB. COMMENTS: This trigger occurred at longitude,latitude = 182.91,10.69 [deg].

Alert arrived at 9:21 AM EDT, during our daily planning telecon.

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GCN CircularTITLE: GCN/SWIFT NOTICENOTICE_DATE: Mon 28 Mar 11 13:18:15 UTNOTICE_TYPE: Swift-BAT GRB PositionTRIGGER_NUM: 450158, Seg_Num: 0GRB_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, statistical only]GRB_INTEN: 0 [cnts] Image_Peak=7382 [image_cnts]TRIGGER_DUR: 1208.000 [sec] (=20.1 [min])TRIGGER_INDEX: 20000 E_range: 15-50 keVBKG_INTEN: 0 [cnts]BKG_TIME: 0.00 SOD {00:00:00.00} UTBKG_DUR: 0 [sec]GRB_DATE: 15648 TJD; 87 DOY; 11/03/28GRB_TIME: 46665.20 SOD {12:57:45.20} UTGRB_PHI: -23.31 [deg]GRB_THETA: 39.76 [deg]SOLN_STATUS: 0x13RATE_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] galactic lon,lat of the burst (or transient)ECL_COORDS: 216.97, 77.54 [deg] ecliptic lon,lat of the burst (or transient)COMMENTS: SWIFT-BAT GRB Coordinates. COMMENTS: This is an image trigger. (The RATE_SIGNIF & BKG_{INTEN, TIME, DUR} are undefined.) COMMENTS: A point_source was found. COMMENTS: This does not match any source in the on-board catalog. COMMENTS: This does not match any source in the ground catalog. COMMENTS: This is a GRB. COMMENTS: This trigger occurred at longitude,latitude = 182.91,10.69 [deg].

Alert arrived at 9:21 AM EDT, during our daily planning telecon.

TITLE: GCN CIRCULARNUMBER: 11823SUBJECT: GRB 110328A: Swift detection of a burstDATE: 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 andlocated 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 systematic uncertainty). As is typical for 20-min long image triggers,the BAT lightcurve does not show anything significant.

The XRT began observing the field at 13:22:19.8 UT, 1474.6 secondsafter the BAT trigger. XRT found a bright, uncatalogued X-ray sourcelocated at RA, Dec 251.2054, +57.5808 which is equivalent to: RA(J2000) = 16h 44m 49.29s Dec(J2000) = +57d 34' 50.8"with an uncertainty of 6.3 arcseconds (radius, 90% containment). Thislocation is 62 arcseconds from the BAT onboard position, within the BATerror circle. No event data are yet available to determine the columndensity using X-ray spectroscopy.

UVOT took a finding chart exposure of 150 seconds with the White filterstarting 1482 seconds after the BAT trigger. No credible afterglow candidatehas been found in the initial data products. The 2.7'x2.7' sub-image covers100% of the XRT error circle. The typical 3-sigma upper limit has been about19.6 mag. The 8'x8' region for the list of sources generated on-board covers100% of the XRT error circle. The list of sources is typically complete toabout 18 mag. No correction has been made for the expected extinctioncorresponding to E(B-V) of 0.02.

Burst Advocate for this burst is J. R. Cummings (jayc AT milkyway.gsfc.nasa.gov). Please contact the BA by email if you require additional informationregarding Swift followup of this burst. In extremely urgent cases, aftertrying the Burst Advocate, you can contact the Swift PI by phone (seeSwift TOO web site for information: http://www.swift.psu.edu/too.html.)

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GCN CircularTITLE: GCN/SWIFT NOTICENOTICE_DATE: Mon 28 Mar 11 13:18:15 UTNOTICE_TYPE: Swift-BAT GRB PositionTRIGGER_NUM: 450158, Seg_Num: 0GRB_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, statistical only]GRB_INTEN: 0 [cnts] Image_Peak=7382 [image_cnts]TRIGGER_DUR: 1208.000 [sec] (=20.1 [min])TRIGGER_INDEX: 20000 E_range: 15-50 keVBKG_INTEN: 0 [cnts]BKG_TIME: 0.00 SOD {00:00:00.00} UTBKG_DUR: 0 [sec]GRB_DATE: 15648 TJD; 87 DOY; 11/03/28GRB_TIME: 46665.20 SOD {12:57:45.20} UTGRB_PHI: -23.31 [deg]GRB_THETA: 39.76 [deg]SOLN_STATUS: 0x13RATE_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] galactic lon,lat of the burst (or transient)ECL_COORDS: 216.97, 77.54 [deg] ecliptic lon,lat of the burst (or transient)COMMENTS: SWIFT-BAT GRB Coordinates. COMMENTS: This is an image trigger. (The RATE_SIGNIF & BKG_{INTEN, TIME, DUR} are undefined.) COMMENTS: A point_source was found. COMMENTS: This does not match any source in the on-board catalog. COMMENTS: This does not match any source in the ground catalog. COMMENTS: This is a GRB. COMMENTS: This trigger occurred at longitude,latitude = 182.91,10.69 [deg].

2nd alert arrived at 9:57 AM EDT, 36 minutes after the first one.

TITLE: GCN CIRCULARNUMBER: 11824SUBJECT: GRB 110328A: a second trigger, probably a hard X-ray transient (Swift J164449.3+573451)DATE: 11/03/28 14:33:10 GMTFROM: 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 onwhat we are tentatively calling GRB 110328A (trigger=450161). The BAT on-board calculated location is consistent with the coordinatesreported 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.)

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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?

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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)

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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

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Clearly not a GRB!

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Extreme properties• Extremely high luminosity => powered by gravity

Eddington Luminosity: 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 – 1048 erg/s) implies a jet (beaming factor ~1000) (Campana 2011, GCN Circ. 11843)

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

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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.

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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)

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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.

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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).

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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).

Tidal disruption of solar-type star by 106 M BH.

t-5/3

t-5/12

Lodato & Rossi 2011

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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).

Tidal disruption of solar-type star by 106 M BH.

t-5/3

t-5/12

t-4/3

Lodato & Rossi 201120 June 2012

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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)

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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?• ?

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Alternative scenarios• Synchrotron vs Inverse ComptonX-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.

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Burrows+2011 Bloom+2011

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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 & Piran 2011)

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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)

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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

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Credit: ESO/MPE/Marc Schartmann

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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-γ absorption => 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 event20 June 2012

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TheEnd

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The End