Transcript burrows_liverpool2012x

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)
– 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.
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
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
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GALEX candidate TDEs
GALEX: Gezari+ 2008
GALEX: 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 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, 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 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] 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,
Alert arrived at 9:21 AM EDT,
during our daily planning telecon.
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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, 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 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] galactic lon,lat of the burst (or
transient)
ECL_COORDS: 216.97, 77.54 [deg] ecliptic lon,lat of the burst (or
transient)
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
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 seconds
after the BAT trigger. XRT found a bright, uncatalogued X-ray source
located 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). This
location is 62 arcseconds from the BAT onboard position, within the BAT
error circle. No event data are yet available to determine the column
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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, 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 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] galactic lon,lat of the burst (or
transient)
ECL_COORDS: 216.97, 77.54 [deg] ecliptic lon,lat of the burst (or
transient)
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
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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
11843)
(Campana 2011, GCN Circ.
• 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 fallback 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
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Tidal disruption
events are
expected to have a
characteristic fallback 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
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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 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
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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
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 event
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The
End
The
End
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