Download ly Searching the Sky: The Swift Mission and High Energy Physics Connections

ly Searching the Sky:
The Swift Mission and
High Energy Physics Connections
John Nousek, Abe Falcone & Miles Smith
(Penn State University)
SnowPAC 2010, Snowbird, UT, 24 March 2010
1
History of GRBs
•
GRBs discovered in 1969 by Ray Klebesadel of LANL
– Vela satellites: monitored Nuclear Test Ban treaty
– Data published in 1973
• Compton Gamma-Ray Observatory launched on 5 April 1991
– BATSE: 2609 bursts in 8.5 years
2
Beppo-SAX & HETE-2 Era
GRB 970228 - BeppoSAX
GRB 971214 - Keck
-rays
Fireball Model
(Meszaros & Rees 1997)
afterglow
Observing Scenario
1. Burst Alert Telescope triggers on GRB, calculates position on sky to ~ 1 arcmin
2. Spacecraft autonomously slews to GRB position in 20-70 s
3. X-Ray Telescope determines position to ~2-3 arcseconds
4. UV/Optical Telescope images field, transmits finding chart to ground
BAT Burst Image
XRT Image
UVOT Image
BAT Error
Circle
T<20 sec
T<90 sec
T<300 sec
4
Swift launch:
20 Nov 2004 !!
5
MOC Facility
Located in State College, PA
~ 4 km. from Penn State campus
Flight Operations Team (FOT)
– responsible for observatory
Health & Safety
Science Operations Team
(SOT)
- responsible for scientific
operation of Swift
Has continuously operated
Swift successfully from L+80
minutes to now!
6
475 GRB as of 1 Nov 2009
85% with X-ray detections
~60% with optical detection
155 with redshift (41 prior to Swift)
46 short GRBs localized (0 prior to Swift)
Swift Statistics
2.3 non-GRB TOOs / day
>165,000 targets
Short GRB
Fast Rise Exponential Decay
Short GRB
7
Redshift and Time Distributions
Era of GRBs
Number of GRBs
Long GRBs
20
10
Swift
Pre-Swift
15
10
5
5
0
0
0.1
1.0
10.0
Redshift (z)
Average Redshift
- Pre-Swift: z = 1.2
- Swift:
z = 2.3
1.0
10.0
Lookback Time (G yr)
Analysis by Neil Gehrels
8
High-z GRB - Opportunity
GRBs are briefly the most luminous sources in the universe
.... across the E-M spectrum!
High-z GRBs offer unique tool for studying:
- Reionization era
- Abundance history of universe
- First stars & first light
- Star formation rate history
- Gas and dust content of early galaxies
239 Swift GRBs with XRT
CHALLENGE:
Fraction with OT
Fraction with z
2005 2006 2007
Difficult to determine redshift for high-z bursts
Bursts not detected in optical can be common dark GRBs or rare
high-z events.
Needed: rapid response, large telescope, IR spectrograph
Needed: redshift indicators, good position on sky for follow-up
9
Dark Ages of Astronomy
(Dark to Light)
Dark
Ages
z=1000
z=5.8
z=0
10
JANUS Objectives
Science Objectives:
(1) Measure SFR 5<z<12 by discovering high-z GRBs & afterglows;
(2) Enumerate brightest quasars over 6<z<10 & measure reionization
contribution;
(3) Enable detailed studies of the reionization history & metal
enrichment in the early Universe;
(4) Provide 3D positions of high-z star-forming galaxies & SMBHs
to next-generation observatories
11
Swift Operations Currently
•
1st mission extension: 2006-2008 – High-z GRBs and the GI Program
– Swift reduces time on late afterglow followup and increases effort on
finding high redshift GRBs
• Swift introduces GI targets, followed by pressure for increased ToO and
monitoring campaigns
– Improved ToO automation allows multiple ToOs in short period without
new schedule (including nights and week-ends)
• Now: Targets of Opportunity and
Monitoring Campaigns dominate time
• 2.3 ToO requests every day
• Many programs involve support of
other missions, especially high
energy astrophysics
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Benefits of Swift Coordination
•
•
•
•
Swift offers improved angular resolution, typically making unique
identification of counterparts
Swift offers broad-band (optical, UV, X-ray, hard X-ray [to 300 keV])
spectral information about targets
Swift offers rapid-response to transient targets (as fast as 40
minutes, with 2-4 hours typical)
Swift offers low overhead process, i.e. moderated public website for
submission of proposals and very rapid approval cycle
13
Broadband Simultaneous Coverage
Swift
Fermi
VERITAS
UV/optical, X-ray Spectrum:
Swift
15 keV - 150 keV
0.2 keV – 10 keV
650 nm - 170 nm
Gamma ray:
Fermi, AGILE,...
30 MeV – 300 GeV
VHE:
VERITAS, HESS, MAGIC, ...
100 GeV – 50 TeV
Mrk501 SED taken from Catanese & Weekes 1999
Fermi "Sources of Interest"
•
0208-512
0235+164
PKS 0528+134
PKS 0716+714
0827+243
OJ 287
For a list of “23 sources of interest," light curves and
some reduced data are being released by Fermi
• Flaring sources also receive ATELs followed by public
release of data
• Most of these sources are blazars
(one X-ray/TeV binary: LS I +61303)
Mrk 421
W Com
Swift Monitoring of GeV-TeV sources
3C 273
3C 279
1406-076
•
H 1426+428
1510-089
PKS 1622-297
•
1633+383
Mrk 501
•
3EGJ1733-1313
1ES 1959+650
PKS 2155-304
BL_Lacertae
•
3C 454.3
1ES 2344+514
LS I +61 303
•
Swift is monitoring each of the above sources on weekly
basis for 1-2 ksec per week for ~4 months per source
Additionally, intensive Swift monitoring sometimes
results as part of larger campaigns and ToOs
Follow-up is frequently coordinated with TeV
observatories, resulting in multiwavelength data from
UVOT, XRT, BAT, Fermi, TeV telescopes, and others
Near-real-time light curves are publicly available:
http://www.swift.psu.edu/monitoring
Contact [email protected] if you are interested in
further coordination for your favorite source
TeV Blazars - Examples
3C 66A
•
•
•
Swift, MDM, Fermi, & VERITAS •
(time averaged) spectral data
during high state on Oct 4-6
•
Due to broadband coverage,
spectrum is tightly constrained
Model including an external
Compton component favored
•
Dashed line: pure SSC, solid line: SSC+EC
See: Reyes et al. 2009, ICRC proc.
Benbow et al. 2010 (2nd Fermi Symp.)
RGB J0710+591
New VERITAS detection with
contemporaneous Swift & Fermi data
SSC model fits data nicely, and EC allowed,
but does not improve fit. Model of Chiang &
Boettcher (2002) is used with TeV photon
absorption model of Franceschini et al.
(2008).
Low, sub-equipartition magnetic field is
implied by the fit (~10 mG), with remarkably
hard electron injection spectrum (q ~ 1.5).
Fortin, Perkins, et al. 2010 (2nd Fermi Symp.)
Acciari et al. 2010
Time dependent Blazar SEDs
3C 279
These Swift and Fermi monitoring data are
being used, in conjunction with other
multiwavelength data, to systematically
study all monitored blazars SEDs and
locate them within the “blazar sequence”
and the time variability of the νpeak location
relative to flux
(Lee et al. 2010; Abdo et al. 2010)
preliminary
17
Other Swift Programs on Astroparticle accelerators
Swift is searching for counterparts to Fermi and
TeV Unassociated sources. We are beginning a
program to spend nearly 1 Msec searching all
Fermi unassociated sources in the first catalog.
Active TeV regions
Selected TeV UnID sources,
Aharonian et al. 2005, 2008
Swift is obtaining multi-wavelength data
on TeV/X-ray binaries which may have
strong particle accelerating jets and/or
wind interaction shocks, e.g. LS I +61303
Active X-ray Regions
Holder, Falcone, Morris 2007; Smith et al. 2008;
Esposito et al. 2007; Acciari et al. 2009
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Neutrinos: IceCube
• Neutrinos interact with
polar ice to produce a
charged particle
• Cherenkov radiation along
particle track can be detected
Update
79 IceCube
strings as of
January 2010
19
Neutrinos: Motivation for Swift
•
UHECRs are known to be extragalactic, but intervening magnetic fields make it
difficult to discover exactly where they come from.
•
The same violent processes (e.g. GRBs) conjectured to produce UHECRs are also
expected to produce neutrinos.
•
Neutrinos point back to their source across a broad energy range.
•
Failure of a relativistic jet to break through the stellar envelope may lead to -dark
bursts, where prompt -rays are not observed.
•
Dark bursts may be 10 times more numerous than GRBs, while many GRBs are
missed because they are not in the FOV of a telescope.
•
Delayed X-ray emission could still be observed with Swift, even without a -ray
trigger. IceCube can provide the trigger, while Swift provides imaging.
20
Neutrinos: Swift follow-up
• IceCube reconstructs the position of each neutrino event (mostly atmospheric ν’s)
• If a neutrino pair is observed, use their angular separation to test if they could both
be from an astrophysical source (rather than pileup of background)
• Search for an X-ray counterpart with Swift in a region around the mean location of
the neutrino pair
• In its 22-string configuration, IceCube discovered a candidate steady neutrino point
source at 2.2σ (later to be ruled out). Swift imaged the region (left). Due to the large
angular resolution of Icecube, 9 pointings were then required to cover the error circle.
IC22 (22 strings)
(May 07 – Apr 08)
X-ray
source
IC79 (79 strings)
(2010 ff)
XRT
FOV
XRT
FOV
1° error
circle
Figure by
Derek Fox
IceCube resolution
for doublet neutrinos
IceCube resolution
21
for single neutrinos
Neutrinos: Significance
• The test case (previous slide) found 36 X-ray point sources in a 1° circle. We need
to reduce the number of candidate sources for each follow-up observation
• Improved IceCube position uncertainty will reduce the number of Swift fields to 4.
• We can also use timing information. Since we are searching for the X-ray afterglow
of a burst-like event, expect to see a strong fall off in intensity with time. Use this
information to distinguish from steady or slowly varying sources
• To understand the significance of a discovery, need to understand the frequency of
serendipitous fading X-ray sources
A typical GRB X-ray light curve
Significance of a Swift-IceCube discovery (1 year)
Single IceCube event rate (mostly atm ν)
6 hr-1
Timing coincidence window (IceCube)
100 sec
Spatial coincidence window (IceCube)
2 deg
Accidental coincidence rate (IceCube)
5 yr-1
Serendipitous fading X-ray sources (Swift)
1 sr-1 (?)
False positive events (Swift+IceCube)
1.7x10-3 yr-1
Significance of 1 Swift+IceCube event
~3.1σ
Significance of 2 Swift+IceCube events
~4.7σ
22
Gravitational Waves: LIGO/Virgo
• The Laser Interferometer Gravitational-Wave
Observatory (LIGO) and it European
counterpart (Virgo) are searching for
gravitational waves
• Each consists of a laser interferometer with
two orthogonal arms 2-4 km long. Multiple
reflections extend the effective optical length to
hundreds of km.
• The nearby (< 100 Mpc) late stage merger of
compact bodies is expected to produce
gravitational waves that can be detected by the
LIGO and Virgo detectors.
• Three gravitational wave detectors can be used
to triangulate the source.
LIGO Observatory in Livingston, LA
LIGO
Hanford
LIGO
Livingston
Virgo
23
Gravitational Waves: Swift follow-up
• LIGO analyzes a candidate trigger by dividing the sky into 0.4°× 0.4° pixels and
assigning a likelihood to each pixel. A combined LIGO/Virgo trigger will produce
a region of ~50 pixels, localizing the candidate gravitational wave source
• Currently, LIGO/Virgo is sensitive out to ~100 Mpc. A real-time catalog search
will identify those pixels that contains a known galaxy within 100 Mpc
(approximately 1 in 5 pixels)
• There is evidence that short GRBs occur in galactic halos, so we will use Swift to
search for X-ray afterglow in an ~20 kpc region around each candidate galaxy
• For galaxies closer than 5.7 Mpc, the search region is
larger than the XRT FOV, so some tiling will be required
• If an X-ray source is discovered, we will identify if it is
fading and use its brightness and distance from the
candidate galaxy to attach a significance to the discovery
Candidate
galaxy
20 kpc
X-ray
source
24
Gravitational Waves: Significance
Assuming n(S) = 1 deg-2
• ~10 candidate galaxies per LIGO trigger must
each be imaged by Swift on separate orbits
Distance to
galaxy (r)
Angular size of
20 kpc search
region
P-value for
discovery of
X-ray source
• If a significant X-ray source is discovered, we
would like to continue imaging that candidate in
lieu of subsequent galaxies in the list
1 Mpc
2.29 deg
0.98
5 Mpc
0.46 deg
0.15
10 Mpc
0.23 deg
0.04
50 Mpc
0.046 deg
0.002
100 Mpc
0.022 deg
0.0004
Fading sources
(unmeasured)
All serendipitous
XRT sources
?
Figure by M. Perri et al
• A real-time significance test requires a
knowing the number of serendipitous XRT
sources n(S) per deg2 above a threshold flux S
• For many galaxies, the angular search area
will be small and a positive result will be
highly significant, even without determining if
the source is fading
• For nearby sources, will need to use time
25
information as an additional tool