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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 12 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 18 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