High Energy Phenomena in Relativistic Outflows III Barcelona, 27 June-1 July 2011 HE and VHE Galactic Highlights Marc Ribó
OUTLINE 1. Introduction 2. HE and VHE Galactic sources 3. Pulsars 4. Globular clusters 5. Pulsar Wind Nebulae 6. X-ray binaries 7. Gamma-ray binaries 8. Conclusions
Two year of Fermi satellite image of the sky (Vandenbroucke et al. 2010) .
Known VHE sources As of 2011 May, there are ~115 sources known! ~50 extragalactic, ~65 galactic. http://www.mppmu.mpg.de/~rwagner/sources/ http://tevcat.uchicago.edu/
HE and VHE Galactic sources HE Galactic sources Supernova Remnants (~10) Pulsars (>60) Globular clusters (~10) Pulsar Wind Nebulae (5) Colliding wind binaries: Eta Carinae (1) Nova in symbiotic binary: V407 Cyg (1) X-ray binaries: Cyg X-3 + Cyg X-1 (1+1?) Gamma-ray binaries (4) VHE Galactic sources Galactic Center and Galactic ridge (1+1) Supernova Remnants and SNR/MC (15) Open clusters and stellar assoc. (2+2?) Pulsars: Crab (1) Globular clusters: Terzan 5 (1?) Pulsar Wind Nebulae (20) X-ray binaries: Cyg X-1 (1?) Gamma-ray binaries (4)
HE and VHE Galactic sources HE/VHE Galactic sources with relativistic outflows HE VHE Pulsars > 80 1 Globular clusters ~ 10 1? Pulsar Wind Nebulae ~ 5 ~ 20 X-ray binaries 1+1? 1? Gamma-ray binaries 4 4 (5 in total)
Pulsars Fermi /LAT has detected (Abdo et al. 2010) : The 6 EGRET pulsars. 24 known radio pulsars , 8 of them MSPs . 16 new gamma-ray pulsars in blind searches . Several more pulsars in more recent works, up to 88 in 2FGL… and counting!
Most important results of the Fermi /LAT pulsar catalog (Abdo et al. 2010) : Spectra can be fitted by a power law with an exponential cutoff at ~1–5 GeV . The rotational energy-loss rate varies from ~3×10 33 erg s − 1 to 5×10 38 erg s − 1 . Apparent efficiencies for conversion to gamma-ray emission from ~0.1% to ~1 . ~ 75% of the pulsars have two peaks , separated by ~0.2 of rotational phase. For most of the pulsars, gamma-ray emission appears to come mainly from the outer magnetosphere , while polar-cap emission remains plausible for a few. Associations reveal that many of these pulsars power pulsar wind nebulae . Gamma-ray-selected young pulsars are born at a rate comparable to that of the radio-selected ones . The birthrate of all young gamma-ray-detected pulsars is a substantial fraction of the expected Galactic supernova rate . The “mystery” of the unidentified EGRET sources is largely solved .
Most important results of the Fermi /LAT pulsar catalog (Abdo et al. 2010) : Spectra can be fitted by a power law with an exponential cutoff at ~1–5 GeV . The rotational energy-loss rate varies from ~3×10 33 erg s − 1 to 5×10 38 erg s − 1 . Apparent efficiencies for conversion to gamma-ray emission from ~0.1% to ~1 . ~ 75% of the pulsars have two peaks , separated by ~0.2 of rotational phase. For most of the pulsars, gamma-ray emission appears to come mainly from the outer magnetosphere , while polar-cap emission remains plausible for a few. Associations reveal that many of these pulsars power pulsar wind nebulae . Gamma-ray-selected young pulsars are born at a rate comparable to that of the radio-selected ones . The birthrate of all young gamma-ray-detected pulsars is a substantial fraction of the expected Galactic supernova rate . The “mystery” of the unidentified EGRET sources is largely solved .
Pulses from the Crab at tens of GeV! MAGIC detected a pulsed signal from the Crab at E > 25 GeV (Aliu et al. 2008) . First pulsar seen by a Cherenkov Telescope . The pulsed signal occurs at the same spin phases as those observed with EGRET ( E > 100 MeV) and simultaneous MAGIC/optical data (central pixel). This has been possible thanks to a new trigger system (sum-trigger). Conclusion : The energy cut-off in the phase-averaged spectrum is relatively high. This indicates that emission happens far out in the magnetosphere . These results exclude the polar cap model and challenge the slot gap model .
Pulses from the Crab at tens of GeV! MAGIC detected a pulsed signal from the Crab at E > 25 GeV (Aliu et al. 2008) . First pulsar seen by a Cherenkov Telescope . The pulsed signal occurs at the same spin phases as those observed with EGRET ( E > 100 MeV) and simultaneous MAGIC/optical data (central pixel). This has been possible thanks to a new trigger system (sum-trigger). Conclusion : The energy cut-off in the phase-averaged spectrum is relatively high. This indicates that emission happens far out in the magnetosphere . These results exclude the polar cap model and challenge the slot gap model .
Globular clusters GeV emitting globular clusters as seen by Fermi /LAT (Abdo et al. 2010) : 8 globular clusters detected. 5 of them show hard spectral power indices (0.7 < Γ < 1.4) and clear evidence for an exponential cut-off in the range 1.0 − 2.6 GeV, which is the characteristic signature of magnetospheric emission from MSPs . 3 of them have no known radio or X-ray MSPs yet still exhibit MSP spectral properties. From the observed gamma-ray luminosities, the total number of MSPs that is expected to be present in these globular clusters can be estimated . These estimates correlate with the stellar encounter rate . 2600 − 4700 MSPs in Galactic GCs , commensurate with previous estimates. See also Tam et al. (2011) and Hui et al. (2011) for recent updates.
Globular clusters HESS J1747-248, overlapping with Terzan 5, detected at TeV energies by HESS (Abramowski et al. 2011) . Terzan 5 has the largest population of identified millisecond pulsars , a very high core stellar density and the brightest GeV range flux as measured by Fermi /LAT. The nature of HESS J1747-248 is uncertain , since no counterpart or model can fully explain the observed morphology. An association with Terzan 5 is tantalizing , but the available data do not firmly prove this scenario.
Pulsar Wind Nebulae Young (<10 5 year old) pulsars produce relativistic winds of electron/positron pairs. In the presence of magnetic fields, these pairs produce synchrotron radiation from radio to keV-MeV energies, and inverse Compton radiation from MeV to TeV energies. The extended morphologies of these radio, X-ray and TeV emissions are often trailing the motion of the pulsar in the ISM. Funk et al. (2007) .
The Pulsar Wind Nebula MSH 15-52 as been detected as an extended source by Fermi /LAT (Abdo et al. 2010) . The extended GeV emission is coincident with the HESS extended emission (contours in the figure). E > 1 GeV E > 10 GeV
HESS J1825–137 (PSR J1826–1334) . Offset position from radio to X-rays. First evidence of energy-dependent morphology at TeV gamma-rays: softening with distance synchrotron cooling . X-ray emitting particles cool faster than TeV emitting ones, hence the smaller X-ray size. Spectral evolution favors leptonic IC scenario , but not sufficient. The high γ -ray luminosity of the source cannot be explained on the basis of constant spin-down power of the pulsar and requires higher injection power in past. Trace the history of the spin- down luminosity (Aharonian et al. 2006) . keV image red – below 0.8 TeV TeV image yellow – 0.8-2.5 TeV blue – above 2.5 TeV
The Crab Nebula flares The standard candle that does not behave as such! The Crab Nebula is powered by the Crab pulsar, which has a rotational energy loss of 5×10 38 erg s − 1 , and a period of 33 ms . Four GeV flares have been detected up to now. Nothing remarkable in the optical, X-ray. Above 1 TeV ARGO-YBJ claimed a factor 3-4 increase in flux, but no enhancement seen by VERITAS and MAGIC. Everything in ATels still. From Tavani (2011, Texas Symposium) .
September 2010 , October 2007 flares seen by AGILE (Tavani et al. 2011) . February 2009 , September 2010 flares The brevity of the flares implies that seen by Fermi /LAT (Abdo et al. 2011) . the gamma rays were emitted via synchrotron radiation from PeV electrons in a region smaller than 1.4 × 10 − 2 pc. These are the highest-energy particles that can be associated with a discrete astronomical source , and they pose challenges to particle acceleration theory (Abdo et al. 2011) .
The spectrum flattens significantly during the 2010 flare as seen by Fermi /LAT (Abdo et al. 2011) .
Conclusions by Bednarek & Idec (2011) : The GeV flaring component seems to be extension of the broadband synchrotron spectrum from the Crab Nebula. It can originate in the relativistic wind of the pulsar when it slows down before reaching the shock. The emission region likely moves with the Lorentz factor of the order of 10 . The end of the synchrotron spectrum might vary up and down in respect to the baseline emission. The level of variability at the TeV energies should be lower than observed at GeV energies . Synchronous several TeV variability might be detected by the CTA .
April 2011 flare as seen by Fermi /LAT (Buehler et al. 2011, Fermi Symposium) . New spectral component of power law of index 1.6 and exponential cutoff at 580 MeV (pulsar like, but no sign of pulsation in flare photons).
GeV/TeV emitting XRBs: ACCRETION vs. NON ACCRETION Mirabel 2006, (Perspective) Science 312, 1759 LS 5039 ? LS I +61 303 ? PSR B1259 − 63 Cygnus X-3, Cygnus X-1 HESS J0632+057 ? 1FGL J1018.6 − 5856 ? Models are not so simple…
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