ASTR344 – Multi-wavelength Astronomy and Astrophysics By Natalia Lewandowska Announcements -instructions for final projects + submission link now on Moodle => Please read them carefully and let me know if you have questions! => Submission deadline: May 22, 5 pm -this week: last week of homework => May 3 – May 14: Submission of outstanding lab reports! X-ray studies with satellites -X-ray observations of M87 with Einstein Observatory -detection of four emission components: 1) broad, diffuse component => associated with hot gas 2) diffuse, asymmetrical X-ray distribution to the east & southwest => similar to radio morphology 3) X-ray source centered on nucleus (with extension of 2”-3”) (4) possible compact nuclear source (weak at X-rays)) 5) structure correlated with radio-optical jet Schreier et al. (1982) X-ray studies with satellites -X-ray observations of M87 with Einstein Observatory -detection of four emission components: 1) broad, diffuse component => associated with hot gas 2) diffuse, asymmetrical X-ray distribution to the east & southwest => similar to radio morphology 3) X-ray source centered on nucleus (with extension of 2”-3”) (4) possible compact nuclear source (weak at X-rays)) 5) structure correlated with radio-optical jet Schreier et al. (1982) X-ray studies with satellites -X-ray observations of M87 with Einstein Observatory -three X-ray emission processes: -thermal emission from hot plasma => halo -synchrotron radiation from relativistic electrons => jet -inverse Compton scattering of microwave background by relativistic electrons => radio lobes Schreier et al. (1982) X-ray studies with satellites -first X-ray study with comparable resolution with optical observations => Chandra X-ray Observatory => subarcsecond time resolution -comparison of jet & nucleus components at X-ray with optical and radio measurements Wilson & Yang (2002) X-ray studies with satellites Radio (6 cm) Optical (V-band) X-ray (0.1-10 keV, 0.7” resolution) Wilson & Yang (2002) X-ray studies with satellites -spectra of nucleus & knots: => X-ray knots D, F & E (?): -displaced toward nucleus from radio and optical counterparts Wilson & Yang (2002) X-ray studies with satellites -spectra of nucleus & knots: Wilson & Yang (2002) X-ray studies with satellites -spectra of nucleus & knots: Wilson & Yang (2002) X-ray studies with satellites -conclusions: -X-ray jet resembles jet at optical & radio wavelengths => until knot C => some knots at X-rays displaced from radio/optical counterparts towards nucleus -spectra + all knots: can be fitted with one power law => conclusion? -X-ray spectra of knots: steeper than radio/optical counterparts => similar photon indices suggest nuclear X-ray emission comes from jet -spectra of at least three knots: need to have turn down in spectra Wilson & Yang (2002) Goals for today 1) Hard X-ray emission from M87 2) Gamma-ray emission from M87 Hard X-ray emission measured with NuStar Hard X-ray emission measured with NuStar Detection of very high energy emission from M87 -very high energy => TeV (1012 eV) -observations with H.E.S.S. (High Energy Stereoscopic System) => Imaging Air Cherenkov Telescopes (IACTs) => observations of gamma-rays from 100 GeV to several TeV -89 hours of observations => collection of 243 gamma-ray events! => coordinates of source at gamma-rays compatible with source at radio wavelengths Aharonian et al. (2006) Detection of very high energy emission from M87 Aharonian et al. (2006) Detection of very high energy emission from M87 -detection of variations in differential spectra: => 2005: spectrum “harder” => gamma: ~2.2 (till above 10 TeV) => 2004: spectrum “softer” => no measurements at 10 TeV! => spectra change on annual basis! Aharonian et al. (2006) Detection of very high energy emission from M87 -variation on shorter timescales? A: nightly gamma-ray flux variations (above 730 GeV) B: average flux values => variations on time scales of about 2 days! Aharonian et al. (2006) Detection of very high energy emission from M87 -no short term flux variations found in earlier years! -fastest variability ever detected for M87! -potential source: nucleus area Aharonian et al. (2006) What does short term variability mean? -time scale of variability: indicator for maximum size of emission region -gamma-rays travel longer to Earth => variability time scales: cannot be shorter than time it takes gamma-rays to cross emission region! -variability measurements: used to constrain size of emission regions => higher accuracy than by measuring extension on the sky! -2 days variability detected by H.E.S.S. => emission region has size of Solar System! => only potential region: nucleus Source: https://www.mpg.de/532048/pressRelease20061025 Gamma-ray emission from M87 (Fermi-LAT) -detection of MeV/GeV emission from M87 with Fermi-LAT -10 months of regular observations => 10 sigma detection of gamma-ray emission => no emission variability detected! Abdo et al. (2009) Detection of gamma-ray emission from M87 with Fermi-LAT -detection of MeV/GeV emission from M87 with Fermi-LAT -10 months of regular observations => 10 sigma detection of gamma-ray emission => no emission variability detected! Abdo et al. (2009) Detection of gamma-ray emission from M87 with Fermi-LAT -detection of MeV/GeV emission from M87 with Fermi-LAT -10 months of regular observations => 10 sigma detection of gamma-ray emission => no emission variability detected! Abdo et al. (2009) Correlation: X-ray & Gamma-ray Emission -observations with VERITAS array (also an IACT) => collection of 44 hours of observations => energy range: > 250 GeV => no short term variability detected! Acciari et al. (2008) Correlation: X-ray & Gamma-ray Emission -search for correlation with X-ray emission -gamma-ray emission: > 730 GeV -X-ray emission: [2:10] keV => detection of annual correlation => no short term variability detected! Acciari et al. (2008) Correlation: X-ray & Gamma-ray Emission -search for correlation with X-ray emission -gamma-ray emission: > 730 GeV -X-ray emission: [2:10] keV => detection of annual correlation => no short term variability detected! Acciari et al. (2008) Group Activity https://jamboard.google.com/d/1kyO_gIHMZWM5qkCCqJVZX4_Gnr58jhKF-DKeOgoZhCY/edit?usp=sharing What have we learned? 1) Hard X-ray emission from M87 The X-ray 2) Gamma-ray emission from M87 The gamma-ray emission from M87 has been observed to be steady at high energies (meaning in the MeV to GeV range), but not at very high energies (in the TeV) range. However, in the latter case differences have been observed between measurements with different IACTs. Observations carried out with the H.E.S.S. IACT revealed gamma-ray variabilities on scales of about 2 days, suggesting the source of that emission to be near the SMBH in the center of M87. Observations carried out with the VERITAS IACT did not reveal any variability at gamma-rays, but unraveled a correlation with X-ray emission on annual time scales.
