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Identification of Very high energy gamma-ray sources

Identification of Very high energy gamma-ray sources. Introduction into the problem Status of the identifications Summary. Outline:. During the first 2 years of operation of H.E.S.S. more than 15 (initially) unidentified gamma-ray sources were found

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Identification of Very high energy gamma-ray sources

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  1. Identification of Very high energy gamma-ray sources • Introduction into the problem • Status of the identifications • Summary Outline:

  2. During the first 2 years of operation of H.E.S.S. more than 15 (initially) unidentified gamma-ray sources were found Mostly found in the Galactic plane survey, but also some serendipitous discoveries in targeted observations on known sources Common properties of these sources: Positioned along the plane Most of the sources (at least) slightly extended Energy spectra generally hard (Photon index ~ 2.2) Unidentified sources e.g. Kookaburra region H.E.S.S. plane survey

  3. Necessary for a firm identification: counterpart at other wavebands Step 1: Positional agreement. Good angular resolution helps against source confusion. Step 2: Viable gamma-ray emission mechanism of the positional counterpart Step 3: Consistent multi-wavelength picture Additionally: if extended - morphological match VHE gamma-astronomy in fortunate situation of “few” sources. For GLAST detailed case-by-case MWL studies for all sources is impossible. • Possible sources: • SNRs • Pulsars and PWN • Microquasars and binaries • Molecular clouds • Background AGN • Others? The Crab Nebula • Possible sources: • SNRs • Pulsars and PWN • Microquasars and binaries • Molecular clouds • Background AGN • Others? ~ 0.1deg per event The Crab Nebula EGRET • Most importantwavebands: • Radio • X-rays • Timing information (periodicity or variability) can provide final proof H.E.S.S • Most importantwavebands: • Radio • X-rays • Timing information (periodicity or variability) can provide final proof EGRET H.E.S.S ~ 0.1deg per event Identifying the sources

  4. Position Emission MWL Status of identification • Following the scheme outlined before try to categorise the sources in the following scheme: • CAT A: Perfect match (all items fulfilled plus morphological match for extended sources) • CAT B: Inconsistency in positional / morphological match • CAT C: Inconsistency in multiwavelength picture • CAT D: No match

  5. Position Emission MWL A: Perfect match • Extended Objects with (perfect) morphological matchto other wavebands (e.g. X-rays) • Association beyond doubt. • Associations with shell-type SNRs and with X-ray plerions • Gather MWL data to understand the emission mechanism • Probably not the typical objects for GLAST due to worse PSF MSH 15-52 RX J1713.7-3946 Vela X RX J0852.0-4622

  6. Position Emission MWL A: Perfect match MSH 15-52 • Extended Objects with (perfect) morphological matchto other wavebands (e.g. X-rays) • Point-like objects - One counterpart candidate • Error on reconstructed position vs distance to the object. • Final proof from correlated variability (if exists) or periodicity. • Gather MWL data to understand the emission mechanism • GLAST likely to find sources of this category RX J0852.0-4622 RX J1713.7-3946 Vela X LS 5039 G0.9-0.1

  7. Position Emission MWL A: Perfect match MSH 15-52 • Extended Objects with (perfect) morphological matchto other wavebands (e.g. X-rays) • Point-like objects – One counterpart candidate • Not quite perfect: Point-like objects – Source confusion • Arcmin angular resolution, Galactic Center still confused region • Only really identifiable via correlated variability in other wavebands • GLAST will be heavily facing this problem in the Galactic plane RX J0852.0-4622 RX J1713.7-3946 Vela X LS 5039 G0.9-0.1 VHE  - H.E.S.S. Radio 90 cm - VLA Sgr A* Sgr A East

  8. Position Emission MWL XMM 2-10 keV B: Problems in position/morphology • H.E.S.S. sees several “offset” PWN, aroundenergetic pulsars, often with X-ray PWN. • Archetypal example: HESS J1825-137 • Same morphology but vastly differentspatial scales for X-rays and g-rays • Reason could be different coolingtimescales for e- emitting synchrotron X-rays emitting IC gamma-rays • Energy dependent morphology in gamma-raysaway from pulsar position supports this picture • Here we can construct a plausible emission mechanism explaining the MWL data, but no direct morphological match H.E.S.S. 0.25-30 TeV 1° 3’

  9. Position Emission MWL C: Inconsistency in MWL picture • Example: HESS J1813-178 • Detected in plane survey, initially unidentified • Shortly afterwards reports on a coincidentunidentified non-thermal strongly absorbedASCA and an INTEGRAL source • Radio (VLA) data show shell-like structure.Another shell-type SNR emitting g-rays? • XMM data show no shell but rather an extended object. Maybe another compositeSNR, but g-rays (most) probably not from shell.

  10. Position Emission MWL D: Unidentified • The first example: HEGRA sourceTeV J2032+4131 in Cygnus region • Another one: HESS J1303-631 • No counterpart so far, recentlyalso no counterpart in a 5 ks Chandra exposure. • Claims of an associated GRB remnant … • There are more of these objects. Currently obtaining XMM/Chandra/Suzaku data in a case-by-case effort. • Still a long way to go …

  11. Position Emission MWL The status so far …

  12. Position Emission MWL Summary • Categorise sources according to their identification status • Clearly gathering good MWL data is the way to go to identify the H.E.S.S. unidentified sources. • What will we learn for GLAST: • Individual identification is very tedious, even with arcmin resolution • Positional match does not suffice • We need another approach than case-by-case MWL studies • Nevertheless we will heavily depend on MWL catalogues for population studies

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