Gamma-ray observations from the COS-B satellite and radio pulse-timing measurements from the Tidb... more Gamma-ray observations from the COS-B satellite and radio pulse-timing measurements from the Tidbinbilla Deep Space Station are used to determine accurately the relative phases of the radio (2295 MHz) and gamma-ray (above 50 MeV) pulses from the Vela pulsar. Two independent analysis procedures are employed, and both show that the peak of the radio pulse leads the peak of the first gamma-ray pulse by 11.2 plus or minus 0.5 ms. This result, together with the data of Manchester et al. (1978), indicates that the phase delay relative to the radio pulse peak of the pulse components at optical and gamma-ray frequencies are about 11 ms (first gamma-ray), 21 ms (first optical), 42 ms (second optical), and 49 ms (second gamma-ray).
We present first results of a systematic search through COMPTEL all-sky maps for evidence of MeV ... more We present first results of a systematic search through COMPTEL all-sky maps for evidence of MeV gamma-ray emission from active galaxies. All-sky maximum-likelihood and flux maps have been produced from publicly-available COMPTEL datasets for individual CGRO viewing periods for the 4.5-year period covering Phases 1 to 4 of the CGRO mission (1991-1995), in four standard energy bins spanning the sensitive
A new bright gamma-ray source was detected in June 1995 near the Galactic plane (GRO J1838-04). S... more A new bright gamma-ray source was detected in June 1995 near the Galactic plane (GRO J1838-04). Subsequent EGRET observations did not detect significant flux from this source. The gamma-ray error box of GRO J1838-04 does not contain any spectrally-flat radio-loud source. GRO J1838-04 provides strong evidence for the existence of a new class of variable gamma-ray sources.
ABSTRACT Limitations in COMPTEL 44Ti line searches arise from uncertainties in different backgrou... more ABSTRACT Limitations in COMPTEL 44Ti line searches arise from uncertainties in different background modelling techniques, and in different event selection criteria to suppress a large part of the background. Therefore, the significance of the reported detections of Cas A and RX J0852-4622/GRO J0852-4642 have been reassessed in great detail. .
Nucleosynthesis models predict the production of 60Fe by the same massive stars which are respons... more Nucleosynthesis models predict the production of 60Fe by the same massive stars which are responsible for 26Al synthesis. With a radioactive decay time similar to 26Al, the gamma-ray line emission at 1.173 and 1.332 MeV is predicted to be ~16% of the 1.809 MeV 26Al line intensity, from the same source regions. We investigate with COMPTEL all-sky data from CGRO Phases 1-5 whether this source of 60Fe can be detected, using the known spectral signature plus the spatial distribution as imaged with COMPTEL 26Al measurements. Uncertainties in spatial signature of the instrumental and continuum background limit the sensitivity, such that only an upper limit of ~44% (2sigma) is quoted at this time.
The authors report on the results of a search for pulsed gamma-ray emission from old radio pulsar... more The authors report on the results of a search for pulsed gamma-ray emission from old radio pulsars in the COS-B data in the energy range 50 MeV to 2 GeV. The analysis has been done by using either pulsar parameters obtained in simultaneous radio and gamma-ray observations or parameters which could be reliably derived by interpolation from radio observations spanning the COS-B observations.
The analysis of all available COMPTEL data collected from the Virgo region of the sky between the... more The analysis of all available COMPTEL data collected from the Virgo region of the sky between the beginning of the Compton Gamma-Ray Observatory mission in April 1991 and the end of its observational Phase III in October 1994 is currently in progress. During this period COMPTEL was pointed for in total 15 weeks directly towards the Virgo region of the
The COMPTEL experiment aboard CGRO, exploring the previously unknown sky at MeV-energies, has so ... more The COMPTEL experiment aboard CGRO, exploring the previously unknown sky at MeV-energies, has so far detected 10 Active Galactic Nuclei (AGN): 9 blazars and the radio galaxy Centaurus A. No Seyfert galaxy has been found yet. With these results COMPTEL has opened the field of extragalactic Gamma-ray astronomy in the MeV-band.
Gamma-ray observations from the COS-B satellite and radio pulse-timing measurements from the Tidb... more Gamma-ray observations from the COS-B satellite and radio pulse-timing measurements from the Tidbinbilla Deep Space Station are used to determine accurately the relative phases of the radio (2295 MHz) and gamma-ray (above 50 MeV) pulses from the Vela pulsar. Two independent analysis procedures are employed, and both show that the peak of the radio pulse leads the peak of the first gamma-ray pulse by 11.2 plus or minus 0.5 ms. This result, together with the data of Manchester et al. (1978), indicates that the phase delay relative to the radio pulse peak of the pulse components at optical and gamma-ray frequencies are about 11 ms (first gamma-ray), 21 ms (first optical), 42 ms (second optical), and 49 ms (second gamma-ray).
We present first results of a systematic search through COMPTEL all-sky maps for evidence of MeV ... more We present first results of a systematic search through COMPTEL all-sky maps for evidence of MeV gamma-ray emission from active galaxies. All-sky maximum-likelihood and flux maps have been produced from publicly-available COMPTEL datasets for individual CGRO viewing periods for the 4.5-year period covering Phases 1 to 4 of the CGRO mission (1991-1995), in four standard energy bins spanning the sensitive
A new bright gamma-ray source was detected in June 1995 near the Galactic plane (GRO J1838-04). S... more A new bright gamma-ray source was detected in June 1995 near the Galactic plane (GRO J1838-04). Subsequent EGRET observations did not detect significant flux from this source. The gamma-ray error box of GRO J1838-04 does not contain any spectrally-flat radio-loud source. GRO J1838-04 provides strong evidence for the existence of a new class of variable gamma-ray sources.
ABSTRACT Limitations in COMPTEL 44Ti line searches arise from uncertainties in different backgrou... more ABSTRACT Limitations in COMPTEL 44Ti line searches arise from uncertainties in different background modelling techniques, and in different event selection criteria to suppress a large part of the background. Therefore, the significance of the reported detections of Cas A and RX J0852-4622/GRO J0852-4642 have been reassessed in great detail. .
Nucleosynthesis models predict the production of 60Fe by the same massive stars which are respons... more Nucleosynthesis models predict the production of 60Fe by the same massive stars which are responsible for 26Al synthesis. With a radioactive decay time similar to 26Al, the gamma-ray line emission at 1.173 and 1.332 MeV is predicted to be ~16% of the 1.809 MeV 26Al line intensity, from the same source regions. We investigate with COMPTEL all-sky data from CGRO Phases 1-5 whether this source of 60Fe can be detected, using the known spectral signature plus the spatial distribution as imaged with COMPTEL 26Al measurements. Uncertainties in spatial signature of the instrumental and continuum background limit the sensitivity, such that only an upper limit of ~44% (2sigma) is quoted at this time.
The authors report on the results of a search for pulsed gamma-ray emission from old radio pulsar... more The authors report on the results of a search for pulsed gamma-ray emission from old radio pulsars in the COS-B data in the energy range 50 MeV to 2 GeV. The analysis has been done by using either pulsar parameters obtained in simultaneous radio and gamma-ray observations or parameters which could be reliably derived by interpolation from radio observations spanning the COS-B observations.
The analysis of all available COMPTEL data collected from the Virgo region of the sky between the... more The analysis of all available COMPTEL data collected from the Virgo region of the sky between the beginning of the Compton Gamma-Ray Observatory mission in April 1991 and the end of its observational Phase III in October 1994 is currently in progress. During this period COMPTEL was pointed for in total 15 weeks directly towards the Virgo region of the
The COMPTEL experiment aboard CGRO, exploring the previously unknown sky at MeV-energies, has so ... more The COMPTEL experiment aboard CGRO, exploring the previously unknown sky at MeV-energies, has so far detected 10 Active Galactic Nuclei (AGN): 9 blazars and the radio galaxy Centaurus A. No Seyfert galaxy has been found yet. With these results COMPTEL has opened the field of extragalactic Gamma-ray astronomy in the MeV-band.
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Papers by W. Hermsen