C. Brink

AE Aquarii - an emitter of pulsed TeV gamma rays resembling optical emission during flares

During optical flares, strong coherent pulsed emission is detected in the frequency interval ∼29.9-30.0 mHz and at F 0 =30.23 mHz (rotation frequency). Evidence is presented of pulsed VHE emission at these frequencies in all our VHE data at the 99.996% significance level covering 4 years of observation. The total time average VHE luminosity at an average threshold energy of ∼2.4 TeV is (1.5±0.3)×10 32 ergs s −1 , which corresponds to a conversion efficiency of 15%. The significance of these features increased steadily with time during the past four years

TeV Gamma-Ray Observations of Compton Gamma-Ray Observatory Pulsars: Evidence against Inverse-Compton Controlled Outer Gaps

We present the first results of TeV γ-ray observations of the Compton Gamma-Ray Observatory γ-ray pulsar PSR 1706-44, indicating a spectral cutoff between ∼20 GeV and 600 GeV. Improved upper limits are also presented for the Vela pulsar and PSR 1509-58. These and other TeV results confirm similar cutoffs for these γ-ray pulsars as well as for Geminga. The polar cap model predicts such a spectral cutoff due to magnetic pair production, whereas the outer gap model for Vela-type pulsars predicts a similar cutoff resulting from the maximum synchrotron energy in the outer gap. The spectral flattening below a certain minimum energy, seen from all of these pulsars, is also consistent with the outer gap prediction

Very high energy gamma rays from isolated radio pulsars : a survey

During the period 1985-1989 a group of 18 isolated radio pulsars (IRPs) was observed with the Nooitgedacht TeV γ-ray telescope. These pulsars were selected from a priority list which was compiled by taking both the astrophysical and observational constraints for their observation into account. All IRPs were analyzed in the same way. Of the 18 IRPs observed only one (PSR 1509-58) gave a positive signal over an extended period (1985-1988). No evidence for pulsed emission was seen during the period between 1989 and 1991, however. Two other IRPs (PSR 1823-13 and PSR 1821-24) gave interesting results which merit further observations

Temporal structure of very high energy gamma radiation from PSR 1509 - 58

Further observations of steady, pulsed TeV gamma-rays from PSR 1509 - 58 which confirm an original detection in 1985 are reported. A final chance probability of 1.7 x 10 to the -5th is obtained. Analysis of the data indicates a switching between an on- and an off-state on a time scale of about 10 days. Episodes of pulsed emission lasting between 10 and 100 min are found. The TeV light curve generally shows a broad structure containing three and sometimes four peaks with variations in the relative intensity of the peaks. 26 refs.

No evidence for TeV gamma radiation from 2CG 006 - 00

A reanalysis of the original 1985 TeV data on PSR 1802 - 23 by DeJager (1987) is reported which reveals a significance for pulsed emission of 98.6 percent, which is seven times less significant than the original claim of 99.8 percent. The tracking mode was used to collect nine times more data during 1986, 1987, and 1988, and the total time ON-source during these three years was also nine times that of 1985. In spite of this, no signal is detected from this pulsar when searching for both steady pulsed emission and transient emission. No indications are found of any DC enhancements. The flux upper limit for steady pulsed TeV gamma rays is 2.6 x 10 to the -11th/sq cm/s, corresponding to an upper limit in TeV gamma-ray luminosity of 1.2 x 10 to the 35th ergs/s. The original detection may therefore be considered as a once-only event or more probably as a statistical fluctuation. 15 refs.

TeV and MeV gamma-rays from binary systems

Abstract We report the third consecutive detection of Vela X-1 as a source of VHE gamma-rays ( E γ > 1 TeV ) with a 99.92 % significance. The pulsed emission shows a broad sinusoidal light curve at a period similar to the X-ray value, with a large negative period derivative over the 60 days of observation. We also report our observations on Cen X-3 in which we were able to confirm the orbitally modulated, pulsed VHE gamma-ray emission from Cen X-3 at the 2σ level. Finally, the possible detection of stable material at one of the Lagrangian points in the system PSR1957+20 is reported. We found indications from VHE gamma-ray data (at the 3σ level) of a DC enhancement at the L4 Lagrangian point. This indication was then independently confirmed at the 99.9% level from COS-B data. This enhancement of radiation in the binary orbit may indicate the existence of stable material with a column density of about 50 g/cm 2 at the Lagrangian point L4.

TeV gamma‐rays from accreting binary systems

Evidence is presented that Vela X‐1 emits steady pulsed emission at the X‐ray period. Another X‐ray binary, Cen X‐3, also show evidence for steady, pulsed emission at the expected X‐ray period, but this emission only occurs in the orbital phase range between 0.5 and 0.75. In both sources the emission occur at a period compatible with the X‐ray period, although slightly shifted. The white dwarf in the cataclysm variable, AE Aqr, shows steady, pulsed emission at the known spin period, and in phase with both the X‐ray and optical emission, indicating the production of gamma‐rays close to the white dwarf.

TeV observations of gamma‐ray pulsar: A test for pulsar models

We present the first results of TeV γ‐ray observations of PSR1706−44, indicating a sharp spectral break between ∼10 GeV and 1000 GeV. Our and other results confirm similar breaks from other γ‐ray pulsars such as Vela, PSR1509−58 and Geminga. Both the polar cap‐ and outer gap models can account for this break, although a much higher TeV flux from Geminga is expected if it is in the post‐Vela phase, given that the gap is controlled by the inverse Compton process. Relatively flat (possibly time variable) spectra from these pulsars are also seen between X‐rays and medium energy γ‐rays, which can also be explained by the outer gap model.

Near simultaneous optical and TeV observations of AE Aquarii

We present results of near simultaneous optical and TeV observations made on Sept. 14, 1990 of the novalike cataclysmic variable AE Aquarii. The optical was in a flaring state resulting in a bolometric luminosity which may have been high enough to give detectable TeV radiation during the TeV observation. During the latter we have seen periodic TeV emission at a frequency redshift of −0.7% relative to the spin frequency which confirms our earlier detection during 1989 at the 99.5% level. Both the optical and TeV did show evidence of a changing frequency with time which appears to be describing a single event. We also show that the shock above the white dwarfs polar cap may be collissionless so that protons may be accelerated to energies above 1 TeV. If the part of the accretion stream from the companion which reprocesses incident X-rays to optical pulsations is magnetized and dense enough, it may trap incident TeV particles for a long enough time to give TeV γ-rays through π° decay with the same period as in optical. The frequency will be constant if the spot of reprocessing is fixed in the binary frame, but shifted if the spot moves.

VHE gamma-rays from radio pulsars and cataclysmic variables

We present the results of observations (above 1 TeV) of radio pulsars and cataclysmic variables with the Potchefstroom air Cerenkov facility. We were able to confirm our previous detection of PSR 1509-58 and the final significance is 1.7×10−5. A DC enhancement at the 10−3 significance level was seen from the L4 Lagrange position in the PSR 1957+20 system. This result was confirmed by COS-B data. We were also able to detect the 5.4 ms pulsar PSR 1855+09 at a marginal significance level of 5%. However, the best and longest observation indicates non-uniformity at the 0.005 significance level. The TeV light curve resembles the radio light curve. The latter is also reminiscent of other millisecond pulsars observed above 1 TeV. The intermediate polar AEAQR (P = 33.08s) shows a period shift which is consistent with recent model predictions. However, the present significance of this results does not allow an unambiguous claim.