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تسجيل مستخدم جديدEvidence for long-term Gamma-ray and X-ray variability from the unidentified TeV source HESS J0632+057
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HESS J0632+057 is one of only two unidentified very-high-energy gamma-ray sources which appear to be point-like within experimental resolution. It is possibly associated with the massive Be star MWC 148 and has been suggested to resemble known TeV binary systems like LS I +61 303 or LS 5039. HESS J0632+057 was observed by VERITAS for 31 hours in 2006, 2008 and 2009. During these observations, no significant signal in gamma rays with energies above 1 TeV was detected from the direction of HESS J0632+057. A flux upper limit corresponding to 1.1% of the flux of the Crab Nebula has been derived from the VERITAS data. The non-detection by VERITAS excludes with a probability of 99.993% that HESS J0632+057 is a steady gamma-ray emitter. Contemporaneous X-ray observations with Swift XRT reveal a factor of 1.8+-0.4 higher flux in the 1-10 keV range than earlier X-ray observations of HESS J0632+057. The variability in the gamma-ray and X-ray fluxes supports interpretation of the ob ject as a gamma-ray emitting binary.
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HESS J0632+057 is the only gamma-ray binary known so far whose position in the sky allows observations with ground-based observatories both in the northern and southern hemispheres. Here we report on long-term observations of HESS J0632+057 conducted
with the VERITAS and H.E.S.S. Cherenkov Telescopes and the X-ray Satellite Swift, spanning a time range from 2004 to 2012 and covering most of the systems orbit. The VHE emission is found to be variable, and is correlated with that at X-ray energies. An orbital period of $315 ^{+6}_{-4}$ days is derived from the X-ray data set, which is compatible with previous results, $P = (321 pm 5$) days. The VHE light curve shows a distinct maximum at orbital phases close to 0.3, or about 100 days after periastron passage, which coincides with the periodic enhancement of the X-ray emission. Furthermore, the analysis of the TeV data shows for the first time a statistically significant ($> 6.5 sigma$) detection at orbital phases 0.6--0.9. The obtained gamma-ray and X-ray light curves and the correlation of the source emission at these two energy bands are discussed in the context of the recent ephemeris obtained for the system. Our results are compared to those reported for other gamma-ray binaries.
New generation TeV gamma-ray telescopes have discovered many new sources, including several enigmatic unidentified TeV objects. HESS J0632+057 is a particularly interesting unidentified TeV source since: it is a point source, it has a possible hard-s
pectrum X-ray counterpart and a positionally consistent Be star, it has evidence of long-term VHE flux variability, and it is postulated to be a newly detected TeV/X-ray binary. We have obtained Swift X-ray telescope observations of this source from MJD 54857 to 54965, in an attempt to ascertain its nature and to investigate the hypothesis that its a previously unknown X-ray/TeV binary. Variability and spectral properties similar to those of the other 3 known X-ray/TeV binaries have been observed, with measured flux increases by factors of approximately 3. X-ray variability is present on multiple timescales including days to months; however, no clear signature of periodicity is present on the timescales probed by these data. If binary modulation is present and dominating the measured variability, then the period of the orbit is likely to be more than 54 days (half of this campaign), or it has a shorter period with a variable degree of flux modulation on successive high states. If the two high states measured to date are due to binary modulation, then the favored period is approximately 35-40 days. More observations are required to determine if this object is truly a binary system and to determine the extent that the measured variability is due to inter-orbit flaring effects or periodic binary modulation.
We study changes in the $gamma$--ray intensity at very high energies observed from the $gamma$--ray binary HESS J0632+057. Publicly available data collected by Cherenkov telescopes were examined by means of a simple method utilizing solely the number
of source and background events. Our results point to time variability in signal from the selected object consistent with periodic modulation of the source intensity.
The gamma-ray binary HESS J0632+057 has been observed at very-high energies (E $>$ 100 GeV) for more than ten years by the major systems of imaging atmospheric Cherenkov telescopes. We present a summary of results obtained with the H.E.S.S., MAGIC, a
nd VERITAS experiments based on roughly 440 h of observations in total. This includes a discussion of an unusually bright TeV outburst of HESS J0632+057 in January 2018. The updated gamma-ray light curve now covers all phases of the orbital period with significant detections in almost all orbital phases. Results are discussed in context with simultaneous observations with the X-ray Telescope onboard the Neil Gehrels Swift Observatory.
Context. After the detection of a 321-days periodicity in X-rays, HESS J0632+057 can be robustly considered a new member of the selected group of gamma-ray binaries. These sources are known to show extended radio structure at scales of milliarcsecond
s (mas). Aims. We present the expected extended radio emission on mas scales from HESS J0632+057. Methods. We observed HESS J0632+057 with the European VLBI Network (EVN) at 1.6 GHz in two epochs: during the January/February 2011 X-ray outburst and 30 days later. Results. The VLBI image obtained during the outburst shows a compact ~0.4 mJy radio source, whereas 30 days later the source has faded and appears extended, with a projected size of ~75 AU. The peak of the emission is displaced between runs 21+/-5 AU, which is bigger than the orbit size. The position of the radio source is compatible with the Be star MWC 148, which sets the proper motion of the binary system below 3 mas yr^-1 in each coordinate. The brightness temperature of the source is above 2 times 10^6 K. We compare the multiwavelength properties of HESS J0632+057 with those of the previously known gamma-ray binaries. Conclusions. HESS J0632+057 displays extended and variable non-thermal radio emission. Its morphology, size, and displacement at AU scales are similar to those found in the other gamma-ray binaries, PSR B1259-63, LS 5039 and LS I +61 303, supporting a similar nature for HESS J0632+057.
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