With great sadness we learned of the untimely death of Dalibor Nedbal, who passed away on May 15, 2012. In Heidelberg - where he received his Ph.D. in 2008, before returning to Charles University in Prague - and within the whole H.E.S.S. collaboration Dalibor was universally liked and respected, as a scientist and colleague. We extend our deepest sympathy to his family.

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News

Very high energy gamma-ray emission detected from PKS 1440-389
April 27, 2012

The BL Lac object PKS 1440-389, located at a tentative redshift of z=0.065, has been reported as a hard, bright, and steady extragalactic source at GeV energies in the Fermi-LAT catalogue. The extrapolation of the Fermi-LAT spectrum to very high energies, together with its brightness in the radio and X-ray bands, makes this BL Lac object a good candidate for VHE emission. PKS 1440-389 was observed with H.E.S.S. for ~6h in the past two months, resulting in a signal exceeding 5 standard deviation in the preliminary onsite analysis. The flux is estimated to be ~3% of the flux of the Crab Nebula above 200 GeV. No significant variability has been detected in the H.E.S.S. data. The discovery was announced as ATel #4072.

H.E.S.S. observations of the Carina nebula and its enigmatic colliding wind binary Eta Carinae
April 27, 2012

The massive binary system Eta Carinae and the surrounding HII complex, the Carina Nebula, are potential particle acceleration sites from which very-high-energy gamma-ray emission could be expected. This paper presents data collected with the H.E.S.S. telescope array from 2004 to 2010, which cover a full orbit of Eta Carinae. In the 33-hour data set no hint of significant gamma-ray emission from Eta Carinae has been found and an upper limit on the gamma-ray flux is derived which, together with the detection of high-energy gamma-ray emission by Fermi-LAT up to 100 GeV, implies a cut-off in the gamma-ray spectrum between 100 and 500 GeV gamma ray energy. The paper is in press in MNRAS and can be found on the preprint server: arXiv:1204.5690.

Discovery of very high energy gammma ray emission from the BL Lac object 1RXS J101015.9-311909
April 10, 2012

1RXS J101015.9-311909 is a galaxy located at a redshift of z=0.14 hosting an active nucleus belonging to the class of bright BL Lac objects. We report on results from observations performed between 2006-2010 with H.E.S.S. VHE emission at a position coincident with 1RXS J101015.9-311909 is detected with H.E.S.S. for the first time. In a total data set of about 49 h, we measure 263 excess counts, corresponding to a significance of 7.1 sigma. Also reported is the analysis of contemporaneous ATOM, Swift and Fermi/LAT data. The paper is in press in A&A and can be found on the preprint server: arXiv:1204.1964.

Discovery of VHE emission towards the Carina arm region: HESS J1018-589
March 20, 2012

The observational coverage with HESS of the Carina region in VHE gamma-rays benefits from deep exposure of the neighboring open cluster Westerlund 2. The observations have revealed a new extended region of VHE gamma-ray emission. The source HESS J1018-589 shows a bright, point-like emission region positionally coincident with the supernova remnant G284.3-1.8 and the Fermi source 1FGL J1018.6 - 5856, and a diffuse extension towards the direction of the pulsar PSR J1016-5857. The paper is in press in A&A and can be found on the preprint server: arXiv:1203.3215.

Search for Dark Matter Annihilation Signals from the Fornax Galaxy Cluster
March 1, 2012

Due to their potentially large boost factors enhancing the annihilation rate of hypothetical dark matter particles, galaxy clusters are an interesting target to search for annihilation signatures. The H.E.S.S. data on the Fornax cluster are used to derive limits on the annihilation cross section for different dark matter models, such as supersymmetric or Kaluza-Klein models. The paper is in press in ApJ and can be found on the preprint server: arXiv:1202.5494 .

A multiwavelength view of the flaring state of PKS 2155-304 in 2006
January 21, 2012

Multiwavelength observations of the blazar PKS 2155-304 during two weeks in July and August 2006, the period when two exceptional flares at very high energies occurred, provide a detailed picture of the evolution of its emission. The complete data set from this campaign is presented, including observations in VHE gamma-rays (H.E.S.S.), X-rays (RXTE, CHANDRA, SWIFT XRT), optical (SWIFT UVOT, Bronberg, Watcher, ROTSE), and in the radio band (NRT, HartRAO, ATCA). Optical and radio light curves from 2004 to 2008 are compared to the available VHE data from this period, to put the 2006 campaign into the context of the long-term evolution of the source. The paper is in press in A&A and can be found on the preprint server: arXiv:1201.4135 .

Discovery of hard-spectrum gamma-ray emission from the BL Lac object 1ES 0414+009
January 18, 2012

The blazar 1ES 0414+009 (at redshift z = 0.287) is a distant high-frequency-peaked BL Lac object, and has long been considered a likely emitter of very-high energy (VHE) gamma-rays due to its high X-ray and radio flux. In observations made between October 2005 and December 2009 with H.E.S.S., 1ES 0414+009 is detected for the first time in the VHE band. An excess of 224 events is measured, corresponding to a significance of 7.8 sigma. In the Fermi (GeV) energy range, the source exhibits a rather hard spectrum, which continues into the H.E.S.S. (TeV) range once corrected for absorption by the extragalactic background light. The paper is in press in A&A and can be found on the preprint server: arXiv:1201.2044 .

The 2010 very high energy gamma-ray flare & 10 years of multi-wavelength observations of M 87
November 25, 2011

The paper covers a 2010 joint campaign on the giant radio galaxy M 87 by the H.E.S.S., MAGIC and VERITAS instruments, by Chandra and by VLBA, including a well-sampled flare at VHE energies. VLBA radio observations of the inner jet regions indicate no enhanced flux in 2010 in contrast to observations in 2008, where an increase of the radio flux of the innermost core regions coincided with a VHE flare. On the other hand, Chandra X-ray observations taken ~3 days after the peak of the VHE gamma-ray emission reveal an enhanced flux from the core. The paper is in press in ApJ and can be found on the preprint server: arXiv:1111.5341 .

H.E.S.S. II telescope structure complete and moving
November 17, 2011

The assembly of the steel structure for the 600 m^2 H.E.S.S. II telescope was completed in mid-November, and the drives installed. Mirrors and camera will be installed in the first half of 2012. (Note that the H.E.S.S. II telescope is located in between the two H.E.S.S. I telescopes shown in the image, not in the foreground! Click on image for larger version.)
HESS II

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Discovery of extended VHE gamma-ray emission from the vicinity of the stellar cluster Westerlund 1
November 14, 2011

A degree-scale extended VHE gamma ray source around the young massive stellar cluster Westerlund 1 is detected in 45 hours of HESS observations in the years 2004 to 2008. As potential sources, the stellar cluster Wd 1, the pulsar PSR J1648-4611, the magnetar CXOU J164710.2-455216 and the X-ray binary 4U 1642-45 are discussed. The paper is in press in A&A and can be found on the preprint server: arXiv:1111.2043 .

Simultaneous multi-wavelength campaign on PKS 2005-489 in a high state
September 25, 2011

The BL Lac object PKS 2005-489 was the target of a multiwavelength campaign with simultaneous observations in the TeV gamma-ray (H.E.S.S.), GeV gamma-ray (Fermi), X-ray (RXTE, Swift), UV (Swift) and optical (ATOM, Swift) bands. The campaign was carried out during a high flux state in the synchrotron regime; the flux in the optical and X-ray bands reached the level of historical maxima. The paper is published in A&A 533 (2011) A110.


Discovery of the source HESS J1356-645 associated with the young and energetic PSR J1357-6429
September 10, 2011

HESS J1356-645 is a new extended source of VHE gamma rays, with a size of about 0.2 degr. and a flux of about 11% of the Crab flux. Radio and X-ray data reveal faint non-thermal diffuse emission coincident with HESS J1356-645. HESS J1356-645 is most likely associated with the young and energetic pulsar PSR J1357-6429. The paper is in press in A&A and can be found on the preprint server: arXiv:1108.2855 .


Very-high-energy gamma-ray emission from the direction of the Galactic globular cluster Terzan 5
June 23, 2011

An extended VHE gamma-ray source is located in the close vicinity of the Galactic globular cluster Terzan 5. The probability of a chance coincidence with Terzan 5 and an unrelated VHE source is quite low. With the largest population of identified millisecond pulsars (msPSRs), a very high core stellar density and the brightest GeV range flux as measured by Fermi-LAT, Terzan 5 stands out among Galactic globular clusters. Interpretation of the available data accommodates several possible origins for this VHE gamma-ray source, although none of them offers a satisfying explanation of its peculiar morphology. The paper is in press in A&A and can be found on the preprint server: arXiv:1106.4069 .


A new SNR with TeV shell-type morphology: HESS J1731-347
May 22, 2011

The discovery of the radio shell-type supernova remnant (SNR), G353.6-0.7, in spatial coincidence with the unidentified TeV source HESS J1731-347 has motivated further observations of this source. The deeper observation of the source - resulting in total in 59 h of data - has revealed a large shell-type structure with similar position and extension as the radio SNR, thus confirming their association and making HESS J1731-347 the fourth SNR with a shell morphology at TeV energies. The paper is in press in A&A and can be found on the preprint server: arXiv:1105.3206 .


Search for a Dark Matter signal from the globular clusters NGC 6388 and M 15
April 17, 2011

Observations of the globular clusters NGC 6388 and M 15 were carried out by the H.E.S.S. array of Cherenkov telescopes for a live time of 27.2 and 15.2 hours, respectively. No hints of dark matter annihilation signals are detected. Based on models of the dark matter content of these clusters, limits on the dark matter self-annihilation cross section are derived. The paper is in press in ApJ and can be found on the preprint server: arXiv:1104.2548 .


Search for a Dark Matter annihilation signal from the Galactic Center halo with H.E.S.S
March 21, 2011

Exploiting the large exposure towards the Galactic Center region, a search for very high energy gamma ray emission from self-annihilating dark matter is performed in a region of projected distance of about 45 to 150 pc from the Galactic Center, exclusing the region of the astrophysical gamma-ray source at the Galactic Center. The background-subtracted gamma-ray spectrum shows no hint of a residual gamma ray flux. The dark matter limits derived are among the best reported so far for the TeV energy range. The paper is in press in PRL and can be found on the preprint server: arXiv:1103.3266 .


HESS J1943+213: a candidate extreme BL Lacertae object
March 5, 2011

The newly detected point-like source HESS J1943+213, located in the Galactic plane, coincides with the X-ray source IGR J19443+2117. Available multi-wavelength data favor an interpretation as an extreme, high-frequency peaked BL Lac object. This would be the first time a blazar is detected serendipitously from ground-based VHE observations, and the first VHE AGN detected in the Galactic Plane. The paper is in press in A&A and can be found on the preprint server: arXiv:1103.0763.


Detection of very-high-energy gamma-ray emission from the vicinity of PSR B1706-44 and G343.1-2.3
Feb. 10, 2011

Pulsar PSR B1706-44 has a long history as suspected source of VHE gamma rays. H.E.S.S. observations now establish the region surrounding the pulsar, with the remnant G343.1-2.3, as a quite extended source of gamma rays. The centroid of the gamma ray source is, however, considerably offset from the pulsar, and no significant emission is detected at the location of the energetic pulsar itself. The paper is in press in A&A and can be found on the preprint server: arXiv:1102.0773.


Search for Lorentz Invariance breaking with a likelihood fit of the PKS 2155-304 Flare Data
Jan. 20, 2011

Several models of Quantum Gravity predict Lorentz Symmetry breaking at energy scales approaching the Planck scale (10^19 GeV), manifesting itself in a dependence of the propagation speed on photon energy, and hence in dispersion of arrival times of photons from burst-like events. Improving upon an earlier publication, analysis of PKS 2155-304 flare gamma ray distributions in energy and time by means of a likelihood fit improves sensitivity by a factor 3, and provides a lower limit on the effective quantum gravity scale of 2.1x10^18 GeV, for linear variation of speed with energy. The paper is in press in Astroparticle Physics and can be found on the preprint server: arXiv:1101.3650.


H.E.S.S. constraints on Dark Matter annihilations towards the Sculptor and Carina Dwarf Galaxies
Jan. 20, 2011

Dwarf spheroidal galaxies such as Sculptor and Carina Dwarf are considered prime targets for signs of dark matter annihilation. Based on about 12 h and 15 h of data, respectively, upper limits on the TeV photon flux and on the dark matter annihilation cross section are reported, also discussing possible enhancements of the gamma ray flux due to the Sommerfeld effect or internal Bremssstrahlung. The paper is in press in Astroparticle Physics and can be found on the preprint server: arXiv:1012.5602.


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