XMM-Newton observations of the first unidentified TeV gamma-ray source TeV J2032+4130

(abridged) The first unidentified very high energy gamma ray source (TeV J2032+4130) in the Cygnus region has been the subject of intensive search for a counterpart source at other wavelengths. A deep ($\approx 50$ ksec) exposure of TeV J2032+4130 with \textit{XMM-Newton} has been obtained. The contribution of point sources to the observed X-ray emission from TeV J2032+4130 is subtracted from the data. The point-source subtracted X-ray data are analyzed using blank sky exposures and regions adjacent to the position of TeV J2032+4130 in the field of view covered by the XMM-Newton telescopes to search for diffuse X-ray emission. An extended X-ray emission region with a full width half maximum (FWHM) size of $\approx 12$ arc min is found. The centroid of the emission is co-located with the position of TeV J2032+4130.The energy spectrum of the emission coinciding with the position and extension of TeV J2032+4130 can be modeled by a power-law model with a photon index $\Gamma=1.5\pm0.2_\mathrm{stat}\pm0.3_\mathrm{sys}$ and an energy flux integrated between 2 and 10 keV of $f_{2-10 \mathrm{keV}} \approx 7\cdot 10^{-13}$ ergs/(cm$^2$ s) which is lower than the very high energy gamma-ray flux observed from TeV J2032+4130. We conclude that the faint extended X-ray emission discovered in this observation is the X-ray counterpart of TeV J2032+4130. Formally, it can not be excluded that the extended emission is due to an unrelated population of faint, hot ($k_BT\approx 10$ keV) unresolved point-sources which by chance coincides with the position and extension of TeV J2032+4130. We discuss our findings in the frame of both hadronic and leptonic gamma-ray production scenarios.Comment: 5 Pages, 3 Figures, accepted for publication in A&

X- and gamma-ray studies of HESS J1731-347 coincident with a newly discovered SNR

In the survey of the Galactic plane conducted with H.E.S.S., many VHE gamma-ray sources were discovered for which no clear counterpart at other wavelengths could be identified. HESS J1731-347 initially belonged to this source class. Recently however, the new shell-type supernova remnant (SNR) G353.6-0.7 was discovered in radio data, positionally coinciding with the VHE source. We will present new X-ray observations that cover a fraction of the VHE source, revealing nonthermal emission that most likely can be interpreted as synchrotron emission from high-energy electrons. This, along with a larger H.E.S.S. data set which comprises more than twice the observation time used in the discovery paper, allows us to test whether the VHE source may indeed be attributed to shell-type emission from that new SNR. If true, this would make HESS J1731-347 a new object in the small but growing class of non-thermal shell-type supernova remnants with VHE emission.Comment: 4 pages, 5 figures, to appear in proceedings of the 31st ICRC, Lodz, Polan

The SED of the TeV BLLac 1ES 1426+428 after correction for the TeV--IR absorption

The recent HEGRA detection and spectrum of 1ES 1426+428 at TeV energies, once corrected for absorption using present estimates of the diffuse extragalactic IR background, suggest that the high energy peak of the Spectral Energy Distribution (SED) could be much higher than the synchrotron one ($L_c/L_s>10$), and lie at energies above 8-10 TeV. To see if such an SED could be accounted for, we have applied a "finite injection time" SSC model, and present here some preliminary results. Within this model, we found the need of an external ("ambient") contribution to the energy density of seed photons, in order to account for both the high Compton dominance and the hard spectrum.Comment: 4 pages, 5 figures, to appear in the proceedings of the conference "Relativistic jets in the Chandra and XMM era", Bologna, 23-27/9/02 (New Astr. Rev.

INTEGRAL observations of TeV plerions

Amongst the sources seen in very high gamma-rays several are associated with Pulsar Wind Nebulae (``TeV plerions''). The study of hard X-ray/soft gamma-ray emission is providing an important insight into the energetic particle population present in these objects. The unpulsed emission from pulsar/pulsar wind nebula systems in the energy range accessible to the INTEGRAL satellite is mainly synchrotron emission from energetic and fast cooling electrons close to their acceleration site. Our analyses of public INTEGRAL data of known TeV plerions detected by ground based Cherenkov telescopes indicate a deeper link between these TeV plerions and INTEGRAL detected pulsar wind nebulae. The newly discovered TeV plerion in the northern wing of the Kookaburra region (G313.3+0.6 powered by the middle aged PSR J1420-6048) is found to have a previously unknown INTEGRAL counterpart which is besides the Vela pulsar the only middle aged pulsar detected with INTEGRAL. We do not find an INTEGRAL counterpart of the TeV plerion associated with the X-ray PWN ``Rabbit'' G313.3+0.1 which is possibly powered by a young pulsar.Comment: 4 pages, 6 figures, proceedings of conference "The Multi-Messenger Approach to High-Energy Gamma-ray Sources" Barcelona/Spain (2006

Constraining the Cosmic Background Light with four BL Lac TeV spectra

The intrinsic BL Lac spectra above few hundreds GeV can be very different from the observed ones due to the absorption effects by the diffuse Extragalactic Background Light (EBL), at present poorly known. With the recent results, there are now 4 sources with good spectral information: Mkn 421 (z=0.031), Mkn 501 (z=0.034), 1ES 1426+428 (z=0.129) and 1ES 1959+650 (z=0.047). Making simple assumptions on the shape of the intrinsic spectra (according to the present blazar knowledge), we have considered the effects of different EBL spectral energy distributions (SED) for the first time on all 4 objects together, deriving constraints for the EBL fluxes. These resulted significantly lower than many direct estimates.Comment: 4 pages, 8 figures; to appear in the proceedings of the 2nd Veritas Symposium: "TeV Astrophysics of extragalactic sources". April 2003, Chicag

XMM-Newton observations of HESS J1813-178 reveal a composite Supernova remnant

We present X-ray and 12CO(J=1-0) observations of the very-high-energy (VHE) gamma-ray source HESS J1813-178 with the aim of understanding the origin of the gamma-ray emission. Using this dataset we are able to undertake spectral and morphological studies of the X-ray emission from this object with greater precision than previous studies. NANTEN 12CO(J=1-0) data are used to search for correlations of the gamma-ray emission with molecular clouds which could act as target material for gamma-ray production in a hadronic scenario. The NANTEN 12CO(J=1-0) observations show a giant molecular cloud of mass 2.5 10^5 M_{\sun} at a distance of 4 kpc in the vicinity of HESS J1813-178. Even though there is no direct positional coincidence, this giant cloud might have influenced the evolution of the gamma-ray source and its surroundings. The X-ray data show a highly absorbed non-thermal X-ray emitting object coincident with the previously known ASCA source AX J1813-178 showing a compact core and an extended tail towards the north-east, located in the centre of the radio shell-type Supernova remnant (SNR) G12.82-0.2. This central object shows morphological and spectral resemblance to a Pulsar Wind Nebula (PWN) and we therefore consider that the object is very likely to be a composite SNR. We discuss the scenario in which the gamma-rays originate in the shell of the SNR and the one in which they originate in the central object. We demonstrate, that in order to connect the core X-ray emission to the VHE gamma-ray emission electrons have to be accelerated to energies of at least 1 PeV.Comment: Submitted to A&

An unidentified TeV source in the vicinity of Cygnus OB2

Deep observation (∼113 hrs) of the Cygnus region at TeV energies using the HEGRA stereoscopic system of air Čerenkov telescopes has serendipitously revealed a signal positionally inside the core of the OB association Cygnus OB2, at the edge of the 95% error circle of the EGRET source 3EG J2033+4118, and ∼0.5° north of Cyg X-3. The source centre of gravity is RA αJ2000: 20hr32m07s± 9.2stats±2.2syss, Dec δJ2000: +41°30′30″2.0stat±0.4′sys. The source is steady, has a post-trial significance of +4.6σ, indication for extension with radius 5.6′ at the ∼3σ level, and has a differential power-law flux with hard photon index of - 1.9 ± 0.3stat ± 0.3sys. The integral flux above 1 TeV amounts ∼3% that of the Crab. No counterpart for the TeV source at other wavelengths is presently identified, and its extension would disfavour an exclusive pulsar or AGN origin. If associated with Cygnus OB2, this dense concentration of young, massive stars provides an environment conducive to multi-TeV particle acceleration and likely subsequent interaction with a nearby gas cloud. Alternatively, one could envisage γ-ray production via a jet-driven termination shock.F. A. Aharonian, ... G. P. Rowell, ... [et al

The Dark Side of ROTSE-III Prompt GRB Observations

We present several cases of optical observations during gamma-ray bursts (GRBs) which resulted in prompt limits but no detection of optical emission. These limits constrain the prompt optical flux densities and the optical brightness relative to the gamma-ray emission. The derived constraints fall within the range of properties observed in GRBs with prompt optical detections, though at the faint end of optical/gamma flux ratios. The presently accessible prompt optical limits do not require a different set of intrinsic or environmental GRB properties, relative to the events with prompt optical detections.Comment: ApJ accepted. 20 pages in draft manuscript form, which includes 6 pages of tables and 2 figure

Status of the ROTSE-III telescope network

ROTSE-III is a homogeneous worldwide array of 4 robotic telescopes. They were designed to provide optical observations of γ-ray burst (GRB) afterglows as close as possible to the start of γ-ray emission. ROTSE-III is fulfilling its potential for GRB science, and provides optical observations for a variety of astrophysical sources in the interim between GRB events