B. Nicholas

A 7 mm line survey of the shocked and disrupted molecular gas towards the W28 field TeV gamma-ray sources

We present 7 mm Mopra observations of the dense molecular gas towards the W28 supernova remnant (SNR) field, following a previous 12 mm line survey of this region. These observations take advantage of the 7 mm beam size to probe the dense and disrupted gas in the region at ∼1 arcmin scales. Our observations are focused towards the north-eastern (NE) HESS J1801−233 and southern HESS J1800−240 B TeV gamma-ray sources, with slightly less observations towards HESS J1800−240 A and C. Using the CS (1–0) transition we reveal multiple regions of dense gas, inline image cm−3. We report the discovery of dense gas towards HESS J1800−240 C, at the site of a 1720 MHz OH maser. The NE molecular cloud is known to be disrupted; many 1720 MHz OH masers and broad CO line emission are detected at the rim of W28. Here, we reveal this shock interaction region contains generally extended clumpy CS, as well as clumpy SiO and CH3OH emission with broad line profiles. The full width at half maximum (FWHM) of the molecular lines extend up to 18 km s−1 on the W28 side of the NE cloud. The detection of SiO towards maser clumps OH C, D, E and F provides further evidence of the shocked conditions in the NE cloud. Several other lines associated with star formation are also detected towards the southern source, notably the energetic H ii complex G5.89−0.39. The spatial match of dense gas with the TeV emission further supports the cosmic ray (CR) origin for the gamma-rays. We estimate the mass of several extended dense clouds within the field and predict the TeV flux from the dense cloud components. The predicted fluxes are of the order of 10−14 to 10−13 photons cm−2 s−1, which should be detectable and possibly resolved by a future TeV instrument, such as the Cherenkov Telescope Array.

12 mm line survey of the dense molecular gas towards the W28 field TeV gamma-ray sources

We present 12 mm Mopra observations of dense molecular gas towards the W28 supernova remnant (SNR) field. The focus is on the dense molecular gas towards the TeV gamma-ray sources detected by the HESS telescopes, which likely trace the cosmic rays from W28 and possibly other sources in the region. Using the NH3 inversion transitions we reveal several dense cores inside the molecular clouds, the majority of which coincide with high-mass star formation and H ii regions, including the energetic ultracompact H ii region G5.89−0.39. A key exception to this is the cloud north-east of W28, which is well known to be disrupted as evidenced by clusters of 1720 MHz OH masers and broad CO line emission. Here we detect broad NH3, up to the (9,9) transition, with linewidths up to 16 km s−1. This broad NH3 emission spatially matches well with the TeV source HESS J1801−233 and CO emission, and its velocity dispersion distribution suggests external disruption from the W28 SNR direction. Other lines are detected, such as HC3N and HC5N, H2O masers, and many radio recombination lines, all of which are primarily found towards the southern high-mass star formation regions. These observations provide a new view on to the internal structures and dynamics of the dense molecular gas towards the W28 SNR field and, in tandem with future higher-resolution TeV gamma-ray observations, will offer the chance to probe the transport of cosmic rays into molecular clouds.

3 to 12 millimetre studies of dense gas towards the western rim of supernova remnant RX J1713.7-3946

The young X-ray and gamma-ray-bright supernova remnant RX J1713.7-3946 (SNR G347.3-0.5) is believed to be associated with molecular cores that lie within regions of the most intense TeV emission. Using the Mopra telescope, four of the densest cores were observed using high critical density tracers such as CS(J= 10, J= 21) and its isotopologue counterparts, NH₃(1, 1) and (2, 2) inversion transitions and N₂H⁺(J= 10) emission, confirming the presence of dense gas ≥10⁴cm⁻³ in the region. The mass estimates for Core C range from 40 (from CS) to 80 M⊙ (from NH₃ and N₂H⁺), an order of magnitude smaller than published mass estimates from CO(J= 1-0) observations. We also modelled the energy-dependent diffusion of cosmic ray protons accelerated by RX J1713.7-3946 into Core C, approximating the core with average density and magnetic field values. We find that for considerably suppressed diffusion coefficients (factors χ= 10⁻³ down to 10⁻⁵ the Galactic average), low-energy cosmic rays can be prevented from entering the inner core region. Such an effect could lead to characteristic spectral behaviour in the GeV to TeV gamma-ray and multi-keV X-ray fluxes across the core. These features may be measurable with future gamma-ray and multi-keV telescopes offering arcminute or better angular resolution, and can be a novel way to understand the level of cosmic ray acceleration in RX J1713.7-3946 and the transport properties of cosmic rays in the dense molecular cores.

Ammonia excitation imaging of shocked gas towards the W28 gamma-ray source HESS J1801−233

We present 12 mm Mopra observations of the dense (>10^3 cm^-3 ) molecular gas towards the north-east (NE) of the W28 supernova remnant (SNR). This cloud is spatially well-matched to the TeV gamma-ray source HESS J1801-233 and is known to be a SNR-molecular cloud interaction region. Shock-disruption is evident from broad NH3 (1,1) spectral line-widths in regions towards the W28 SNR, while strong detections of spatially-extended NH3(3,3), NH3(4,4) and NH3(6,6) inversion emission towards the cloud strengthen the case for the existence of high temperatures within the cloud. Velocity dispersion measurements and NH3(n,n)/(1,1) ratio maps, where n=2, 3, 4 and 6, indicate that the source of disruption is from the side of the cloud nearest to the W28 SNR, suggesting that it is the source of cloud-disruption. Towards part of the cloud, the ratio of ortho to para-NH3 is observed to exceed 2, suggesting gas-phase NH3 enrichment due to NH3 liberation from dust grain mantles. The measured NH3 abundance with respect to H2 is ~(1.2+/-0.5)*10^-9, which is not high, as might be expected for a hot, dense molecular cloud enriched by sublimated grain-surface molecules. The results are suggestive of NH3 sublimation and destruction in this molecular cloud, which is likely to be interacting with the W28 SNR shock.

H.E.S.S Observations of the Microquasars Cir X‐1, Cyg X‐1 and 4U 1755‐33

A number of microquasars exhibit parsec‐scale jets, which in some cases are known to interact with the interstellar medium (ISM). A famous example is the SS‐433 system. Here, we summarise H.E.S.S. observations of three further examples in this category with arc‐minute scale jets and/or jet/ISM interaction features. The small line‐of‐sight angle in the Cir X‐1 jet makes this source a potential ‘microblazar’. An arc‐minute bow‐shock radio feature has been blown out by the Cyg X‐1 jet, and the MAGIC telescope has also detected a VHE flare on 24 Sept. 2006 from Cyg X‐1 (H.E.S.S. obs. were taken ∼1 month earlier). Persistent bi‐lobal (∼7 arcmin long) ‘fossil’ jets of 4U1755‐33 have been seen in X‐rays. This report summarises our observations, searching for pointlike VHE emission at the central sources and for extended emission from their jets and/or jet/ISM interaction regions.