G. Castelletti

NEUTRAL PION EMISSION FROM ACCELERATED PROTONS IN THE SUPERNOVA REMNANT W44

We present the AGILE gamma-ray observations in the energy range 50 MeV-10 GeV of the supernova remnant (SNR) W44, one of the most interesting systems for studying cosmic-ray production. W44 is an intermediate-age SNR ({approx}20, 000 years) and its ejecta expand in a dense medium as shown by a prominent radio shell, nearby molecular clouds, and bright [S II] emitting regions. We extend our gamma-ray analysis to energies substantially lower than previous measurements which could not conclusively establish the nature of the radiation. We find that gamma-ray emission matches remarkably well both the position and shape of the inner SNR shocked plasma. Furthermore, the gamma-ray spectrum shows a prominent peak near 1 GeV with a clear decrement at energies below a few hundreds of MeV as expected from neutral pion decay. Here we demonstrate that (1) hadron-dominated models are consistent with all W44 multiwavelength constraints derived from radio, optical, X-ray, and gamma-ray observations; (2) ad hoc lepton-dominated models fail to explain simultaneously the well-constrained gamma-ray and radio spectra, and require a circumstellar density much larger than the value derived from observations; and (3) the hadron energy spectrum is well described by a power law (with index s = 3.0 {+-}morexa0» 0.1) and a low-energy cut-off at E{sub c} = 6 {+-} 1 GeV. Direct evidence for pion emission is then established in an SNR for the first time.«xa0less

The low-frequency radio emission and spectrum of the extended SNR W44: new VLA observations at 74 and 324 MHz

Aims. We present new Very Large Array (VLA) radio images at 74 and 324 MHz of the SNR W44. The VLA images, obtained with unprecedented angular resolution and sensitivity for such low frequencies ( HPBW 37″ at 74 MHz, and 13″ at 324 MHz), have been used in combination with existing 1442 MHz radio data, Spitzer IR data, and ROSAT and Chandra X-ray data to investigate morphological and spectral continuum properties of this SNR. Methods. The observations were carried out with the VLA simultaneously at 74 and 324 MHz in the A and B configurations and at 324 MHz in the C and D configurations. The radio continuum spectral index distribution was derived through direct comparison of the combined data at 74, 324, and 1442 MHz. In addition, to isolate and identify different spectral components, tomographic spectral analysis was performed. Results. We measured total flux densities of 634 Jy and 411 Jy at 74 and 324 MHz, respectively, for W44, and from a careful assessment of published values between 22 and 10 700 MHz derived a global integrated continuum spectral index

High-resolution radio study of SNR IC 443 at low radio frequencies

alpha=-0.37 pm 0.02

Radio and X-ray study of two multi-shell supernova remnants: Kes 79 and G352.7-0.1

. The spatially resolved spectral index study revealed that the bright filaments, both around and across the SNR, have a straight spectrum between 74 and 1442 MHz, with

The most complete and detailed X-ray view of the SNR Puppis A

alphasim -0.5

First high-resolution radio study of the supernova remnant G338.3-0.0 associated with the gamma-ray source HESS J1640-465

, with two clear exceptions: a short portion of the SNR limb to the southeast, with α varying between 0 and +0.4 and a bright arc to the west where the spectrum breaks around 300 MHz and becomes concave down. We conclude that at the shell and along the internal filaments, the electrons responsible for the synchrotron emission were accelerated at the shock according to a simple diffusive shock model. The positive spectrum corresponds to a location where the SN shock is running into a molecular cloud and the line of sight intersects the photo dissociation region of an HII region and a young stellar object is present. Such spectral inversion is a classic signature of thermal absorption, either from ionized gas in the postshock region, from the HII region itself, or both. The curved spectrum on the westernmost bright arc is explained as the consequence of strong post-shock densities and enhanced magnetic fields after the interaction of the SN shock with a coincident molecular cloud. No spectral index trace was found indicating any connection between the associated pulsar PSR B1953+0.1 and the surrounding shell, nor between the SNR and the 3EG 1853+0114 γ -ray source proposed to be associated with W44. The comparison of the 324 MHz image with a 4.5 μ m IR image obtained with Spitzer underscored an impressive correspondence between emission both to the north and west sides of W44, while the comparison with ROSAT and Chandra images confirm that the synchrotron radio emission surrounds the thermal X-ray radiation.

HIGH SPATIAL RESOLUTION X-RAY SPECTROSCOPY OF THE IC 443 PULSAR WIND NEBULA AND ENVIRONS

Fil: Castelletti, Gabriela Marta. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Oficina de Coordinacion Administrativa Ciudad Universitaria. Instituto de Astronomia y Fisica del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomia y Fisica del Espacio; Argentina

A hadronic scenario for HESS J1818–154

Aims. We investigate two multi-shell galactic supernova remnants (SNRs), Kes 79, and G352.7−0.1, to understand the causes of this morphology. Methods. The research was carried out based on new and reprocessed archival VLA observations and XMM-Newton archival data. The surrounding gas was investigated based on data extracted from the HI Canadian Galactic Plane Survey, the 13 CO Galactic Ring Survey, and the HI Southern Galactic Plane Survey. Results. The present study infers that the overall morphology of both SNRs is the result of the mass-loss history of their respective progenitor stars. Kes 79 is likely to be the product of the gravitational collapse of a massive O9 star evolving near a molecular cloud and within the precursor’s wind-driven bubble, while G352.7−0.1 should be the result of interactions of the SNR with an asymmetric wind from the progenitor together with projection effects. No radio point source or pulsar wind nebula was found to be associated with the X-ray pulsar CXOU J185238.6+004020 in Kes 79. The X-ray study of G352.7−0.1 found that most of the thermal X-ray radiation completely fills the interior of the remnant and originates in heated ejecta. Characteristic parameters, such as radio flux, radio spectral index, age, distance, shock velocity, initial energy, and luminosity, were estimated for both SNRs.

A complete radio study of SNR G15.4+0.1 from new GMRT observations

Aims. With the purpose of producing the first detailed full view of Puppis A in X-rays, we carried out new XMM-Newton observations covering the missing regions in the southern half of the supernova remnant (SNR) and combined them with existing XMM-Newton and Chandra data. Methods. Two pointings toward the south and southwest of Puppis A were observed with XMM-Newton. We combined these data with archival XMM-Newton and Chandra data and produced images in the 0.3−0.7, 0.7−1.0, and 1.0−8.0 energy bands. Results. We present the first sensitive complete X-ray image of Puppis A. We investigated its morphology in detail, carried out a multiwavelength analysis, and estimated the flux density and luminosity of the whole SNR. The complex structure observed across the remnant confirms that Puppis A evolves in an inhomogeneous, probably knotty interstellar medium. The southwestern corner includes filaments that perfectly correlate with radio features suggested to be associated with shock/cloud interaction. In the northern half of Puppis A the comparison with Spitzer infrared images shows an excellent correspondence between X-rays and 24 and 70 μm emission features, while to the south there are some matched and other unmatched features. X-ray flux densities of 12.6 × 10 −9 , 6.2 × 10 −9 , and 2.8 × 10 −9 erg cm −2 s −1 were derived for the 0.3−0.7, 0.7−1.0, and 1.0−8.0 keV bands, respectively. At the assumed distance of 2.2 kpc, the total X-ray luminosity between 0.3 and 8.0 keV is 1.2 ×10 37 erg s −1 . We also collected and updated the broad-band data of Puppis A between radio and GeV γ-ray range, producing its spectral energy distribution. To provide constraints to the high-energy emission models, we re-analyzed radio data, estimating the energy content in accelerated particles to be Umin = 4.8 × 10 49 erg and the

The environment of the γ-ray emitting SNR G338.3−0.0: a hadronic interpretation for HESS J1640−465

Aims: We perform a multifrequency radio study of the supernova remnant (SNR) G338.3-0.0, in positional coincidence with the TeV source HESS J1640 - 465. We study the morphological and spectral properties of this remnant and its surroundings searching for plausible radio counterparts to the gamma-ray emission. Methods: We observed the SNR G338.3-0.0 using the Giant Metrewave Radio Telescope (GMRT) at 235, 610, and 1280 MHz. We also reprocessed archival data from the Australia Telescope Compact Array (ATCA) at 1290 and 2300 MHz. We conducted a search for radio pulsations towards a central point-like source, using the GMRT antennas at 610 and 1280 MHz. The molecular material in the region of the SNR was investigated based on observations made with the NANTEN telescope in the 12CO (J = 1-0) emission line. Results: The new radio observations revealed a remnant with a bilateral morphology, which at 235 MHz has a western wing that is completely attenuated because of absorption caused by foreground ionized gas. The quality of these new images allows us to provide accurate estimates of the total radio flux density of the whole SNR at different radio frequencies. From both these new and existing flux density estimates between 235 MHz and 5000 MHz, we derived for the whole remnant a spectral index α = -0.51 ± 0.06 with a local free-free continuum optical depth at 235 MHz of τ235 = 0.9 ± 0.3. No radio pulsations were detected towards the only radio point-like source within the HESS error circle. We derived upper limits of 2.0 mJy and 1.0 mJy at 610 MHz and 1280 MHz, respectively, for the pulsed flux towards this source. No radio counterpart was found for the pulsar wind nebula discovered in X-rays. The inspection of the interstellar molecular gas towards G338.3-0.0 and its surroundings indicates that there is no associated dense cloud that might explain a hadronic origin for the TeV detection.