E. B. Giacani

The molecular clouds in the environs of the supernova remnants G349.7+0.2 and G18.8+0.3

We present the results of a new high-resolution study of the molecular gas associated with the supernova remnants (SNRs) G349.7+0.2 and G18.8+0.3. The observations were performed with the SEST telescope in the 12 CO J = 1-0, 2-1 and 3-2 lines (beams of 45, 23 and 15, respectively). The present observations have provided, for the two SNRs, new evidence in support of the existence of physical interaction between the SN shocks and the adjoining molecular clouds. In the case of G349.7+0.2, the new observations revealed for the first time the internal structure of the shocked cloud, as well as the kinematical consequences of the impact of the SNR shock on the molecular cloud. From these observations we were able to constrain the conditions of the pre-shocked gas. The molecular cloud associated with G349.7+0.2, centered near ν LSR = +16.2 km s -1 , has a linear size of about 7 pc, a mass of ∼10 4 M ○. and a volume density of ∼10 3 cm -3 . The high line ratios derived are indicative of the existence of shocks in the cloud. From the asymmetries observed in the line shapes we propose that the SN shock cloud is running into the denser part of the cloud and has probably begun to disrupt it, pushing the eastern component clumps away from us, and the western fragments toward us. After comparing our estimates of the column density of the intervening gas with similar calculations based on ASCA X-rays spectral fitting we conclude that the best way to make these results compatible is by assuming that the associated cloud is placed behind G349.7+0.2 along the line of sight, and the SNR/molecular cloud encounter is taking place on the far side of the SNR. This model also provides a natural explanation for the lack of strong X-ray absorption in the central region of G349.7+0.2. Evaporation of part of the associated cloud must be responsible for the central X-ray emission. The comparison with IRAS infrared data provides additional support for the hypothesis of SNR/cloud physical interaction. From the study of the molecular gas in the neighborhood of the five OH (1720 MHz) masers detected in G349.7+0.2 we find that in three cases the maser peak velocity coincides with the local CO peak velocity, while in the remaining two cases the maser peak velocity agrees with a secondary, blended CO component. We conclude that the masers are excited at the sites where a non-dissociative C-type shock, locally transverse to the line of sight (or forming a large angle with it), hits a denser molecular clump. For the SNR G18.8+0.3, the new higher resolution observations have revealed excellent morphological agreement between one of the cloud components and the SNR shock front towards the eastern limb. The associated molecular mass is estimated to be ∼4.4 x 10 4 M ○. and the cloud volume density ∼1200 cm -3 . The analysis of the line ratios in this case revealed a maximum of R 2-1/1-0 = 1.25 at a position that exactly matches an indentation in the radio continuum emission in the remnants shell, providing additional evidence of SNR/molecular cloud interaction.

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

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

A new study of the supernova remnant G344.7-0.1 located in the vicinity of the unidentified TeV source HESS J1702-420

Context. The identification of counterparts of dark gamma-ray sources adds greatly to our understanding of their underlying astrophysical processes. Aims. We investigate the physical properties of the supernova remnant (SNR) G344.7−0.1, to clarify whether it hosts a pulsar wind nebula (PWN), and the possible physical relationship between the SNR and the gamma-ray source HESS J1702−420. Methods. The research was carried out based on new high-resolution radio images produced from archival ATCA and VLA data in combination with X-ray archival XMM-Newton data. The ambient interstellar medium was investigated in HI, 12 CO and mid IR (λ 24 μm) with data from the public SGPS, CfA CO and MIPSGAL surveys, respectively. Results. Based on the radio images and the comparison with X-ray and IR observations, we confirm that there is no PWN within G344.7−0.1; the observed emission highlights sites where the SN blast wave is encountering dense material. No radio counterpart is found for the X-ray object CXOU J170357.8-414302. The X-ray radiation completely fills in the interior of the SNR, being thermal in nature and originating in heated ejecta. From the spectral analysis it is inferred that G344.7−0.1 is the result of a core-collapse SN that exploded about 3000 yr ago. On the basis of HI absorption and emission we redetermined its distance in (6.3 ± 0.1) kpc. From the study of the surrounding gas, we conclude that G344.7−0.1 has evolved within an HI bubble created by the SN precursor. This bubble is, in turn, part of a larger HI/IR ring created by the stellar wind of prior-generation stars, about 2.6 × 10 6 yr ago. A second generation of stars formed in this compressed gas and about 3000 yr ago one of these stars exploded, creating the SNR G344.7−0.1. This study suggests that G344.7−0.1 and its turbulent environment is a plausible counterpart for HESS J1702−420.

Study of the γ-ray source 1AGL J2022+4032 in the Cygnus region

Context. Identification of -ray-emitting Galactic sources is a long-standing problem in astrophysics. One such source, 1AGL J2022+4032, coincident with the interior of the radio shell of the supernova remnant Gamma Cygni (SNR G78.2+2.1) in the Cygnus Region, has recently been identified by Fermi as a -ray pulsar, LAT PSR J2021+4026. Aims. We present long-term observations of 1AGL J2022+4032 with the AGILE -ray telescope, measuring its flux and light curve. Methods. We compare the light curve of 1AGL J2022+4032 with that of 1AGL J2021+3652 (PSR J2021+3651), showing that the flux variability of 1AGL J2022+4032 appears to be greater than the level predicted from statistical and systematic e ects and producing detailed simulations to estimate the probability of the apparent observed variability. Results. We evaluate the possibility that the -ray emission may be due to the superposition of two or more point sources, some of which may be variable, considering a number of possible counterparts. Conclusions. We consider the possibility of a nearby X-ray quiet microquasar contributing to the flux of 1AGL J2022+4032 to be more likely than the hypotheses of a background blazar or intrinsic -ray variabilty of LAT PSR J2021+4026.

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

G0.570-0.018: A Young Supernova Remnant? INTEGRAL and VLA Observations

We report INTEGRAL IBIS γ-ray and VLA radio observations of G0.570-0.018, a diffuse X-ray source recently discovered by ASCA and Chandra in the Galactic center region. Based on its spectrum and morphology, G0.570-0.018 has been proposed to be a very young supernova remnant. In this scenario, the presence of γ-ray lines coming from the short-lived radioactive nucleus 44Ti and synchrotron radio continuum emission are expected. The first could provide information on nucleosynthesis environments in the interior of exploding stars, and the latter could probe the interaction between the supernova blast wave and the circumstellar/interstellar matter. We have not detected 44Ti lines or any conspicuous radio feature associated with this source down to the achieved sensitivities. From the derived upper limits we set constraints on the nature of G0.570-0.018.

Study of the luminous blue variable star candidate G26.47+0.02 and its environment

Aims. The luminous blue variable (LBV) stars are peculiar very massive stars. The study of these stellar objects and their surroundings is important for understanding the evolution of massive stars and its effects on the interstellar medium. We study the LBV star candidate G26.47+0.02. Methods. Using several large-scale surveys in different frequencies we performed a multiwavelength study of G26.47+0.02 and its surroundings. Results. We found a molecular shell (seen in the 13CO J = 1–0 line) that partially surrounds the mid-infrared nebula of G26.47+0.02, which suggests an interaction between the strong stellar winds and the molecular gas. From the HI absorption and the molecular gas study we conclude that G26.47+0.02 is located at a distance of ∼4.8 kpc. The radio continuum analysis shows both thermal and non-thermal emission toward this LBV candidate, pointing to wind-wind collision shocks from a binary system. This hypothesis is supported by a search of near-IR sources and the Chandra X-ray analysis. Additional multiwavelength and long-term observations are needed to detect some possible variable behavior, and if that is found, to confirm the binary nature of the system.

Study of the molecular clump associated with the high-energy source HESS J1858+020

Aims. HESS J1858+020 is a weak γ-ray source lying near the southern border of the SNR G35.6-0.4. A molecular cloud, composed of two clumps, shows signs of interaction with both the SNR and a nearby extended HII region. In particular, the southernmost clump coincides with the center of the H.E.S.S. source. We study this clump in detail to help us identify the nature of the very-high energy emission. Methods. We observed the aforementioned molecular clump using the Atacama Submillimeter Telescope Experiment (ASTE) in the 12 CO J = 3−2, 13 CO J = 3−2, HCO + J = 4−3, and CS J = 7−6 lines with an angular resolution of 22 �� . To complement these observations, we analyzed IR and submillimeter continuum archival data. Results. From the 12 CO and 13 CO J = 3−2 lines and the 1.1 mm continuum emission, we derive a density of between 10 3 and 10 4 cm −3 for the clump. We discover a young stellar object (YSO), probably a high mass protostar, embedded in the molecular clump. However, we do not find any evidence of molecular outflows from this YSO that would represent a thermal jet capable of generating the observed γ-rays. We conclude that the most probable origin of the TeV γ-ray emission is a hadronic interaction between the molecular gas and the cosmic rays accelerated by the shock front of the SNR G35.6-0.4.

The molecular gas around the luminous blue variable star G24.73+0.69

Aims. We study the molecular environment of the luminous blue variable star G24.73+0.69 to investigate the origin of the two infrared shells around this massive star and determine its effects on the surrounding interstellar medium. Methods. We analyze the distribution of the molecular gas using the 13 CO J = 1–0 emission extracted from the Galactic Ring Survey. We use near- and mid-infrared data from 2MASS and GLIMPSE to identify the young stellar objects in the field. Results. We discover the molecular counterpart to the outer infrared shell around G24.73+0.69. The CO shell was probably blown by the stellar wind of the star mainly during its main sequence phase. We also find molecular gas that corresponds to the inner infrared shell, although its origin remains uncertain. We identify seven young stellar objects within the molecular material, whose birth might have been triggered by the stellar wind of the luminous blue variable star. We suggest that both G24.73+0.69 and the progenitor of the nearby supernova remnant G24.7+0.6 were formed from the same natal cloud and represent the most evolved members of a so far undetected cluster of massive stars.

An X-ray study of the supernova remnant G20.0-0.2 and its surroundings

Fil: Petriella, Alberto. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Oficina de Coordinacion Administrativa Ciudad Universitaria. Instituto de Astronomia y Fisica del Espacio(i); Argentina; Universidad de Buenos Aires; Argentina;