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Register a new userA Detailed Study of Molecular Clouds toward the TeV Gamma-Ray SNR G347.3-0.5
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We present a detailed study of molecular gas toward the supernovae remnant G347.3-0.5 (J1713.7-3946) obtained with the 4m mm/sub-mm telescope NANTEN . This study has revealed that several intensity peaks and the overall distribution of the molecular gas with radial velocities from -12 km s-1 to -3 km s-1 show a remarkably good correlation with the X-ray features, strongly supporting the kinematic distance ~ 1 kpc derived by Fukui et al. (2003), as opposed to 6 kpc previously claimed. In addition, we show that absorption of X-rays is caused by local molecular gas at softer X-ray bands. Subsequent measurements of the CO(J=3-2) made with the ASTE 10 m and CSO 10.4 m telescopes toward the molecular intensity peaks have revealed higher excitation conditions, most likely higher temperatures above ~ 30 K as compared to that of the typical gas in low mass dark clouds. This is most likely caused by enhanced heating by the high energy events in the SNR, where possible mechanisms include heating by X-rays, gamma-rays, and/or cosmic ray protons, although we admit additional radiative heating by young protostars embedded may be working as well. In one of the CO peaks, we have confirmed the presence of broad molecular wings of ~ 20 km s-1 velocity extent in the CO(J=3-2) transition. The SNR evolution is well explained as the free expansion phase based on the distance of 1 kpc.
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Recent ASCA observations of G347.3-0.5, an SNR discovered in the ROSAT All-Sky Survey, reveal nonthermal emission from a region along the northwestern shell (Koyama et al. 1997). Here we report on new pointed ASCA observations of G347.3-.5 which confirm this result for all the bright shell regions and also reveal similar emission, although with slightly different spectral properties, from the remainder of the SNR. Curiously, no thermal X-ray emission is detected anywhere in the remnant. We derive limits on the amount of thermal emitting material present in G347.3-0.5 and present new radio continuum, CO and infrared results which indicate that the remnant is distant and of moderate age. We show that our observations are broadly consistent with a scenario that has most of the supernova remnant shock wave still within the stellar wind bubble of its progenitor star, while part of it appears to be interacting with denser material. A point source at the center of the remnant has spectral properties similar to those expected for a neutron star and may represent the compact relic of the supernova progenitor.
Although the connection of the Chinese guest star of 393 AD with the Galactic supernova remnant RX J1713.7-3946 (G347.3-0.5) made by Wang et al. in 1997 is consistent with the remnants relatively young properties and the guest stars projected position within the `tail of the constellation Scorpius, there are difficulties with such an association. The brief Chinese texts concerning the 393 AD guest star make no comment about its apparent brightness stating only that it disappeared after 8 months. However, at the remnants current estimated 1 - 1.3 kpc distance and A_v ~ 3 mag, its supernova should have been a visually bright object at maximum light (-3.5 to -5.0 mag) and would have remained visible for over a year. The peak brightness ~ 0 magnitude adopted by Wang et al. and others would require the RX J1713.7-3946 supernova to have been a very subluminous supernova event similar to or fainter than CCSNe like SN 2005cs. We also note problems connecting SN 393 with a European record in which the Roman poet Claudian describes a visually brilliant star in the heavens around 393 AD that could be readily seen even in midday. Although several authors have suggested this account may be a reference to the Chinese supernova of 393, Scorpius would not be visible near midday in March when the Chinese first reported the 393 guest star. We review both the Chinese and Roman accounts and calculate probable visual brightnesses for a range of supernova subtypes and conclude that neither the Chinese nor the Roman descriptions are easily reconciled with an expected RX J1713.7-3946 supernova brightness and duration.
We report the discovery of an unidentified, extended source of very-high-energy (VHE) gamma-ray emission, VER J2019+407, within the radio shell of the supernova remnant SNR G78.2+2.1, using 21.4 hours of data taken by the VERITAS gamma-ray observatory in 2009. These data confirm the preliminary indications of gamma-ray emission previously seen in a two-year (2007-2009) blind survey of the Cygnus region by VERITAS. VER J2019+407, which is detected at a post-trials significance of 7.5 standard deviations in the 2009 data, is localized to the northwestern rim of the remnant in a region of enhanced radio and X-ray emission. It has an intrinsic extent of 0.23^{circ} pm 0.03^{circ} (stat)+0.04^{circ}_{-0.02}^{circ}(sys) and its spectrum is well-characterized by a differential power law (dN/dE = N_0 times (E/TeV)^{-Gamma}) with a photon index of {Gamma} = 2.37 pm 0.14 (stat) pm 0.20 (sys) and a flux normalization of N0 = 1.5 pm 0.2 (stat) pm 0.4(sys) times 10^-12 ph TeV^{-1} cm^{-2} s^{-1}. This yields an integral flux of 5.2 pm 0.8 (stat) pm 1.4 (sys) times 10^-12 ph cm^{-2} s^{-1} above 320 GeV, corresponding to 3.7% of the Crab Nebula flux. We consider the relationship of the TeV gamma-ray emission with the GeV gamma-ray emission seen from SNR G78.2+2.1 as well as that seen from a nearby cocoon of freshly accelerated cosmic rays. Multiple scenarios are considered as possible origins for the TeV gamma-ray emission, including hadronic particle acceleration at the supernova remnant shock.
We present a new analysis of the interstellar protons toward the TeV $gamma$-ray SNR RX J0852.0$-$4622 (G266.2$-$1.2, Vela Jr.). We used the NANTEN2 $^{12}$CO($J$ = 1-0) and ATCA & Parkes HI datasets in order to derive the molecular and atomic gas associated with the TeV $gamma$-ray shell of the SNR. We find that atomic gas over a velocity range from $V_mathrm{LSR}$ = $-4$ km s$^{-1}$ to 50 km s$^{-1}$ or 60 km s$^{-1}$ is associated with the entire SNR, while molecular gas is associated with a limited portion of the SNR. The large velocity dispersion of the HI is ascribed to the expanding motion of a few HI shells overlapping toward the SNR but is not due to the Galactic rotation. The total masses of the associated HI and molecular gases are estimated to be $sim2.5 times 10^4 $ $M_{odot}$ and $sim10^3$ $M_{odot}$, respectively. A comparison with the H.E.S.S. TeV $gamma$-rays indicates that the interstellar protons have an average density around 100 cm$^{-3}$ and shows a good spatial correspondence with the TeV $gamma$-rays. The total cosmic ray proton energy is estimated to be $sim10^{48}$ erg for the hadronic $gamma$-ray production, which may still be an underestimate by a factor of a few due to a small filling factor of the SNR volume by the interstellar protons. This result presents a third case, after RX J1713.7$-$3946 and HESS J1731$-$347, of the good spatial correspondence between the TeV $gamma$-rays and the interstellar protons, lending further support for a hadronic component in the $gamma$-rays from young TeV $gamma$-ray SNRs.
It is widely believed that the bulk of the Galactic cosmic rays are accelerated in supernova remnants (SNRs). However, no observational evidence of the presence of particles of PeV energies in SNRs has yet been found. The young historical SNR Cassiopeia A (Cas A) appears as one of the best candidates to study acceleration processes. Between December 2014 and October 2016 we observed Cas A with the MAGIC telescopes, accumulating 158 hours of good-quality data. We derived the spectrum of the source from 100 GeV to 10 TeV. We also analysed $sim$8 years of $Fermi$-LAT to obtain the spectral shape between 60 MeV and 500 GeV. The spectra measured by the LAT and MAGIC telescopes are compatible within the errors and show a clear turn off (4.6 $sigma$) at the highest energies, which can be described with an exponential cut-off at $E_c = 3.5left(^{+1.6}_{-1.0}right)_{textit{stat}} left(^{+0.8}_{-0.9}right)_{textit{sys}}$ TeV. The gamma-ray emission from 60 MeV to 10 TeV can be attributed to a population of high-energy protons with spectral index $sim$2.2 and energy cut-off at $sim$10 TeV. This result indicates that Cas A is not contributing to the high energy ($sim$PeV) cosmic-ray sea in a significant manner at the present moment. A one-zone leptonic model fails to reproduce by itself the multi-wavelength spectral energy distribution. Besides, if a non-negligible fraction of the flux seen by MAGIC is produced by leptons, the radiation should be emitted in a region with a low magnetic field (B$lessapprox$100$mu$G) like in the reverse shock.)
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