* Astronomy

Twisted magnetic loop in the Giraffe galaxy IC 342

Magnetic fields exist everywhere in the Universe, but there is still little idea how important they are for the evolution of cosmic objects. Radio waves are an ideal means to measure magnetic fields in galaxies. In a long-standing effort, Rainer Beck from the Max Planck Institute for Radio Astronomy (MPIfR) in Bonn, Germany, gathered a huge data set of the nearby galaxy IC 342 from observations with two of the world's largest radio telescopes, NRAO's Very Large Array and the 100-m radio telescope of the MPIfR, in four different wavelength bands, from 2.8 cm to 21 cm. An ordered magnetic field mostly aligned along the optical spiral arms was discovered. The discovery helps to explain how galactic spiral arms are formed. The same study also shows how gas can be funneled inward toward the center of IC 342.
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Title: Discovery of a Quasi-Periodic Oscillation in the Ultraluminous X-ray Source IC 342 X-1: XMM-Newton Results
Author: V.K. Agrawal, Anuj Nandi

We report the discovery of a quasi-periodic oscillation (QPO) at 642 mHz in an XMM-Newton observation of the ultraluminous X-ray source (ULX) IC 342 X-1. The QPO has a centroid at QPO=642±20 mHz, a coherence factor of Q=11.6, and an amplitude (rms) of 4.1% with significance of 3.6sigma. The energy dependence study shows that the QPO is stronger in the energy range 0.3 - 5.0 keV. A subsequent observation (6 days later) does not show any signature of the QPO in the power density spectrum. The broadband energy spectra (0.3 - 40.0 keV) obtained by quasi-simultaneous observations of XMM-Newton and NuSTAR can be well described by an absorbed diskbb plus cutoffpl model. The best fitted spectral parameters are power-law index (Gamma) ~ 1.1, cutoff energy (Ec) ~ 7.9 keV and disc temperature (kT_in) ~ 0.33 keV, where the QPO is detected. The unabsorbed bolometric luminosity is ~ 5.34 x 10³⁹ erg~s^-1. Comparing with the well known X-ray binary GRS 1915+105, our results are consistent with the mass of the compact object in IC 342 X-1 being in the range ~20-65 solar masses. We discuss the possible implications of our results.

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NASA's NuSTAR Catches Black Holes in Galaxy Web

NASA's Nuclear Spectroscopic Telescope Array, or NuSTAR, set its X-ray eyes on a spiral galaxy and caught the brilliant glow of two black holes lurking inside.
The new image is being released Monday along with NuSTAR's view of the supernova remnant Cassiopeia A, at the American Astronomical Society meeting in Long Beach, Calif.
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Title: Giant Molecular Clouds in the Spiral Arm of IC 342
Authors: Akihiko Hirota, Nario Kuno, Naoko Sato, Hiroyuki Nakanishi, Tomoka Tosaki, Kazuo Sorai

We present results of 12CO (1-0) and 13CO (1-0) observations of the northeastern spiral arm segment of IC 342 with a ~ 50pc resolution carried out with the Nobeyama Millimeter Array. Zero-spacing components were recovered by combining with the existing data taken with the Nobeyama 45m telescope. Prime target is to investigate the variation of cloud properties across the spiral arm with a resolution comparable to size of giant molecular clouds (GMCs). The observations cover a 1 kpc x 1.5 kpc region located ~2 kpc away from the galactic center, where a giant molecular association (GMA) is located at trailing side and associated star forming regions at leading side. The spiral arm segment was resolved into a number of clouds whose size, temperature and surface mass density are comparable to typical GMCs in the Galaxy. 26 clouds were identified from the combined data cube and the identified clouds followed the linewidth-size relation of the Galactic GMCs. The identified GMCs were divided into two categories according to whether they are associated with star formation activity or not. Comparison between both categories indicated that the active GMCs are more massive, have smaller linewidth, and are closer to virial equilibrium compared to the quiescent GMCs. These variations of the GMC properties suggest that dissipation of excess kinetic energy of GMC is a required condition for onset of massive star formation.

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