Gamma-rays from pulsar wind nebulae in starburst galaxies

Recently, gamma-ray emission at TeV energies has been detected from the starburst galaxies NGC253 (Acero et al., 2009) and M82 (Acciari et al., 2009. It has been claimed that pion production due to cosmic rays accelerated in supernova remnants interacting with the interstellar gas is responsible for the observed gamma rays. Here, we show that the gamma-ray pulsar wind nebulae left behind by the supernovae contribute to the TeV luminosity in a major way. A single pulsar wind nebula produces about ten times the total luminosity of the Sun at energies above 1 TeV during a lifetime of 10^5 years. A large number of 3x10^4 pulsar wind nebulae expected in a typical starburst galaxy at a distance of 4 Mpc can readily produce the observed TeV gamma rays.Comment: 5 pages, 2 figures, accepted for publication in Astropart. Phy

No X-Ray Excess from the HESS J1741-302 Region except a New Intermediate Polar Candidate

With the Suzaku satellite, we observed an unidentified TeV gamma-ray source HESS J1741$-$302 and its surroundings. No diffuse or point-like X-ray sources are detected from the bright southern emission peak of HESS J1741$-$302. From its neighborhood, we found a new intermediate polar candidate at the position of (\alpha, \delta)_{\rm J2000.0} = (\timeform{17h40m35.6s}, \timeform{-30D14m16s}), which is designated as Suzaku J174035.6$-$301416. The spectrum of Suzaku J174035.6$-$301416 exhibits emission lines at the energy of 6.4, 6.7 and 7.0 keV, which can be assigned as the K$\alpha$ lines from neutral, He-like and H-like iron, respectively. A coherent pulsation is found at a period of 432.1 $\pm$ 0.1 s. The pulse profile is quasi-sinusoidal in the hard X-ray band (4$-$8 keV), but is more complicated in the soft X-ray band (1$-$3 keV). The moderate period of pulsation, the energy flux, and the presence of the iron K$\alpha$ lines indicate that Suzaku J174035.6$-$301416 is likely an intermediate polar, a subclass of magnetized white dwarf binaries (cataclysmic variables). Based on these discoveries, we give some implications on the origin of GCDX and brief comments on HESS J1741$-$302 and PSR B1737$-$30.Comment: Accepted by PAS

GRIPS - Gamma-Ray Imaging, Polarimetry and Spectroscopy

We propose to perform a continuously scanning all-sky survey from 200 keV to 80 MeV achieving a sensitivity which is better by a factor of 40 or more compared to the previous missions in this energy range. The Gamma-Ray Imaging, Polarimetry and Spectroscopy (GRIPS) mission addresses fundamental questions in ESA's Cosmic Vision plan. Among the major themes of the strategic plan, GRIPS has its focus on the evolving, violent Universe, exploring a unique energy window. We propose to investigate $\gamma$-ray bursts and blazars, the mechanisms behind supernova explosions, nucleosynthesis and spallation, the enigmatic origin of positrons in our Galaxy, and the nature of radiation processes and particle acceleration in extreme cosmic sources including pulsars and magnetars. The natural energy scale for these non-thermal processes is of the order of MeV. Although they can be partially and indirectly studied using other methods, only the proposed GRIPS measurements will provide direct access to their primary photons. GRIPS will be a driver for the study of transient sources in the era of neutrino and gravitational wave observatories such as IceCUBE and LISA, establishing a new type of diagnostics in relativistic and nuclear astrophysics. This will support extrapolations to investigate star formation, galaxy evolution, and black hole formation at high redshifts.Comment: to appear in Exp. Astron., special vol. on M3-Call of ESA's Cosmic Vision 2010; 25 p., 25 figs; see also www.grips-mission.e

Energy Estimation of Cosmic Rays with the Engineering Radio Array of the Pierre Auger Observatory

The Auger Engineering Radio Array (AERA) is part of the Pierre Auger Observatory and is used to detect the radio emission of cosmic-ray air showers. These observations are compared to the data of the surface detector stations of the Observatory, which provide well-calibrated information on the cosmic-ray energies and arrival directions. The response of the radio stations in the 30 to 80 MHz regime has been thoroughly calibrated to enable the reconstruction of the incoming electric field. For the latter, the energy deposit per area is determined from the radio pulses at each observer position and is interpolated using a two-dimensional function that takes into account signal asymmetries due to interference between the geomagnetic and charge-excess emission components. The spatial integral over the signal distribution gives a direct measurement of the energy transferred from the primary cosmic ray into radio emission in the AERA frequency range. We measure 15.8 MeV of radiation energy for a 1 EeV air shower arriving perpendicularly to the geomagnetic field. This radiation energy -- corrected for geometrical effects -- is used as a cosmic-ray energy estimator. Performing an absolute energy calibration against the surface-detector information, we observe that this radio-energy estimator scales quadratically with the cosmic-ray energy as expected for coherent emission. We find an energy resolution of the radio reconstruction of 22% for the data set and 17% for a high-quality subset containing only events with at least five radio stations with signal.Comment: Replaced with published version. Added journal reference and DO

The Third Fermi Large Area Telescope Catalog of Gamma-ray Pulsars

We present 294 pulsars found in GeV data from the Large Area Telescope (LAT) on the Fermi Gamma-ray Space Telescope. Another 33 millisecond pulsars (MSPs) discovered in deep radio searches of LAT sources will likely reveal pulsations once phase-connected rotation ephemerides are achieved. A further dozen optical and/or X-ray binary systems co-located with LAT sources also likely harbor gamma-ray MSPs. This catalog thus reports roughly 340 gamma-ray pulsars and candidates, 10% of all known pulsars, compared to $\leq 11$ known before Fermi. Half of the gamma-ray pulsars are young. Of these, the half that are undetected in radio have a broader Galactic latitude distribution than the young radio-loud pulsars. The others are MSPs, with 6 undetected in radio. Overall, >235 are bright enough above 50 MeV to fit the pulse profile, the energy spectrum, or both. For the common two-peaked profiles, the gamma-ray peak closest to the magnetic pole crossing generally has a softer spectrum. The spectral energy distributions tend to narrow as the spindown power $\dot E$ decreases to its observed minimum near $10^{33}$ erg s$^{-1}$, approaching the shape for synchrotron radiation from monoenergetic electrons. We calculate gamma-ray luminosities when distances are available. Our all-sky gamma-ray sensitivity map is useful for population syntheses. The electronic catalog version provides gamma-ray pulsar ephemerides, properties and fit results to guide and be compared with modeling results.Comment: 142 pages. Accepted by the Astrophysical Journal Supplemen

Discovery of an extended X-ray jet in AP librae

Chandra observations of the low-energy-peaked BL Lac object (LBL) AP Librae (AP Lib) revealed the clear discovery of a non-thermal X-ray jet. AP Lib is the first LBL with an extended non-thermal X-ray jet that shows emission into the very high energy range. The X-ray jet has an extension of ~15''(˜ 14 kpc). The X-ray jet morphology is similar to the radio jet observed with Very Large Array at 1.36 GHz emerging in the southeast direction and bends by 50° at a distance of 12'' toward the northeast. The intensity profiles of the X-ray emission studied are consistent with those found in the radio range. The spectral analysis reveals that the X-ray spectra of the core and jet region are both inverse-Compton-(IC)-dominated. This adds to a still small sample of BL Lac objects whose X-ray jets are IC-dominated and thus more similar to the high-luminosity Fanaroff-Riley II sources than to the low-luminosity Fanaroff-Riley I objects, which are usually considered to be the parent population of BL Lac objects