tag:blogger.com,1999:blog-89172868223228254912024-02-08T09:30:10.559-08:00astro-ph.HE : High Energy Astrophysical PhenomenaSite for <a href="http://communitypeerreview.blogspot.com/">Community Peer Review</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.comBlogger5645125tag:blogger.com,1999:blog-8917286822322825491.post-29625974676723912962013-08-06T00:05:00.039-07:002013-08-06T00:05:36.565-07:001308.0595 (Y. T. Tanaka et al.)<h2 class="title"><a href="http://arxiv.org/abs/1308.0595">Fermi Large Area Telescope Detection of Two Very-High-Energy (E>100 GeV)
Gamma-ray Photons from the z = 1.1 Blazar PKS 0426-380</a> [<a href="http://arxiv.org/pdf/1308.0595">PDF</a>]</h2>Y. T. Tanaka, C. C. Cheung, Y. Inoue, L. Stawarz, M. Ajello, C. D. Dermer, D. L. Wood, A. Chekhtman, Y. Fukazawa, T. Mizuno, M. Ohno, D. Paneque, D. J. Thompson<a name='more'></a><blockquote class="abstract">We report the Fermi Large Area Telescope (LAT) detection of two very-high-energy (VHE, E>100 GeV) gamma-ray photons from the directional vicinity of the distant (redshift, z = 1.1) blazar PKS 0426-380. The null hypothesis probability that both the 134 and 122 GeV photons originate from unrelated sources can be rejected at the 6.1 sigma confidence level. We therefore claim that at least one of the two VHE photons is securely associated with the blazar, making PKS 0426-380 the most distant VHE emitter known to date. The results are in agreement with the most recent Fermi-LAT constraints on the Extragalactic Background Light (EBL) intensity, which imply a $z \simeq 1$ horizon for $\simeq$ 100 GeV photons. The LAT detection of the two VHE gamma-rays coincided roughly with flaring states of the source, although we did not find an exact correspondence between the VHE photon arrival times and the flux maxima at lower gamma-ray energies. Modeling the gamma-ray continuum of PKS 0426-380 with daily bins revealed a significant spectral hardening around the time of detection of the first VHE event (LAT photon index \Gamma\ $\simeq$ 1.4) but on the other hand no pronounced spectral changes near the detection time of the second one. This combination implies a rather complex variability pattern of the source in gamma rays during the flaring epochs. A possible flat component is present above ~10 GeV in the EBL-corrected Fermi-LAT spectrum accumulated over the ~8-month high state.</blockquote>View original: <a href="http://arxiv.org/abs/1308.0595">http://arxiv.org/abs/1308.0595</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-8917286822322825491.post-88999218622605834722013-08-06T00:05:00.037-07:002013-08-06T00:05:35.827-07:001308.0594 (F. Massaro et al.)<h2 class="title"><a href="http://arxiv.org/abs/1308.0594">Blazars spectral properties at 74 MHz</a> [<a href="http://arxiv.org/pdf/1308.0594">PDF</a>]</h2>F. Massaro, M. Giroletti, A. Paggi, R. D'Abrusco, G. Tosti, S. Funk<a name='more'></a><blockquote class="abstract">Blazars are the most extreme class of active galactic nuclei (AGNs). Despite a previous investigation at 102 MHz for a small sample of BL Lacs and our recent analysis of blazars detected in the Westerbork Northern Sky Survey (WENSS), a systematic study of the blazar spectral properties at frequencies below 100 MHz has been never carried out. In this paper, we present the first analysis of the radio spectral behavior of blazars based on the recent Very Large Array Low-Frequency Sky Survey (VLSS) at 74 MHz. We search for blazar counterparts in the VLSS catalog confirming that they are detected at 74 MHz. We then show that blazars present radio flat spectra {(i.e., radio spectral indices ~0.5)} when evaluated also about an order of magnitude in frequency lower than previous analyses. Finally, we discuss the implications of our findings in the context of the blazars - radio galaxies connection since the low frequency radio data provide a new diagnostic tool to verify the expectations of the unification scenario for radio-loud active galaxies.</blockquote>View original: <a href="http://arxiv.org/abs/1308.0594">http://arxiv.org/abs/1308.0594</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-8917286822322825491.post-65901819340354135932013-08-06T00:05:00.035-07:002013-08-06T00:05:35.178-07:001308.0609 (Angela Sandrinelli et al.)<h2 class="title"><a href="http://arxiv.org/abs/1308.0609">Long and short term variability of seven blazars in six
near-infrared/optical bands</a> [<a href="http://arxiv.org/pdf/1308.0609">PDF</a>]</h2>Angela Sandrinelli, Stefano Covino, Aldo Treves<a name='more'></a><blockquote class="abstract">Context. We present the light curves of six BL Lac objects, PKS 0537-441, PKS 0735+17, OJ 287, PKS 2005-489, PKS 2155-304, W Comae, and of the flat spectrum radio quasar PKS 1510-089, as a part of a photometric monitoring program in the near-infrared/optical bands started in 2004. All sources are Fermi blazars. Aims. Our purpose is to investigate flux and spectral variability on short and long time scales. Systematic monitoring, independent of the activity of the source, guarantees large sample size statistics, and allows an unbiased view of different activity states on weekly or daily time scales for the whole timeframe and on nightly timescales for some epochs. Methods. Data were obtained with the REM telescope located at the ESO premises of La Silla (Chile). Light curves were gathered in the optical/near-infrared VRIJHK bands from April 2005 to June 2012. Results. Variability >= 3 mag is observed in PKS 0537-441, PKS 1510-089 and PKS 2155-304, the largest ranges spanned in the near-infrared. The color intensity plots show rather different morphologies. The spectral energy distributions in general are well fitted by a power law, with some deviations that are more apparent in low states. Some variability episodes during a night interval are well documented for PKS 0537-441 and PKS 2155-304. For the latter source the variability time scale implies a large relativistic beaming factor.</blockquote>View original: <a href="http://arxiv.org/abs/1308.0609">http://arxiv.org/abs/1308.0609</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-8917286822322825491.post-84035413680536793152013-08-06T00:05:00.033-07:002013-08-06T00:05:34.205-07:001308.0610 (Nahee Park et al.)<h2 class="title"><a href="http://arxiv.org/abs/1308.0610">Study of high energy cosmic ray acceleration in Tycho SNR with VERITAS</a> [<a href="http://arxiv.org/pdf/1308.0610">PDF</a>]</h2>Nahee Park, for the VERITAS Collaboration<a name='more'></a><blockquote class="abstract">Supernova Remnants (SNRs) are broadly accepted as the main accelerators of Galactic cosmic rays (GCRs) with energies up to the knee region. Recent measurements of pion bumps in IC 443 and W 44 by Fermi-LAT show indirect evidence of the acceleration of hadronic particles in SNRs. But, whether SNRs are the powerhouses for GCR acceleration all the way up to the knee region still remains an unsolved question. Tycho is a promising target for this study because it has been widely studied in multi-wavelength observations from IR to TeV and it is a young type Ia SNR located in a relatively clean environment. Though recently developed models generally agree on the likely hadronic origin of the gamma-ray emission from Tycho, the details of the models vary considerably because the current data in the GeV-TeV range are weakly constraining. Since the initial detection, VERITAS has increased its data size by more than 40%. We also recently upgraded the telescope cameras and the analysis packages, which will allow us to extend the measurements toward both lower and higher energies. In this talk, I present updates on the VHE gamma-ray measurements of Tycho with VERITAS, focusing on the interpretation of the additional data in the context of hadronic GCR acceleration models.</blockquote>View original: <a href="http://arxiv.org/abs/1308.0610">http://arxiv.org/abs/1308.0610</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-8917286822322825491.post-7345614013967852152013-08-06T00:05:00.031-07:002013-08-06T00:05:33.272-07:001308.0612 (Yang Bai et al.)<h2 class="title"><a href="http://arxiv.org/abs/1308.0612">Fermion Portal Dark Matter</a> [<a href="http://arxiv.org/pdf/1308.0612">PDF</a>]</h2>Yang Bai, Joshua Berger<a name='more'></a><blockquote class="abstract">We study a class of simplified dark matter models in which one dark matter particle couples with a mediator and a Standard Model fermion. In such models, collider and direct detection searches probe complimentary regions of parameter space. For Majorana dark matter, direct detection covers the region near mediator-dark matter degeneracy, while colliders probe regions with a large dark matter and mediator mass splitting. For Dirac and complex dark matter, direct detection is effective for the entire region above the mass threshold, but colliders provide a strong bound for dark matter lighter than a few GeV. We also point out that dedicated searches for signatures with two jets or a mono-jet not coming from initial state radiation, along missing transverse energy can cover the remaining parameter space for thermal relic dark matter.</blockquote>View original: <a href="http://arxiv.org/abs/1308.0612">http://arxiv.org/abs/1308.0612</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-8917286822322825491.post-16047743218673531002013-08-06T00:05:00.029-07:002013-08-06T00:05:32.524-07:001308.0808 (I. Marti-Vidal et al.)<h2 class="title"><a href="http://arxiv.org/abs/1308.0808">Limit to the radio emission from a putative central compact source in
SN1993J</a> [<a href="http://arxiv.org/pdf/1308.0808">PDF</a>]</h2>I. Marti-Vidal, J. M. Marcaide<a name='more'></a><blockquote class="abstract">SN1993J in M81 is the best studied young radio-luminous supernova in the Northern Hemisphere. We recently reported results from the analysis of a complete set of VLBI observations of this supernova at 1.7, 2.3, 5.0, and 8.4 GHz, covering a time baseline of more than one decade. Those reported results were focused on the kinematics of the expanding shock, the particulars of its evolving non-thermal emission, the density profile of the circumstellar medium, and the evolving free-free opacity by the supernova ejecta. In the present paper, we complete our analysis by performing a search for any possible signal from a compact source (i.e., a stellar-mass black hole or a young pulsar nebula) at the center of the expanding shell. We have performed a stacking of all our VLBI images at each frequency, after subtraction of our best-fit shell model at each epoch, and measured the peak intensity in the stacked residual image. Given the large amount of available global VLBI observations, the stacking of all the residual images allows us to put upper limits to the eventual emission of a putative compact central source at the level of $\sim102$ $\mu$Jy at 5 GHz (or, more conservatively, $\sim192$ $\mu$Jy, if we make a further correction for the ejecta opacity) and somewhat larger at other wavelengths.</blockquote>View original: <a href="http://arxiv.org/abs/1308.0808">http://arxiv.org/abs/1308.0808</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-8917286822322825491.post-77238649851480438402013-08-06T00:05:00.027-07:002013-08-06T00:05:31.596-07:001308.0820 (J. R. T. de Mello Neto et al.)<h2 class="title"><a href="http://arxiv.org/abs/1308.0820">Anisotropy studies with the Pierre Auger Observatory</a> [<a href="http://arxiv.org/pdf/1308.0820">PDF</a>]</h2>J. R. T. de Mello Neto, for the Pierre Auger Collaboration<a name='more'></a><blockquote class="abstract">We report recent results from the Pierre Auger Observatory about the study of the anisotropy in the arrival directions of ultra-high energy cosmic rays. We present the results of the search for a dipolar anisotropy at the EeV energy scale. Measurements of the phase and the amplitude of the first harmonic modulation in the right-ascension distribution are discussed. For cosmic rays with energies above 55 EeV, we present an update of the search for correlations between their arrival directions and the positions of active galactic nuclei from the Veron-Cetty and Veron catalog. We also discuss the results of correlation analyses applied to other populations of extragalactic objects. Finally we present the search for anisotropies in the data without the usage of astronomical catalogues.</blockquote>View original: <a href="http://arxiv.org/abs/1308.0820">http://arxiv.org/abs/1308.0820</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-8917286822322825491.post-9883476424740762882013-08-06T00:05:00.025-07:002013-08-06T00:05:30.849-07:001308.0829 (Wakana Iwakami et al.)<h2 class="title"><a href="http://arxiv.org/abs/1308.0829">Parametric Study of Flow Patterns behind the Standing Accretion Shock
Wave for Core-Collapse Supernovae</a> [<a href="http://arxiv.org/pdf/1308.0829">PDF</a>]</h2>Wakana Iwakami, Hiroki Nagakura, Shoichi Yamada<a name='more'></a><blockquote class="abstract">The systematic research of flow patterns behind the accretion shock wave is conducted using three-dimensional hydrodynamics simulations for core-collapse supernovae in this study. Changing the accretion rate and neutrino luminosity, the steady solutions of the one-dimensional irrotational accretion flow passing through the spherical shock wave are evolved by imposing a random perturbation with 1% amplitude at the onset of the simulations. Depending on the accretion rate and neutrino luminosity, various flow patterns appear behind the shock wave. We classified them into the three fundamental flow patterns: (1) sloshing motion, (2) spiral motion, (3) multiple high-entropy bubbles, and the two anomalous flow patterns: (4) spiral motion with buoyant bubbles, and (5) spiral motion with pulsating rotational velocity. The sloshing and spiral motions tend to be dominant in the higher accretion rate and lower neutrino luminosity, and the generations of multiple buoyant bubbles tend to prevail in the lower accretion rate and higher neutrino luminosity. Near the critical neutrino luminosity, the dominant pattern does not always identical between the semi-nonlinear and nonlinear phases, and the anomalous pattern appear in the nonlinear phase. Moreover, we confirm the reproducibility of these flow patterns, imposing the various random perturbations with 1% amplitude on the initial flow. The different realizations reveal that most of flow patterns reappear while the direction of rotational axis of the flow behind the shock wave can change in various directions. However, there are some differences among realizations for specific cases: the spiral motion with pulsating rotational velocity, and the bistability of two flow patterns.</blockquote>View original: <a href="http://arxiv.org/abs/1308.0829">http://arxiv.org/abs/1308.0829</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-8917286822322825491.post-4036215840897974532013-08-06T00:05:00.023-07:002013-08-06T00:05:29.797-07:001308.0846 (T. Ergin et al.)<h2 class="title"><a href="http://arxiv.org/abs/1308.0846">Studying the Supernova Remnant G31.9+0.0 in Gamma and X-Rays</a> [<a href="http://arxiv.org/pdf/1308.0846">PDF</a>]</h2>T. Ergin, A. Sezer, L. Saha, P. Majumdar, E. N. Ercan<a name='more'></a><blockquote class="abstract">G31.9+0.0 (3C 391) is a Galactic mixed-morphology supernova remnant observed in GeV gamma rays by Fermi Gamma Ray Space Telescope's LAT (Fermi-LAT), as well as in the 0.3-10 keV X-ray band by Suzaku. In this paper, we will present the analysis results of X- and gamma-ray data of 3C 391 taken with Suzaku and Fermi-LAT. The X-ray spectrum of 3C 391 was fitted to a single-temperature variable abundance non-equilibrium ionization model with an electron temperature of kTe ~ 0.57 keV, an absorbing column density of NH ~ 3.1 x 10^{22} cm^{-2} and a very high ionization age (\tau > 10^{12} cm^{-3} s), which suggest that the plasma has reached ionization equilibrium. The spectrum shows clearly detected emission lines of Mg, Si, and S. 3C 391 was detected in GeV gamma rays with a significance of ~ 13 sigma. The spectrum was fitted with a log-parabola function, where the spectral index and beta parameters were found to be \alpha = 2.35 +- 0.07 and \beta = 0.366 +- 0.339. The integrated flux above 200 MeV was found as F = (1.36 +- 0.62) x 10^{-8} ph cm^{-2} s^{-1}. These results are in agreement with the Fermi-LAT results given in the 2nd Fermi-LAT catalog.</blockquote>View original: <a href="http://arxiv.org/abs/1308.0846">http://arxiv.org/abs/1308.0846</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-8917286822322825491.post-63630912591094926162013-08-06T00:05:00.021-07:002013-08-06T00:05:28.857-07:001308.0876 (Yun-Wei Yu et al.)<h2 class="title"><a href="http://arxiv.org/abs/1308.0876">Bright "merger-nova" from the remnant of a neutron star binary merger: A
signature of a newly born, massive, millisecond magnetar</a> [<a href="http://arxiv.org/pdf/1308.0876">PDF</a>]</h2>Yun-Wei Yu, Bing Zhang, He Gao<a name='more'></a><blockquote class="abstract">A massive millisecond magnetar may survive a merger of a neutron star (NS) binary, which could continuously power the merger ejecta and accelerate it to a mildly-relativistic speed. We develop a generic dynamic model for the merger ejecta, where the transition from sub-relativistic to relativistic is well described. We show that the ejecta emission (the "merger-nova") powered by the magnetar can have an optical peak brightness comparable to a supernova, which is a few tens or hundreds times brighter than the radioactive-powered merger-novae (the so-called macro-nova or kilo-nova). However, the duration of the magnetar-powered merger-nova peaks earlier and has a duration significantly shorter than that of a supernova. An X-ray bump appears even earlier in time. Such merger-novae may be detected with NS-NS merger events with or without a short gamma-ray burst, and could be a bright electromagnetic counterpart for gravitational wave bursts due to NS-NS mergers. If detected, it suggests that the merger leaves behind a massive NS, which has important implications in understanding the equation-of-state of nuclear matter.</blockquote>View original: <a href="http://arxiv.org/abs/1308.0876">http://arxiv.org/abs/1308.0876</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-8917286822322825491.post-72652435095093050382013-08-06T00:05:00.019-07:002013-08-06T00:05:28.024-07:001308.0906 (H. Baty et al.)<h2 class="title"><a href="http://arxiv.org/abs/1308.0906">Explosive reconnection of double tearing modes in relativistic plasmas:
application to the Crab flares</a> [<a href="http://arxiv.org/pdf/1308.0906">PDF</a>]</h2>H. Baty, J. Petri, S. Zenitani<a name='more'></a><blockquote class="abstract">Magnetic reconnection associated to the double tearing mode (DTM) is investigated by means of resistive relativistic magnetohydrodynamic (RRMHD) simulations. A linearly unstable double current sheet system in two dimensional cartesian geometry is considered. For initial perturbations of large enough longitudinal wavelengths, a fast reconnection event is triggered by a secondary instability that is structurally driven by the nonlinear evolution of the magnetic islands. The latter reconnection phase and time scale appear to weakly depend on the plasma resistivity and magnetization parameter. We discuss the possible role of such explosive reconnection dynamics to explain the MeV flares observed in the Crab pulsar nebula. Indeed the time scale and the critical minimum wavelength give constraints on the Lorentz factor of the striped wind and on the location of the emission region respectively.</blockquote>View original: <a href="http://arxiv.org/abs/1308.0906">http://arxiv.org/abs/1308.0906</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-8917286822322825491.post-87903459347607464322013-08-06T00:05:00.017-07:002013-08-06T00:05:27.366-07:001308.0910 (F. G. Schröder et al.)<h2 class="title"><a href="http://arxiv.org/abs/1308.0910">The Tunka Radio Extension (Tunka-Rex): Status and First Results (ICRC
2013)</a> [<a href="http://arxiv.org/pdf/1308.0910">PDF</a>]</h2>F. G. Schröder, N. M. Budnev, O. A. Gress, A. Haungs, R. Hiller, T. Huege, Y. Kazarina, M. Kleifges, A. Konstantinov, E. N. Konstantinov, E. E. Korosteleva, D. Kostunin, O. Krömer, L. A. Kuzmichev, R. R. Mirgazov, L. Pankov, V. V. Prosin, G. I. Rubtsov, C. Rühle, E. Svetnitsky, R. Wischnewski, A. Zagorodnikov<a name='more'></a><blockquote class="abstract">Tunka-Rex is a new radio antenna array which extends the Tunka experiment in Siberia close to lake Baikal. It consists of 20 antennas on an area of 1 km^2 which measure the radio emission of high-energy air showers. Tunka-Rex is triggered by the photomultiplier array of Tunka measuring air-Cherenkov light of air showers in the energy range from about 10 PeV to 1 EeV. This configuration allows for the worldwide first hybrid measurements of the radio and air-Cherenkov signal for the same events: an ideal situation to perform a cross-calibration between both methods. Consequently, the main goal of Tunka-Rex is to determine the achievable energy and Xmax precision of radio measurements by comparing them to the reconstruction of the air-Cherenkov measurements. Tunka-Rex started operation in autumn 2012, and already detected air-shower events. In this paper we present the status of Tunka-Rex and first results which indicate that Tunka-Rex measures indeed the radio emission by air showers and that is is sensitive to their energy.</blockquote>View original: <a href="http://arxiv.org/abs/1308.0910">http://arxiv.org/abs/1308.0910</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-8917286822322825491.post-14772026208686343072013-08-06T00:05:00.015-07:002013-08-06T00:05:26.565-07:001308.0917 (R. Hiller et al.)<h2 class="title"><a href="http://arxiv.org/abs/1308.0917">The Tunka-Rex antenna station (ICRC 2013)</a> [<a href="http://arxiv.org/pdf/1308.0917">PDF</a>]</h2>R. Hiller, N. M. Budnev, O. A. Gress, A. Haungs, T. Huege, Y. Kazarina, M. Kleifges, A. Konstantinov, E. N. Konstantinov, E. E. Korosteleva, D. Kostunin, O. Krömer, L. A. Kuzmichev, R. R. Mirgazov, L. Pankov, V. V. Prosin, G. I. Rubtsov, C. Rühle, F. G. Schröder, E. Svetnitsky, R. Wischnewski, A. Zagorodnikov<a name='more'></a><blockquote class="abstract">Tunka-Rex is the radio extension of Tunka-133, a 1 km^2 air-Cherenkov Detector for air showers in Siberia. Tunka-Rex began operation on October 8th 2012 with 20 radio antennas. Its main goals are to explore the possible precision of the radio detection technique in determination of primary energy and mass. Each radio antenna station consists of two perpendicular aligned active SALLA antennas, which receive the radio signal from air showers. The preamplified radio signal is transmitted to local cluster centers of the Tunka-133 DAQ, where it is filtered, amplified and digitized. To reconstruct the radio signal it is crucial to understand how it is affected in each of these steps. Thus, we have studied the combined response of the antenna, with its directional pattern and the analog electronics chain, consisting of a Low-Noise Amplifier and a filter amplifier. We discuss the hardware setup of Tunka-Rex and how a description of its response is obtained. Furthermore, we estimate systematic uncertainties on the reconstructed radio signal due to hardware effects (e.g., slight variations of the electronics properties). Finally, we present background measurements with the actual Tunka-Rex antennas.</blockquote>View original: <a href="http://arxiv.org/abs/1308.0917">http://arxiv.org/abs/1308.0917</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-8917286822322825491.post-84389710261959680332013-08-06T00:05:00.013-07:002013-08-06T00:05:25.825-07:001308.0919 (Moti R. Dugair et al.)<h2 class="title"><a href="http://arxiv.org/abs/1308.0919">Detection of a variable QPO at ~41 mHz in the Be/X-ray transient pulsar
4U 0115+634</a> [<a href="http://arxiv.org/pdf/1308.0919">PDF</a>]</h2>Moti R. Dugair, Gaurava K. Jaisawal, Sachindra Naik, S. N. A. Jaaffrey<a name='more'></a><blockquote class="abstract">We report the detection of quasi-periodic oscillation (QPO) at ~41 mHz in the transient high-mass Be/X-ray binary pulsar 4U~0115+634 using data from the Rossi X-Ray Timing Explorer (RXTE) observatory. The observations used in the present work were carried out during X-ray outbursts in 1999 March-April, 2004 September-October and 2008 March-April. This frequency of the newly detected QPO was found to vary in 27-46 mHz range. This ~41 mHz QPO was detected in four of the 36 pointed RXTE Proportional Counter Array (PCA) observations during 1999 outburst where as during 2004 and 2008 outbursts, it was detected in four and three times out of 33 and 26 observations, respectively. Though QPOs at ~2 mHz, and ~62 mHz were reported earlier, the ~41 mHz QPO and its first harmonic were detected for the first time in this pulsar. There are three RXTE/PCA observations where multiple QPOs were detected in the power density spectrum of 4U~0115+634. Simultaneous presence of multiple QPOs is rarely seen in accretion powered X-ray pulsars. Spectral analysis of all the pointed RXTE/PCA observations revealed that the 3-30 keV energy spectrum was well described by Negative and Positive Power-law with EXponential cutoff (NPEX) continuum model along with interstellar absorption and cyclotron absorption components. During the three X-ray outbursts, however, no systematic variation in any of the spectral parameters other than the earlier reported anti-correlation between cyclotron absorption energy and luminosity was seen. Presence of any systematic variation of QPO frequency and rms of QPO with source flux were also investigated yielding negative results.</blockquote>View original: <a href="http://arxiv.org/abs/1308.0919">http://arxiv.org/abs/1308.0919</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-8917286822322825491.post-81183637218825240692013-08-06T00:05:00.011-07:002013-08-06T00:05:25.063-07:001308.0944 (Simone Dall'Osso et al.)<h2 class="title"><a href="http://arxiv.org/abs/1308.0944">Binary Pulsar J0737-3039: Evidence for a new core collapse and neutron
star formation mechanism</a> [<a href="http://arxiv.org/pdf/1308.0944">PDF</a>]</h2>Simone Dall'Osso, Tsvi Piran, Nir Shaviv<a name='more'></a><blockquote class="abstract">The binary pulsar J0737-3039 is the only known system having two observable pulsars, thus offering a unique laboratory to test general relativity and explore pulsar physics. Based on the low eccentricity and the position within the galactic plane, Piran & Shaviv (2004, 2005) argued that pulsar B had a non-standard formation scenario with little or no mass ejection. They have also predicted that the system would have a very slow proper motion. Pulsar timing measurements (Kramer et al. 2006; Deller et al. 2009) confirmed this prediction. The recent observations of the alignment between the spin of pulsar A and the binary orbit is also in agreement with this scenario. Detailed simulations of the formation process of pulsar B enable us to show that its progenitor, just before the collapse, was a massive O-Ne-Mg white dwarf surrounded by a tenuous, 0.1-0.16 M_sun, envelope. This envelope was ejected when the white dwarf collapsed to form a neutron star. Pulsar B was born as a slow rotator (spin period ~ 1 s) and a kick received when the pulsar formed changed its spin direction to the current one. This realization sheds light on the angular momentum evolution of the progenitor star, a process which is strongly affected by interaction with the binary companion. The slow proper motion of the system also implies that the system must have undergone a phase of mass transfer in which Star A shed a significant fraction of its mass onto B.</blockquote>View original: <a href="http://arxiv.org/abs/1308.0944">http://arxiv.org/abs/1308.0944</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-8917286822322825491.post-68265894163913175242013-08-06T00:05:00.009-07:002013-08-06T00:05:24.319-07:001308.0950 (Iwona Mochol et al.)<h2 class="title"><a href="http://arxiv.org/abs/1308.0950">Radiative damping and emission signatures of strong superluminal waves
in pulsar winds</a> [<a href="http://arxiv.org/pdf/1308.0950">PDF</a>]</h2>Iwona Mochol, John G. Kirk<a name='more'></a><blockquote class="abstract">We analyse the damping by radiation reaction and by Compton drag of strong, superluminal electromagnetic waves in the context of pulsar winds. The associated radiation signature is found by estimating the efficiency and the characteristic radiation frequencies. Applying these estimates to the gamma-ray binary containing PSR B1259-63, we show that the GeV flare observed by Fermi-LAT can be understood as inverse Compton emission by particles scattering photons from the companion star, if the pulsar wind termination shock acquires a precursor of superluminal waves roughly 30 days after periastron. This constrains the mass-loading factor of the wind $\mu=L/\dot{N}mc^2$ (where $L$ is the luminosity and $\dot{N}$ the rate of loss of electrons and positrons) to be roughly $6\times 10^4$.</blockquote>View original: <a href="http://arxiv.org/abs/1308.0950">http://arxiv.org/abs/1308.0950</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-8917286822322825491.post-64500636614685293772013-08-06T00:05:00.007-07:002013-08-06T00:05:23.577-07:001308.0973 (J. Petri)<h2 class="title"><a href="http://arxiv.org/abs/1308.0973">Phase-resolved polarization properties of the pulsar striped wind
synchrotron emission</a> [<a href="http://arxiv.org/pdf/1308.0973">PDF</a>]</h2>J. Petri<a name='more'></a><blockquote class="abstract">Since the launch of the Fermi telescope more than five years ago, many new gamma-ray pulsars have been discovered with intriguing properties challenging our current understanding of pulsar physics. Observation of the Crab pulsar furnish today a broad band analysis of the pulsed spectrum with phase-resolved variability allowing to refine existing model to explain pulse shape, spectra and polarization properties. The latter gives inside into the geometry of the emitting region as well as on the structure of the magnetic field. Based on an exact analytical solution of the striped wind with finite current sheet thickness, we analyze in detail the phase-resolved polarization variability emanating from the synchrotron radiation. We assume that the main contribution to the wind emissivity comes from a thin transition layer where the dominant toroidal magnetic field reverses its polarity, the so-called current sheet. The resulting radiation is mostly linearly polarized. In the off-pulse region, the electric vector lies in the direction of the projection onto the plane of the sky of the rotation axis of the pulsar. This property is unique to the wind model and in good agreement with the Crab data. Other properties such as a reduced degree of polarization and a characteristic sweep of the polarization angle within the pulses are also reproduced. These properties are qualitatively unaffected by variations of the wind Lorentz factor, the lepton injection power law index, the contrast in hot and cold particle, the obliquity of the pulsar and the inclination of the line of sight.</blockquote>View original: <a href="http://arxiv.org/abs/1308.0973">http://arxiv.org/abs/1308.0973</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-8917286822322825491.post-34919427338028065962013-08-06T00:05:00.005-07:002013-08-06T00:05:22.887-07:001308.0978 (J. Petri)<h2 class="title"><a href="http://arxiv.org/abs/1308.0978">General-relativistic electromagnetic fields around a slowly rotating
neutron star: stationary vacuum solutions</a> [<a href="http://arxiv.org/pdf/1308.0978">PDF</a>]</h2>J. Petri<a name='more'></a><blockquote class="abstract">Pulsars are thought to be highly magnetized rotating neutron stars accelerating charged particles along magnetic field lines in their magnetosphere and visible as pulsed emission from the radio wavelength up to high energy X-rays and gamma-rays. Being highly compact objects with compactness close to $\Xi = R_s/R\approx0.5$, where $\Rs=2\,G\,M/c^2$ is the Schwarzschild radius and $\{M,R\}$ the mass and radius of the neutron star, general-relativistic effects become important close to their surface. This is especially true for the polar caps where radio emission is supposed to emanate from, leading to well defined signatures such as linear and circular polarization. In this paper, we derive a general formalism to extend to general relativity the Deutsch field solution valid in vacuum space. Thanks to a vector spherical harmonic expansion of the electromagnetic field, we are able to express the solution to any order in the spin parameter $\Omega$ of the compact object. We hope this analysis to serve as a benchmark to test numerical codes used to compute black hole and neutron star magnetospheres.</blockquote>View original: <a href="http://arxiv.org/abs/1308.0978">http://arxiv.org/abs/1308.0978</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-8917286822322825491.post-81690052461988864962013-08-06T00:05:00.003-07:002013-08-06T00:05:21.835-07:001308.1001 (B. Gendre et al.)<h2 class="title"><a href="http://arxiv.org/abs/1308.1001">The diversity of progenitors and emission mechanisms for ultra-long
bursts</a> [<a href="http://arxiv.org/pdf/1308.1001">PDF</a>]</h2>B. Gendre, G. Stratta, J. L. Atteia, S. Basa, M. Boer, D. M. Coward, S. Cutini, V. D'Elia, E. J. Howell, A. Klotz, S. Oates, M. De Pasquale, L. Piro<a name='more'></a><blockquote class="abstract">GRB 111209A is the longest ever recorded burst. This burst was detected by Swift and Konus-Wind, and we obtained TOO time from XMM-Newton as well as prompt data from TAROT. We made a common reduction using data from these instruments together with other ones. This allows for the first time a precise study at high signal-to-noise ratio of the prompt to afterglow transition. We show that several mechanisms are responsible of this phase. In its prompt phase, we show that its duration is longer than 20 000 seconds. This, combined with the fact that the burst fluence is among the top 5% of what is observed for other events, makes this event extremely energetic. We discuss the possible progenitors that could explain the extreme duration properties of this burst as well as its spectral properties. We present evidences that this burst belong to a new, previously unidentified, class of GRBs. The most probable progenitor of this new class is a low metalicity blue super-giant star. We show that selection effects could prevent the detection of other bursts at larger redshift and conclude that this kind of event is intrinsically rare in the local Universe. The afterglow presents similar features to other normal long GRBs and a late rebrightening in the optical wavelengths, as observed in other long GRBs. A broad band SED from radio to X-rays at late times does not show significant deviations from the expected standard fireball afterglow synchrotron emission.</blockquote>View original: <a href="http://arxiv.org/abs/1308.1001">http://arxiv.org/abs/1308.1001</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-8917286822322825491.post-55511400777242773782013-08-06T00:05:00.001-07:002013-08-06T00:05:20.997-07:001308.1058 (G. R. Mamatsashvili et al.)<h2 class="title"><a href="http://arxiv.org/abs/1308.1058">Revisiting linear dynamics of non-axisymmetric perturbations in weakly
magnetized accretion discs</a> [<a href="http://arxiv.org/pdf/1308.1058">PDF</a>]</h2>G. R. Mamatsashvili, G. D. Chagelishvili, G. Bodo, P. Rossi<a name='more'></a><blockquote class="abstract">We investigate linear dynamics of non-axisymmetric perturbations in incompressible, vertically stratified Keplerian discs with a weak vertical magnetic field in the shearing box approximation. Perturbations are decomposed into shearing waves whose evolution is followed via numerical integration of the linearized ideal MHD equations. There are two basic modes in the system -- inertia-gravity waves and magnetic mode, which displays the magnetorotational instability (MRI). As distinct from previous studies, we introduce `eigenvariables' characterizing each (counter-propagating) component of the inertia-gravity and magnetic modes, which are governed by a set of four first order coupled ordinary differential equations. This allowed us to identify a new process of linear coupling of the two above non-axisymmetric modes due to the disc's differential rotation. We did a comparative analysis of the dynamics of non-axisymmetric and axisymmetric magnetic mode perturbations. It is shown that the growth of optimal and close-to-optimal non-axisymmetric harmonics of this mode, having transient nature, can prevail over the exponential growth of axisymmetric ones (i.e., over the axisymmetric MRI) during dynamical time. A possible implication of this result for axisymmetric channel solutions is discussed. Specifically, the formation of the channel may be affected/impeded by non-axisymmetric modes already at the early linear stage leading to its untimely disruption -- the outcome strongly depends on the amplitude and spectrum of initial perturbation. So, this competition may result in an uncertainty in the magnetic mode's non-linear dynamics. It is also shown that a maximum non-axisymmetric growth is at vertical wavelengths close to the scale-height for which compressibility effects are important. This indirectly suggests that compressibility plays a role in the dynamics of the non-axisymmetric MRI.</blockquote>View original: <a href="http://arxiv.org/abs/1308.1058">http://arxiv.org/abs/1308.1058</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-8917286822322825491.post-39203545786551987562013-08-05T00:04:00.025-07:002013-08-05T00:04:23.572-07:001308.0328 (Amy E. Reines et al.)<h2 class="title"><a href="http://arxiv.org/abs/1308.0328">Dwarf Galaxies with Optical Signatures of Active Massive Black Holes</a> [<a href="http://arxiv.org/pdf/1308.0328">PDF</a>]</h2>Amy E. Reines, Jenny E. Greene, Marla Geha<a name='more'></a><blockquote class="abstract">We present a sample of 151 dwarf galaxies (10^8.5 < M_stellar < 10^9.5 Msun) that exhibit optical spectroscopic signatures of accreting massive black holes (BHs), increasing the number of known active galaxies in this stellar mass range by more than an order of magnitude. Utilizing data from the Sloan Digital Sky Survey Data Release 8 and stellar masses from the NASA-Sloan Atlas, we have systematically searched for active BHs in ~25,000 emission-line galaxies with stellar masses comparable to the Magellanic Clouds and redshifts z<0.055. Using the narrow-line [OIII]/H-beta versus [NII]/H-alpha diagnostic diagram, we find photoionization signatures of BH accretion in 136 galaxies, a small fraction of which also exhibit broad H-alpha emission. For these broad-line AGN candidates, we estimate BH masses using standard virial techniques and find a range of 10^5 < M_BH < 10^6 Msun and a median of M_BH ~ 2 x 10^5 Msun. We also detect broad H-alpha in 15 galaxies that have narrow-line ratios consistent with star-forming galaxies. Follow-up observations are required to determine if these are true type 1 AGN or if the broad H-alpha is from stellar processes. The median absolute magnitude of the host galaxies in our active sample is Mg = -18.1 mag, which is ~1-2 magnitudes fainter than previous samples of AGN hosts with low-mass BHs. This work constrains the smallest galaxies that can form a massive BH, with implications for BH feedback in low-mass galaxies and the origin of the first supermassive BH seeds.</blockquote>View original: <a href="http://arxiv.org/abs/1308.0328">http://arxiv.org/abs/1308.0328</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-8917286822322825491.post-80547232627633561132013-08-05T00:04:00.023-07:002013-08-05T00:04:22.531-07:001308.0330 (F. Massaro et al.)<h2 class="title"><a href="http://arxiv.org/abs/1308.0330">Unveiling the nature of the unidentified gamma-ray sources III:
gamma-ray blazar-like counterparts at low radio frequencies</a> [<a href="http://arxiv.org/pdf/1308.0330">PDF</a>]</h2>F. Massaro, R. D'Abrusco, M. Giroletti, A. Paggi, N. Masetti, G. Tosti, M. Nori, S. Funk<a name='more'></a><blockquote class="abstract">About one third of the gamma-ray sources listed in the second Fermi LAT catalog (2FGL) have no firmly established counterpart at lower energies so being classified as unidentified gamma-ray sources (UGSs). Here we propose a new approach to find candidate counterparts for the UGSs based on the 325 MHz radio survey performed with Westerbork Synthesis Radio Telescope (WSRT) in the northern hemisphere. First we investigate the low-frequency radio properties of blazars, the largest known population of gamma-ray sources; then we search for sources with similar radio properties combining the information derived from the Westerbork Northern Sky Survey (WENSS) with those of the NRAO VLA Sky survey (NVSS). We present a list of candidate counterparts for 32 UGSs with at least one counterpart in the WENSS. We also performed an extensive research in literature to look for infrared and optical counterparts of the gamma-ray blazar candidates selected with the low-frequency radio observations to confirm their nature. On the basis of our multifrequency research we identify 23 new gamma-ray blazar candidates out of 32 UGSs investigated. Comparison with previous results on the UGSs are also presented. Finally, we speculate on the advantages on the use of the low-frequency radio observations to associate UGSs and to search for gamma-ray pulsar candidates.</blockquote>View original: <a href="http://arxiv.org/abs/1308.0330">http://arxiv.org/abs/1308.0330</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-8917286822322825491.post-24027054584788397152013-08-05T00:04:00.021-07:002013-08-05T00:04:21.813-07:001308.0334 (Anthony L. Piro et al.)<h2 class="title"><a href="http://arxiv.org/abs/1308.0334">Reconciling 56Ni Production in Type Ia Supernovae with Double Degenerate
Scenarios</a> [<a href="http://arxiv.org/pdf/1308.0334">PDF</a>]</h2>Anthony L. Piro, Todd A. Thompson, Christopher S. Kochanek<a name='more'></a><blockquote class="abstract">Binary white dwarf (WD) coalescence driven by gravitational waves or collisions in triple systems are potential progenitors of Type Ia supernovae (SNe Ia). We combine the distribution of 56Ni inferred from observations of SNe Ia with the results of both sub-Chandrasekhar detonation models and direct collision calculations to estimate what mass WDs should be exploding in each scenario to reproduce the observations. These WD mass distributions are then compared with the observed Galactic WD mass distribution and Monte Carlo simulations of WD-WD binary populations. For collisions, we find that the average mass of the individual components of the WD-WD binary must be peaked at ~0.75Msun, significantly higher than the average WD mass in binaries or in the field of ~0.55-0.60Msun. Thus, if collisions indeed produce a large fraction of SNe Ia, then a mechanism must exist that favors large mass WDs. In particular, collisions between WDs of average mass must be highly suppressed. For sub-Chandrasekhar detonations, we find that the average mass of the exploding WDs must be peaked at ~1.1Msun, consistent with the average sum of the masses in WD-WD binaries. This interesting similarity should be tested by future calculations of the 56Ni yield from double degenerate mergers. These models may also explain why SNe Ia are on average dimmer in early-type hosts: in old environments binaries evolve too quickly to have mergers between two high mass WDs at current times. As future simulations explore the 56Ni yield over a wider range of parameters, the general framework discussed here will be an important tool for continuing to assess double degenerate scenarios.</blockquote>View original: <a href="http://arxiv.org/abs/1308.0334">http://arxiv.org/abs/1308.0334</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-8917286822322825491.post-59490619070567140832013-08-05T00:04:00.019-07:002013-08-05T00:04:19.996-07:001308.0338 (Kathryn M. Zurek)<h2 class="title"><a href="http://arxiv.org/abs/1308.0338">Asymmetric Dark Matter: Theories, Signatures, and Constraints</a> [<a href="http://arxiv.org/pdf/1308.0338">PDF</a>]</h2>Kathryn M. Zurek<a name='more'></a><blockquote class="abstract">We review theories of Asymmetric Dark Matter (ADM), their cosmological implications and detection. While there are many models of ADM in the literature, our review of existing models will center on highlighting the few common features and important mechanisms for generation and transfer of the matter-anti-matter asymmetry between dark and visible sectors. We also survey ADM hidden sectors, the calculation of the relic abundance for ADM, and how the DM asymmetry may be erased at late times through oscillations. We consider cosmological constraints on ADM from the cosmic microwave background, neutron stars, the Sun, and brown and white dwarves. Lastly, we review indirect and direct detection methods for ADM, collider signatures, and constraints.</blockquote>View original: <a href="http://arxiv.org/abs/1308.0338">http://arxiv.org/abs/1308.0338</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-8917286822322825491.post-75562156780765503422013-08-05T00:04:00.017-07:002013-08-05T00:04:19.277-07:001308.0340 (Avery E. Broderick et al.)<h2 class="title"><a href="http://arxiv.org/abs/1308.0340">Implications of Plasma Beam Instabilities for the Statistics of the
Fermi Hard Gamma-ray Blazars and the Origin of the Extragalactic Gamma-Ray
Background</a> [<a href="http://arxiv.org/pdf/1308.0340">PDF</a>]</h2>Avery E. Broderick, Christoph Pfrommer, Ewald Puchwein, Philip Chang<a name='more'></a><blockquote class="abstract">Fermi has been instrumental in constraining the luminosity function and redshift evolution of gamma-ray bright blazars. This includes limits upon the spectrum and anisotropy of the extragalactic gamma-ray background (EGRB), redshift distribution of nearby Fermi active galactic nuclei (AGN), and the construction of a log(N)-log(S) relation. Based upon these, it has been argued that the evolution of the gamma-ray bright blazar population must be much less dramatic than that of other AGN. However, critical to such claims is the assumption that inverse Compton cascades reprocess emission above a TeV into the Fermi energy range, substantially enhancing the strength of the observed limits. Here we demonstrate that in the absence of such a process, due, e.g., to the presence of virulent plasma beam instabilities that preempt the cascade, a population of TeV-bright blazars that evolve similarly to quasars is consistent with the population of hard gamma-ray blazars observed by Fermi. Specifically, we show that a simple model for the properties and luminosity function is simultaneously able to reproduce their log(N)-log(S) relation, local redshift distribution, and contribution to the EGRB and its anisotropy without any free parameters. Insofar the naturalness of a picture in which the hard gamma-ray blazar population exhibits the strong redshift evolution observed in other tracers of the cosmological history of accretion onto halos is desirable, this lends support for the absence of the inverse Compton cascades and the existence of the beam plasma instabilities.</blockquote>View original: <a href="http://arxiv.org/abs/1308.0340">http://arxiv.org/abs/1308.0340</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0