The superbubble origin for galactic cosmic rays

The source of energy for cosmic-ray acceleration appears to be shock waves driven by supernova (SNe) ejecta. The great majority (80–90%) of SNe (SNII and SNIb) are formed by the core collapse of young, massive O and B stars. However, it has been known for more than forty years that the births of such massive stars in stellar clumps, termed OB associations, are correlated in space and time. The combined ejecta of core-collapse SNe, occurring at the deaths of these massive stars, create low-density (∼5.0 × 10⁻³ cm⁻³) superbubbles that reach dimensions of several hundred pc. The occurrence of correlated SNe in superbubbles affects not just the source of cosmic-ray energy, SNe shock waves, it impinges as well on the elemental and isotopic source abundances of cosmic-ray nuclei. We argue that the well-known anomalous cosmic-ray ²²Ne/²⁰Ne ratio, a factor of five times the Solar System ratio, results from a mixing of freshly synthesized nucleosynthetic material in supernova active cores of superbubbles. Although diluted by mixing with older, lower metallicity interstellar gas, the mean metallicities in the superbubble, SNe-dominated cores are high ∼3 times the Solar System value.     

Progress in laboratory performance verification of the R-process Isotope Observer

The source of galactic cosmic rays (GCR) remains unknown, despite many decades of research. It is generally accepted among high-energy astrophysicists that GCR are accelerated by supernova (SN) shocks in the interstellar medium, but the evidence for this remains indirect. However, the fact that the cosmic-ray spectrum continues far past the limit of SN shock acceleration is a serious problem for this model. Most SNae occur in superbubbles – regions of the interstellar medium containing massive stars and SN remnants. Thus, SNae should be accelerating the ejecta of other SNae. The local medium of the superbubble will be enhanced in freshly synthesized R-process material. We are currently developing the R-process Isotope Observer (RIO), which could make the first measurements of the isotopic abundances of the “ultraheavy” GCR (those in the range 32 ⩽ Z ⩽ 42) in order to determine the fractional contribution of freshly synthesized R-process material in GCR through the measurement of several key isotopic ratios. We have recently performed a series of tests of the RIO detector with 400 A MeV ⁸⁴Kr at the HIMAC accelerator in Japan. The results of these tests indicate that a mass resolution of ∼0.3 u can be achieved with RIO. We also discuss the prospects for accommodation of the RIO mission.     

A Gemini observation of the anomalous X-ray pulsar 1RXS J170849-400910

The anomalous X-ray pulsars (AXPs) represent a growing class of neutron stars discovered at X-ray energies. While the nature of their multi-wavelength emission mechanism is still under debate, evidence has been recently accumulating in favor of their magnetar nature. Their study in the optical and infrared (IR) wavelengths has recently opened a new window to constrain the proposed models. We here present a brief overview of AXPs and our Gemini-South observation of 1RXS J170849-400910, which is a relatively bright AXP discovered with ROSAT and later found to be an 11 s X-ray pulsar by ASCA. The observation was taken with the near-IR imager Flamingos in J (1.25 μm), H (1.65 μm), and K_s (2.15 μm). We confirm the recent detection by (ApJ, 589, L93–L96) of a source coincident with the CHANDRA source (candidate ‘A’). Our derived magnitudes of J = 20.6 (0.2), H = 18.6 (0.2), and K_s = 17.1 (0.2) are consistent with those derived by (ApJ, 589, L93–L96), and indicate that if this source is indeed the IR counterpart to 1RXS J170849-400910, then there is no evidence of variability from this AXP. However, given the lack of IR variability and the relatively high IR to X-ray flux of this source when compared to the other AXPs, we conclude that this source is unlikely the counterpart of the AXP, and that the other source (candidate ‘B’) within the CHANDRA error circle should not be ruled out as the counterpart. Further monitoring of these sources and a deep observation of this complex field are needed to confirm the nature of these sources and their association with the AXP.     

Storm time spatial variations in TEC during moderate geomagnetic storms in extremely low solar activity conditions (2007–2009) over Indian region

The total electron content (TEC) measurements from a network of GPS receivers were analyzed to investigate the storm time spatial response of ionosphere over the Indian longitude sector. The GPS receivers from the GPS Aided Geo Augmented Navigation (GAGAN) network which are uniquely located around the ∼77°E longitude are used in the present study so as to get the complete latitudinal coverage from the magnetic equator to low mid-latitude region. We have selected the most intense storms but of moderate intensity (−100 nT < Dst < −50 nT) which occurred during the unusually extremely low solar activity conditions in 2007–2009. Though the storms are of moderate intensity, their effects on equatorial to low mid-latitude ionosphere are found to be very severe as TEC deviations are more than 100% during all the storms studied. Interesting results in terms of spatial distribution of positive/negative effects during the main/early recovery phase of storms are noticed. The maximum effect was observed at crest region during two storms whereas another two storms had maximum effect near the low mid-latitude region. The associated mechanisms like equatorial electrodynamics and neutral dynamics are segregated and explained using the TIMED/GUVI and EEJ data during these storms. The TEC maps are generated to investigate the storm time development/inhibition of equatorial ionization anomaly (EIA).     

Heliospheric implications of structure in the interstellar medium

Equilibrium models of diffuse interstellar material (ISM) near the Sun show a range of cloud densities, ionization, and temperatures which are consistent with data, although the local ISM must be inhomogeneous over ∼2 pc scales. The ISM close to the Sun has properties that are consistent with the sheetlike warm neutral (and partially ionized) gas detected in the Arecibo Millennium Survey. Local interstellar magnetic fields are poorly understood, but data showing weak polarization for nearby stars indicate dust may be trapped in fields or currents in the heliosheath nose region. Implications of this dust capture are widespread, and may impact the interpretation of the cosmic microwave background data. Observations of interstellar H⁰ inside of the solar system between 1975 and 2000 do not suggest any variation in the properties or structure of local interstellar H⁰ over distance scales of ∼750 AU to within the uncertainties.     

High energy emission from pulsars: Outer gap scenario

I will give a brief review of the recent development in the emission models of isolated, rapidly rotating neutron stars, focusing on the γ-ray radiation mechanism in their outer magnetospheres. By examining the Poisson equation for the electrostatic potential, I show that an active particle accelerator must extend from the vicinity of the neutron star surface to the vicinity of light cylinder. Furthermore, combining the Poisson equation with the Boltzmann equations for electrons/positrons and γ-rays, and assuming that the gap trans-field thickness is large compared to the longitudinal width, I demonstrate that the energy distribution of ultra-relativistic particles cannot be described by a power-law but by a quasi-monoenergetic distribution at the terminal Lorentz factor. The particles are accelerated in the gap and escape from it with large Lorentz factors. Is is shown that such energetic particles migrating outside of the gap contribute significantly to the γ-ray luminosity and reproduce the observed soft γ-ray spectrum between 100 MeV and 3 GeV for the Vela pulsar.     

Spectral filter for signal identification in the kHz SLR measurements of the fast spinning satellite Ajisai

The high repetition rate satellite laser ranging (SLR) measurements to the fast spinning satellites contain a frequency signal caused by the rotational motion of the corner cube reflector (CCR) array. The spectral filter, developed here, is based on the Lomb algorithm, and is tested with the simulated and the observed high repetition rate SLR data of the geodetic satellite Ajisai (spin period ∼2 s). The filter allows for the noise elimination from the SLR data, and for identification of the returns from the single CCRs of the array – even for the low return rates. Applying the spectral filter to the simulated SLR data increases the S/N ratio by a factor 40–45% for all return rates. Filtering out the noise from the observed data strengthens the frequency signal by factor of ∼25 for the low return rates, which significantly helps to determine the spin phase of the satellite. The spectral filter is applied to the Graz SLR data and the spin rates of Ajisai are determined by two different methods: the frequency analysis and the phase determination of the spinning retroreflector array.The analysis of more than 8 years of the Graz SLR measurements indicates an exponential spin rate trend: f = 0.67034 exp(−0.0148542 Y) [Hz], RMS = 0.085 mHz, where Y is the year since launch. The highly accurate spin rate information demonstrates periodic changes related to the precession of the orbital plane of Ajisai, as it determines the amount of energy received by the satellite from the Sun. The rate of deceleration of Ajisai is not constant: the half life period of the satellite’s spin oscillates around 46.7 years with an amplitude of about 5 years.     

Development of a 2.8 μm film for scientific balloons

Development of a balloon to fly at higher altitudes is one of the most attractive challenges in scientific balloon technologies. After reaching the highest record setting balloon altitude of 53.0 km using the 3.4 μm film in 2002, we tried to make a thinner balloon film. In 2003, we developed a forming die and an air-ring and succeeded in forming a film with a thickness of 3.0 μm and a width of 220 cm. Using this film, we manufactured a balloon with a volume of 5000 m³ and succeeded in flying the balloon up to an altitude of 46.0 km. We then searched for a good combination of resins to make a thinner and wider film and obtained films with widths of 280 cm, and a thickness of 3.0 μm at first, and then 2.8 μm. In 2004, we performed balloon experiments making a 30,000 m³ balloon with the 3.0 μm film and a 5000 m³ balloon with the 2.8 μm film. Both balloons were well manufactured and reached the highest altitudes of 50.7 and 42.6 km, respectively.     

Hard X-ray footpoint motions in solar flares: Comparing magnetic reconnection models with observations

Hard X-ray observations from the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) of the October 29, 2003 GOES X10 two-ribbon flare are used together with magnetic field observations from the Michelson Doppler Imager (MDI) onboard SoHO to compare footpoint motions with predictions from magnetic reconnection models. The temporal variations of the velocity v of the hard X-ray footpoint motions and the photospheric magnetic field strength B in footpoints are investigated. The underlying photospheric magnetic field strength is generally higher (B ∼ 700–1200 G) in the slower moving (v ∼ 20–50 km s⁻¹) western footpoint than in the faster (v ∼ 20–100 km s⁻¹) moving eastern source (∼100–600 G). Furthermore, a rough temporal correlation between the HXR flux and the product vB² is observed.     

Giant radio pulses from the Crab pulsar

Individual giant radio pulses (GRPs) from the Crab pulsar last only a few microseconds. However, during that time they rank among the brightest objects in the radio sky reaching peak flux densities of up to 1500 Jy even at high radio frequencies. Our observations show that GRPs can be found in all phases of ordinary radio emission including the two high frequency components (HFCs) visible only between 5 and 9 GHz [Moffett, D.A., Hankins, T.H. Multifrequency radio observations of the Crab pulsar. Astrophys. J. 468, 779–783, 1996]. This leads us to believe that there is no difference in the emission mechanism of the main pulse (MP), inter pulse (IP) and HFCs. High resolution dynamic spectra from our recent observations of giant pulses with the Effelsberg telescope at a center frequency of 8.35 GHz show distinct spectral maxima within our observational bandwidth of 500 MHz for individual pulses. Their narrow band components appear to be brighter at higher frequencies (8.6 GHz) than at lower ones (8.1 GHz). Moreover, there is an evidence for spectral evolution within and between those structures. High frequency features occur earlier than low frequency ones. Strong plasma turbulence might be a feasible mechanism for the creation of the high energy densities of ∼6.7 × 10⁴ erg cm⁻³ and brightness temperatures of ∼10³¹ K.     

Excitations of nonmigrating diurnal tides in the mesosphere and lower thermosphere simulated by the Kyushu-GCM

Excitation mechanisms of nonmigrating diurnal tides in the MLT region simulated by the Kyushu-GCM are examined. It is shown that the westward propagating diurnal tide with zonal wavenumber s = 2 is mainly excited by nonlinear interactions between the migrating diurnal tide and the stationary planetary wave with zonal wavenumber s = 1, while the nonlinear excitation of the standing diurnal tide with zonal wavenumber s = 0 is less important than the excitation by tropospheric heating. Nonlinear interactions between the migrating diurnal tide and the stationary planetary wave with zonal wavenumber s = 2 are not dominant to excite the westward propagating diurnal tide with zonal wavenumber s = 3, and it is shown that the excitation by tropospheric heating is comparable to the nonlinear excitation. It is also shown that other nonmigrating diurnal tides are excited by tropospheric heating.     

On the production of highest energy solar protons at 20 January 2005

On January 20, 2005, 7:02–7:05 UT the Aragats Multidirectional Muon Monitor (AMMM) located at 3200 m a.s.l. registered enhancement of the high energy secondary muon flux (threshold ∼5 GeV). The enhancement, lasting for 3 min, has statistical significance of ∼4σ and is related to the X7.1 flare seen by the GOES, and very fast (>2500 km/s) CME seen by SOHO, and the Ground Level Enhancements (GLE) #69 detected by the world-wide network of neutron monitors and muon detectors. The energetic and temporal characteristics of the muon signal from the AMMM are compared with the characteristics of other monitors located at the Aragats Space-Environmental Center (ASEC) and with other neutron and muon detectors. Since secondary muons with energies >5 GeV are corresponding to solar proton primaries with energies 20–30 GeV we conclude that in the episode of the particle acceleration at 7:02–7:05 UT 20 January 2005 solar protons were accelerated up to energies in excess of 20 GeV.     

Hard X-ray component in Sco X-1 spectrum: Synchrotron emission from a nano quasar

Sco X-1 is a low mass X-ray binary system and with the recent observations of a resolved radio jet, the source has been included in the list of galactic microquasars. The observed spectral data in the 2–20 keV energy band fits a thermal emission. Above 20 keV, a hard tail has been reported on occasions. During our continuing balloon borne X-ray survey in the 20–200 keV region using high sensitivity Large Area Scintillation counter Experiment, Sco X-1 was observed on two different occasions. Even though the total X-ray luminosity of the source was different, the spectral nature of the source did not show any variation. The presence of hard X-ray flux is unmistakable. We present the spectral and temporal data in the hard X-ray band and discuss the results in terms of geometrical characteristics of X-ray source and its observed temporal properties. We note that the jet activity is similar to the microquasars, however, the absence of the large magnitude abrupt changes in X-ray light curve compared to GRS1915 + 105 suggest that the quasar-like behaviour is at a nano scale.     

F2 layer characteristics and electrojet strength over an equatorial station

The data presented in this work describes the diurnal and seasonal variation in hmF2, NmF2, and the electrojet current strength over an African equatorial station during a period of low solar activity. The F2 region horizontal magnetic element H revealed that the Solar quiet Sq(H) daily variation rises from early morning period to maximum around local noon and falls to lower values towards evening. The F2 ionospheric current responsible for the magnetic field variations is inferred to build up at the early morning hours, attaining maximum strength around 1200 LT. The Sq variation across the entire months was higher during the daytime than nighttime. This is ascribed to the variability of the ionospheric parameters like conductivity and winds structure in this region. Seasonal daytime electrojet (EEJ) current strength for June solstice, March and September equinoxes, respectively had peak values ranging within 27–35 nT (at 1400 LT) , 30–40 nT (at 1200 LT) and 35–45 nT (at 1500 LT). The different peak periods of the EEJ strength were attributed to the combined effects of the peak electron density and electric field. Lastly, the EEJ strength was observed to be higher during the equinoxes than the solstice period.     

A radio study of the mouse,G359.23 − 0.82

The recent detection of a young pulsar powering “the Mouse”, G359.23 − 0.82, as well as detailed imaging of surrounding nebular X-ray emission, have motivated us to investigate the structural details and polarization characteristics of the radio emission from this axisymmetric source with a supersonic bow shock. Using polarization data at 3.6 and 6 cm, we find that the magnetic field wraps around the bow-shock structure near the apex of the system, but downnstream runs parallel to the inferred direction of the pulsar’s motion. The rotation measure (RM) distribution of the Mouse also suggests that the low degree of polarization combined with a high RM ahead of the pulsar result from internal plasma within the bow-shock region. In addition, using sub-arcsecond radio image of the Mouse, we identify modulations in the brightness distribution of the Mouse that may be associated with the unshocked pulsar wind behind the pulsar. Lastly, we discuss the relationship between the Mouse and its neighboring shell-type supernova remnant G359.1 − 0.5 and argue that these two sources could potentially have the same origin.     

Supernova remnant 1987A: The latest report from the Chandra X-ray Observatory

We continue monitoring supernova remnant (SNR) 1987A with the Chandra X-ray Observatory. As of 2004 January, bright X-ray spots in the northwest and the southwest are now evident in addition to the bright eastern ring. The overall X-ray spectrum, since 2002 December, can be described by a planar shock with an electron temperature of ∼2.1 keV. The soft X-ray flux is now 8 × 10⁻¹³ ergs cm⁻² s⁻¹, which is about five times higher than four years ago. This flux increase rate is consistent with our prediction based on an exponential density distribution along the radius of the SNR between the HII region and the inner ring. We still have no direct evidence of a central point source, and place an upper limit of L_X = 1.3 × 10³⁴ ergs s⁻¹ on the 3–10 keV band X-ray luminosity.     

Detection of meteors and sub-relativistic dust grains by the fluorescence detectors of ultra high energy cosmic rays

Fluorescence detectors of ultra high energy cosmic rays (UHECR) allow to record not only the extensive air showers, initiated by the UHECR particles, but also to detect light, produced by meteors and by the fast dust grains. It is shown that the fluorescence detector operated at the mountain site can register signals from meteors with kinetic energy threshold of about 25 J (meteor mass ∼ 5 × 10⁻⁶ g, velocity ∼ 3 × 10⁶ cm/s). The same detector might be used for recording of the dust grains of smaller mass (of about 10⁻¹⁰ g) but with velocity 10⁹ cm/s, close to the light velocity (sub-relativistic dust grains). The light signal from a sub-relativistic dust grain is expected in much shorter time scale (∼0.001 s), in comparison with the meteor signal (∼0.1–1 s), and much longer than duration of the UHECR signals (tens of μs). The fluorescence detector capable to register various phenomena: from meteors to UHECR – should have a variable pixel and selecting system integration time. A study of the new phenomenon of sub-relativistic grains will help to understand the mechanism of particle and dust grain acceleration in astrophysical objects (in SN explosions, for example).     

The high altitude student platform (HASP) for student-built payloads

An outstanding issue with aerospace workforce development is what should be done at the university level to attract and prepare undergraduates for an aerospace career. One approach adopted by many institutions is to lead students through the design and development of small payloads (less than about 500 grams) that can be carried up to high altitude (around 30 km) by a latex sounding balloon. This approach has been very successful in helping students to integrate their content knowledge with practical skills and to understand the end-to-end process of aerospace project development. Sounding balloons, however, are usually constrained in flight duration (∼30 min above 24 km) and payload weight, limiting the kinds investigations that are possible. Student built picosatellites, such as CubeSats, can be placed in low Earth orbit removing the flight duration constraint, but the delays between satellite development and launch can be years. Here, we present the inexpensive high altitude student platform (HASP) that is designed to carry at least eight student payloads at a time to an altitude of about 36 km with flight durations of 15–20 h using a small zero-pressure polyethylene film balloon. This platform provides a flight capability greater than sounding balloons and can be used to flight-test compact satellites, prototypes and other small payloads designed and built by students. The HASP includes a standard mechanical, power and communication interface for the student payload to simplify integration and allows the payloads to be fully exercised. HASP is lightweight, has simple mission requirements providing flexibility in the launch schedule, will provide a flight test opportunity at the end of each academic year.     

The spatial distribution of galactic and anomalous cosmic rays in the heliosphere at solar minimum

The spatial distributions of galactic and anomalous cosmic rays in the heliosphere at the solar minima of Cycles 20/22 (qA > 0) and of Cycle 21 (qA < 0) are studied, using data from IMP 8, Voyagers 1/2 and Pioneer 10. It is found that the radial dependences of intensities J can be approximated by a power of radial distance r as J ∝ r^α with a different value of a constant in the inner and outer heliosphere with a transition at a radial distance of 10–15 AU. To study the physical meaning of these radial intensity profiles we examined the rigidity dependences of the intensity gradients by determining the particle mean free paths, using a simple one-dimensional modulation model. The particle mean free path λ was assumed to be a separable function of distance of the form r^γ and rigidity R of R^δ over the range of 0.5–3.0 GV in the inner and outer heliosphere. It was shown that λ of rigidity dependence of R^1.6 determined for Cycle 20/22 (qA > 0) with anomalous He is about 4–5 times larger than that of Cycle 21 (qA < 0) with R^0.9 at around 1 GV in the outer heliosphere, and that the radial dependences are r^1.4 and r^1.1, respectively, for Cycles 20/22 and for Cycle 21.     

Centre-to-limb variation of photospheric facular radiance and image resolution

We study the effect of the angular resolution on the determination of the angular properties of the facular radiance. We analyze photospheric intensity in the continuum, around the Ni 676.8 nm line, and longitudinal magnetic field along the line of sight, measured by the MDI instrument aboard SOHO with two spatial resolutions, 4″ and 1.2″ (2″ and 0.6″ pixels, respectively). The effect of the limited photometric sensitivity of the instrument and the limited information on the angular structure of the magnetic field tubes are considered. Our study of the high-resolution data shows that intensity contrast of magnetic features between 80 and 600 Gauss increases from centre to limb up to a maximum that occurs at higher heliocentric angles (θ) when obtained with higher resolution data than for lower resolution data. There is a suggestion that at heliocentric angles below about 75° there is only a monotonic increase in the contrast as one goes from cos (θ) = 1 to cos (θ) = 0.2.