Yang Su

Imaging coronal magnetic-field reconnection in a solar flare

Magnetic-field reconnection is believed to play a fundamental role in magnetized plasma systems throughout the Universe(1), including planetary magnetospheres, magnetars and accretion disks around black holes. This letter presents extreme ultraviolet and X-ray observations of a solar flare showing magnetic reconnection with a level of clarity not previously achieved. The multi-wavelength extreme ultraviolet observations from SDO/AIA show inflowing cool loops and newly formed, outflowing hot loops, as predicted. RHESSI X-ray spectra and images simultaneously show the appearance of plasma heated to >10MK at the expected locations. These two data sets provide solid visual evidence of magnetic reconnection producing a solar flare, validating the basic physical mechanism of popular flare models. However, new features are also observed that need to be included in reconnection and flare studies, such as three-dimensional non-uniform, non-steady and asymmetric evolution.

CAVITY OF MOLECULAR GAS ASSOCIATED WITH SUPERNOVA REMNANT 3C 397

3C 397 is a radio and X-ray bright Galactic supernova remnant (SNR) with an unusual rectangular morphology. Our CO observation obtained with the Purple Mountain Observatory at Delingha, Qinghai Province, China reveals that the remnant is well confined in a cavity of molecular gas and embedded at the edge of a molecular cloud (MC) at the local standard of rest systemic velocity of similar to 32 km s(-1). The cloud has a column density gradient increasing from southeast to northwest, perpendicular to the Galactic plane, in agreement with the elongation direction of the remnant. This systemic velocity places the cloud and SNR 3C 397 at a kinematic distance of similar to 10.3 kpc. The derived mean molecular density (similar to 10-30 cm(-3)) explains the high volume emission measure of the X-ray emitting gas. A (12)CO line broadening of the similar to 32 km s(-1) component is detected at the westmost boundary of the remnant, which provides direct evidence of the SNR MC interaction and suggests multi-component gas there with dense (similar to 10(4) cm(-3)) molecular clumps. We confirm the previous detection of an MC at similar to 38 km s(-1) to the west and south of the SNR and argue, based on H I self-absorption, that the cloud is located in the foreground of the remnant. A list of Galactic SNRs presently known and suggested to be in physical contact with environmental MCs is appended in this paper.

LOW-ALTITUDE RECONNECTION INFLOW-OUTFLOW OBSERVATIONS DURING A 2010 NOVEMBER 3 SOLAR ERUPTION

For a solar flare occurring on 2010 November 3, we present observations using several SDO/AIA extreme-ultraviolet (EUV) passbands of an erupting flux rope followed by inflows sweeping into a current sheet region. The inflows are soon followed by outflows appearing to originate from near the termination point of the inflowing motion-an observation in line with standard magnetic reconnection models. We measure average inflow plane-of-sky speeds to range from {approx}150 to 690 km s{sup -1} with the initial, high-temperature inflows being the fastest. Using the inflow speeds and a range of Alfven speeds, we estimate the Alfvenic Mach number which appears to decrease with time. We also provide inflow and outflow times with respect to RHESSI count rates and find that the fast, high-temperature inflows occur simultaneously with a peak in the RHESSI thermal light curve. Five candidate inflow-outflow pairs are identified with no more than a minute delay between detections. The inflow speeds of these pairs are measured to be {approx}10{sup 2} km s{sup -1} with outflow speeds ranging from {approx}10{sup 2} to 10{sup 3} km s{sup -1}-indicating acceleration during the reconnection process. The fastest of these outflows are in the form of apparently traveling density enhancements along the legsmorexa0» of the loops rather than the loop apexes themselves. These flows could possibly either be accelerated plasma, shocks, or waves prompted by reconnection. The measurements presented here show an order of magnitude difference between the retraction speeds of the loops and the speed of the density enhancements within the loops-presumably exiting the reconnection site.«xa0less

The Metal-enriched Thermal Composite Supernova Remnant Kesteven 41 (G337.8-0.1) in a Molecular Environment

We present ALMA Cycle-0 observations of the CO (6-5) line emission and of the 435 mu m dust continuum emission in the central kiloparsec of NGC 1614, a local luminous infrared galaxy at a distance of 67.8 Mpc (1 = 329 pc). The CO emission is well resolved by the ALMA beam (0. 26x0. 20) into a circumnuclear ring, with an integrated flux of f(C O(6-5)) = 898 (+/- 153) Jy km s(-1), which is 63(+/- 12)% of the total CO (6-5) flux measured by Herschel. The molecular ring, located between 100 pc < r < 350 pc from the nucleus, looks clumpy and includes seven unresolved (or marginally resolved) knots with median velocity dispersion of similar to 40 km s(-1). These knots are associated with strong star formation regions with Sigma(SFR) similar to 100M(circle dot) yr(-1) kpc(-2) and Sigma(Gas) similar to 10(4) M-circle dot pc(-2). The nondetections of the nucleus in both the CO (6-5) line emission and the 435 mu m continuum rule out, with relatively high confidence, a Compton-thick active galactic nucleus in NGC 1614. Comparisons with radio continuum emission show a strong deviation from an expected local correlation between Sigma(Gas) and Sigma(SFR), indicating a breakdown of the Kennicutt-Schmidt law on the linear scale of similar to 100 pc.

DISCOVERY OF A PRE-EXISTING MOLECULAR FILAMENT ASSOCIATED WITH SUPERNOVA REMNANT G127.1+0.5

We performed millimeter observations in CO lines toward the supernova remnant (SNR) G127.1+0.5. We found a molecular filament at 4--13 km s

INTERACTION BETWEEN SUPERNOVA REMNANT G22.7–0.2 AND THE AMBIENT MOLECULAR CLOUDS

^{-1}

THE DISTANT OUTER GAS ARM BETWEEN l = 35° AND l = 45°

consisting of two distinct parts: a straight part coming out of the remnant region and a curved part in the remnant region. The curved part is coincides well with the bright SNR shell detected in 1420 MHz radio continuum and mid-infrared observations in the northeastern region. In addition, redshifted line wing broadening is found only in the curved part of the molecular filament, which indicates a physical interaction. These provide strong evidences, for the first time, to confirm the association between an SNR and a pre-existing long molecular filament. Multi-band observations in the northeastern remnant shell could be explained by the interaction between the remnant shock and the dense molecular filament. RADEX radiative transfer modeling of the quiet and shocked components yield physical conditions consistent with the passage of a non-dissociative J-type shock. We argue that the curved part of the filament is fully engulfed by the remnants forward shock. A spatial correlation between aggregated young stellar objects (YSOs) and the adjacent molecular filament close to the SNR is also found, which could be related to the progenitors activity.

Double hard X-ray peaks in RHESSI flares as evidence of chromospheric evaporation and implications for modifying the Neupert effect

We have carried out 12CO (J = 1-0 and 2-1), 13CO (J = 1-0), and C18O (J = 1-0) observations in the direction of the supernova remnant (SNR) G22.7–0.2. A filamentary molecular gas structure, which is likely part of a larger molecular complex with V LSR ~ 75-79 km s–1, is detected and is found to surround the southern boundary of the remnant. In particular, the high-velocity wing (77-110 km s–1) in the 12CO (J = 1-0 and J = 2-1) emission shows convincing evidence of the interaction between SNR G22.7–0.2 and the 75-79 km s–1 molecular clouds (MCs). Spectra with redshifted profiles, a signature of shocked molecular gas, are seen in the southeastern boundary of the remnant. The association between the remnant and the 77 km s–1 MCs places the remnant at the near distance of 4.4 ± 0.4 kpc, which agrees with a location on the Scutum-Crux arm. We suggest that SNR G22.7–0.2, SNR W41, and H II region G022.760-0.485 are at the same distance and are associated with GMC G23.0–0.4.

On the positronium continuum and 0.511 MeV line in solar flares

The Galactic plane has been mapped from l=34.75d to 45.25d and b=-5.25d to 5.25d in the CO (J=1-0) emission with the 13.7 m telescope of the Purple Mountain Observatory. The unbiased survey covers a large area of 100 square degrees sampled every 30 with a velocity resolution of ~0.2km/s. In this paper, we present the result of an unbiased CO survey of this longitude and latitude range in the velocity range from -60km/s to -10km/s. Over 500 molecular clouds (MCs) are picked out from the 12CO emission, and 131 of these MCs are associated with 13CO emission.The distant MCs, which lie beyond the solar circle and are mostly concentrated in the Galactic plane, trace the large-scale molecular gas structure over 10 degrees of Galactic azimuth. We suggest that the CO emission of the segment is from the Outer Arm. The physical mid-plane traced by the Outer Arm seems to be slightly displaced from the IAU-defined plane on a large scale, which could be explained by the warped plane at large Galactocentric distances of >~10 kpc and the apparent tilted mid-plane to the projected IAU-defined plane caused by the Suns z-height above the disk for distances near and within the Solar circle. If the inner plane of our Galaxy is flat, we can derive an upper limit of the Suns offset of ~17.1 pc above the physical mid-plane of the Milky Way. We also discuss the correlations between the physical parameters of the distant MCs, which is quite consistent with the result of other studies of this parameter.

L1188: A Promising Candidate for Cloud–Cloud Collisions Triggering the Formation of Low- and Intermediate-mass Stars

Among the RHESSI flare samples, we concentrated on a kind of flare that presents two successive peaks (that is, it presents both an impulsive phase and a gradual phase) in 12 - 25 keV light curves. Taking the CIA flare on 2002 August 12 as an example, we studied the light curves, spectra, and images in detail. Making full use of the capabilities of RHESSI, we showed some evidence to support the expected causal relationship between these two peaks: the first peak is mainly nonthermal, while the second peak is mainly thermal; the energy carried by nonthermal electrons during the first peak seems to be comparable to the thermal energy of the second peak. The morphologies of X-ray images and their evolutions provide additional evidence for this causality. We conclude that two such peaks in the 12 - 25 keV light curve are good evidence for the chromospheric evaporation. However, the maximum time of the second peak is later than the end time of the first peak, suggesting that for some events, a modification of the traditional Neupert effect could be necessary by inclusion of a time delay, which might be partly related to the filling of the loop by evaporated material.