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A number of minor geomagnetic storms were observed during the period of 21-25 December 2014, and we identified anomalous magnitudes and polarities of the electric field perturbations over the equatorial F region in the Indian sector on many occasions. In this work, we focus on the post-midnight space weather-induced electric field perturbations. These electric field perturbations are inferred based on the variations in the night-time vertical drifts over the Indian dip equatorial station, Tirunelveli (8.7N, 77.7E, dip angle 1.7). The post-midnight vertical drift variations over Tirunelveli on 21 and 23 December 2014 suggest the influence of overshielding electric field. However, larger vertical drifts are noticed when magnitude of the overshielding effect is less and vice-versa. These anomalous behaviors in the equatorial vertical drift are shown to be due to the additional effects of substorm, IMF By and disturbance dynamo. This result is important as it suggests influence of the multiple space weather drivers acting in tandem to determine the magnitude and polarity of the disturbance electric field over the dip equatorial ionosphere. This result will be discussed in detail., The 28th IUGG General Assembly (IUGG2023) (Berlin 2023)

Although the enhancements in the alpha-proton ratio in the solar wind (expressed as $A_{He} = N_{a}/N_p*100$) in the Interplanetary Coronal Mass Ejections (ICMEs) have been studied in the past, $A_{He}$ enhancements at the stream interface region received very little attention so far. In this letter, by extensively analyzing the stream interaction region (SIR) events observed in solar cycle 23 and 24, we show that the stream interface of alphas starts separating out from that of protons from the minimum of solar cycle 23. We show that more alpha particles are distributed towards higher pitch angles as compared to protons in the fast wind region compared to background solar wind. By analysing the differential velocities of alphas and protons, we also show that the faster alpha particles accumulate near the fast wind side of the stream interface region leading to enhancement of $A_{He}$. The investigation brings out, for the first time, the salient changes in $A_{He}$ in SIRs for the two solar cycles and highlight the important roles of pitch angle and differential velocities of alpha and protons in the fast wind region for the changes in $A_{He}$ in SIRs.

This investigation is directed to understand the asymmetry in $Δ$X variations caused due to the relative roles played by IMF Bz and IMF By in a particular interval (22:22 - 22:55 UT), during the main phase of a strong geomagnetic storm event of April 06, 2000 (Ap = 236). Two pairs of antipodal stations, being part of the SuperMAG network, are considered here. Ionospheric convection maps from SuperDARN network are used to understand spatio-temporal evolution of the DP2 ionospheric convection patterns over high-latitudes. The two-dimensional maps of equivalent currents are used to show signatures of global DP2 currents associated with the interplay effect between the two IMF components. Observations show increases in the difference in $Δ$X variations between nearly antipodal stations from the Japanese-European/African sector with respect to the same between the nearly antipodal stations from the Pacific/American-Indian sector. This asymmetry is observed during the period when the absolute magnitude of IMF By is larger than that of IMF Bz resulting in a significant and conspicuous enhancement in IMF |By/Bz|. It is suggested that the distortions in DP2 cells and associated rotation of electrodynamic day-night divider, bring one pair of stations under the same DP2 cell and one station of the other pair under a different DP2 cell and throat flow region leading to the asymmetry in $Δ$X variations between the antipodal stations. Therefore, the work highlights the importance of the interplay between IMF Bz and IMF By in determining the ionospheric impact over low latitudes during strong geomagnetic conditions., Accepted for publication in JGR Space Physics on 04 January 2023

This work is directed to explore the efficacy of strong and consistent correlations between the $\Delta$X component of magnetic field at two equatorial/low-latitude stations at nearly antipodal locations during geomagnetic storms. The antipodal stations considered are Huancayo (HUA: 12.06$^\circ$S, 75.21$^\circ$W geographic; magnetic dip 0.3$^\circ$N) in the Peruvian longitude sector and Alibag (ABG: 18.64$^\circ$N, 72.87$^\circ$E geographic; magnetic dip 10$^\circ$N) in the Indian longitude sector. Six strong geomagnetic storm events during the period 2000-2005, falling in the maximum-to-declining phase of solar cycle 23, are analyzed for this study. These stations are part of the SuperMAG network and data from these stations are openly available. It is noted that although $\Delta$X variations over these two stations are, in general, uncorrelated, significant correlations are observed on certain occasions. Correlation coefficient of at least 75$\%$ for 10 minutes is defined as a requisite criterion to infer the possible connection between the $\Delta$X variations over these two stations. The ionospheric convection maps from the SuperDARN network are also used to understand the Spatio-temporal evolution of the two-cell ionospheric convection patterns over high-latitudes during these periods of observations. This exercise reveals that the $\Delta$X variations over the antipodal locations are significantly correlated when the two-cell convection maps show appropriate rotations and both the stations possibly come under the single cell. Therefore, this investigation brings out a novel method to identify the IMF $B_y$ influence over the low/equatorial latitudes based on the openly available data., Comment: Manuscript will be submitted soon

The Aditya-L1 is the first space-based solar observatory of the Indian Space Research Organization (ISRO). The spacecraft will carry seven payloads providing uninterrupted observations of the Sun from the first Lagrangian point. Aditya-L1 comprises four remote sensing instruments, {\it viz.} a coronagraph observing in visible and infrared, a full disk imager in Near Ultra-Violet (NUV), and two full-sun integrated spectrometers in soft X-ray and hard X-ray. In addition, there are three instruments for in-situ measurements, including a magnetometer, to study the magnetic field variations during energetic events. Aditya-L1 is truly a mission for multi-messenger solar astronomy from space that will provide comprehensive observations of the Sun across the electromagnetic spectrum and in-situ measurements in a broad range of energy, including magnetic field measurements at L1., Comment: 10 pages, 6 figures, Submitted to the Proceedings of IAU 372: The Era of Multi-Messenger Solar Physics"

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Swift J1858.6-0814 is a recently discovered X-ray binary notable for extremely strong variability (by factors of >100 in soft X-rays) in its discovery state. We present the detection of five thermonuclear (Type I) X-ray bursts from Swift J1858.6-0814, implying that the compact object in the system is a neutron star (NS). Some of the bursts show photospheric radius expansion, so their peak flux can be used to estimate the distance to the system. The peak luminosity, and hence distance, can depend on several system parameters; for the most likely values, a high inclination and a helium atmosphere, D = 12.8(-0.6)(+0.8) kpc, although systematic effects allow a conservative range of 9-18 kpc. Before one burst, we detect a QPO at 9.6 +/- 0.5 mHz with a fractional rms amplitude of 2.2 +/- 0.2 per cent (0.5-10 keV), likely due to marginally stable burning of helium; similar oscillations may be present before the other bursts but the light curves are not long enough to allow their detection. We also search for burst oscillations but do not detect any, with an upper limit in the best case of 15 per cent fractional amplitude (over 1-8 keV). Finally, we discuss the implications of the NS accretor and this distance on other inferences which have been made about the system. In particular, we find that Swift J1858.6-0814 was observed at super-Eddington luminosities at least during bright flares during the variable stage of its outburst.

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A detailed investigation was carried out to understand a prolonged (~44 hours) weakly southward interplanetary magnetic field (IMF-Bz) condition during May 02--04, 1998. In-situ observations, during the period, showed the passage of an expanding magnetic cloud embedded in an interplanetary coronal mass ejection (ICME), followed up by a shock and an interplanetary discontinuity driven by another ICME. It is the arrival of the ICMEs and the upfront shocks that cause the prolonged southward IMF-Bz condition. The magnetic configuration of the source regions of the IMF associated with the ICME interval were also examined, which showed open magnetic field structures, emanating from a small active region on the north of the heliospheric current sheet (HCS). The structures remained constantly to the north of the HCS, both on April 29 and May 01, suggesting no change in their polarity. The draping of these outward directed radial field lines around the propagating CMEs in the shocked plasma explained the observed polarity changes of the IMF-Bz at 1 AU. In addition, multiple enhancements were also detected in the geomagnetic field variations, which showed a distinct one-to-one correspondence with the density pulses observed at 1 AU, during 0700--1700 UT on May 03. The spectral analysis of both the variations showed the same discrete frequencies of 0.48, 0.65 and 0.75 mHz, demonstrating that the solar wind density enhancements can cause detectable global geomagnetic disturbances. The observations, thus, provide a deeper insight into the possible causes and geomagnetic consequences of a prolonged weakly southward IMF-Bz condition., Comment: JGR (Space Physics), Accepted

As with all measurements, the measurement of examinee ability, in terms of scores that the examinee obtains in a test, is also error-ridden. The quantification of such error or uncertainty in the test score data--or rather the complementary test reliability--is pursued within the paradigm of Classical Test Theory in a variety of ways, with no existing method of finding reliability, isomorphic to the theoretical definition that parametrises reliability as the ratio of the true score variance and observed (i.e. error-ridden) score variance. Thus, multiple reliability coefficients for the same test have been advanced. This paper describes a much needed method of obtaining reliability of a test as per its theoretical definition, via a single administration of the test, by using a new fast method of splitting of a given test into parallel halves, achieving near-coincident empirical distributions of the two halves. The method has the desirable property of achieving splitting on the basis of difficulty of the questions (or items) that constitute the test, thus allowing for fast computation of reliability even for very large test data sets, i.e. test data obtained by a very large examinee sample. An interval estimate for the true score is offered, given an examinee score, subsequent to the determination of the test reliability. This method of finding test reliability as per the classical definition can be extended to find reliability of a set or battery of tests; a method for determination of the weights implemented in the computation of the weighted battery score is discussed. We perform empirical illustration of our method on real and simulated tests, and on a real test battery comprising two constituent tests., Comment: 30 pages

© 2014 SPIE. The Large Observatory For x-ray Timing (LOFT) was studied within ESA M3 Cosmic Vision framework and participated in the final downselection for a launch slot in 2022-2024. Thanks to the unprecedented combination of effective area and spectral resolution of its main instrument, LOFT will study the behaviour of matter under extreme conditions, such as the strong gravitational field in the innermost regions of accretion flows close to black holes and neutron stars, and the supranuclear densities in the interior of neutron stars. The science payload is based on a Large Area Detector (LAD, 10 m2 effective area, 2-30 keV, 240 eV spectral resolution, 1° collimated field of view) and a Wide Field Monitor (WFM, 2-50 keV, 4 steradian field of view, 1 arcmin source location accuracy, 300 eV spectral resolution). The WFM is equipped with an on-board system for bright events (e.g. GRB) localization. The trigger time and position of these events are broadcast to the ground within 30 s from discovery. In this paper we present the status of the mission at the end of its Phase A study.

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Understanding of the kinematic evolution of Coronal Mass Ejections (CMEs) in the heliosphere is important to estimate their arrival time at the Earth. It is found that kinematics of CMEs can change when they interact or collide with each other as they propagate in the heliosphere. In this paper, we analyze the collision and post-interaction characteristics of two Earth-directed CMEs, launched successively on 2012 November 9 and 10, using white light imaging observations from STEREO/SECCHI and in situ observations taken from WIND spacecraft. We tracked two density enhanced features associated with leading and trailing edge of November 9 CME and one density enhanced feature associated with leading edge of November 10 CME by constructing J-maps. We found that the leading edge of November 10 CME interacted with the trailing edge of November 9 CME. We also estimated the kinematics of these features of the CMEs and found a significant change in their dynamics after interaction. In in situ observations, we identified distinct structures associated with interacted CMEs and also noticed their heating and compression as signatures of CME-CME interaction. Our analysis shows an improvement in arrival time prediction of CMEs using their post-collision dynamics than using pre-collision dynamics. Estimating the true masses and speeds of these colliding CMEs, we investigated the nature of observed collision which is found to be close to perfectly inelastic. The investigation also places in perspective the geomagnetic consequences of the two CMEs and their interaction in terms of occurrence of geomagnetic storm and triggering of magnetospheric substorms., Comment: 34 pages, 9 figures, Accepted for publication in "Solar Physics"

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An earlier measurement on the 4$^+$ to 2$^+$ radiative transition in $^8$Be provided the first electromagnetic signature of its dumbbell-like shape. However, the large uncertainty in the measured cross section does not allow a stringent test of nuclear structure models. The present paper reports a more elaborate and precise measurement for this transition, via the radiative capture in the $^4$He+$^4$He reaction, improving the accuracy by about a factor of three. The {\it ab initio} calculations of the radiative transition strength with improved three-nucleon forces are also presented. The experimental results are compared with the predictions of the alpha cluster model and {\it ab initio} calculations., Comment: 5 pages and 7 figures, Submitted to Physical Review Letters

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Since the start of its current X-ray outburst on 2008 Sep 21 (ATel #1728), the accretion-powered millisecond pulsar SAX J1808.4-3658 has been observed for roughly 10 ks per day with the RXTE PCA. Coherent 401 Hz pulsations are clear throughout at an amplitude of 3-6% rms (2-16 keV). We have derived a pulse timing solution for this new outburst by phase connecting the pulsations observed during the interval MJD 54731-54739.

Fish community structure and water chemistry of two tropical rivers of West Bengal, an eastern province of India, were studied for 2 annual cycles (January 2003-December2004) and a higher degree of pollution was found in one river (the Churni) than in the other river (the Jalangi). This was reflected in the water quality as well as in fish community structure of the rivers. About 63.6% of fish species appeared to have been eliminated from the polluted Churni River since 1983 in 20 years. For protection of fish biodiversity and enhancement of fish production, a rational management programme should be implemented for the river Churni. Keywords: River pollution; fish community structure; trophic level; degradation; habitat orientation; similarity index > Tropical Freshwater Biology Vol. 15 2006: pp. 55-69

During a ~0.8 ksec pointed Swift/XRT observation performed on June 6, 2007 (18:26-21:38 UT), we did not detect the accreting millisecond pulsar HETE J1900.1-2455. We can set a 2-10 keV upper limit on the source flux of ~(5-15)E-14 erg/cm2/s (depending on the assumed spectral model). This is more than a factor of 10 weaker than the X-ray flux observed with Swift/XRT last week, on May 31 (ATEL #1091).

As part of an existing Chandra program for the accurate localization of neutron-star X-ray transients, we observed the very-faint X-ray transient XMMU J174716.1-281048 (Del Santo et al. 2007, astro-ph/0704.2134) with the ACIS-S detector aboard Chandra, since this source was found to be still actively accreting in May 2007 (ATel #1078).

Following the non-detection of HETE J1900.1-2455 on June 6 (ATel #1098), we find this system considerably brighter in a ~5 ksec Swift/XRT observation performed on June 10, 2007 (2:25-12:14 UT). The X-ray spectrum can be well described by an absorbed powerlaw plus blackbody model, with Nh~0.19, kT~0.16 keV and a photon index of ~2.24. The inferred 2.0-10.0 keV flux is ~2.8E-10 erg/cm2/s, which corresponds to an X-ray luminosity ~8.4E35 (d/5kpc) erg/s.

Galloway et al. (2007; ATEL #1086) reported that the X-ray luminosity of the accreting millisecond pulsar HETE J1900.1-2455 exhibited a steady decay between 14 and 27 May, and suggested that the source may be finally returning to quiescence after an outburst of ~2 years. A similar declined was seen in the optical flux of the source (ATEL #1090). To follow the X-ray luminosity and spectral behavior of the source, we observed it with Swift/XRT during a ~1 ksec exposure performed on May 31, 2007 (00:02-00:18 UT).

We report on long-term monitoring of the anomalous X-ray pulsar 1E 1048.1-5937 using the Rossi X-ray Timing Explorer. This pulsar's timing behavior is different from that of other AXPs. In particular, the pulsar shows significant deviations from simple spin-down such that phase-coherent timing has not been possible over time spans longer than a few months. We show that in spite of the rotational irregularities, the pulsar exhibits neither pulse profile changes nor large pulsed flux variations. We discuss the implications of our results for AXP models. We suggest that 1E 1048.1-5937 may be a transition object between the soft gamma-ray repeater and AXP populations, and the AXP most likely to one day undergo an outburst., Comment: 6 pages, to appear in Proceedings of the 20th Texas Symposium on Relativistic Astrophysics, AIP press

LOFT (Large area Observatory For x-ray Timing) is an innovative mission concept for the next generation of X-ray experiments, submitted to the ESA Call for Medium size missions “M3”. Recent developments in the field of Silicon detectors allowed us to design a realistic observatory devoted to X-ray timing studies with an effective area above 10 m2, operating in the energy range 2-30 keV with an energy resolution of ∼250 eV. Such an exceedingly large area (20 times that of RXTE/PCA), with a time resolution better than 10 µs, will enable unprecedently fast and accurate time variability studies related to accreting collapsed objects (e.g. fast coherent pulsations and QPOs). The scientific payload is complemented by a coded-mask wide field monitor based on similar detectors. In this paper we present the mission concept, the payload design and the expected performances.

LOFT (Large area Observatory For x-ray Timing) is an innovative mission submitted in response to the Cosmic Vision "Call for a Medium-size mission opportunity for a launch in 2022" recently issued by ESA. LOFT is an ideal candidate for the next generation of (extremely) large experiments for X-ray timing dedicated to the study of the physics of compact objects and to the understanding of the behavior of matter in strong gravitational fields. Recent developments in the field of large area monolithic silicon detectors allowed us to reach an effective area ∼12 m2 (15 m2 goal), more than a order of magnitude larger that RXTE/PCA, in the energy range 2-30 keV (1-40 keV goal). This Large Area Detector (LAD) will have both high timing resolution (

Following the recent re-brightening (ATel #2608) and RXTE-PCA detection of X-ray bursts from the peculiar X-ray binary Cir X-1 between May 15 and 25 (ATel #2643), we obtained a series of Swift-XRT observations of the field (see also ATel #2650). Swift-XRT detected an X-ray burst on 2010-05-28 at 12:08:19 UTC, which lasted about 60 seconds and had a FRED profile, typical of type I X-ray bursts.

We report the detection of a type I X-ray burst with burst oscillations during an RXTE-PCA observation of the recently discovered accreting millisecond pulsar (AMP) IGR J17498-2921 (ATels #3551, #3555, #3556, #3558, #3559, #3560, #3561, #3562, #3563). The burst intensity peaked on 2011-08-16 at 15:21:45 UTC. We find a rise time of ~0.4s (time span for burst intensity to go from 25% to 90% of net peak value) and an approximate total duration in the RXTE-PCA bandpass of 30s.

In Atel#1760 we posted an incorrect definition of the ascending node as "the point at 90 degrees mean longitude". The correct definition of the ascending node is "the point at 0 degrees true longitude". The orbital elements themselves are correct as given in Atel#1760.