Sujay Pal

Possible Photometric Evidence of Ejection of Bullet-like Features in the Relativistic Jet Source SS 433

SS 433 is well known for its precessing twin jets having optical bullets inferred through spectroscopic observation of Hα lines. Recently, Chakrabarti et al. described processes that may be operating in the accretion disk of SS 433 to produce these bullets. In a recent multiwavelength campaign, we find a sharp rise in intensity in timescales of a few minutes in X-ray, IR, and radio waves through photometric studies. We interpret them to be possible evidence of ejection of bullet-like features from accretion disks.

SS 433: results of a recent multiwavelength campaign

We conducted a multiwavelength campaign in 2002 September-October, to observe SS 433. We used the Giant Meter Radio Telescope for radio observations, the Physical Research Laboratory Infrared Telescope at Mt Abu for infrared (IR), the ARIES telescope at Nainital for optical photometry, the telescope at the Vainu Bappu observatory for spectral measurements and the Rossi X-ray Timing Explorer for X-ray observations. We find sharp variations in intensity on time-scales of a few minutes in the X-ray, IR and radio wavelengths. Differential photometry in the IR observations clearly indicates significant intrinsic variations on short time-scales of minutes throughout the campaign. Combining the results for these wavelengths, we find a signature of delay of about two days between the IR and radio signals. The X-ray spectrum yielded double Fe line profiles which corresponded to red and blue components of the relativistic jet. We also present the broad-band spectrum averaged over the campaign duration.

Characteristics of lightning associated transient perturbations in low latitude VLF paths

Here we have reported some characteristics of lightning associated transient perturbations of Very Low Frequency signals detected over two tropical VLF paths; VTX-Kolkata and NWC-Kolkata. All types of events with positive and negative perturbations, very short to long recovery time have been found in nighttime. We explain positive and negative VLF amplitude deviations due to lightning events using the most well-known Long Wavelength Propagation Capability (LWPC) code. We find the location and size of ionospheric perturbations on the propagation paths by comparing the model results with observations.

Effect of solar flares on ionospheric VLF radio wave propagation, modeling with GEANT4 and LWPC and determination of effective reflection height

Solar flares are among the most prominent transient events affecting the radio wave propagation in the ionosphere. In this paper we model the ionizing effect on VLF wave, reflected from D-layer of the ionosphere during different classes of flares and compare with observed VLF modulation. A well known detector simulation software GEANT4 is used to calculate the ionization produced in different heights (~ 60-80 km) of the D layer. The chemical balancing between the ions and neutrals in the region is taken into account with a simplified chemical model, the GPI model. The VLF modulation is reproduced with LWPC. We have seen that the peaks of electron density arise at different times at different heights. Matching with the time delay of the VLF signals we have proposed an alternative effective reflection height during such events.

Response of the sub-ionospheric VLF/LF signals to the major SSW event of 2009

In this paper, sub-ionospheric Very Low Frequency/Low Frequency (VLF/LF) radio signals over the North Atlantic zone and North Pacific zone have been analysed during the major Sudden Stratospheric Warming (SSW) event of January, 2009. Signals from the transmitters like, NAA (24.0 kHz) and NKR (37.5 kHz) received at Germany and signals from the transmitters like, NLK (24.8 kHz) and NPM (21.4 kHz) received at Japan are considered for possible lower ionospheric response to the SSW event. Very clear and significant increase/decrease of average nighttime and daytime VLF/LF amplitudes from the quiet signals have been found associated with the SSW event.

Remote sensing of atmospheric gravity waves (GWs) and planetary wave type oscillations (PWTOs) in the upper mesosphere-lower ionosphere system using the very low frequency transmitter data

We present the use of VLF radio data to study the short-period (~min to hrs) GWs and long-period (~days) PWTOs. To show the presence of GWs, we analyse the VLF data from several places obtained by ICSP-VLF network during the solar eclipse of July, 2009. We find dominant wave periods ranging from 10 minutes to 1 hour around the time of maximum eclipse phase which could be associated with atmospheric gravity waves excited due to the solar eclipse. We also analyse nearly 4 years of VLF amplitude data received at ICSP, Kolkata from the VTX (18.2 kHz) transmitter and also from the NWC (19.8 kHz) transmitter for planetary wave type oscillations (PWTOs) in the mesosphere-lower ionosphere system. Fourier and wavelet analysis show the presence of PWTOs in both the radio paths having periodicity in the range 5-27 days. The PW spectrum of VLF data are also correlated with the PW spectrum of Ozone data.

Low latitude sub-ionospheric VLF signal behaviour during the two recent solar eclipses: Observation and simulation

We present the VLF observational data from the VTX (18.2 kHz) and NWC (19.8 kHz) transmitters during the solar eclipses of July 22, 2009 and January 15, 2010. The data were collected at several receiving stations in India and the corresponding VLF amplitudes show all possible behaviour with respect to different propagation conditions. We simulate the observed behaviour of the VLF signals using the most-well known Long Wave Propagation Capability (LWPC) code and find the corresponding ionospheric parameters during the solar eclipses. We also show that the VLF radio data during solar eclipses incorporate the effects of short-period (~min to hrs) atmospheric gravity waves. Dominant wave periods ranging from 10 minutes to 1 hour around the time of maximum eclipse phase have been found. We also present the anomalies in the topside ionosphere during these two solar eclipses. Measurements of the densities and temperatures of the thermal electrons and ions were provided by the DEMETER satellite, which flew near India during the time of partial solar obscuration. We find decrease in plasma density, electron and ion temperatures along the orbit by several unit.

Study of low-latitude ionospheric D-region negative ion profile during an M-class solar flare using VLF propagation effects

We dealt with the negative ion contents of the lower ionospheric D-region during an M-class solar flare. We did a generalized study of the variation of the λ-parameter both with D-region height and time. In this purpose, we numerically solved the D-region electron continuity equation, where, we supplied the Ne-profile calculated from Long Wave Propagation Capability code results. The results generally agree with those present in the literature, namely, the effect on the negative ion density during that flare due to photo-electron detachment and photo-dissociation processes. However, for our VLF propagation path of interest, we found that the negative ions exist till somewhat higher altitudes (~ 73-74 km) than the high-latitude D-region heights. Other workers did model study on Cl ions and its complex compounds at night-time in high latitude ionosphere. They reported that, though negative ions are less abundant in daytime, in lower latitudes its availability increases, which supports our results.