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The Large Area Telescope (LAT) onboard the Fermi Gamma Ray Space Telescope has detected γ-ray emission in about half-a-dozen Narrow Line Seyfert 1 (NLSy1) galaxies. This indicates the presence of relativistic jets in these sources similar to blazars and radio galaxies. In an attempt to have an idea of the intranight optical variability (INOV) characteristics of these γ-ray loud NLSy1 galaxies, we have carried out optical flux monitoring observations of three NLSy1 galaxies detected by Fermi/LAT: 1H 0323+342, PMN J0948+0022 and PKS 1502+036. These optical monitoring observations in R C band carried out during January − May 2012, showed the presence of rapid optical flux variations in these sources. The intranight differential light curves of these sources have revealed flux variations on time scales of hours with amplitudes of variability > 3 percent for most of the time. However, for one source, PMN J0948+0022 we observed amplitude of variability as large as 52 percent. On using the F-statistics to classify the variability nature of these sources, we obtained a duty cycle (DC) of INOV of ∼85 percent. Alternatively, the more commonly used C-statistics gave a DC of INOV of ∼57 percent. Such high DC of INOV are characteristics of the BL Lac class of AGN. The results of our monitoring observations thus indicate that there is similarity in the INOV nature of γ-ray loud NLSy1 galaxies and BL Lac objects, arguing strongly for the presence of relativistic jets aligned closely to the observers line of sight in γ-ray loud NLSy1s. Moreover, our dense monitoring observations on some of the nights have led to the clear detection of some mini-flares superimposed on the flux variations during the night over timescales as short as 12 minutes. The detection of short timescale flux variability in the sources studied here is clearly due to stronger time compression leading to the jets in these sources having large doppler factors, similar to that of the inner jets of TeV blazars.

The Swift satellite has enabled us to follow the evolution of gamma-ray burst (GRB) fireballs from the prompt gamma-ray emission to the afterglow phase. The early x-ray and optical data obtained by telescopes aboard the Swift satellite show that the source for prompt gamma-ray emission, the emission that heralds these bursts, is short lived and that its source is distinct from that of the ensuing, long-lived afterglow. Using these data, we determine the distance of the gamma-ray source from the center of the explosion. We find this distance to be 1e15-1e16 cm for most bursts and we show that this is within a factor of ten of the radius of the shock-heated circumstellar medium (CSM) producing the x-ray photons. Furthermore, using the early gamma-ray, x-ray and optical data, we show that the prompt gamma-ray emission cannot be produced in internal shocks, nor can it be produced in the external shock; in a more general sense gamma-ray generation mechanisms based on shock physics have problems explaining the GRB data for the ten Swift bursts analyzed in this work. A magnetic field dominated outflow model for GRBs has some attractive features, although the evidence in its favor is inconclusive. Finally, the x-ray and optical data allow us to provide an upper limit on the density of the CSM of about 10 protons per cubic cm at a distance of about 5e16 cm from the center of explosion.Comment: Accepted to MNRAS Letters. 6 pages, 2 figures, & 2 table

We present results based on follow-up observations of the Type II-plateau supernova (SN) 2013ej at 6 epochs spanning a total duration of ∼37 d. The R c -band linear polarimetric observations were carried out between the end of the plateau and the beginning of the nebular phases as noticed in the photometric light curve. The contribution due to interstellar polarization (ISP) was constrained by using couple of approaches, i.e. based upon the observations of foreground stars lying within 5 ′ and 10• radius of the SN location and also investigating the extinction due to the Milky Way and host galaxy towards the SN direction. Our analysis revealed that in general the intrinsic polarization of the SN is higher than the polarization values for the foreground stars and exhibits an increasing trend during our observations. After correcting the ISP of ∼0.6 per cent, the maximum intrinsic polarization of SN 2013ej is found to be 2.14 ± 0.57 per cent. Such a strong polarization has rarely been seen in Type II-P SNe. If this is the case, i.e., the 'polarization bias' effect is still negligible, the polarization could be attributed to the asymmetry of the inner ejecta of the SN because the ISP towards the SN location is estimated to be, at most, 0.6 per cent.

We present multiwavelength observations of the latest two GRB detected by Hete-2 in 2005. For GRB 051022, no optical/nIR afterglow has been detected, in spite of the strong gammaray emission and the reported X-ray afterglow discovered by Swift. A mm afterglow was discovered at PdB confirming the association of this event with a luminous (M V = 21.5) galaxy within the X-ray error box. Spectroscopy of this galaxy shows strong a strong [O II] emission line at z = 0.807, besides weaker [O III] emission. The X-ray spectrum showed evidence of considerable absorption by neutral gas with N H X ray = 4.5 ¢ 10 22 cm 2 (at rest frame). ISM absorption by dust in the host galaxy at z = 0.807 cannot certainly account for the non-detection of the optical afterglow, unless the dust-to-gas ratio is quite different than that seen in our Galaxy. It is possible then that GRB 051022 was produced in an obscured, stellar forming region in its parent host galaxy.For GRB 051028, the data can be interpreted by collimated emission (a jet model with p = 2.4) moving in an homogeneous ISM and with a cooling frequency ν c still above the X-rays at 0.5 days after the burst onset. GRB 051028 can be classified as a "gray" or "potentially dark" GRB. The Swift/XRT data are consistent with the interpretation that the reason for the optical dimness is not extra absorption in the host galaxy, but rather the GRB taking place at high-redshift.