Radio followup of ransient sources: Feasibility and practicality

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1 Radio followup of ransient sources: Feasibility and practicality C. H. Ishwara Chandra National Centre for Radio Astrophysics Tata Institute of Fundamental Research Pune University Campus, Pune - India Collaborators: Mamta Pandey, Pramesh Rao,, Ph. Durouchoux, R. K. Manchanda, J. S. Yadav, S. Pal, J. M. Paredes, J. Marti

2 Will cover.. Radio mainly from GMRT perspective Advantage of observations at frequencies <1.4 GHz Some examples of transient followup with GMRT Prospects for Astrosat- advantages and limitations.

3 Radio X-ray Connection Interesting coupling seen between hard X-ray behavior and non-thermal radio emission (Radio emission is almost always seen in X-Ray hard state). Radio emission indicates the presence of relativistic electrons and magnetic field. The jets/relativistic bulk motions are due to outflows from the accretion disk environment. Microquasars implication to AGN physics..

4 Giant Metrewave Radio Telescope (GMRT) GMRT consists of 30 antennas, each of 45 meter diameter, spread over 25 km, 90 km off Pune, India It is the world s largest radio telescope at metre-waves. Sky coverage entire sky north of -50 degree declination Frequency (MHz) Primary Beam (degree) * 1400/f Resolution (arcsec) Best rms achived (mjy) ~ (5 MHz) (5MHz) (16MHz) (32MHz) (32MHz)

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6 GMRT Observations of GRS (Ishwara-Chandra, Yadav, Pramesh Rao, A&A Lett. 2002), Observed for 8 days at 1.28 GHz in June 2001 No major flare, series of small and some isolated events Applying adiabatic models to the flare, a new method to get spectral index from single frequency radio observation was suggested.

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9 Adiabatic expansion model..

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14 40 min = 3360 Actual radio flare of first IR peak

15 GMRT and VLA Observations of V4641 Sgr during major radio flare (May 2002). V4641 Sgr is a HMXB and BH Candidate and exhibits optical and radio flares GMRT and VLA Observations during major flare in May 22, 2002 Observed at 610 and 241 MHz from May 23 to 29, 2002 with GMRT. VLA data immediately after the burst on May 22 shows spectral turn over at ~17 GHz. After couple of days, the source was not detected with VLA at higher radio frequencies, but started to rise at low frequencies (GMRT). 610 MHz Peak after three days of flare (May 25) Increase in 241 MHz flux (first two days no observation next two days) Clear spectral evolution from optically thick to thin state. (Ishwara-Chandra and Rao, 2005, ChJAS, 5, 269)

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17 GMRT Measurements on May 23.9 and 24.8 UT VLA Measurements half a day before GMRT. Observations after 27 th May did not detect at higher frequencies. Simple cartoon for spectral change with time.

18 Other X-Ray transients observed with GMRT GRS1915 extensively at all GMRT frequencies. Many INTEGRAL Sources, other X-Ray binaries (GROJ1655, Cyg X-1, GX339, XTEJ. etc) (Mamta Pandey s thesis) SS433 extensively by Chakrabarti and team Cyg X-3 during May 2006 flare (spectral change seen between 610 and 235 MHz) Un-indentified VHE sources, GC transients, etc. Over a dozen papers on X-Ray binaries published since 2002 using GMRT.

19 Advantage with GMRT frequencies GMRT is primarily a low frequency instrument (150 MHz to 1.4 GHz) This will be an excellent complement to VLA mainly at 5, 8.3 and 15 GHz.. Does the spectra turn over at low frequency? Compactness of the source Is there non-thermal extended emission? Lobe Emission, Steep Spectrum., stronger at low frequencies! Radio emission peaks at low frequencies with a delay gets more time for setting up the observations Radio emission lasts longer at low frequencies The source is visible over longer duration.

20 Practical Issues To get telescope time at short notice! (TOO proposal to be submitted and peer reviewed). Availability of right LST slot at right frequency. This need to be addressed at institute level to have dedicated programme. Data analysis time consuming (multi-channel, multi-facet imaging, RFI, etc) - Couple of hours (610 MHz) to upto full day (325 MHz).

21 Practical Issues To get telescope time at short notice! (TOO proposal to be submitted and peer reviewed). Availability of right LST slot at right frequency. This need to be addressed at institute level to have dedicated programme. Data analysis time consuming (multi-channel, multi-facet imaging, RFI, etc) - Couple of hours (610 MHz) to upto full day (325 MHz). We should overcome these!