Alok Chandra Gupta

Research Summary:

Most of my research interest for the last few years have been Multi-wavelengths variability of different classes of Active Galactic Nuclei and Photometric studies of Star Clusters in the Milky Way.

Optical Photometric Observations of &gamma -Ray Loud Blazars: We reported results of our optical photometric observations of ten γ-ray loud blazars namely: 0219+128 (3C66A), PKS 0420-014 (OA 129), S5 0716+714, 0754+100 (OI 090.4), 0827+243 (OJ 248), 1652+398 (Mrk 501), 2200+120 (BL Lacertae), 2230+114 (CTA 102), 2251+158 (3C 454.3) and 2344+514. The observations were carried out in September-October 2000 using the 70 cm optical telescope at Abstumani Observatory, Georgia. We found intra-day variations in PKS 0420-014, S5 0716+714, BL Lacertae and CTA 102. A variation of 0.3 magnitude over a time scale of about 3 hours was observed in the R passband in BL Lacertae on JD 2451827. We did not detect any variation in 3C66A, Mrk 501 and 3C454.3 during our observations. We did not detect any clear evidence of variation in 1ES 2344+514 during our two weeks observing run of the TeV gamma-ray source.

Near Infrared Intra-day Variability of Mrk 421: We reported results from our monitoring of the BL Lac object Mrk 421 in the near-IR J band. The observations, aimed at studying the intra-day variability (IDV) of the object, were carried out systematically over an extended (and near-continuous) period of eight nights from the 1.2 meter Mount Abu Infrared Telescope, India. There are limited studies for Mrk 421 in the J band for such an extended period. The observation epoch for this study (25 February-5 March 2003) was chosen to significantly overlap other concurrent studies of Mrk 421 in the X-ray/γ-ray regions being conducted using the Rossi X-ray timing explorer (RXTE) and the solar tower atmospheric Cherenkov effect experiment (STACEE). Hence these results could be useful for a multi-wavelength analysis of the variability behavior of Mrk 421. We find that Mrk 421 was quite active during the observed period and showed significant IDV and short term variability. A maximum variation of 0.89 magnitudes is seen over the entirety of the observed period. Flaring activity, with typical brightness variations of &sim 0.4, are also seen on several occasions. The extent of the variability observed by us is compared with the results of other similar studies of Mrk 421 in the J band.

Intra-night Optical Variability of BL Lacs, Radio-Quiet Quasars and Radio-Loud Quasars: We reported monitoring observations of 20 high-luminosity active galaxies, 12 of which are radio-quiet quasars (RQQs). Intra-night optical variability (INOV) was detected for 13 of the 20 AGN, including 5 of the 12 RQQs. The variations are stronger and more frequent for blazars than for RQQs, which is in accord with our recently reported results for another sample. By combining these data with the INOV results obtained earlier in our programme, we have formed an enlarged sample consisting of 9 BL Lacs, 19 RQQs and 11 lobe-dominated radio-loud quasars (LDQs). The moderate level of INOV found for both RQQs and LDQs shows that INOV is not directly linked to the presence of radio emission. Further, we supplemented these new observations of 3 BL Lacs with additional data from the literature for 17 other BL Lacs. In this extended sample of 20 BL Lacs, stronger INOV is found for the EGRET detected subset.

Publications:

• Optical Photometric Observations of &gamma -Ray Loud Blazars,
  J. H. Fan, O. M. Kurtanidze, M. G. Nikolashvili, A. C. Gupta, J. S. Zhang & Y. H. Yuan
  (2004), Chin. J. Astron. Astrophys., 4, 133-142

• Near Infrared Intraday Variability of Mrk 421,
  A. C. Gupta, D. P. K. Banerjee, N. M. Ashok & U. C. Joshi
  (2004), Astronomy & Astrophysics, (in press)

• Intra-night Optical Variability of BL Lacs, Radio-Quiet Quasars and Radio-Loud Quasars,
  C. S. Stalin, Alok. C. Gupta, Gopal-Krishna, Paul J. Wiita & Ram Sagar
  (2004) (submitted to Monthly Notices Roy. Astron. Soc.)

Preprints:

• CCD Photometric Observations of the Galactic Globular Clusters NGC 1904 and NGC 6341,
  A. C. Gupta (astro-ph 0311443)

• Near Infrared Intraday Variability of Mrk 421,
  A. C. Gupta, D. P. K. Banerjee, N. M. Ashok & U. C. Joshi (astro-ph 0405186)

Conference/Workshops Attended:

Advanced School on the Physics of Galaxy Formation during December 16-30, 2003 at HRI, Allahabad.

Visits to other Institutes:

• State Observatory, Nainital during September 02-07, 2003.

• Physical Research Laboratory (PRL), Ahmedabad during February 01-14, 2004.

• Tata Institute of Fundamental Research (TIFR), Mumbai during April 26-28, 2004.

• Physical Research Laboratory (PRL), Ahmedabad during May 09 to June 05, 2004.

Invited Lectures/Seminars:

Variability in different classes of Active Galactic Nuclei, April 27, 2004 at Tata Institute of Fundamental Research (TIFR), Mumbai.

Academic Recognition and Awards:

I am the principal investigator in the project Optical and Near Infrared Observations of Blazars. Telescope time during May 10-20, 2004 was alloted to our project for observations on 1.2 meter PRL Optical/IR telescope at Gurushikhar, Mount Abu.

Other Activities:

• Teaching: A complete course on Multi-wavelength Observations and Data Analysis Techniques at HRI in the year 2003-2004.

• Project Supervised: Mr. Abhay Kumar Gupta from Department of Information Technology, Meerut Institute of Engineering and Technology, Meerut spent 2 months (July-August, 2003) at HRI and did Project on Online Multi-wavelength Database for Blazars.