Follow-up of GW-EM in Optical and NIRG.C. Anupama

Indian Institute of Astrophysics

EM counterparts of GW SourcesElectromagnetic Observations • Nature of GW source – BH events, BNS, Collapse of massive

stars, WD collapse (?) • Pinning down the position of the sources • Identify the host galaxy and environment • Suite of telescopes and instruments spread across the globe

• (γ − rays, X-rays, UV), Optical, NIR, (mm, radio) - Photometry, spectroscopy, polarization

• Wide field optical and NIR transient search observations • Deep observations – several transients – important to have rapid

spectroscopic observations for source classification • Long term monitoring

Observing Facilities in India

• Longitudinal Advantage

Existing Facilities

Vainu Bappu Observatory■ Established in late 1960s ■ Location: 12d 34m N; 78d 50m E; Altitude: 720m ■ 175kms South-East of Bangalore

2.3 metre Vainu Bappu Telescope F/3.25 primary mirror; F/13 Cassegrain focus

• Cassegrain OMR low resolution spectrograph (R=500-2000) • VBT Fiber-fed Echelle Spectrograph (Prime focus fiber feed; R=30000, 70000)

1 metre Zeiss telescope F/13 Cassegrain focus

• Low resolution spectrograph (UAGS) • PhotoPolarimeter

1.3 metre Telescope F/8 Cassegrain focus; 30 arcminute corrected field.

• 2K X 4K imager and 1K X 1K rapid imager • FoV: 5.5 X 11 arcmin

Indian Astronomical Observatory Mt. Saraswati (Digpa-ratsa Ri), Hanle

■ Location: 32d46m46s N; 78d57m51s E ■ Altitude: 4500m (15000ft) ■ ~260 clear nights/yr (~190 photometric); Median

seeing ~1 arcsec

■ 2m Optical/NIR telescope – The Himalayan Chandra Telescope (HCT)

■ 0.7m GROWTH-India Telescope

■ High altitude Gamma Ray Array Telescope (HAGAR) ■ 22m Imaging Cherenkov Telescope (MACE) – under

installation ■ Site characterization instruments ■ Aluminizing facility, LN2 plant ■ Observatory powered by solar power (with backup diesel

generators)

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Himalayan Chandra Telescope

● 2m aperture; f/1.75 primary; f/9 Cassegrain ● Instruments mounted on a cube with 4 side ports and one

on-axis port ● Hanle Faint Object Spectrograph Camera (HFOSC) –

300-920nm range Imaging and low-medium resolution spectroscopy [R~150-4500], UBVRI, Narrow band filters (on-axis port)

● TIFR Near-Infrared Spectrometer Camera (TIRSPEC) – 0.9-2.5 micron range. Imaging and low-medium resolution spectrosocopy [R~1200] (side port)

● Hanle Echelle Spectrometer (HESP) – 350-920 nm range. High resolution spectroscopy (R~30000; 60000) [V~12 mag @60,000] (Cassegrain interface on side port)

● Autoguider – common for all instruments (side port) ●Telescope, Dome and Instruments Controlled remotely using a dedicated satellite link from IIA's CREST campus at Hoskote, Bengaluru [3MHz + 1.45MHz]

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HCT Science - Transients● Cataclysmic Variables -

Novae ● Photometry and

spectroscopy of supernovae

● Afterglows of gamma-ray burst sources

● Tidal Disruption Events ● GW Sources – EM

counterpart ● Fast Transients (eg.

AT2018cow)

M31N 2008-12A

AT2018cow

SN 2009ig

SN 2012cg

GW 170817 - Initial follow-up• 6 neutrinos within ±500 s : HCT follow-up • (IceCube: GCN 21508; HCT: GCN 21554)

9Slide Credit: Varun Bhalerao

• Missed EM counterpart observations with HCT due to • Low visibility from Hanle • Poor sky conditions over the following nights

GROWTH India Telescope (GIT)

• GROWTH - Global Relay of Observatories Watching Transients Happen [Funded by DST-SERB under the PIRE programme. Administered by IUSSTF]

• 0.7m Telescope • Wide field – 0.7 deg FOV; CDK design • Sub-arcsec tracking for <600s • ~ 3 arcsec pointing accuracy

• Observations of Transients • Supernovae, Gamma-Ray burst sources, EM

counterparts of Gravitational wave sources • Near Earth Objects (asteroids, comets)

• Installed in June 2018

GROWTH is an International Project led by M. Kasliwal (Caltech, U.S.A) GROWTH-India PIs: G.C. Anupama, IIA and Varun Bhalerao, IITB

On Sky Performance• Recurrent Nova M31N

2008-12A • g = 21.08 (0.19)

• GRB181201A (△t=3.415) • g = 19.97 (0.13) [600s]

• Blazar BZQJ0348-2749 (airmass 2.7) • r=16.37 (0.35); i=16.07

(0.23) • SN 2018kpo (AT2018bcde)

[1.3 d after discovery] • g = 17.36 (0.04); r = 17.61

(0.04); i=17.85 (0.08) • SN 2018ilu (ATLAS18zek)

GIT - Next• Full automation of operations

• Robust pipeline for data reduction, image subtraction and photometry

• Integration with GROWTH marshal

• Implementation of slew optimization algorithm (Shreya Anand, Javed Rana)

• Improve the imager design (correct for the vignetting)

• Second set of filters

Future

Thirty Meter Telescope (TMT)

TMT

Proposed by Time Domain ISDT

INDIAN SPECTROSCOPIC AND IMAGING SPACE TELESCOPE (1m)

Wide field UV equivalent of HST Imaging and spectroscopic survey telescope UV complement for LSST

PI: Annapurni Subramaniam (IIA)

10-m Class National Optical-InfraRed Telescope

● Strong need for a 10-m class telescope in the country for (a) synergy with other future facilities; (b) science generation for larger telescopes; (c) training young astronomers to be able to use the 30-m telescope; (d) being competitive internationally

● Ladakh region has some of the best astronomical sites in the country ● Experience gained by participation in the TMT will enable indigenous development ● Current Status

● Developing a Detailed project proposal for funding - Optics design (segmented primary), Primary Mirror Support System design, Telescope structure design ● Development of a prototype segmented mirror telescope – 1.6m, 7 spherical segments

Google map showing the sites being characterized for NLOT. Sites identified based on accessibility, altitude and horizon clearance

IAO, Hanle appears to be best suited in terms of PWV, Accessibility and available infrastructure

LIGO-India Era: A network of 1-2m class robotic telescopes across the country?

Himalaya Faint Object Spectrograph Camera (HFOSC)

• Mounted on the on-axis port

• Low-medium resolution spectroscopy using a range of grisms- R~150-4500

• Broad band and narrow band imaging.

• Filters: UBVRIz; H-alpha, [OIII], [OII], [SII]

• CCD – 2048 x 4096 • FOV: 10'X10' @ 0.297

arcsec/pixel

TIFR NIR Imager and Spectrometer (TIRSPEC)

• 1024 x 1024 Hawaii-1 array • 0.3 ”/pixel - ~5 arcmin FOV • Pixel size = 18 µm • Wavelength range = 1 – 2.5

µm • Grism Spectroscopy @

~1500 resolving power (0.9 arcsecond/3 pixel slit @H and K)

Hanle Echelle Spectrometer (HESP)

• General purpose Spectrograph

• Spectral resolution R = 30000; R = 60000 (with image slicer)

• Mechanical stability 200m/s

• Radial velocity accuracy 20m/s (ThAr reference mode)

• Peak Efficiency ~ 20% (including telescope and detector in the range 400-700nm)

• Scattered light ~0.07% for bright stars

• Faintest limit ~12mag (@R=60000)

• Continuous wavelength coverage (350-1000nm in single exposure)