Galactic Sources at Low Radio Frequencies

Ishwara Chandra CHNCRA‐TIFR, Pune India

Paula Benaglia (Argentina),  Michael de Becker (Belgium) and Anandmayee Tej (India)

Plan of the talk

• GMRT (and upgraded GMRT)

• The Cygnus OB2 region with GMRT

• Other Galactic Sources with GMRT

• Concluding remarks

Giant Metrewave Radio Telescope

GMRT consists of 30 antennas, of 45 meter dia, spread  over 30 km area, at Khodad, 90 km off Pune. 

It is among the world’s largest radio interferometer operating at metre‐waves, fully open to the community. 

Frequency of operation 130 to 1500 MHzDesigned and fabricated in India, in operation since 2002Observing modes – pulsar, continuum and spectral line

GMRT is run by National Center for Radio Astrophysics of the Tata Institute of Fundamental Research, Pune

URL: http://www.ncra.tifr.res.in

The Legacy GMRT

30 dishes of  45 m dia each

12 dishes in a central 1 km x 1 km area (central square)

Rest  in 3  Y‐shaped array

Shortest baseline : ~ 200 mLongest baseline :  ~ 25 km

GMRT antennas at Khodad, 90km off Pune

The Legacy GMRT

Effective collecting area (2‐3% of SKA) :30,000 sq m at lower frequencies20,000 sq m at highest frequencies

Modes of operation :Interferometry (continuum and line)Array mode (incoherent & coherent)

Frequency range : 130‐170 MHz  (150 MHz band) 225‐245 MHz  (235 MHz band) 300‐360 MHz  (325 MHz band) 580‐660 MHz  (610 MHz band) 1000‐1450 MHz  (L‐band)

Max instantaneous BW = 32 MHz, 512 channels

GMRT: Scientific ObjectivesThe GMRT is a powerful instrument to probe several astrophysical

objects and phenomena :

The Sun, extra‐solar planets, Pulsars,  Galactic objects (SNR,  micro‐quasars etc), Transients events like Gamma Ray Bursts, FRBs

Ionized and neutral Hydrogen gas (in our Galaxy, nearby galaxies), Cosmology and the Epoch of Re‐ionization

Galaxy Clusters,  Radio Galaxies and Quasars,   All sky surveys such as the 150 MHz TGSS and many interesting new results have been produced

Next Generation: The uGMRTGMRT has been working well on the global stage; however, it was time to  upgrade the facility, keeping in mind  global efforts such as the SKA. 

The main goals for the upgraded GMRT (uGMRT) were identified as :

•Seamless frequency coverage from ~ 30 MHz to 1500 MHz with completely new feeds and receiver 

•Improved receivers with better dynamic range and G/Tsys

•Increased instantaneous bandwidth of 400 MHz, new correlator

•Modern, versatile control and monitor system  

•(Telescope Manager work‐package for SKA is being led by India, prototyping at uGMRT)

Done without compromising availability of existing GMRT to users

Upgraded GMRT–Now SKA Pathfinder!

Fractional Bandwidth – legacy and upgraded

The uGMRT: final bands

Band 5 (1000 – 1450 MHz ) : existing wide‐band feed + improved dynamic range receivers with appropriate RFI filters 

Band 4 (550 – 850 MHz) : new feed with matching receiver system Band 3 (250 – 500 MHz) : new feed + matching receiver 

Band 2 (120 – 250 MHz) : modified Kildal feed + matching electronics

Band 1 (30 – 80 MHz) : on hold at present.

Digital backend: upto 400 MHz with upto 32K channels

Currently operational in all 30 antennas:

The uGMRT vs SKA, JVLA, LOFAR

The uGMRT nicely fills the frequency gap between LOFAR and JVLAOnly SKA-I will do better thanuGMRT at cm wavelengths

The uGMRT vs SKA, JVLA, LOFAR

SKA Fact sheet, 2018

GMRT User statistics

Proposal Deadline –January 15 and July 15.

The uGMRT: take home message

Near seamless frequency coverage from 130 to 1460 MHz, good for HI and other lines at any redshift

Wide band upto 400 MHz instantaneous bandwidth, full polarization capability

Upto 32K channels in 100/200/400 MHz correlator bandwidth

Excellent  UV coverage due to large fractional bandwidth

uGMRT is SKA Pathfinder, excellent preview for SKA‐mid band‐1

The uGMRT: Early Science resultsPULSAR B1508+55

33 MHz at Lband (centered at 1390 MHz)

vs

120 MHz at Lband (1330 – 1450 MHz)

Simultaneous observations using same # of antennas in phased array mode.Y. Gupta et al.

The uGMRT: New window (band-4)

Credits: Nissim Kanekar

First light results - Associated HI absorption out to redshift 1 – new window

Binary NS merger GW170817Possibly the lowest frequency detection – at 610 MHz – of the binary Neutron Star merger GW170817

7 to 8 sigma detection, multiple epochs (rms 15 to 20 microJy/beam)

Band-3 planned.

ApJ in press

Deep Band-3 image of COMA ClusterBand 3, rms 30 microJy/beam – 1.6 degree X 1.2 degreeOnly 2 hours ON source

Ishwara-Chandra and Dharam Lal

XMMLSS - 20’X 15’; rms ~ 20 microJy/beam; resolution 6.7X5.4”(equivalent of 8 microJy at 1.4 GHz)

XMMLSS with uGMRT – ongoing...

So many submJy radio sources with photo-z > 1? (Celiegi et al 2005)

Ishwara-Chandra et al,

Deepest image of XMMLSS field at 300 – 500 MHz band; Ishwara Chandra et al.

The uGMRT: take home message

The uGMRT has been producing very deep and high‐resolution images at low radio frequencies, down to a few tens of microJy

Steep spectrum radio emission, often missed at GHz frequencies, clearly seen.

Cygnus OB2 region with GMRT• Survey of a region of about 5 to 6 sq. deg around Cyg OB2, OB8 and OB9 region, at 325 and 610 MHz.• < 1 GHz is best to trace non‐thermal emission.• Best resolutions – 7” at 325 MHz and 4 ” at 610 MHz.

o Chandra Cygnus OB2 Legacy Survey: 1.08 Ms Chandra survey of a 1 sq deg region centered on the Cygnus OB2 association.

o Wealth of IR and optical data.

Why Cygnus OB2 region ?The region is rich; wide range of sources across  EM spectrum.

Protostars, young massive stars,  Colliding wind binaries,  X‐ray sources (microquasars?) Unidentified VHE sources, Shells, bubbles, shocks.. UN‐anticipated sources?

Why Radio?

• O and B category stars are > 10 times solar mass• Most early type stars are detected in IR and Radio.• Radiation mechanism – free‐free emission  processes (White & Barlow 1975; Panagia & Felli 1975)

Some early‐type stars show significant variation from this• Spectral indices less than 0.6• Brightness temperature of radio emission higher ( 107K) compared to thermal emission ( 104K) • Radio variability

Why Radio?Non‐thermal emission – synchrotron radiation (White 1985)• Existence of magnetic field• Population of relativistic electrons

Particle acceleration is through Fermimechanism in the presence of hydrodynamical shocks

Population of relativistic electrons may also emit in the high energies

There are several high energy sources,  half of them un‐identified

Cygnus OB2 region with GMRT

About  200 hours allotted in Cycle 25, 27, 28, 30,

• 5  pointings at 325 MHz (near full synthesis)• 40 pointings at 610 MHz ( 2 hours per pointing)• 1 pointing at 1280 MHz (full synthesis, two epoch)

Data analysis in AIPS as well as SPAM

Cygnus OB2 region

Colliding-wind binaries

Thermal radio emission

Sync

hrot

ron

radi

o em

issi

on

VLBA, Dougherty & Beasley 2010

WR

140

Indicators of a PACWB

Non‐thermal radio emission Deviation of spectral index from 0.6 Variable radio flux  Stronger radio emission than predicted by thermal

CaveatsThese sources are scarce, hence large area survey neededRadio flux is weak (< mJy), sensitive observations needed

PACWB CatalogueDe Becker & Raucq 2013

Multiplicity

Cygnus OB2 region with GMRT325 MHz, 5 fields, r = 90’ 610 MHz, 36 fields, r = 45’rms 100 – 300 microJy/beam rms – 60 to 100 microJy/beam

✓ ✓

Cygnus OB2 regionGMRT 325 MHz

Cygnus OB2 regionGMRT 325 MHz – zoomed view – plenty of sources!

Cygnus OB2 regionGMRT 610 MHz

Cygnus OB2 regionGMRT 610 MHz – zoomed view – plenty of sources

With two frequency data, spectral index for large number of sources available

PACWBs with the GMRT Main Cygnus OB2 binaries: observations at 325,

610 and 1280 MHz, at two epochs (De Becker+)

New candidates (Tyc 8313)… Cycle 33

Star Sp. type 1280MHz 610MHz 325MHz

OB2 5 Ep.1:Ep.2:

Of/WN9 + O7I + O? + B0

2.7 ± 0.11.8 ± 0.3

2.85 ± 0.04 1.5 ± 0.1

OB2 8A Ep.1:Ep.2:

O6I + O5.5III 1.64 ± 0.062.0 ± 0.4

----- -----

OB2 9 O5I + O6-7I ----- ----- -----

OB2 12 Ep.1:Ep.2:

LBV candidate 1.3 ± 0.074.9 ± 1.5

0.7 ± 0.1 -----

OB2 335 O7V off 4.4 ± 0.3 1.4 ± 0.2

WR 144 WC5 off ----- -----

WR 145 WN7/CE + O7V(f)

off ----- -----

WR 145a WN4/5-6/7 off 27.0 ± 0.4 10.9 ± 0.3

=

• None of the objects has a negative spectral index. • All objects have a preferential direction towards the center of the

association Cygnus OB2. • For some of them, a SED could be drawn.

…proplyds log(S2/S1)log(2/1)

+ 2”

GMRT 325 MHz self-calibrated data

Isequ

illaet

al 2

018

ATCA data, Garay+ 2003

Massive protostellar system IRAS16547-4247

Red=GMRT, green=IR Glimpse,blue=XMM X-rays.

Peri et al 2017

GMRT 610 MHz

WR 11GMRT obs at 150, 325, 610 and 1400 MHz

Cometary HII regions

870 µm, 24 µm, 8 µm

(Das et al., 2018)

8 µm, 4.5 µm, 3.6 µm(Veena et al., 2016)

IRAS 17256-3631G346.077-0.056 G346.056-0.021

Cometary HII regions

Cometary HII regions

IRAS 17256‐3631

(Mac-Low et al. 1991)

Bow - shock

( Tenorio-Tagle 1979)

Champagne flow

Mechanisms involved

Bow‐shockStand-off distance

Trapping parameter

Column density map+ radio contourFavours the Champagne flow model

G346.077-0.056 G346.056-0.021

IRAS 17256‐3631

Proposed models of velocity structure

IRAS 17256‐3631

MALT90

Infrared Dust Bubbles

(Dinil Bose et al., in prep)

610 MHz map (8.8’’ x 5.43’’)Int Flux : 5.6 Jy

1280 Mhz map (6’’ x 6’’)Int. Flux : 3.3 Jy

GMRT Observations

Spectral Index Map Error Map

IR Dust Bubble N10

Candidate Supernova Remenant

Concluding remarks

• The upgraded GMRT, SKA Pathfinder, is a sensitive low frequency radio telescope, open to community. 

• We have initiated a  wide area survey of one of the most active region of the galaxy – Cygnus Rift at 610 & 325 MHz.

• Radio counterparts and spectra for wide category of objects.

• Extensive use of GMRT (and uGMRT) for high‐mass star formation

The Metrewavelength Sky ‐ II

Celebrating the 90th year of Govind Swarup and the 1st year of the upgraded GMRT

National Centre for Radio Astrophysics, Pune, Indiahttp://www.ncra.tifr.res.in/mwsky2

Dates: March 18 ‐ 22, 2019

The GMRT has recently undergone a major upgrade (the ``uGMRT'' project) that hassignificantly improved its scientific capabilities, opening up a wide range of interestingscience areas to the radio community. The first uGMRT results are now beginning toappear and the uGMRT will be formally opened in 2019. March 2019 will also mark the90th birthday of Govind Swarup, who conceived of, and led, the original GMRT project. Tocelebrate both of these events, the National Centre for Radio Astrophysics of the TataInstitute of Fundamental Research (NCRA‐TIFR) will host an international conference onradio astronomy in Pune, India, over March 18‐22, 2019.