spectroscopy of grbs - tifrtifrjet/presentations/basak_jet_tifr.pdf · of polish academy of...

N. Copernicus Astronomical CenterN. Copernicus Astronomical Centerof Polish Academy of Science, Warsawof Polish Academy of Science, Warsaw

Jet Triggering Mechanisms in Black Hole Sources, TIFR, January 21, 2016Jet Triggering Mechanisms in Black Hole Sources, TIFR, January 21, 2016

Rupal BasakRupal Basak

Spectroscopy of GRBs: Spectroscopy of GRBs: clues for the radiation mechanism and jet geometryclues for the radiation mechanism and jet geometry

Spectroscopy of GRBs: Spectroscopy of GRBs: clues for the radiation mechanism and jet geometryclues for the radiation mechanism and jet geometry

Mangano+06

Mangano+06

We aim to study the radiation process, specifically that of the prompt emission We aim to study the radiation process, specifically that of the prompt emission

GRB spectroscopy Rupal Basak, NCAC, Warsaw

Background and Motivation

Meszaros+01

Meszaros+01

1. Distance scale: cosmologicalRedshift: ~400/1400 (Swift era)

2. Phenomenon: Two phase.i. Prompt emissionii. Afterglow

3. Geometry: Possibly jet. Achromatic break and energy. ''Missing jet-break'' in Swift era

4. Progenitor: Long (collapsar), Short (compact object mergers). Supernova association, also host, environment etc.Two Long bursts with no supernova

5. Radiation process: Prompt emission highly debated Reasons:1. Rapid spectral evolution, 2. Poor resolution of GRB detectors

Central engine(Blackhole or magnetar)

Radiation process: synchrotron vs. thermal

Credit: Meszaros (2001), Science

● Prompt emission spectrum of a typical GRB has a non-thermal shape. Fitted with empirical Band function (Band+93).

● Standard scenario: internal shock in the GRB jet, electron acceleration, optically thin synchrotron emission

α=−1 β=−2.5






Low-energy photon index, α

Kaneko+06● Problem: Synchrotron line of death - photon index of the spectrum restricted below -1.5.

α=−1 β=−2.5






Low-energy photon index, α

Kaneko+06● Problem: Synchrotron line of death - photon index of the spectrum restricted below -1.5.

●Additional thermal component.

THERMAL+NONTHERMAL (blackbody+powerlaw or BBPL model)

α=−1 β=−2.5

Ryde+09


We found:

● The thermal emission is consisting of two smoothly evolving balckbodies.

● Origin: spine-sheath jet. Also explains the non-thermal component

Sample for the talk:

● 090902B: A GRB with high signal-to-noise data (Rao, Basak + 14, RAARao, Basak + 14, RAA)

● 090618: Overlapping BAT-XRT observation (Basak & Rao 2015, ApJ 812, 156Basak & Rao 2015, ApJ 812, 156)

● 130925A: Ultra-long GRB with NuSTAR observation (Basak & Rao 2015, ApJ 807, 34Basak & Rao 2015, ApJ 807, 34)

Take-home messageTake-home message


Note: shown for all types: (a) GRBs with single pulse, (b) multiple separable pulses, (c) GRBs with rapid variability, (d) those with high GeV emission.

χre

d2

Band

BBPL

2BBPL

νF

νχ

Observations


νF

ννF

νχ

χ

1. GRB 090902B (Rao, Basak + 2014)

2. GRB 090618 (Basak & Rao 2015a)

T1

T2

T3 T

4

T1

T2

T3

T4

XRT● BAT

BBPL = Blackbody+powerlaw2BBPL = Two blackbodies+powerlaw

A burst with highly variable lightcurve.

A burst with multiple separable pulses.

Open: BAT or XRTFilled: Joint data

Symbols:

Page+12

Current and Future Research Rupal Basak

3. GRB 130925A (Basak & Rao 2015b), An ultra-long GRB

Bellm+14 (NuSTAR and Chandra)

Piro+14 (XRT)

Physical Interpretation:

A spine-sheath jet

Observations

High GeV emission

High GeV emission

Low GeV emission

Low GeV emission

(Alt: Shabnam's talk)

Two possible mechanismof non-thermal emission:

1. Compton.2. Synchrotron.

Basak & Rao (2013), ApJ

Future directions● Early observation with focusing detectors (NuSTAR). ToO proposals.

● A sample of 78 GRBs with BAT-XRT overlap in the final prompt phase.

● ASTROSAT Cadmium Zinc Telluride Imager will detect ~ 50 GRBs/year. Polarization measurement (Tanmoy's talk). GRB 151006 (Vikas' talk).

● Developing a spine-sheath model and implement the synthetic spectrum in XSPEC. Measure the physical quantities like the Lorentz factor, and find the actual photospheric radius.

● Final aim: using GRBs as cosmological tools e.g., trace the cosmic star formation history, even using GRBs as luminosity indicators.

Current involvements:

Forming a group at NCAC. OPUS Grant proposal. Two members of H.E.S.S. consortium. Aim: Observation of GRBs at TeV energies and constrain models.

Thermal component in GRB prompt emission Rupal Basak, NCAC, Warsaw

Re: Major Conclusions

● Smoothly evolving blackbodies are found in the pulses of GRBs during the prompt emission phase.

● Two blackbodies are also found in the afterglow data. High significance. Possibly a tail emission of the prompt phase.

● Radiation mechanism in ultra-long GRBs is possibly similar as long GRBs with longer time scale.

● Our finding is consistent with a spine-sheath structure of GRB jet.

Thermal component in GRB prompt emission Rupal Basak, NCAC, Warsaw

spectroscopy of grbs - tifrtifrjet/presentations/basak_jet_tifr.pdf · of polish academy of...

Documents