Multi-band study of the Blazar PKS 2155-304 with XMM-Newton

Alok C. Gupta, ARIES, Nainital, India

alok@aries.res.in, acgupta30@gmail.com

Explosive Transient Sources (large range in

energies, a time-variable sky)

Extragalactic < 5ms radio burst (Lorimer et al. 2007)

γ-rays in cosmological GRBs

Common origin of supernovae, novae and GRBs

SDSS I supernovae survey nearby supernovae

cosmological focus distant supernovae

redshift desert (0.1 < z < 0.3) where few supernovae are found

do SDSS II supernovae survey remove redshift desert?

Ultra High Energy Cosmic Rays (UHECRs) at energies of 1019eV UHECRs emission from Seyfert & Radio Galaxies (Moskalenko et al. 2008; Nagar & Matulich 2008)

No UHECRs from Blazars (Harari 2007)

Neutrino emission from Blazars? (Neronov & Semikoz 2002)

And many more ……………

Challenge: universal inner engine for producing non-thermal high

energy emissions from regions with low opacity

The Transient Universe

Explosive Transient Sources (large range in

energies, a time-variable sky)

In last few years studies on Transient Sources as producing

Tsunami of Papers

Talk Outline

Introduction

Multi-band (Optical/UV and X-ray) XMM-Newton Data

Motivation on the Blazar PKS 2155 – 304 studies

X-ray Intra-Day Variability (IDV)

X-ray QPO detection

X-ray emission modeling on IDV timescale

Multi-band (Optical/UV & X-ray Long Term Variability)

Multi-band Spectral modeling

Important Results & Discussion

Future Projects with ASTROSAT

Conclusion

Ph. D. Students: Dr. Haritma Gaur & Mr. Jai Bhagwan

ARIES, Nainital

Collaborators:

1. Prof. Paul J. Wiita, USA

2. Dr. Pawel Lachowicz, Poland

3. Prof. I. Papadakis, Greece

AGN Cartoon AGN Unification

Jets : along axis Blazars modest angles RLQSOs large angles Radio Galaxies

No Jets: Luminous Quasars nearly perpendicular to disk Type 1 & 2 Seyferts modest angle with disk.

Radio-loud AGN F5GHz / FB ≥ 10

(10-15% AGN)

Blazar (A rare but most powerful class of AGN) Properties subclass of radio-loud AGN

BL Lacs (Featureless optical spectra) + FSRQs (prominent emission lines

in optical spectra)

Flux Variability (in complete EM)

Variable Polarization radio to optical bands

Non-thermal radiation (predominantly)

Jet axis angle < 100 (Urry & Padovani 1995)

Classification:

LBL ↔ RBL (Red ↔ Low Energy ↔ Radio selected)

HBL ↔ XBL (Blue ↔ High Energy ↔ X-ray selected)

Spectral Energy Distribution (SED)

LBL IR/optical GeV

HBL UV/X-rays TeV

SED Peaks

Emission Mechanism Low Energy Synchrotron Radiation

High Energy Inverse Compton

(probably)

Low energy part of SED well

understood

1. Non-thermal Radiation in High

State

2. Thermal + Non-thermal Radiation

in Low State

High Energy Part of SED is not well

understood. It is usually explained

as arising from inverse-Compton

(IC) scattering of the same electrons

producing the synchrotron emission.

These electrons interacts with

1. synchrotron photons SSC

2. External photons originating in

the local environment EC

Alternative Hadronic Models where

Gamma-rays are produced by high

energy proton either via proton

synchrotron radiation or via

secondary emission from photo-pion

and photo-pair-production

A lot of challenges to understand high energy part of SED of BLAZARS

which can be better understood with existing and upcoming multi-

wavelength facilities (e.g. ASTROSAT, MACE, etc.).

Why to Study Blazars?

Blazars are multi-wavelength, and multi-time scale phenomena

Intraday (IDV) – several minutes to less than a day

Short term (STV) – few days to few months

Long term (LTV) – few months to several years

AGN Models

What cause flux / polarization variability?

How to locate emission region?

It can be a tool probe physics near BH?

How to get BH mass of AGN?

Does QPO phenomena happen in AGN?........ etc?

Hot Spot on/above Accretion

Disk

Helical Jet Structure Model

Binary Black Hole Model

SKC + AM + PJW

Blandford,

Marscher

Sillanapaa

et al.

X-ray observations of PKS 2155-304 with XMM-Newton

Gaur, Gupta, Lachowicz & Wiita, 2010, ApJ, 718, 279.

Multi-band (Optical/UV and X-ray) data of PKS 2155-304 from

XMM-Newton

Bhagwan, Gupta, Papadakis & Wiita, 2014a, MNRAS, 444, 3647

Multi-band XMM-Newton data of the Blazar PKS 2155 – 304

Project 1. X-ray Flux variability in the Blazar on IDV timescales

14 observations in X-ray bands (EPIC/PN observations)

Gaur, Gupta, Lachowicz, Wiita, 2010, ApJ, 718, 279

Project 2. X-ray Quasi Periodic Oscillation (QPO) in the Blazar

1 observation in X-ray bands (EPIC/PN observations) from Project 1

Lachowicz, Gupta, Gaur, Wiita, 2009, A&A Letters, 506, L17

Project 3. X-ray Flux Variation and SED of the Blazar

3 observations in X-ray bands (EPIC/PN observations) from Project 1

Bhagwan, Gupta, Wiita, Papadakis, 2014b, MNRAS (in revision).

Project 4. Simultaneous Multi-wavelength Flux variability and Spectral

Energy Distributions (SEDs) of the Blazar

5 observations from Project 1 + 15 New Observations of (EPIC/PN + OM)

Bhagwan, Gupta, Papadakis, Wiita, 2014a, MNRAS, 444, 3647

Results & Discussion Project 1.: X-ray Variability of the Blazar PKS 2155-304 on IDV Timescale

Evidence of jet and accretion disk based models

Gaur, Gupta, Lachowicz, Wiita, 2010, ApJ, 718, 279

• Out of 14 LCs, only 7 have shown IDV timescales in the range of 15.7 to 41.4 ks.

• On 6 occasions, IDV timescale is longer than the data length. • Hint of QPO (possible period ~ 5.9 ks) on one occasion.

Project 2: Presence of QPOs are fairly common in micro-

quasars but rare in AGN

GRS 1915+105 (Strohmayer) Greiner et al.

High frequency QPOs (e.g. 40 & 67 Hz repeat in GRS)

Galactic Black Hole Binary (GRB)

Cartoon Active Galactic Nuclei (AGN) Cartoon

Jet propelled by B-fields twisted by BH

Accretion disk

Hot spot on accretion disk can possibly explain QPO on IDV

timescale but this model is ruled out

for STV & LTV timescales because BH

mass exceeded 10^10 M_sun

Another QPO in XMM-Newton LC of a narrow line Seyfert 1 galaxy (RE

J1034+396) on the timescale of ~ 1h (Gierlinski et al. 2008) using PSD method.

EM

Band

QPO Results Time

Scale

Methods Ref.

optical QPO in S5 0716+714 on 5 occasions

25 to 73

min.

wavelet ACG, AKS, PJW,

ApJ, 690, 216 (2009)

X-ray QPO in AO 0235+164

QPO in 1ES 2321+419

17 days

420 days

SF, DCF, LSP, Data Folding

BR, PJW, ACG,

ApJ, 696, 2170 (2009)

X-ray QPO in PKS 2155-304 4.6 hour

SF, wavelet, PSD, MHAoV, data folding

PL, ACG, HG, PJW,

A&A Lett. 506, L17 (2009)

X-ray Hint of QPO in ON 231

Hint of QPO in PKS 2155-304

3.3 hour

1.9 hour

SF, PSD HG, ACG, PL, PJW,

ApJ, 718, 279 (2010)

optical QPO in S5 0716+714

Fastest QPO ever detected in any AGN

15 min SF, PSD, LSP, data folding

BR, ACG, UCJ, SG, PJW, ApJL, 719, L153 (2010)

optical Weak QPO in S5 0716+714

1.1 days SF, PSD, wavelet, MHAoV, data folding

ACG, et al. (34 authors)

MNRAS, 425, 2625 (2012)

Project 2. Our Results

XMM-Newton data of PKS 2155-304

4.6 hour QPO & 3.8 cycles

Lachowicz, Gupta, Gaur, Wiita, 2009, A&A Lett., 506, L17

Black Hole Mass Estimation with Periodic or QPO Timescale

Causality argument gives the size of emitting region R <= c delta T (obs).

Minimum size of such an emitting region is fairly closely related to the

gravitational radius of BH,

The minimum likely period corresponds to the orbital period at the inner

edge of the accretion disk, which is usually is given by marginally stable

orbit, Rms

For a non rotating (Schwarzschild) BH

The simplest of these models for BHs would attribute the quasi-periods to

particularly strong orbiting hotspots on the disks at, or close to, the innermost

stable circular orbit allowed by general relativity (e.g., Abramowicz et al. 1991;

Mangalam & Wiita 1993). If such simple models apply in this case, and the QPO

is indeed real, then we would estimate the BH mass for PKS 2155−304 to be

3.29 × 107 M (Sun) for a non-rotating BH and 2.09 × 108 M (Sun) for a

maximally rotating BH.

A shock propagating down a jet which contains quasi-helical structures, whether

in electron density or magnetic field, can produce a QPO, with successive peaks

seen each time the shock meets another twist of the helix at the angle that

provides the maximum boosting for the observer (e.g., Camenzind &

Krockenberger 1992). Instabilities in jets just might be able to excite such helical

modes capable of yielding fluctuations that are observed to occur on the time-

scale seen in PKS 2155−304 (e.g., Romero 1995). Or they could arise as the jet

plasma is launched in the vicinity of SMBH and thus actually originate in the

accretion flow but become amplified in the jet. Another very plausible origin for a

short-lived QPO would be turbulence behind the shock in the relativistic jet (e.g.

Marscher et al. 1992), as again intrinsically modest fluctuations could be

Doppler boosted.

Lachowicz, Gupta, Gaur, Wiita, 2009, A&A Lett., 506, L17

• During the years 2000 – 2012,

PKS 2155 – 304 has 20 observations simultaneously in OM and EPIC-PN. • We find significant variations, in all bands, on time-scale of years with an rms amplitude of ~ 35 – 45 %. • Our visual inspection show that in the long term LCs, optical & UV bands are well correlated and the same is true for hard and soft X-ray bands. • Variability amplitude increases slightly from soft to hard X-ray bands. • Variability amplitude decreases from optical to UV bands.

Project 4:

Bhagwan, Gupta, Papadakis, Wiita, 2014a, MNRAS, 444, 3647

Bhagwan, Gupta, Papadakis, Wiita, 2014a, MNRAS, 444, 3647

Flux Variations in Optical/UV are not correlated with X-rays Optical/UV emissions in this blazar may arise from different population of leptons.

Bhagwan, Gupta, Papadakis, Wiita, 2014a, MNRAS, 444, 3647

Log Parabolic (LP) Model

Log Parabolic + Power Law (LPPL) Model

• We made the SEDs for all 20

observations which span more than 3 order of magnitude in frequencies. • We first fitted with log – parabolic (LP) model (left panel). The fits were poor. • We then fitted with log – parabolic (LP) + Power Law (PL) (LPPL) model which show significant improvement. • These models indicate that the optical/UV and X-ray flux variations are mainly driven by model normalization, but the X-ray band flux is also affected by spectral variations, as parameterized with the model curvature parameter. • The energy at which the emitted power is maximum correlates positively with the total flux. As spectrum shifts to higher frequencies, the spectral curvature increases.

Bhagwan, Gupta, Papadakis, Wiita, 2014a, MNRAS, 444, 3647

PLLP Model fits multi-band SED in much better way than simple PL model

Bhagwan, Gupta, Papadakis, Wiita, 2014a, MNRAS, 444, 3647

Bhagwan, Gupta, Papadakis, Wiita, 2014a, MNRAS, 444, 3647

Evidence of jet and accretion disk based models

Bhagwan, Gupta, Wiita, Papadakis 2014b, MNRAS, (in revision)

• In sub-segments: 1(a) flux is stable; 1(b) & 3(a) flux decreases; 1(c) & 3(b) show flux

rising trend. • In sub-segment: (2) a hint of weak QPO is detected (Gaur, et al. 2010). • By calculating normalized excess variance and fractional root mean square variability, we found significant variabilities in different sub-section ranging from 1.5 – 19.4 %.

Bhagwan, Gupta, Wiita, Papadakis, 2014b, MNRAS, (in revision)

• We fitted power-law, broken power-

law and log-parabolic models with galactic and extragalactic absorption to all 6 sub-segments. • All three models are statistically acceptable and the values of reduced ^2 for each model are nearly same. • Data/model ratios for all models follow the same trend.

Sub-segment 3(b)

Bhagwan, Gupta, Wiita, Papadakis, 2014b, MNRAS, (in revision)

Bhagwan, Gupta, Wiita, Papadakis, 2014b, MNRAS, (in revision)

• The spectral changes are best illustrated as a

correlation between flux and photon index. The “clock wise motion”, shown by arrow, is clearly exhibited by our results. • The figure shows spectra becoming steeper in the declining phase and harder in the brightening phase of the blazar. This indicates that the variation of hard X-ray emission always leads the soft X-ray emission in both the increasing and decreasing brightness phases. • In such a flux-index plot, if the loop is traced in a clockwise direction the physics would be controlled by synchrotron cooling mechanism (Tashiro et al. 1995).

Why HBLs are potential candidates for ASTROSAT?

Revolution due to Fermi and recent development in VHE Gamma-rays

(GeV - TeV) facilities

HESS High Energy Stereoscopic

System

Other similar facilities

MAGIC (Europe); VERITAS (USA);

CANGAROO (JAPAN &

AUSTRALIA) ; TACTIC, HAGAR

MACE (upcoming in India)

Till 2005 no. of HBLs known 6

Till 2014 no. of HBLs known 44

HESS Telescope in Namibia; 37 institutes, 12 countries and about 200

scientists upcoming HESS II, CTA

Conclusion HBLs are unique sources for simultaneous multi-wavelenth emission in the complete EM spectrum and their emission mechanism is not yet well understood. Multi-wavelength observations of HBLs http://tevcat.uchicago.edu/ by ASTROSAT can be done to search for variability on diverse timescales, search for QPOs and to understand the emission mechanism of these sources.

THANKS