Third eclipsing Black Widow Third eclipsing Black Widow

PSR J1544+4937 in a Fermi sourcePSR J1544+4937 in a Fermi source

Bhaswati Bhattacharyya

IUCAA

1SINP, 18th Oct 2012

Bhaswati Bhattacharyya (IUCAA)

Jayanta Roy (NCRA)

Paul Ray (NRL)

Yashwant Gupta (NCRA)

Dipankar Bhattacharya (IUCAA)

Michael T. Wolff (NRL)

Roger Romani (Stanford)

Fermi pulsar search consortium

People Involved

2

Bhattacharyya & Roy et al. 2012 (in preparation)

Publication (1) “Discovery of an eclipsing Black Widow PSR J1544+4937 in aFermi source with the GMRT”

(2) “Multi –frequency study of eclipse mechanism of PSR J1544+4937” Bhattacharyya & Roy et al. 2013 (in preparation)

OUTLINE

Frequency dependent eclipsing; ingress phase shift, short eclipse

Eclipse mechanism

Binary Vs Isolated MSPs : formation scenario

Pulsar classification with P-Pdot diagram

Black Widow pulsar : a missing link GMRT discovery of an eclipsing BW MSP Follow-up timing and ephemaris

Detection of Gamma-ray pulsation Summary

3

Pulsar classification

4

2000 known radio Pulsars in our galaxy

Young – Energetic, with significant spin-down noise and glitches.

Normal – Slower, More stable, Mostly isolated

Recycled pulsars -Faster, Most in binaries, extremely stable rotators ->MILLISECOND PULSARS

5

Equation of state at > nuclear densities

Relativistic dynamics in binary systems

Gravitational wave detection

Interstellar medium

Binary evolution

Atomic physics (atmospheres)

Solid state physics (crusts)

Plasma physics (eclipses, magnetospheres)

Millisecond pulsars are Superb Tools for Fundamental Physics

Neutron Stars and Pulsars – Early HistoryFranco Pacini 1968

Pulsars are formed after supernovae explosion!

6

Millisecond pulsars are a small population compared to the normal pulsars, magnetic Field ~109GMajority of MSPs are in binary MSPs are detected in the radio, x-ray and gamma-rays

Origin of millsecond pulsars is yet

not pinned down.

Leading theory : MSPs begin their life as longer

period pulsar but are spun up or recycled through accretion

thus millisecond pulsars are often called recycled pulsars.

Millisecond Millisecond

pulsarspulsarsBinary system

MSP formation

7

Binary and isolated MSPs

Majority of MSPs are naturally expected to be in binaries about 87% of MSPs are in binaries

What about Isolated MSPs?

Isolated MSPs are conceived to be formed in binary

systems where the pulsar radiation can ablate the companion !

8

“Black widow systems” – Missing link between Binary and isolated MSPs

The pulsar is destroying its own companion

Eclipses seen for very large duration

Very low mass companion ~ 20 Jupiter mass

Black Widow pulsars

9

Black Widow spider

The eclipse material extends well beyond the maximum radius at which it remain gravitationally bound to companion.

The pulsar is ablating its companion by creating significant amount of intra binary emission to obscure/block pulsar emission.

The compactness of the orbit and relatively high spin down The compactness of the orbit and relatively high spin down energy of the MSP can give rise to such phenomenonenergy of the MSP can give rise to such phenomenon

10

Eclipsing BLACK WIDOW pulsars

-- Provide better understanding of evolutionary history of isolated MSPs

-- Study of eclipse mechanism

-- Study of the relativistic pulsar winds

-- Probing pulsar magnetosphere

11

Two such eclipsing BW systems in the Galactic disk reported before the launch of Fermi -- PSR B1957+20 (Fruchter et al. 1988) -- PSR J2051−0827 (Stappers et al. 1996)

Black Widow Pulsars Before Fermi Launch

Black Widow Pulsars After Fermi Launch

According to Ray et al. (2012) among the 43 new MSPs found in Fermi directed searches, there are at least 10 BWs (few are eclipsing).

Black widow pulsars have high Edot which favors gamma-ray emission

GMRT

Low frequency facility

Searching for millisecond pulsations with GMRT as a part of Fermi pulsar search consortium (PSC) (ellaborated in Jayanta’s Talk)

12

J1544+4937 : Third eclipsing black widow !

PSR J1544+4937 is in a “Black Widow” system :Orbit is very tight (2.9hrs) Eclipses ~ 13% of its orbit by a very low-mass companion

13

14

GMRT discovery of PSR J1544+4937

At 607 MHz with 61 micro second resolutionPeriod: 2.16 ms Dispersion measure: 23.2 pc/ccAcceleration: 2.25 m/s2

15

Follow up timing

Individual pulses Mean profile

Follow up timing of J1544+4937

With accurate pulsar position timing can be done with 490 days of data

PSR with 2.9 hrs orbit : One of the shortest Fermi MSPs

Orbital velocity curve (Bhattacharyya & Nityananda 2008)

30

20000 )(

6

1)(

2

1)( ttttttm

Timing model

Timing residual m

16

17

Timing ephemeris

18

Frequency dependent eclipsing

244 MHz : Eclipse 322 MHz: Eclipse 607 MHz: No eclipse

19

Frequency dependent eclipsing

Eclipses for large fraction of its orbit (13%) at 322 MHz

Eclipses are centered around binary phase 0.24 with 22m duration

According to Eggleton 1983, Roche lobe radius

Opaque portion of the companion’s orbit is 0.98 Rsun, >> RL

Volume occupied by the eclipsing body is well outside RL Thus not gravitationally bound to companion

Indicate that pulsar is a Black Widow where the pulsar is ablating companion creating significant amount of intrabinary material obscuring pulsar emission

20

We sampled six eclipses at 322 MHz and two eclipses at 610 MHz

Top: @ 322 MHz variation of timing residual and hence electron column density around the eclipse phase Bottom: @ 607 MHz

Timing residuals around eclipse phase

Flux fading at 607 MHz near eclipse phase

Maximum delay in pulse arrival time at 607 MHz ~ 300 micro secondCorresponding increase in Dispersion measure value 0.027 pc/cc

Added electron density at superior conjunction ~ 8x1016 cm -2

21

A number of physical mechanism explaining the phenomenon of eclipsing is detailed in Thompson et al. (1994)

(a)Refraction : demands a order of magnitude higher delay (~tens of ms) than observed for PSR J1544+4937 (250 micro sec at 322 MHz)

(b) Free-free absorption : demands very low temperature or very high Clumping, both of which is not physically possible

(c)Pulse smearing : predicts ~374 micro sec smearing at 322 MHz in mid eclipse phase, which is less than 1/5 th of pulse period.

(d) Scattering : no significant scattering around the eclipse boundary

(e) Induced Compton scattering : calculated optical depth <<1

(f) Cyclotron absorption : We consider cyclotron absorption of the radiowaves by the electrons , as cause of eclipsing.For a fixed temperature optical depth for cyclotron absorption drops with harmonics, which may explain the lack of absorption seen at 607 MHz.Require further observations to better constrain the eclipse models

Eclipse Mechanism

22

A temporal shift in eclipse ingress phase:for 2 eclipses the ingress phase is shifted to 0.16 (from 0.18)

This may indicate that our line of sight is probing a wind zone where there is systematic outflow of eclipse material.

Such asymmetric increase of eclipse duration (repeatedlyseen in two epochs) is very unique to this BW

23

Additional short eclipses and phase changes around the eclipse boundary : observations

24

Additional short eclipses observed around eclipse boundary : observations

The duration of these features ~10s−20s, Hence is not seen in Fig (generated with 42s integration). In one epoch modulations lasted longer − phase modulation of duration of 100s, followed by a short eclipse of ~ 180s, then regular emission resumes for 500s after that main eclipse starts (zoomed).

25

Additional short eclipses observed around eclipse boundary : Implication

These interesting modulationsare not reported for other Black widow pulsars Indicate fluctuation of plasma density around eclipsing spot.

Fragmented blobs of plasma randomly oriented around eclipsing spot and obscuring radiation from pulsar can explain observed short eclipses before and after main eclipse.

Life span of the system

26

The orbital decay time scale ~ 1.5 × 107 years (typical for such systems)

Provides an estimate of the short life span But this can be largely contributed by which require longer monitoring

For Black Widow systems measured value of is an order of magnitude higher than the other binaries, indicative of higher energy flux to ablate the companion.

For PSR J1544+4937 we calculate ~ 8.4 ×1033 which is highest among other BW systems in Galactic disk

Higher energy of Black Widow Pulsars

Gamma-ray detectability measure

27

Considering the DM distance and ˙E of PSRJ1544+4937, the gamma-ray detectability measure ~ 7.6 × 1016 erg1/2 kpc−2 s−1/2 ~ 10-2 x Vela(Similar to that of other gamma-ray detected MSPs )

Fig. 12 of (Abdo et al. 2010)

MSPs

Young pulsars

Searchedbut not detected

Gamma-ray Pulsation detected from the Fermi source by folding LAT data with accurate radio ephemeris

28

No Optical/X-ray counter part detected

Detection of Gamma-ray pulsations

We report the discovery of an eclipsing Black Widow millisecond pulsar PSR J1544+4937 in a Fermi source at the GMRTOur discovery is the first Galactic millisecond pulsation at India.PSR J1544+4937 is the third eclipsing Black Widow pulsar known

Summary

29

Orbital decay time scale ~ 1.5 × 107 years Indicate short life span of such systems

From regular timing campaign at the GMRT we could get phase connected TOAs in TEMPO with 7 micro-sec timing residual.Best achieved from the GMRT. Detection of Gamma-ray pulsations

We observe frequency dependent eclipsing for this Black widow.We have studied eclipse characteristics of this pulsar from multi-frequency multi epoch observations.

For PSR J1544+4937 we calculate ~ 8.4 ×1033 which is highest among other BW systems in Galactic disk

Thank youThank you

Contact :

Bhaswati Bhattachrayya

IUCAA

Ph: 2560 4121

Email: bhaswati@iucaa.ernet.in

Website: http://www.iucaa.ernet.in/~bhaswati

31