Solar Storm and Pulsar Mode Switch Identified as Sources of Timing Noise in uGMRT Observations

Breaking: Indian Radio Telescope Identifies Two Causes Behind Pulsar Timing Anomalies, Boosting gravitational-Wave Searches

In a breakthrough for pulsar timing, researchers using the upgraded Giant Metrewave Radio Telescope in India have distinguished two distinct sources of timing irregularities seen in distant pulsars. The revelation clarifies what disturbs these cosmic clocks adn strengthens efforts to detect gravitational waves with pulsars.

What happened

Two pulsars were scrutinized: PSR J1022+1001 and PSR J2145−0750. The team relied on the uGMRT near Pune, a 30-dish array with 45‑meter antennas spread over roughly 25 kilometers.

For PSR J1022+1001,a sharp delay spike on August 9,2022,was not a stellar fault but a space-weather event. Coronal Mass Ejection material crossed the line of sight between the telescope and the pulsar, as confirmed by solar satellites from NASA and the European Space Agency. The electron fog from the solar storm slowed the radio waves, producing a temporary delay and marking one of the clearest detections of a solar storm impacting a pulsar timing experiment.

In contrast, PSR J2145−0750 exhibited a different phenomenon.Rather than an external disturbance, the pulsar itself underwent a mode change, a shift in its magnetic environment that altered the shape of the radio pulse.the researchers showed that this was an internal reboot of the star’s emission, not interference from our solar system.

Why it matters

The work provides a physics-based framework to separate external solar-weather effects from intrinsic pulsar behavior.Knowing the difference allows scientists to calibrate instruments more precisely, enhancing the ability to detect gravitational waves.

Researchers caution that solar-satellite data during the CME were incomplete. They also call for higher-resolution observations to determine whether the pulsar’s magnetic polarization changed during the mode shift.

Key facts at a glance

Fact	Details
Pulsars studied	PSR J1022+1001 and PSR J2145−0750
Instrument	Upgraded Giant Metrewave Radio Telescope (uGMRT), pune, India
Array specs	30 dishes, 45 m diameter, spanning about 25 km
External cause observed	Coronal Mass Ejection crossing the line of sight (aug 9, 2022)
Internal cause observed	Mode change in PSR J2145−0750
Data sources	Cross-referenced with solar satellites from NASA and ESA
Publication status	ArXiv preprint

Evergreen insights

Pulsars are extraordinarily precise celestial clocks. Understanding how solar storms and intrinsic pulsar dynamics affect their signals is essential for gravitational-wave astronomy and for building robust space-weather models.

As researchers refine methods to separate environmental noise from genuine signals, pulsar timing remains a promising window into gravity and the history of the universe.

What readers should know

Two takeaways stand out. External solar events can momentarily distort deep-space signals, and pulsars themselves can undergo rapid internal changes that mimic timing anomalies. Together, they underscore the need for complementary observations and higher-resolution data.

For broader context on space weather and gravitational waves, exploreNASA’s solar data and ESA’s Space Science programs:

NASA Solar data and ESA Space Science.

Readers are welcome to share their thoughts below. How might enhanced solar-weather data improve deep-space experiments in the coming years? Should future pulsar timing arrays routinely verify for internal mode changes to ensure pristine gravitational-wave signals?

Share your thoughts in the comments and stay tuned for updates as scientists expand the pulsar-time toolbox.

Timing Noise in uGMRT: Definition and Impact

• Timing noise refers to stochastic variations in pulsar pulse time‑of‑arrival (TOA) measurements that exceed the expected radiometer noise.
• In the upgraded Giant Metrewave Radio Telescope (uGMRT), timing noise limits the sensitivity of pulsar timing arrays (PTAs) used for gravitational‑wave detection and precision astrophysics.
• Sources include instrumental instabilities, interstellar medium (ISM) scattering, ionospheric fluctuations, solar activity, and intrinsic pulsar phenomena such as mode switching.

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Solar Storms as a Primary Source of Timing Noise

1.Solar wind‑driven ionospheric disturbances

• Coronal mass ejections (CMEs) and high‑speed solar wind streams increase the total electron content (TEC) of the ionosphere, causing frequency‑dependent phase delays.
• At uGMRT’s low‑frequency bands (300–850 MHz), even small TEC variations translate into TOA shifts of several microseconds.

2. Radio‑frequency interference (RFI) enhancement

• Solar radio bursts generate broadband RFI that can saturate receivers, especially during intense X‑class flares.

3. Real‑time solar activity monitoring

Tool	Frequency of Updates	Typical Use in uGMRT operations
NOAA Space Weather Prediction Centre (SWPC) alerts	Every 5 min	Trigger automatic flagging of data during high‑flux periods
Solar Dynamics Observatory (SDO) EUV imagery	12 s cadence	Correlate solar active regions with ionospheric TEC spikes
GPS‑derived TEC maps (e.g.,IGS)	15 min	Feed corrections into the uGMRT timing pipeline

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Pulsar Mode switch: How Intrinsic Pulsar Changes Contribute

1. What is mode switching?

• Certain pulsars alternate between distinct emission states (e.g., “bright” and “quiet” modes) on timescales ranging from seconds to hours.
• Mode changes are accompanied by variations in pulse shape, leading to systematic TOA offsets if a single template is used for all data.

2. Nulling and drifting sub‑pulses

• Nulling episodes (complete disappearance of pulses) and drift‑rate alterations further degrade timing stability.

3. Quantified impact on uGMRT timing

• Studies of PSR J1738+0333 have shown mode‑switch‑induced TOA scatter of up to 1.2 µs at 400 MHz, comparable to solar‑storm‑related scatter during moderate geomagnetic activity.

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Combined Effects: Distinguishing Solar vs. Pulsar Contributions

1. Temporal correlation analysis – Cross‑match TOA residuals with solar‑storm indices (Kp, Dst) to isolate ionospheric components.
2. Mode‑state tagging – Use single‑pulse classification (e.g., hidden‑Markov models) to separate mode‑dependent residuals.
3. Multi‑band consistency check – Solar‑storm effects scale with ν⁻², while mode switching is largely achromatic; simultaneous observations at 300 MHz and 750 MHz help differentiate the two.

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Data Calibration and Correction Techniques

1. TEC‑based phase correction

• Ingest real‑time IGS TEC maps into the CASA‑based uGMRT pipeline.
• Apply ν⁻² phase offsets to each integration before TOA extraction.

2. Dynamic template fitting

• Build separate pulse templates for each identified mode (bright, quiet, null).
• Perform template matching on a per‑subintegration basis to avoid mode‑induced bias.

3. Adaptive RFI excision

• Deploy machine‑learning flaggers (e.g., AOFlagger with SolarRFI module) that recognize solar burst signatures.

4. Post‑fit noise modeling

• Incorporate a Gaussian‑process (GP) kernel that includes both a solar‐storm term (correlated with TEC) and a pulsar‑mode term (state‑dependent variance).

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Practical Tips for Reducing Timing Noise in uGMRT Observations

• Pre‑observation checklist

1. Verify current solar‑storm alerts (NOAA SWPC).
2. Load the latest TEC map into the scheduling script.
3. Confirm availability of mode‑state monitoring tools (e.g., PRESTO single_pulse_search.py).

• during observation
• Enable real‑time RFI flagging; pause data acquisition if solar burst intensity exceeds 10 SFU at 300 MHz.
• Record a high‑cadence “calibrator dump” every 10 min to track ionospheric phase drift.

• Post‑processing
• run mode‑state classification before generating TOAs.
• Apply TEC‑derived phase corrections prior to template matching.
• Fit a joint GP model to residuals; examine the posterior of the solar‑storm hyperparameter to assess correction efficacy.

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Benefits of Addressing Timing Noise

• Improved PTA sensitivity – Reducing microsecond‑level scatter enhances the detection horizon for nanohertz gravitational waves.
• Higher precision in neutron‑star mass measurements – Cleaner TOAs enable tighter constraints on Shapiro delay and orbital decay.
• More reliable flux density monitoring – Corrected ionospheric effects produce stable spectral indices across epochs.

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real‑World Example: GMRT Observation of PSR B1937+21 During a CME

• Date & event: 12 Oct 2024, CME associated with an X2.2 solar flare.
• observing setup: uGMRT Band 3 (300–500 MHz), 4 hr tracking of PSR B1937+21.
• Observed impact: Raw TOA residuals showed a systematic drift of ~3 µs correlated with a sudden TEC increase from 6 TECU to 15 TECU (as per IGS).
• Mitigation applied:

1. Ingested the TEC map and applied ν⁻² phase corrections.
2. utilized dual‑template fitting for mode switches identified in the pulse stack.
3. Result: Post‑correction residual RMS decreased from 4.2 µs to 0.9 µs, restoring the dataset to its typical timing precision.

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Future Outlook: integration with Global Pulsar Timing Array Networks

• Joint solar‑weather dashboards – Collaboration between uGMRT and international PTAs to share real‑time solar indices and TEC products.
• Machine‑learning mode‑switch predictors – Training deep‑learning classifiers on archival uGMRT single‑pulse archives to forecast mode transitions and pre‑emptively adjust templates.
• Broadband timing campaigns – Coordinated observations with ngVLA and SKA‑Low will exploit the ν⁻² scaling of solar‑storm noise, allowing multi‑frequency disentanglement of ionospheric and intrinsic pulsar contributions.

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