Paarmita Pandey

Paarmita Pandey

she/her

Research

Cosmic Ray Acceleration in Young Star-Forming Regions

Keywords: Fermi-LAT, Stellar Winds, Diffusion Coefficient

Cosmic rays play a key role in shaping galaxies, influencing how they form and evolve. Understanding where these high-energy particles come from is therefore essential for modeling galaxy evolution and cosmic-ray feedback. While supernova remnants are traditionally considered the main accelerators of cosmic rays, recent observations suggest that young, massive star-forming regions may also contribute significantly.

In this work, we use Fermi-LAT gamma-ray observations to investigate cosmic-ray acceleration in two such environments.

First, we look at the young star-forming region RCW 38 (age < 0.5 Myr), where we detect gamma-ray emission at a 22σ significance level, providing strong evidence that stellar winds can accelerate cosmic-ray particles. These observations allow us to constrain the cosmic-ray acceleration efficiency, diffusion timescales, and pressure within the region.

Multiwavelength image of RCW 38, with IR Spitzer image in red, the Chandra X-ray broad-band data in green, and the background subtracted >2 GeV Fermi-LAT counts map in blue.

We also identify a new class of Fermi gamma-ray sources associated with explosive outflows, focusing on DR21 in the Cygnus-X star-forming complex, detected at 35σ significance. For this system, we quantify the acceleration efficiency of explosive outflows and evaluate their contribution to the overall galactic cosmic-ray budget.

Overall, our results show that star-forming regions younger than ~3 Myr are efficient cosmic-ray accelerators, with important implications for galaxy simulations and for understanding the origin of galactic cosmic rays.

Gamma-ray luminosity versus mechanical power for EDOs and young star-forming regions.
  • Read the RCW 38 paper here: ADS
  • Read the Explosive dispersal outflows paper here: ADS

Unraveling the Nature of the Nuclear Transient AT2020adpi

Keywords: Active Galactic Nuclei, Tidal Disruption Events

I study transient events associated with supermassive black holes, which offer unique insights into accretion physics in galactic nuclei. In a recent multiwavelength study, I analyzed AT2020adpi, a luminous optical/UV nuclear transient at z = 0.26 that does not fit into existing categories such as tidal disruption events or standard AGN variability.

Its unusual light curve, strong mid-infrared flare, and evolving emission-line features suggest an accretion episode driven by either a stellar disruption within an active disk or instabilities in an active nucleus. This event highlights both the diversity of nuclear transients and the importance of coordinated, multiwavelength observations.

Comparison of AT2020adpi with other known transients in the optical absolute magnitude versus characteristic timescale parameter space
  • Read the Paper here: ADS