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GCN Circulars

GCN Circulars are rapid astronomical bulletins submitted by and distributed to community members worldwide. They are used to share discoveries, observations, quantitative near-term predictions, requests for follow-up observations, or future observing plans related to high-energy, multi-messenger, and variable or transient astrophysical events. See the documentation for help with subscribing to or submitting Circulars.

Search for Circulars by submitter, subject, or body text (e.g. 'Fermi GRB').
To navigate to a specific circular, enter the associated Circular ID (e.g. 'gcn123', 'Circular 123', or '123').
  1. GRB 250327A: Swift-XRT refined Analysis
  2. GRB 250327B: GOTO optical counterpart detection
  3. GRB 250327B: SVOM/VT optically bright counterpart
  4. GRB 250327B: SAO RAS optical candidate
  5. GRB 250327B: SVOM detection of a burst
  6. FRB 20250316A: Gemini Imaging and Spectroscopy of the Sub-arcsecond Localization Region of FRB 20250316A
  7. FRB 20250316A: The sub-arcsecond localization of FRB 20250316A using CHIME/FRB Outriggers coincides with reported X-ray counterparts
  8. GRB 250327A: J-band observations with WINTER
  9. GRB 250327A: SVOM/VT optical candidate
  10. FRB 20250316A: Pan-STARRS r and i-band imaging and photometry
  11. GRB 250327A: Fermi GBM observation
  12. Fermi GRB 250327A: Global MASTER-Net observations report
  13. Swift GRB 250327A: Global MASTER-Net observations report
  14. GRB 250327A: DDOTI Optical Observations
  15. GRB 250327A: COLIBRÍ optical upper limit
  16. GRB 250327A: Swift detection of a burst
  17. GRB 250327A: Fermi GBM Final Real-time Localization
  18. Fermi trigger No 764700395: Global MASTER-Net observations report
  19. LIGO/Virgo/KAGRA S250326y: Updated Sky localization
  20. Konus-Wind detection of GRB 250322A (short)
  21. IPN triangulation of GRB 250322B
  22. LIGO/Virgo/KAGRA S250326y: Identification of a GW compact binary merger candidate
  23. EP250321a: Mondy AZT-33IK Continued Optical Observations
  24. Swift follow-up observations of FRB250316A and EP J120944.2+585060
  25. GRB 250322A: third epoch of NOT optical observations
  26. GRB 250322A: Swift-BAT refined analysis
  27. The EP-WXT trigger 01709133021 (designated as EP250324a) is not a real source
  28. GRB 250321B: ISON-Kitab RC-36 Optical Upper Limit
  29. FRB 250316A: NOT optical upper limit for the X ray source EP J120944.2+585060
  30. GRB 250322A: further NOT optical observations
  31. EP-WXT trigger 01709133021: Optical upper limit through Kinder observations
  32. GRB 250322A: Swift/UVOT Upper Limits
  33. EP250324A: COLIBRÍ/DDRAGO Optical Observations
  34. GRB 250322A: VLT/X-shooter redshift confirmation of the putative host galaxy
  35. FRB 250316A: COLIBRÍ/DDRAGO Optical follow up of the X ray source EP J120944.2+585060
  36. GRB 250322B: NuSTAR detection of the prompt emission and regular dips during the burst
  37. GRB 250321B: Swift-XRT observations
  38. GRB 250322A: Swift-XRT refined Analysis
  39. EP250321a: TNOT Observation of Optical Counterpart
  40. FRB 250316A: DDOTI Continued Optical Observations (Third Epoch)
  41. GRB 250322A: Gemini-North redshift of candidate host galaxy
  42. EP250304a: VLT/MUSE spectroscopic observation of its associated supernova SN 2025fhm
  43. SVOM/sb25032302: SVOM detection of a long X-ray transient
  44. GRB 250322A: AstroSat CZTI detection of a short burst
  45. GRB 250322B: AstroSat CZTI detection of a bright long burst
  46. GRB250322A: STEP/T80S optical limits
  47. GRB 250322A: Gemini-South optical observations
  48. GRB 250322A: VLT optical observations
  49. GRB 250322A: VLT near-infrared observations
  50. FRB 250316A: DDOTI Continued Optical Observations
  51. GRB 250322A: NOT optical upper limits
  52. GRB 250322A: Enhanced Swift-XRT position
  53. GRB 250321B: SVOM/COLIBRÍ (F-GFT) follow-up observations
  54. FRB 20250316A: Kinder optical upper limits of the Einstein Probe candidate X-ray source EP J120944.2+585060
  55. GRB 250322A: MASTER optical observation
  56. EP250321a: Liverpool Telescope optical follow-up
  57. EP250321a: Mondy AZT-33IK Optical Observations
  58. GRB 250322A: Swift detection of a short burst
  59. FRB 20250316A: detection of a candidate associated X-ray source EP J120944.2+585060 by Einstein Probe
  60. EP250321a: refined analysis of the EP-WXT and EP-FXT observations
  61. EP250321a: KAIT optical observations
  62. EP250321A: COLIBRÍ Continuing Optical Observations
  63. GRB 250225B: GECAM-A detection
  64. GRB 250312A: GECAM-A detection
  65. GRB 250321B: Swift ToO observations
  66. EP250321a: WFST optical observations
  67. GRB 250320B: NuSTAR detection of the prompt emission from two broad bursts and preliminary analysis
  68. GRB 250321C: Fermi GBM Final Real-time Localization
  69. GRB 250320A: NuSTAR Detection of the Prompt Emission and Preliminary Results
  70. GRB 250320B: Fermi GBM Observation
  71. EP250321a: Xinglong 216 decaying optical observations
  72. GRB 250321A: Swift-BAT refined analysis
  73. GRB 250321A: Swift-XRT refined Analysis
  74. GRB 250320B: Fermi-LAT detection
  75. GRB 250321B: SVOM detection of a sub-threshold transient event
  76. EP250321a: SVOM/VT optical observation
  77. EP 250321A: Optical counterpart detection by LCO.
  78. EP250321a: Kinder optical follow-up observations
  79. GRB 250321A: Swift/UVOT Upper Limits
  80. GRB 250320B: SVOM/GRM observation of a long burst
  81. EP250321a: LCO optical counterpart detection
  82. EP250321a: Swift-XRT detection of an X-ray source
  83. EP250321A: COLIBRÍ Optical Observations
  84. EP250321a: VLT/X-shooter redshift z = 4.368
  85. GRB 250320B: AstroSat CZTI detection
  86. EP250321a: REM optical/NIR afterglow detection
  87. Fermi GRB 250320B: Global MASTER-Net observations report
  88. EP250321a: BOOTES-5/JGT optical afterglow detection
  89. EP250321a: TRT optical counterpart detection
  90. EP250321a: Global MASTER-Net observations report
  91. Swift GRB 250321A: Global MASTER-Net observations report
  92. Fermi GRB 250321A: Global MASTER-Net observations report
  93. EP250321a: Einstein Probe detection of an X-ray transient
  94. GRB 250321A: GOTO optical upper limits
  95. GRB 250321A: Swift-XRT localisation
  96. GRB 250314A: Keck/NIRC2 J-band upper limit
  97. EP250226a/GRB 250226A: KAIT optical observations
  98. GRB 250321A: Fermi GBM Observation
  99. GRB 250321A: Swift detection of a burst
  100. GRB 250321A: Fermi GBM Final Real-time Localization

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