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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 250327B: Las Cumbres optical counterpart detection
  2. GRB 250327B: Swift-XRT detection of the X-ray afterglow
  3. GRB 250327B: 1.6m Mephisto optical observations
  4. GRB 250327B: NOT spectroscopic redshift z = 3.035
  5. GRB 250327A: Swift-XRT refined Analysis
  6. GRB 250327B: GOTO optical counterpart detection
  7. GRB 250327B: SVOM/VT optically bright counterpart
  8. GRB 250327B: SAO RAS optical candidate
  9. GRB 250327B: SVOM detection of a burst
  10. FRB 20250316A: Gemini Imaging and Spectroscopy of the Sub-arcsecond Localization Region of FRB 20250316A
  11. FRB 20250316A: The sub-arcsecond localization of FRB 20250316A using CHIME/FRB Outriggers coincides with reported X-ray counterparts
  12. GRB 250327A: J-band observations with WINTER
  13. GRB 250327A: SVOM/VT optical candidate
  14. FRB 20250316A: Pan-STARRS r and i-band imaging and photometry
  15. GRB 250327A: Fermi GBM observation
  16. Fermi GRB 250327A: Global MASTER-Net observations report
  17. Swift GRB 250327A: Global MASTER-Net observations report
  18. GRB 250327A: DDOTI Optical Observations
  19. GRB 250327A: COLIBRÍ optical upper limit
  20. GRB 250327A: Swift detection of a burst
  21. GRB 250327A: Fermi GBM Final Real-time Localization
  22. Fermi trigger No 764700395: Global MASTER-Net observations report
  23. LIGO/Virgo/KAGRA S250326y: Updated Sky localization
  24. Konus-Wind detection of GRB 250322A (short)
  25. IPN triangulation of GRB 250322B
  26. LIGO/Virgo/KAGRA S250326y: Identification of a GW compact binary merger candidate
  27. EP250321a: Mondy AZT-33IK Continued Optical Observations
  28. Swift follow-up observations of FRB250316A and EP J120944.2+585060
  29. GRB 250322A: third epoch of NOT optical observations
  30. GRB 250322A: Swift-BAT refined analysis
  31. The EP-WXT trigger 01709133021 (designated as EP250324a) is not a real source
  32. GRB 250321B: ISON-Kitab RC-36 Optical Upper Limit
  33. FRB 250316A: NOT optical upper limit for the X ray source EP J120944.2+585060
  34. GRB 250322A: further NOT optical observations
  35. EP-WXT trigger 01709133021: Optical upper limit through Kinder observations
  36. GRB 250322A: Swift/UVOT Upper Limits
  37. EP250324A: COLIBRÍ/DDRAGO Optical Observations
  38. GRB 250322A: VLT/X-shooter redshift confirmation of the putative host galaxy
  39. FRB 250316A: COLIBRÍ/DDRAGO Optical follow up of the X ray source EP J120944.2+585060
  40. GRB 250322B: NuSTAR detection of the prompt emission and regular dips during the burst
  41. GRB 250321B: Swift-XRT observations
  42. GRB 250322A: Swift-XRT refined Analysis
  43. EP250321a: TNOT Observation of Optical Counterpart
  44. FRB 250316A: DDOTI Continued Optical Observations (Third Epoch)
  45. GRB 250322A: Gemini-North redshift of candidate host galaxy
  46. EP250304a: VLT/MUSE spectroscopic observation of its associated supernova SN 2025fhm
  47. SVOM/sb25032302: SVOM detection of a long X-ray transient
  48. GRB 250322A: AstroSat CZTI detection of a short burst
  49. GRB 250322B: AstroSat CZTI detection of a bright long burst
  50. GRB250322A: STEP/T80S optical limits
  51. GRB 250322A: Gemini-South optical observations
  52. GRB 250322A: VLT optical observations
  53. GRB 250322A: VLT near-infrared observations
  54. FRB 250316A: DDOTI Continued Optical Observations
  55. GRB 250322A: NOT optical upper limits
  56. GRB 250322A: Enhanced Swift-XRT position
  57. GRB 250321B: SVOM/COLIBRÍ (F-GFT) follow-up observations
  58. FRB 20250316A: Kinder optical upper limits of the Einstein Probe candidate X-ray source EP J120944.2+585060
  59. GRB 250322A: MASTER optical observation
  60. EP250321a: Liverpool Telescope optical follow-up
  61. EP250321a: Mondy AZT-33IK Optical Observations
  62. GRB 250322A: Swift detection of a short burst
  63. FRB 20250316A: detection of a candidate associated X-ray source EP J120944.2+585060 by Einstein Probe
  64. EP250321a: refined analysis of the EP-WXT and EP-FXT observations
  65. EP250321a: KAIT optical observations
  66. EP250321A: COLIBRÍ Continuing Optical Observations
  67. GRB 250225B: GECAM-A detection
  68. GRB 250312A: GECAM-A detection
  69. GRB 250321B: Swift ToO observations
  70. EP250321a: WFST optical observations
  71. GRB 250320B: NuSTAR detection of the prompt emission from two broad bursts and preliminary analysis
  72. GRB 250321C: Fermi GBM Final Real-time Localization
  73. GRB 250320A: NuSTAR Detection of the Prompt Emission and Preliminary Results
  74. GRB 250320B: Fermi GBM Observation
  75. EP250321a: Xinglong 216 decaying optical observations
  76. GRB 250321A: Swift-BAT refined analysis
  77. GRB 250321A: Swift-XRT refined Analysis
  78. GRB 250320B: Fermi-LAT detection
  79. GRB 250321B: SVOM detection of a sub-threshold transient event
  80. EP250321a: SVOM/VT optical observation
  81. EP 250321A: Optical counterpart detection by LCO.
  82. EP250321a: Kinder optical follow-up observations
  83. GRB 250321A: Swift/UVOT Upper Limits
  84. GRB 250320B: SVOM/GRM observation of a long burst
  85. EP250321a: LCO optical counterpart detection
  86. EP250321a: Swift-XRT detection of an X-ray source
  87. EP250321A: COLIBRÍ Optical Observations
  88. EP250321a: VLT/X-shooter redshift z = 4.368
  89. GRB 250320B: AstroSat CZTI detection
  90. EP250321a: REM optical/NIR afterglow detection
  91. Fermi GRB 250320B: Global MASTER-Net observations report
  92. EP250321a: BOOTES-5/JGT optical afterglow detection
  93. EP250321a: TRT optical counterpart detection
  94. EP250321a: Global MASTER-Net observations report
  95. Swift GRB 250321A: Global MASTER-Net observations report
  96. Fermi GRB 250321A: Global MASTER-Net observations report
  97. EP250321a: Einstein Probe detection of an X-ray transient
  98. GRB 250321A: GOTO optical upper limits
  99. GRB 250321A: Swift-XRT localisation
  100. GRB 250314A: Keck/NIRC2 J-band upper limit

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