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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').
Advanced Search

To narrow the search results, use advanced search syntax. This allows for specifying which circular field to search (submitter, subject, and/or body). For additional information, refer to the advanced search documentation.

Advanced Search Examples (click to copy):

subject:"Swift"
body:"GRB"
submitter:"Judith Racusin"
  1. GRB 250327A: SVOM/VT upper limits on the XRT position
  2. LIGO/Virgo/KAGRA S250328ae: Identification of a GW compact binary merger candidate
  3. GRB 250327B: SVOM/COLIBRÍ (F-GFT) follow-up observations
  4. GRB 250327B: Las Cumbres optical counterpart detection
  5. GRB 250327B: Swift-XRT detection of the X-ray afterglow
  6. GRB 250327B: 1.6m Mephisto optical observations
  7. GRB 250327B: NOT spectroscopic redshift z = 3.035
  8. GRB 250327A: Swift-XRT refined Analysis
  9. GRB 250327B: GOTO optical counterpart detection
  10. GRB 250327B: SVOM/VT optically bright counterpart
  11. GRB 250327B: SAO RAS optical candidate
  12. GRB 250327B: SVOM detection of a burst
  13. FRB 20250316A: Gemini Imaging and Spectroscopy of the Sub-arcsecond Localization Region of FRB 20250316A
  14. FRB 20250316A: The sub-arcsecond localization of FRB 20250316A using CHIME/FRB Outriggers coincides with reported X-ray counterparts
  15. GRB 250327A: J-band observations with WINTER
  16. GRB 250327A: SVOM/VT optical candidate
  17. FRB 20250316A: Pan-STARRS r and i-band imaging and photometry
  18. GRB 250327A: Fermi GBM observation
  19. Fermi GRB 250327A: Global MASTER-Net observations report
  20. Swift GRB 250327A: Global MASTER-Net observations report
  21. GRB 250327A: DDOTI Optical Observations
  22. GRB 250327A: COLIBRÍ optical upper limit
  23. GRB 250327A: Swift detection of a burst
  24. GRB 250327A: Fermi GBM Final Real-time Localization
  25. Fermi trigger No 764700395: Global MASTER-Net observations report
  26. LIGO/Virgo/KAGRA S250326y: Updated Sky localization
  27. Konus-Wind detection of GRB 250322A (short)
  28. IPN triangulation of GRB 250322B
  29. LIGO/Virgo/KAGRA S250326y: Identification of a GW compact binary merger candidate
  30. EP250321a: Mondy AZT-33IK Continued Optical Observations
  31. Swift follow-up observations of FRB250316A and EP J120944.2+585060
  32. GRB 250322A: third epoch of NOT optical observations
  33. GRB 250322A: Swift-BAT refined analysis
  34. The EP-WXT trigger 01709133021 (designated as EP250324a) is not a real source
  35. GRB 250321B: ISON-Kitab RC-36 Optical Upper Limit
  36. FRB 250316A: NOT optical upper limit for the X ray source EP J120944.2+585060
  37. GRB 250322A: further NOT optical observations
  38. EP-WXT trigger 01709133021: Optical upper limit through Kinder observations
  39. GRB 250322A: Swift/UVOT Upper Limits
  40. EP250324A: COLIBRÍ/DDRAGO Optical Observations
  41. GRB 250322A: VLT/X-shooter redshift confirmation of the putative host galaxy
  42. FRB 250316A: COLIBRÍ/DDRAGO Optical follow up of the X ray source EP J120944.2+585060
  43. GRB 250322B: NuSTAR detection of the prompt emission and regular dips during the burst
  44. GRB 250321B: Swift-XRT observations
  45. GRB 250322A: Swift-XRT refined Analysis
  46. EP250321a: TNOT Observation of Optical Counterpart
  47. FRB 250316A: DDOTI Continued Optical Observations (Third Epoch)
  48. GRB 250322A: Gemini-North redshift of candidate host galaxy
  49. EP250304a: VLT/MUSE spectroscopic observation of its associated supernova SN 2025fhm
  50. SVOM/sb25032302: SVOM detection of a long X-ray transient
  51. GRB 250322A: AstroSat CZTI detection of a short burst
  52. GRB 250322B: AstroSat CZTI detection of a bright long burst
  53. GRB250322A: STEP/T80S optical limits
  54. GRB 250322A: Gemini-South optical observations
  55. GRB 250322A: VLT optical observations
  56. GRB 250322A: VLT near-infrared observations
  57. FRB 250316A: DDOTI Continued Optical Observations
  58. GRB 250322A: NOT optical upper limits
  59. GRB 250322A: Enhanced Swift-XRT position
  60. GRB 250321B: SVOM/COLIBRÍ (F-GFT) follow-up observations
  61. FRB 20250316A: Kinder optical upper limits of the Einstein Probe candidate X-ray source EP J120944.2+585060
  62. GRB 250322A: MASTER optical observation
  63. EP250321a: Liverpool Telescope optical follow-up
  64. EP250321a: Mondy AZT-33IK Optical Observations
  65. GRB 250322A: Swift detection of a short burst
  66. FRB 20250316A: detection of a candidate associated X-ray source EP J120944.2+585060 by Einstein Probe
  67. EP250321a: refined analysis of the EP-WXT and EP-FXT observations
  68. EP250321a: KAIT optical observations
  69. EP250321A: COLIBRÍ Continuing Optical Observations
  70. GRB 250225B: GECAM-A detection
  71. GRB 250312A: GECAM-A detection
  72. GRB 250321B: Swift ToO observations
  73. EP250321a: WFST optical observations
  74. GRB 250320B: NuSTAR detection of the prompt emission from two broad bursts and preliminary analysis
  75. GRB 250321C: Fermi GBM Final Real-time Localization
  76. GRB 250320A: NuSTAR Detection of the Prompt Emission and Preliminary Results
  77. GRB 250320B: Fermi GBM Observation
  78. EP250321a: Xinglong 216 decaying optical observations
  79. GRB 250321A: Swift-BAT refined analysis
  80. GRB 250321A: Swift-XRT refined Analysis
  81. GRB 250320B: Fermi-LAT detection
  82. GRB 250321B: SVOM detection of a sub-threshold transient event
  83. EP250321a: SVOM/VT optical observation
  84. EP 250321A: Optical counterpart detection by LCO.
  85. EP250321a: Kinder optical follow-up observations
  86. GRB 250321A: Swift/UVOT Upper Limits
  87. GRB 250320B: SVOM/GRM observation of a long burst
  88. EP250321a: LCO optical counterpart detection
  89. EP250321a: Swift-XRT detection of an X-ray source
  90. EP250321A: COLIBRÍ Optical Observations
  91. EP250321a: VLT/X-shooter redshift z = 4.368
  92. GRB 250320B: AstroSat CZTI detection
  93. EP250321a: REM optical/NIR afterglow detection
  94. Fermi GRB 250320B: Global MASTER-Net observations report
  95. EP250321a: BOOTES-5/JGT optical afterglow detection
  96. EP250321a: TRT optical counterpart detection
  97. EP250321a: Global MASTER-Net observations report
  98. Swift GRB 250321A: Global MASTER-Net observations report
  99. Fermi GRB 250321A: Global MASTER-Net observations report
  100. EP250321a: Einstein Probe detection of an X-ray transient

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