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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. LIGO/Virgo/KAGRA S250326y: Identification of a GW compact binary merger candidate
  2. EP250321a: Mondy AZT-33IK Continued Optical Observations
  3. Swift follow-up observations of FRB250316A and EP J120944.2+585060
  4. GRB 250322A: third epoch of NOT optical observations
  5. GRB 250322A: Swift-BAT refined analysis
  6. The EP-WXT trigger 01709133021 (designated as EP250324a) is not a real source
  7. GRB 250321B: ISON-Kitab RC-36 Optical Upper Limit
  8. FRB 250316A: NOT optical upper limit for the X ray source EP J120944.2+585060
  9. GRB 250322A: further NOT optical observations
  10. EP-WXT trigger 01709133021: Optical upper limit through Kinder observations
  11. GRB 250322A: Swift/UVOT Upper Limits
  12. EP250324A: COLIBRÍ/DDRAGO Optical Observations
  13. GRB 250322A: VLT/X-shooter redshift confirmation of the putative host galaxy
  14. FRB 250316A: COLIBRÍ/DDRAGO Optical follow up of the X ray source EP J120944.2+585060
  15. GRB 250322B: NuSTAR detection of the prompt emission and regular dips during the burst
  16. GRB 250321B: Swift-XRT observations
  17. GRB 250322A: Swift-XRT refined Analysis
  18. EP250321a: TNOT Observation of Optical Counterpart
  19. FRB 250316A: DDOTI Continued Optical Observations (Third Epoch)
  20. GRB 250322A: Gemini-North redshift of candidate host galaxy
  21. EP250304a: VLT/MUSE spectroscopic observation of its associated supernova SN 2025fhm
  22. SVOM/sb25032302: SVOM detection of a long X-ray transient
  23. GRB 250322A: AstroSat CZTI detection of a short burst
  24. GRB 250322B: AstroSat CZTI detection of a bright long burst
  25. GRB250322A: STEP/T80S optical limits
  26. GRB 250322A: Gemini-South optical observations
  27. GRB 250322A: VLT optical observations
  28. GRB 250322A: VLT near-infrared observations
  29. FRB 250316A: DDOTI Continued Optical Observations
  30. GRB 250322A: NOT optical upper limits
  31. GRB 250322A: Enhanced Swift-XRT position
  32. GRB 250321B: SVOM/COLIBRÍ (F-GFT) follow-up observations
  33. FRB 20250316A: Kinder optical upper limits of the Einstein Probe candidate X-ray source EP J120944.2+585060
  34. GRB 250322A: MASTER optical observation
  35. EP250321a: Liverpool Telescope optical follow-up
  36. EP250321a: Mondy AZT-33IK Optical Observations
  37. GRB 250322A: Swift detection of a short burst
  38. FRB 20250316A: detection of a candidate associated X-ray source EP J120944.2+585060 by Einstein Probe
  39. EP250321a: refined analysis of the EP-WXT and EP-FXT observations
  40. EP250321a: KAIT optical observations
  41. EP250321A: COLIBRÍ Continuing Optical Observations
  42. GRB 250225B: GECAM-A detection
  43. GRB 250312A: GECAM-A detection
  44. GRB 250321B: Swift ToO observations
  45. EP250321a: WFST optical observations
  46. GRB 250320B: NuSTAR detection of the prompt emission from two broad bursts and preliminary analysis
  47. GRB 250321C: Fermi GBM Final Real-time Localization
  48. GRB 250320A: NuSTAR Detection of the Prompt Emission and Preliminary Results
  49. GRB 250320B: Fermi GBM Observation
  50. EP250321a: Xinglong 216 decaying optical observations
  51. GRB 250321A: Swift-BAT refined analysis
  52. GRB 250321A: Swift-XRT refined Analysis
  53. GRB 250320B: Fermi-LAT detection
  54. GRB 250321B: SVOM detection of a sub-threshold transient event
  55. EP250321a: SVOM/VT optical observation
  56. EP 250321A: Optical counterpart detection by LCO.
  57. EP250321a: Kinder optical follow-up observations
  58. GRB 250321A: Swift/UVOT Upper Limits
  59. GRB 250320B: SVOM/GRM observation of a long burst
  60. EP250321a: LCO optical counterpart detection
  61. EP250321a: Swift-XRT detection of an X-ray source
  62. EP250321A: COLIBRÍ Optical Observations
  63. EP250321a: VLT/X-shooter redshift z = 4.368
  64. GRB 250320B: AstroSat CZTI detection
  65. EP250321a: REM optical/NIR afterglow detection
  66. Fermi GRB 250320B: Global MASTER-Net observations report
  67. EP250321a: BOOTES-5/JGT optical afterglow detection
  68. EP250321a: TRT optical counterpart detection
  69. EP250321a: Global MASTER-Net observations report
  70. Swift GRB 250321A: Global MASTER-Net observations report
  71. Fermi GRB 250321A: Global MASTER-Net observations report
  72. EP250321a: Einstein Probe detection of an X-ray transient
  73. GRB 250321A: GOTO optical upper limits
  74. GRB 250321A: Swift-XRT localisation
  75. GRB 250314A: Keck/NIRC2 J-band upper limit
  76. EP250226a/GRB 250226A: KAIT optical observations
  77. GRB 250321A: Fermi GBM Observation
  78. GRB 250321A: Swift detection of a burst
  79. GRB 250321A: Fermi GBM Final Real-time Localization
  80. GRB 250320B: Fermi GBM Final Real-time Localization
  81. GRB 250309B: Proof-of-concept for Joint ZTF+EP Experiment
  82. GRB 250317B: Mondy AZT-33IK Continued Optical Observations
  83. GRB 250320A: Fermi GBM Final Real-time Localization
  84. Fermi GRB 250319B: Global MASTER-Net observations report
  85. FRB 20250316A: Upper limits for gamma-ray transient from Insight-HXMT/HE observations
  86. GRB 250313A: GRBAlpha detection
  87. LIGO/Virgo/KAGRA S250206dm: LIGHETR followup observations of AT2025azn
  88. GRB 250317B: SVOM/COLIBRI (F-GFT) follow-up observations
  89. GRB 250319B: Fermi GBM Final Localization
  90. GRB 250319A: Fermi GBM Final Localization
  91. GRB 250317D: EIRSAT-1 GMOD Detection
  92. LIGO/Virgo/KAGRA S250319bu: Updated Sky localization
  93. GRB 250314A: ATCA radio upper limits
  94. EP250302a: VLA observations
  95. GRB 250317B: OHP/T193 continued follow-up
  96. LIGO/Virgo/KAGRA S250319bu: Identification of a GW compact binary merger candidate
  97. GRB 250317C: SVOM/GRM observation of a long burst
  98. GRB 250317B: Leavitt Observatory optical upper limit
  99. GRB 250309B/AT2025dws: further ATCA observations
  100. GRB 250317B: Mondy AZT-33IK Optical Observations

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